- Open Access
Molecular analysis and intestinal expression of SAR1 genes and proteins in Anderson's disease (Chylomicron retention disease)
- Amandine Georges1,
- Jessica Bonneau2,
- Dominique Bonnefont-Rousselot3,
- Jacqueline Champigneulle4,
- Jean P Rabès2, 8,
- Marianne Abifadel2,
- Thomas Aparicio5,
- Jean C Guenedet4, 9,
- Eric Bruckert6,
- Catherine Boileau2, 8,
- Alain Morali1,
- Mathilde Varret2,
- Lawrence P Aggerbeck7 and
- Marie E Samson-Bouma2Email author
© Georges et al; licensee BioMed Central Ltd. 2011
- Received: 7 October 2010
- Accepted: 14 January 2011
- Published: 14 January 2011
Anderson's disease (AD) or chylomicron retention disease (CMRD) is a very rare hereditary lipid malabsorption syndrome. In order to discover novel mutations in the SAR1B gene and to evaluate the expression, as compared to healthy subjects, of the Sar1 gene and protein paralogues in the intestine, we investigated three previously undescribed individuals with the disease.
The SAR1B, SAR1A and PCSK9 genes were sequenced. The expression of the SAR1B and SAR1A genes in intestinal biopsies of both normal individuals and patients was measured by RTqPCR. Immunohistochemistry using antibodies to recombinant Sar1 protein was used to evaluate the expression and localization of the Sar1 paralogues in the duodenal biopsies.
Two patients had a novel SAR1B mutation (p.Asp48ThrfsX17). The third patient, who had a previously described SAR1B mutation (p.Leu28ArgfsX7), also had a p.Leu21dup variant of the PCSK9 gene. The expression of the SAR1B gene in duodenal biopsies from an AD/CMRD patient was significantly decreased whereas the expression of the SAR1A gene was significantly increased, as compared to healthy individuals. The Sar1 proteins were present in decreased amounts in enterocytes in duodenal biopsies from the patients as compared to those from healthy subjects.
Although the proteins encoded by the SAR1A and SAR1B genes are 90% identical, the increased expression of the SAR1A gene in AD/CMRD does not appear to compensate for the lack of the SAR1B protein. The PCSK9 variant, although reported to be associated with low levels of cholesterol, does not appear to exert any additional effect in this patient. The results provide further insight into the tissue-specific nature of AD/CMRD.
- Plasma Total Cholesterol
- Duodenal Biopsy
- Intestinal Biopsy
- Exocrine Pancreatic Insufficiency
Anderson' disease (AD) (OMIM 246700) or Chylomicron Retention Disease (CMRD) are the terms used to describe a disorder characterized by hypobetalipoproteinemia with selective absence of apoB48 in the post prandial state [1–26]. It is a very rare recessively inherited disease with less than 50 cases having been reported in the literature. Subjects with this disorder exhibit the clinical manifestations initially described by Anderson and her colleagues which consist of a malabsorption syndrome with steatorrhea and failure to thrive . Endoscopy shows a typical white stippling, like hoar frosting, covering the mucosal surface of the small intestine. The enterocytes in intestinal biopsies contain accumulations of large lipid droplets free in the cytoplasm as well as membrane-bound lipoprotein-sized structures [2, 8, 10–14, 17]. Neuro-retinal manifestations are occasionally present in young patients [8, 10, 11, 19, 24]. However, neurological signs may develop more frequently later in untreated individuals and consist most frequently of the loss of deep tendon reflexes [8, 10, 19, 24]. When diagnosis and treatment do not occur until adulthood, neurological signs, including areflexia, ataxia and myopathy, may be more severe [4, 5, 21]. Recently, myolysis was reported in 8 patients with AD . In all the patients reported in the literature, there is an absence of apoB48-containing lipoproteins. ApoB100-containing lipoproteins are present, although frequently in decreased amounts. There are low levels of plasma high density lipoprotein (HDL)-cholesterol, total lipids, cholesterol, phospholipids, carotenoids and lipid soluble vitamins (particularly vitamin E) whereas fasting triglyceride levels are in the low normal range. Plasma apoB100 and apoAI levels are 20-70% of normal. Increased amounts of apoB48, apoAI and apoAIV have been found in enterocytes [5, 6, 8]. Acanthocytosis is exceptional and there have been no reports of retinitis pigmentosa. A low fat diet supplemented with lipid soluble vitamins (A and E) results in the resumption of normal growth with abatement of the gastrointestinal symptoms.
In several patients (Table as Additional file 1), the molecular basis for the defect in chylomicron secretion has been shown to be a mutation in the SAR1B ( formerly SARA2) gene which encodes the SAR1B protein [18–24, 26]. This protein belongs to the Sar1-ADP-ribosylation factor family of small GTPases and it is involved in the vesicular coat protein complex II (COPII)-dependent transport of proteins from the endoplasmic reticulum to the Golgi apparatus [27–30]. Recent studies of chylomicron assembly have shown that the Sar1/COPII protein complex also is required for fusion of the specific chylomicron transport vesicle, the PCTV (pre-chylomicron transport vesicle), with the Golgi [31–35]. The SAR1B gene (OMIM 607690) is located at 5q31.1. It is composed of 8 exons and alternative splicing of exon 2 is predicted to lead to two transcripts (NM_001033503, NM_016103). To date, 15 SAR1B gene mutations (frameshifts, missense or deletions, Figure as Additional file 2) have been described in patients with AD or CMRD [18–24]. A second human protein isoform of Sar1, SAR1A, is encoded by the SAR1A gene (OMIM 607691) which is located at 10q22.1. SAR1A also is composed of 8 exons. As in the case of SAR1B, alternative splicing of exon 2 is predicted to lead to two transcripts (NM_001142648, NM_020150). To date, no mutation in the SAR1A gene has been described in patients with AD/CMRD.
We describe here three individuals with mutations in the SAR1B gene from two previously undescribed families. Two children in the first family carry a novel mutation. In the second family, one child carries a previously described mutation in the SAR1B gene and, unexpectedly, a polymorphism in the PCSK9 gene (Proprotein convertase subtilisin/kexin type 9). This polymorphism is of interest because heterozygous variations in the PCSK9 gene have been found, recently, to be a major additional determinant of circulating levels of LDL-cholesterol in humans [36–39].
Finally, for the first time, we describe the differential expression of the SAR1A and SAR1B genes and the localization of the Sar1 proteins in the enterocytes of intestinal biopsies from Anderson's disease patients as compared to healthy individuals.
Patient AD1, a boy born in 1998, was the first of 3 children of Turkish consanguineous first degree parents. The plasma total cholesterol levels of the father (2.4 g/L) and the mother (2.6 g/L) and their LDL cholesterol levels (2.0 and 1.55 g/L, respectively) were in the normal range for the laboratory. The patient was admitted to the university hospital at 10 months of age with chronic diarrhea (from the age of 3 months) as the main clinical symptom along with moderate growth retardation (-1SD in weight) and a distended abdomen. The neurological examination was normal.
Patient AD2, a girl born in 2003, is AD1's sister. She was first admitted to the hospital at one month of age for moderate growth retardation (-1SD in weight), sub-acute diarrhea and a distended abdomen.
Patient AD3, a girl born in 1990, was the last of 8 children from unrelated Moroccan parents. The mother's cholesterol level was normal. The father is no longer a participant in the family and his lipid levels are not available. Diarrhea, which began at 3 months of age, was the main clinical symptom. At 8 months of age, the patient was hospitalized for growth retardation (-2 SD in weight and -2 SD in height) and a distended abdomen.
Blood samples and intestinal biopsies were collected from the patients and normal control subjects, using the procedures and the experimental methods approved by INSERM (RBM 0256) and by a bioethics committee (Comité Consultatif de Protection des Personnes dans la Recherche Biomédicale de Paris Bichat-Claude Bernard, Paris, France, CCPPRB Bichat-C. Bernard-2003/05). Informed, written consent was obtained from all participants or from their legal guardians.
For diagnostic purposes, duodenal biopsies were obtained, after a 12-15 hour fast, from the patients and from 7 healthy subjects (2 children, 4 and 8 years old, respectively, 1 young adult, 23 years old and 4 older adults, 54 to 64 years old) undergoing endoscopy for causes unrelated to malabsorption and who were following their normal diet. Duodenal biopsies either were fixed in buffered formalin and further embedded in paraffin for standard histology and immunohistochemistry or were directly frozen in liquid nitrogen for oil red O staining of the lipids and for the analysis of intestinal SAR1A and SAR1B gene and protein expression. Electron microscopy of the biopsies was performed as previously described .
Lipid and lipoprotein analysis
Venous blood samples were drawn after a 12-hour fast (T0) and then 90 min. (T90) and 180 min. (T180) after a standard lipid load. The lipid load was a 620 kcal-meal that was given at T0 immediately after the drawing of the fasting blood samples. It contained about 66% lipids, with monounsaturated fatty acids present in a higher proportion than the saturated fatty acids. Typically, it was composed of 200 mL of unskimmed milk with sweetener, 50 g of bread, 10 g of butter and 100 g of cream (30% fat) with sweetener. Total cholesterol (TC) and triglyceride concentrations were determined by automated enzymatic methods (Konelab, Thermoclinical Labsystems, Cergy Pontoise, France, and Biomerieux, Marcy L'Etoile, France, respectively) [40, 41]. HDL-cholesterol (HDL-C) was determined by a direct method according to Egloff et al. . LDL-cholesterol (LDL-C) was calculated using Friedewald's equation . ApoAI and apoB were measured by immunonephelometry using anti-apoAI and anti-apoB antisera (Dade-Behring) and a BN II nephelometer analyzer from Behring (Dade Behring, Marburg GmbH, Germany) . Total lipoproteins were isolated by ultracentrifugation (d < 1.21 g/mL for 4 hours at 90,000 rpm in a NVT 90 Beckman rotor) and analyzed by SDS-polyacrylamide gel electrophoresis. Western blotting was performed with three monoclonal antibodies (generous gift of Y. Marcel) to detect the presence of apoB48, apoB100 and possible truncated forms of apoB [45, 46]: the antibodies are specific for 1) the N-terminal side of apoB100 and apo B48 (antibody 1D1 recognizes epitopes located between amino acids 474 and 539 of the protein), 2) for the C-terminal side of apoB100 (antibody L3 recognizes the epitopes close to amino acid 4355) and 3) for the central part of apoB (antibody L9 is specific for amino acids located between residues 2835 and 2922 present in both apoB48 and apoB100).
Gene sequencing of SAR1A, SAR1B, PCSK9 and exon 7 of the LDLR
Genomic DNA was isolated from whole blood containing EDTA with a PSS Magtration 8 Lx machine using a magnetic marble technique, according to the manufacturer's instructions. The 8 exons of SAR1A, the 8 exons of SAR1B, the 12 exons of PCSK9 and exon 7 of the LDLR genes and their flanking intronic sequences, were amplified by the polymerase chain reaction (primer sequences and PCR conditions are available on request). These genes were tested because of their known roles in the secretory pathway and/or their involvement in hypocholesterolemic syndromes. Exon 7 of the LDLR gene encodes the EGF A repeat domain of the LDL receptor which is essential for PCSK9 binding. Bidirectional fluorescent sequencing of purified PCR products (ExoSAP-IT, GE Healthcare) was carried out with the Big Dye® Terminator v1.1 Cycle Sequencing kit on an ABI-PRISM® 3130XL genetic analyzer (Applied Biosystems, Applera France SA). Electrophoretograms were analyzed using Gensearch DNA sequence analysis software (Phenosystems SA., Belgium).
Immunohistochemical studies of the intestinal biopsies
The localization of Sar1 proteins in duodenal biopsies from the 3 AD patients and from 3 of the healthy subjects was assessed by immunostaining with Nova Red (VECTOR) using a chicken polyclonal antibody against recombinant human SAR1A protein (ABCAM 14270, dilution 1:100) and anti-chicken horseradish peroxidase-conjugated antibody (ABCAM 6877, dilution 1:2000).
Expression of the SAR1A and SAR1B genes in the intestine
For the analysis of gene expression, intestinal biopsies were frozen immediately in liquid nitrogen and then stored in liquid nitrogen or at -80°C. Total RNA was extracted from the frozen intestinal biopsies using the RNeasy Mini kit (Qiagen) and treated according to the manufacturer's recommendations. The quantity and quality of the RNA were assessed using a Nanodrop ND-1000 spectrophotometer (Thermo Fisher Scientific Inc.). The integrity of the RNA was evaluated by agarose gel electrophoresis. Reverse transcription was performed using the Superscript II Reverse Transcriptase protocol for random hexamer-mediated cDNA synthesis (Invitrogen).
Real time quantitative PCR was performed with the ABI Prism model 7300 Sequence Detection System (Applied Biosystems), using the Taqman MGB specific probes for SAR1A (Hs00833068_s1), for SAR1B (Hs01011583_m1) (Applied Biosystems), and Absolute blue QPCR ROX mix (Abgene). The GAPDH (Hs99999905_m1) and POLR2A (Hs00172187_m1) genes were used as housekeeping control genes after validation (Applied Biosystems). The assays amplified single, gene-specific amplicons of the correct sizes (without non-specific products) and with uniform PCR efficiencies. All probes were validated in triplicate by the use of serial cDNA dilutions. Target and reference amplifications exhibited 100 ± 5% efficiency (R2>99% for the standard curve). The range of the Ct values was 10-35. The standard deviation for the Ct values of each sample was less than 0.3. Each sample was analyzed in triplicate and then differences in the expression of each gene among the samples were quantified using the (ΔΔCt) approach using both endogenous controls GAPDH and POLR2A (both gave similar results) . The difference in expression between the AD sample and the sample from each healthy subject was evaluated by Student's t test.
The diagnosis of Anderson's disease in the three patients was made on the basis of the observations described below which, collectively, are pathognomonic for the disease. Celiac disease, cystic fibrosis and cow's milk allergy were all ruled out.
Biological results and intestinal structure and ultrastructure
Clinical and biological data of Patients.
Age of onset of symptoms
- 2 SD
- 2 SD
diarrhea, abdominal distension
Deep tendon reflexes
Steatorrhea (g/24 hr)
Cholesterol (N: 1.50 - 2.80)
LDL-cholesterol (N: 0.80 - 1.50)
(g/L) HDL-cholesterol (N >0.45)
Triglycerides (N: 0.50 - 1.70)
ApoA-1 (N: 1 - 2.15)
ApoB (N: 0.55 - 1.40)
Vitamin E (N: 8 - 17 mg/L)
Vitamin E/Lipid (N >1.9 mg/g)
Vitamin A (N: 240 - 900 mg/L)
ASAT (x ULN)
ALAT (x ULN)
CK (x ULN)
Currently, despite a normal fat diet, the patient (now 11 1/2 years old) is doing well and, surprisingly, no diarrhea has been reported. Following vitamin E (α-tocopherol 50 mg/kg/d) and exogenous pancreatic enzyme supplementation, the plasma vitamin E and fecal elastase levels have become normal and steatorrhea is absent. The total plasma cholesterol (1 g/L), HDL-cholesterol (0.11 g/L) and LDL-cholesterol (0.76 g/L) values, however, remain low. The plasma CK levels are increased (2.6 fold greater than the upper limit of normal) but the CK-MB levels are normal. There are no neuro-ophtalmic, hepatic or cardiac abnormalities.
In patient AD2, the plasma concentration of fat-soluble vitamin A and the ratio of vitamin E to total lipids were decreased (Table 1). The plasma total cholesterol, LDL-cholesterol, HDL-cholesterol, apoAI, and apoB levels were low whereas the triglyceride level was normal (Table 1). The values for ASAT and CK were increased whereas CK-MB levels were normal (Table 1). Steatorrhea was present and fecal elastase levels were low (47 μg/g) when the patient was evaluated initially. Exogenous enzyme supplementation did not modify pancreatic function. The video-endoscopy of the intestine and the microscopic appearance of the intestinal biopsy (staining with oil red and electron microscopy), shown in Figures 1 and 2 along with images for AD3, were similar to that of patient AD1. At 2 months of age, the patient was given liposoluble vitamins and MCT supplementation as for AD1.
Currently, the patient (now 7 years old), like her brother, consumes a normal fat diet supplemented with vitamins D, E (α-tocopherol 30 mg/kg/d) and K as well as with exogenous pancreatic enzymes. She is a healthy young girl without digestive symptoms. The values for liposoluble vitamins and fecal elastase are in the normal range and steatorrhea is absent. The plasma total cholesterol, HDL- and LDL-cholesterol remain low (1.2, 0.18 and 0.86 g/L, respectively). The plasma CK and ASAT levels are increased (1.2 fold and 1.4 fold greater than the upper limit of normal, respectively) whereas the CK-MB levels are normal. Similarly to her brother, there are no neuro-ophtalmic, hepatic or cardiac abnormalities.
In patient AD3, there was a very low ratio of vitamin E to [cholesterol + triglyceride] whereas the vitamin A level was normal (Table 1). The plasma total cholesterol, LDL-cholesterol, HDL-cholesterol and apoAI levels were very low, whereas triglycerides and apoB levels were normal (Table 1). Fecal elastase level was normal. Anemia (normochromic, normocytic and then microcytic) with decreased serum iron and decreased saturation was present. A few acanthocytes were observed (5%). The video-endoscopy of the intestine and the microscopic appearance of the intestinal biopsy (staining with oil red and electron microscopy) resembled that of patient AD2 (Figures 1 and 2). A low fat diet as well as liposoluble vitamin supplementation (a-tocopherol 60 mg/kg/j) was initiated at 9 months of age.
Currently, the patient (now 19 ½ years old) follows a self-imposed low fat diet with vitamin D and E (oral tocofersolan 300 mg/d) supplementation but without strict adherence. The growth curve remains below the normal range (-1.5 SD) which, however, must be interpreted in the context of a short familial and ethnic height (BMI 30th percentile). The digestive symptoms now have disappeared. The deep tendon reflexes are present and there are no muscular symptoms. There is no steatorrhea and the fecal elastase level is normal. The plasma total cholesterol, HDL-cholesterol and LDL-cholesterol levels remain low (0.68, 0.14, 0.39 g/L respectively). The ratio of vitamin E to total lipids and the vitamin D level (55 μg/L) are now normal. The electromyogram shows neither neurogenic nor myogenic abnormalities. Nerve conduction velocity is normal. The CK levels are slightly increased (2-fold higher than the upper limit of normal) although CK-MB and transaminase levels are normal. There is no hepatic steatosis (normal abdominal ultrasound), no cardiomyopathy (normal cardiac ultrasound) and no ophthalmic abnormality.
Plasma lipid, apolipoprotein, and lipoprotein analysis in two AD subjects after a fat load*.
Fasting normal range
After a fat load, T90-T180
Chylomicrons in serum
Presence of apoB48 in isolated lipoproteins
Presence of apoB100 in isolated lipoproteins
As far as can be determined from the literature, the acquisition of tolerance to fat in the diet is limited to only a few cases (the two reported here and [[11, 12], and ]). In all the other instances reported, the patients' gastrointestinal symptoms recur when fat is reintroduced into the diet. Charcosset and colleagues  have proposed that network(s) of modifier genes are involved in the mechanism(s) that determine(s) the phenotype of the disease in a given individual. Whether this could be a mechanism that is involved in the acquisition of tolerance to fat is unknown at present.
Mutations in the SAR1B and PCSK9 genes
Patient AD3 has a homozygous two base pair deletion (c.83_84delTG) in exon 4 (formerly exon 3) of the SAR1B gene (Figure 3b). This deletion substitutes an arginine for the leucine normally present at position 28. A frameshift, resulting in a premature stop codon (p.Leu28ArgfsX7), produces a truncated protein that has only 17% of the length of the normal protein and 14% of the normal sequence. This mutation has been reported previously in patients of European and Moroccan origin [18, 23] (Table as Additional file 1). Because of their different ethnic origins, it is very unlikely that the mutational event reported here and in Cefalu et al. in patients from North Africa are the same as the one described by Jones et al..
The PCSK9 gene was also sequenced in these patients because it has been found to be a determinant in the levels of circulating LDL-cholesterol. In patient AD3, there was also a hypocholesterolemic variant in the PCSK9 gene. AD3 is a heterozygous carrier of a 3-base duplication (c.61_63dupCTG formerly designated c.43_44insCTG) in the first exon of PCSK9 (Figure 3c). The predicted amino acid change is a leucine duplication (p.Leu21dup formerly designated p.L15_16insL) in the leucine stretch of the PCSK9 signal peptide which leads to 10 leucine repeats (allele denoted L10) instead of the nine leucine repeats (L9) in the normal allele. This PCSK9 hypocholesterolemic variant has been reported previously . There was no mutation in the 12 exons or intron-exon boundaries of PCSK9 in patients AD1 and AD2.
Finally no mutation in the SAR1A gene or in exon 7 of the LDLR gene was detected in any of the three patients.
Distribution of the Sar1 proteins in duodenal biopsies from normal individuals and AD patients
In the 3 patients with Anderson's disease, the enterocytes were distended by large accumulated lipid droplets. As in the case of healthy individuals, the immunostaining for the Sar1 proteins was heterogeneously distributed along the villi. However, the staining was decreased as compared to the healthy subjects and was restricted to the area surrounding the lipid droplets (Figure 4b, c). The Sar1 isoforms differ by only 20 amino acid residues, which occur throughout the entire sequence of the protein, and the polyclonal antibodies used do not discriminate between the two human protein isoforms, Sar1a and Sar1b. Therefore, we decided to analyse the expression of the SAR1A and SAR1B genes in the intestinal biopsies.
Expression of the SAR1A and SAR1B genes in duodenal biopsies
In addition to manifesting the clinical, biochemical and intestinal ultrastructural features typical of AD, including mutations in the SAR1B gene, the 3 new patients that we describe here (which have now been followed for 7-10 years) exhibit some heretofore unseen features.
The expression of SAR1B in sites other than the intestine [18, 50, 51] suggests that other clinical manifestations might occur in AD patients, such as the recently reported muscular and cardiac manifestations . As in several other cases of AD/CMRD [1–3, 7, 10, 12–14, 21, 23], AD3 manifests anemia and decreased levels of serum iron. Although the mechanism is not entirely clear, these observations are of interest in light of a report of the preferential expression of SAR1B during erythropoiesis  and considering that mutations in SEC23B, with which SAR1 interacts in the COPII secretory coat complex, cause congenital dyserythropoietic anemia type II . Further, two of our patients manifest slight acanthocytosis as do four other cases reported in the literature [5, 8, 10, 13] and two other instances not published. In abetalipoproteinemia (ABL, MIM 200100), acanthocytosis (generally more than 50% ) has been proposed to be due to changes in the fluidity of the red blood cell membrane as a consequence of changes in its composition (decreased cholesterol and phospholipids leading to a relative increase in sphingomyelin ). The origin of the slight acanthocytosis (always less than 5%) in AD/CMRD is not clear. There is only one investigation of red blood cell lipids in AD/CMRD patients  and it showed that although total cholesterol and phospholipids were decreased, there was no variation in the phospholipid composition and the phosphatidylcholine to sphingomyelin ratio was similar to that in normal subjects (but no acanthocytosis was reported in those patients). Other factors may be involved. Normal erythrocytes acquire an acanthocytic form after transfusion into and circulation in ABL patients  but incubation of normal erythrocytes with plasma from ABL patients does not result in these modifications [57, 58]. This suggests that the mechanism(s) of formation of the acanthocytes in ABL are complex and do not simply result from the passive exchange of lipids between the erythrocyte membrane and the plasma but also may reflect exchange with the vessel wall membranes. There are no acanthocytes in the bone marrow of AD3  which also suggests a peripheral acquisition in AD/CMRD. The decreases in cholesterol and phospholipids in AD/CMRD may be at the limit at which changes in membrane fluidity induce changes in erythrocyte morphology thus making the finding of acanthocytes inconstant and variable in the disorder.
Osteoporosis/osteopenia have been described in several cases of AD [1–3, 10, 11, 14, 24] although none of the 3 cases reported here exhibit such abnormalities. In these 3 new patients, except for slightly increased CK levels, there is no neuro-ophtalmic, hepatic or cardiac abnormality. Further, none of the patients have any abnormal clinical or biological signs related to the spleen, kidney or lungs. The retardation in growth, which is milder than previously reported for patients with AD, underscores once more the importance of an early diagnosis which permits the implementation, early in life, of a low fat diet supplemented with liposoluble vitamins.
In both AD1 and AD2, exocrine pancreatic insufficiency (EPI) was suspected because of low fecal elastase levels. Whether and to what extent SAR1B gene mutations  can affect the levels of fecal elastase is unknown. Even though the low fecal elastase levels in AD1 and AD2 (AD3 had a normal fecal elastase level) could be due to diarrhea-related dilution and there are no other indications of pancreatic dysfunction, investigation of pancreatic function may still be prudent in patients with Anderson's disease or in those with unclear phenotypes.
In addition to a mutation in the SAR1B gene, patient AD3 also has a polymorphism in the PCSK9 gene (OMIM 607786), which encodes the Proprotein Convertase Subtilisin/Kexin type 9. It is linked to autosomal dominant hypercholesterolemia and is involved in cholesterol homeostasis [36–39] and gain-of-function mutations cause increased degradation of the LDL receptor and result in high levels of LDL cholesterol [61, 62]. Some mutations of PCSK9 cause variable degrees of hypocholesterolemia in homozygous or compound heterozygous carriers [63, 64]. However, these PCSK9 hypocholesterolemias appear to be clinically benign. The PCSK9 polymorphism found in patient AD3 was found to be present at a higher frequency in a low LDL-C population than in a normal population and to segregate with the "apoB- negative" Familial Hypobetalipoproteinemia phenotype in 3 families . This polymorphism could be an additional genetic hypocholesterolemic variation that might account for the high variability in lipid levels of some patients with AD. We did not find, in any of the three patients, a mutation in exon 7 of the LDLR gene which encodes the EGF A repeat domain of the LDL receptor which is essential for PCSK9 binding . A mutation in this binding site could prevent the degradation of the LDL receptor by PCSK9 and also could lead to hypocholesterolemia due to an increase in LDL catabolism . The variation in the PCSK9 gene is the second example of a mutation in the SAR1B gene being accompanied by a mutation/variation in another gene. In the cases of CMRD-MSS (Marinesco-Sjogren Syndrome), there is, in addition to a mutation in the SAR1B gene, a mutation in the SIL1 gene . In these patients, CMRD and MSS are distinct diseases.
Although chylomicron retention disease or Anderson's disease has been shown to be attributable to variations in the SAR1B gene, a full understanding of the relationship between genotype and phenotype and the origins of tissue-specific manifestations is lacking.
The SAR1B gene mutations in the three AD patients described here are predicted to lead to severely truncated SAR1B proteins that possess only 33 or 63 amino acids, respectively, the first 27 or 47 of which correspond to the amino-terminal sequence of the wild type protein. These truncated proteins lack numerous essential conserved residues that are involved in guanine nucleotide binding, in GTP hydrolysis and for interacting with guanine nucleotide exchange factors (GEF) and GTPase-activating proteins (GAP). We expect that the SAR1B proteins produced are non-functional in these patients. The vast majority of SAR1B gene mutations in AD/CMRD affect regions that are involved in nucleotide binding and hydrolysis as well as other functions (see Table and Figure as Additional files 1 and 2). A few others affect primarily regions in proximity to the membrane which would also be suspected to severely alter the function of the protein [12, 18, 19, 22, 66].
Sarl plays at least two roles in the secretory pathway. Sar1 is a significant participant in the coat protein complex II (COPII), a multi-protein complex which is responsible for the formation, at the endoplasmic reticulum, of membrane vesicles involved in protein transport (protein transport vesicles, PTVs) to the Golgi compartment [27–30]. Sar1, a small GTPase, associates with the smooth ER membrane via the action of Sec12, a GTP/GDP exchange factor. After having bound GTP, Sar1 binds Sec23-Sec24 (the inner coat) to form a prebudding complex. This complex, via Sec24 and perhaps Sec23 and Sar1, as well, interacts with vesicle cargos. Sec13-Sec31, which form the outer coat, are recruited by the Sar1-Sec23-Sec24 complex, which is membrane bound. The outer coat stimulates the GTPase-activating protein Sec23 which activates Sar1 GTP hydrolysis allowing depolymerisation of the coat and recycling of its components. PTVs transport a wide range of soluble and membrane bound cargo in a COPII dependent manner.
In a novel paradigm, Sar1 plays a role in an intestinal chylomicron-specific transport mechanism that employs a pre-chylomicron transport vesicle (PCTV). However, in this mechanism, it is L-FABP that initiates and organizes the PCTV budding machinery  which is modified and regulated, in part, by the phosphorylation of a currently unidentified 9 kDa protein . It is of interest in this context that FABP gene disrupted mice exhibit a delayed appearance of dietary triglycerides in the blood [68, 69]. PCTVs, similarly to PTVs require ATP. In contrast to PTVs, the PCTVs do not require GTP and the vesicle size is markedly larger (200-500 nm for PCTVs as opposed to 60-90 nm for PTVs). Further, the PCTV does not require Sar1 to bud from the ER but rather employs all the COPII proteins, and in particular Sec24C, for docking and fusion with the cis-Golgi [31, 33, 34, 70, 71]. Prior binding of Sar1 to PCTVs is apparently necessary for the binding of Sec24C . Finally, VAMP7 is the v-SNARE present on PCTVs, whereas Ykt6 and r22b are the v-SNAREs on PTVs .
Given the important role of Sar1 in COPII assembly and in the secretory pathway, it is remarkable that AD/CMRD patients have a pathology which is limited primarily to the intestine. Recent studies of cranio-lenticulo-sutural dysplasia CLSD [28, 72, 73] and congenital dyserythropoietic anemia type II, CDAII,  in humans and craniorachischisis in mice  provide important insights. The mutation in CLSD affects SEC23A, and the pathological effects are also limited. There are two paralogues of Sec23 and it appears that the second paralogue, SEC23B, can compensate for the loss of activity of SEC23A. Manifestation of the disease occurs, presumably, in tissues where there is not enough SEC23B to compensate for the loss of the other paralogue. However, in CDAII, in which a specific erythropoietic phenotype is observed, SEC23A can not compensate for the paralogue, SEC23B, which is important in the cell cycle of erythroid cells and their cytokinesis . In contrast, in craniorachischisis, Sec24b is affected but also with rather limited effects (although severe). In this case, transport of a specific cargo is strictly dependent on Sec24b indicating that cargo specificity has evolved among the four Sec24 paralogues.
The question arises as to whether in AD/CMRD and for the case of SAR1, for which there are also two human paralogues, the disease becomes manifest only in tissues in which there is insufficient amounts of the second paralogue to compensate for the loss of activity of the first paralogue or whether a specific cargo (chylomicrons) is strictly dependent on a specific paralogue(s) of the secretion machinery. Both the SAR1A and SAR1B genes are expressed in the intestine [18, 50, 51]. Our results show that the expression of the SAR1B gene in the duodenal biopsies from the patient AD3 was markedly decreased as compared to healthy individuals. In contrast, the expression of the normal SAR1A gene was significantly increased in AD3. The increased expression of the SAR1A gene and, presumably, of its encoded protein, SAR1A, does not appear to be sufficient to compensate for the defect in SAR1B. This is consistent with a Sar1 paralogue-specific and cargo-specific transport of chylomicrons.
In AD/CMRD, Sar1 paralogue- and cargo-specific transport could explain the rather modest and tissue specific manifestations of the disease. If, in enterocytes, the SAR1B paralogue is used specifically in PCTV vesicles, for the transport of chylomicrons, and if the SAR1A paralogue is used in PTVs, for the transport of small soluble and membrane bound proteins, then mutations in SAR1B would be expected to affect primarily or only chylomicron transport. Indeed, it has been shown that SAR1B has a weaker affinity for SEC13-SEC31A which could lead to a less constrained structure . This less constrained structure would allow the formation of larger COPII vesicles (which could transport large cargos such as chylomicrons) as compared to those assembled with SAR1A which has a stronger affinity for SEC13-31A [28, 75].
It has been proposed, in fact, that mutated SAR1B protein leads to an absence of chylomicronemia in AD because the PCTVs that are produced in the absence of Sar1 do not fuse with the Golgi and are retained in the cytosol . In contrast, in a COPII-GTP-dependent model and by analogy to the disease CLSD in humans, a mutated Sar1 protein might be expected to lead to the accumulation of tubular extensions, devoid of a coat, projecting from distended peripheral ER compartments as a consequence of defective budding [28, 72, 73]. Electron micrographs of appropriate resolution might be able to distinguish between these two possibilities but, to the present, the heavily lipid-laden nature of the enterocytes obtained from patients with AD, even in the fasted state, has precluded this.
With respect to the liver, the lack of hepatic manifestations in most cases of AD, (hepatic steatosis has been reported in only 4 patients [8, 12]) could be explained by differences in intestinal and hepatic trafficking pathways which might also use different COPII paralogues and, in particular, SAR1A for the secretion of apoB100-containing lipoproteins. It has been proposed that a smaller VLDL-specific transport vesicle, the VTV, requires Sar1 (it is not clear as to the isoform involved) to exit from the ER and also involves the ER-to Golgi vSNARE, rSec22b, which is not present in the intestinal PCTV [71, 76, 77]. Gusarova et al. also have reported that the exit of apoB100 from ER membranes in the rat liver requires COPII proteins but that the size of the lipoprotein entering the vesicle is small with further lipidation occurring downstream from COPII dependent events . Interestingly, patients with CLSD (SEC23A mutation) are not reported to have decreased cholesterol levels, malabsorption or hepatic steatosis which could point to the importance of the different COPII coat paralogues in the PTV, PCTV and VTV transport systems. Differences in the protein composition of the PTV, PCTV and VTV vesicles could also account for the differences in their cargo proteins. Taken together, the data from AD/CMRD patients suggest that specific sequences of SAR1B are essential for the intracellular processing of intestinal chylomicrons and are less important for hepatic VLDL secretion.
A final remark concerns the amount and the localization of the Sar1 protein observed by immunostaining. Sar1 immunostaining was found to localize heterogeneously in the villi and in the enterocytes of both healthy individuals and patients. Immunostaining was frequently observed on only one side of the villus and was concentrated in the apical region of the enterocytes. This pattern has been described previously for lipid droplets in AD, in CRD- Marinesco-Sjoren syndrome [14, 15] as well as for proteins involved in the chylomicron secretory pathway, including hepatic FABP  which is purported to be involved in the budding step of the PCTV . This pattern is reminiscent of the mosaicism observed for other proteins [80–82]. Whether this distribution is related to several populations of enterocytes arising from different stem cells  or to some other physiological mechanism is not known. Further, although the I and L-FABP genes have been reported as not being responsible for AD , L-FABP has been shown to be present but in reduced amounts in the enterocytes of AD patients as assessed by immunohistochemical analysis . The reason for this and its possible role in the pathology of AD remains unexplained.
The complexity of the secretory machinery and the numerous combinations of the different paralogues suggests that phenotypes similar to AD/CMRD could arise from other mutations in either tissue specific or common elements belonging to the intestinal and hepatic apoB-containing lipoprotein secretory pathways. We have, in fact, now found four families with 6 affected individuals that exhibit the AD/CMRD phenotype in which the SAR1B gene is normal (unpublished results). We are currently in the process of defining the genetic defect in these families.
The authors thank Pr J Schmitz (Département de Pédiatrie, Hôpital Necker-Enfants Malades, AP-HP, 75015 Paris) for invaluable brain storming in order to understand these 3 new cases of Anderson's disease, MC Federspiel (UF de Biochimie des Maladies Métaboliques, Service de Biochimie Métabolique, Groupe Hospitalier Pitié-Salpêtrière, AP-HP), S. Faïna (Service de Biochimie et Génétique Moléculaire, CHU A Paré, AP-HP et Faculté de Médecine (PIFO-UVSQ), Boulogne) for their expert technical assistance in lipoprotein analysis and PCSK9 gene sequencing respectively, D Thiébaut (Laboratoire d'Anatomie et Cytologie Pathologiques CHU Brabois, Nancy) for her technical assistance in immunochemistry and electron microscopy and JP Laigneau (INSERM, Faculté de Médecine X Bichat, Paris, France) for his expertise in illustration.
These studies were supported by INSERM (AG, JB, JPR, MA, CB, AM, MV, MES), CNRS (LPA) and by grants from PHRC (AOMO6024), (JB, JPR, MA, CB, MV, MES) and ANR (ANR-08-GENO-002-01), (JB, JPR, MA, CB, MV, MES).
- Anderson CM, Townley RRW, Freeman M, Johansen P: Unusual causes of steatorrhoea in infancy and childhood. Med J Australia. 1961, ii: 617-622.Google Scholar
- Polonovski C, Navarro J, Fontaine JL, de Gouyon F, Saudubray JM, Cathelineau L: Maladie d'Anderson. Ann Pediatr. 1970, 17: 342-354.Google Scholar
- Costil J: Maladie d'Anderson. Journées Parisiennes de Pédiatrie. Flammarion Editeurs Paris; 1976, 229-239.Google Scholar
- Scott BB, Miller JP, Losowski MS: Hypobetalipoproteinemia - a variant of the Bassen-Kornzweig syndrome. Gut. 1979, 20: 163-168. 10.1136/gut.20.2.163.PubMed CentralView ArticlePubMedGoogle Scholar
- Gauthier S, Sniderman A: Action tremor as a manifestation of chylomicron retention disease. Ann Neurol. 1983, 14: 591. 10.1002/ana.410140517.View ArticlePubMedGoogle Scholar
- Bouma ME, Beucler I, Aggerbeck LP, Infante R, Schmitz J: Hypobetalipoproteinemia with accumulation of an apoprotein B-like protein in intestinal cells. J Clin Invest. 1986, 78: 398-410. 10.1172/JCI112590.PubMed CentralView ArticlePubMedGoogle Scholar
- Polenco I, Mellado MJ, Lama R, Larrauri J, Zapata A, Redondo E, Vazquez C: Anderson's disease. An Esp Pediatr. 1986, 24: 185-188.Google Scholar
- Roy CC, Levy E, Green PHR, Sniderman A, Letartre J, Buts JP, Orquin J, Brochu P, Weber AM, Morin CL, et al: Malabsorption, hypocholesterolemia and fat-filled enterocytes with increased intestinal apoprotein B. Gastroenterology. 1987, 92: 390-399.PubMedGoogle Scholar
- Levy E, Marcel Y, Deckelbaum RJ, Milne R, Lepage G, Seidman E, Bendayan M, Roy CC: Intestinal apoB synthesis, lipids, and lipoproteins in chylomicron retention disease. J Lipid Res. 1987, 28: 1263-1274.PubMedGoogle Scholar
- Lacaille F, Bratos M, Bouma ME, Jos J, Schmitz J, Rey J: Anderson's disease. Clinical and morphologic study of 7 cases. Arch Fr Pediatr. 1989, 46: 491-498.PubMedGoogle Scholar
- Strich D, Goldstein R, Phillips A, Shemer R, Goldberg Y, Razin A, Freier S: Anderson's disease : no linkage to the apo B locus. J Pediatr Gastroenterol Nutr. 1993, 16: 257-264. 10.1097/00005176-199304000-00006.View ArticlePubMedGoogle Scholar
- Nemeth A, Myrdal U, Veress B, Rudling M, Berglund L, Angelin B: Studies on lipoprotein metabolism in a family with jejunal chylomicron retention. Eur J Clin Invest. 1995, 25: 271-280. 10.1111/j.1365-2362.1995.tb01559.x.View ArticlePubMedGoogle Scholar
- Benavent MO, Casanova MC, Perez AP, Konickx CR, Calvete JF: Anderson's disease (steatorrhea due to the retention of chylomicrons) : diagnostic criteria. An Esp Pediatr. 1997, 47: 195-198.Google Scholar
- Dannoura AH, Berriot-Varoqueaux N, Amati P, Abadie V, Verthier N, Schmitz J, Wetterau JR, Samson-Bouma ME, Aggerbeck LP: Anderson's disease : exclusion of apolipoprotein and intracellular lipid transport genes. Arterioscler Thromb Vasc Biol. 1999, 19: 2494-2508.View ArticlePubMedGoogle Scholar
- Aguglia U, Annesi G, Pasquinelli G, Spadafora P, Gambardella A, Annesi F, Pasqua AA, Cavalcanti F, Crescibene L, Bagala A, et al: Vitamin E deficiency due to chylomicron retention disease in Marinesco-Sjogren syndrome. Ann Neurol. 2000, 47: 260-264. 10.1002/1531-8249(200002)47:2<260::AID-ANA21>3.0.CO;2-V.View ArticlePubMedGoogle Scholar
- Biselli R, Boldrini R, D'Altilia M, Bosman C: Celiac disease or chylomicron retention disease?. Pathologica. 2000, 92: 130.PubMedGoogle Scholar
- Boldrini R, Biselli R, Bosman C: Chylomicron retention disease--the role of ultrastructural examination in differential diagnosis. Pathol Res Pract. 2001, 197: 753-757.PubMedGoogle Scholar
- Jones B, Jones EL, Bonney SA, Patel HN, Mensenkamp AR, Eichenbaum-Voline S, Rudling M, Myrdal U, Annesi G, Naik S, et al: Mutations in a Sar1 GTPase of COPII vesicles are associated with lipid absorption disorders. Nat Genet. 2003, 34: 29-31. 10.1038/ng1145.View ArticlePubMedGoogle Scholar
- Charcosset M, Sassolas A, Peretti N, Roy CC, Deslandres C, Sinnett D, Levy E, Lachaux A: Anderson or chylomicron retention disease: molecular impact of five mutations in the SAR1B gene on the structure and the functionality of Sar1b protein. Mol Genet Metab. 2008, 93: 74-84. 10.1016/j.ymgme.2007.08.120.View ArticlePubMedGoogle Scholar
- Annesi G, Aguglia U, Tarantino P, Annesi F, De Marco EV, Civitelli D, Torroni A, Quattrone A: SIL1 and SARA2 mutations in Marinesco-Sjogren and chylomicron retention diseases. Clin Genet. 2007, 71: 288-289. 10.1111/j.1399-0004.2007.00759.x.View ArticlePubMedGoogle Scholar
- Silvain M, Bligny D, Aparicio T, Laforet P, Grodet A, Peretti N, Menard D, Djouadi F, Jardel C, Begue J, et al: Anderson's disease (chylomicron retention disease): a new mutation in the SARA2 gene associated with muscular and cardiac abnormalities. Clin Genet. 2008, 74: 546-552. 10.1111/j.1399-0004.2008.01069.x.View ArticlePubMedGoogle Scholar
- Treepongkaruna S, Chongviriyaphan N, Suthutvoravut U, Charoenpipop D, Choubtum L, Wattanasirichaigoon D: Novel missense mutations of SAR1B gene in an infant with chylomicron retention disease. J Pediatr Gastroenterol Nutr. 2009, 48: 370-373. 10.1097/MPG.0b013e318183188f.View ArticlePubMedGoogle Scholar
- Cefalu AB, Calvo PL, Noto D, Baldi M, Valenti V, Lerro P, Tramuto F, Lezo A, Morra I, Cenacchi G, et al: Variable phenotypic expression of chylomicron retention disease in a kindred carrying a mutation of the Sara2 gene. Metabolism. 2010, 59: 463-467. 10.1016/j.metabol.2009.07.042.View ArticlePubMedGoogle Scholar
- Peretti N, Roy CC, Sassolas A, Deslandres C, Drouin E, Rasquin A, Seidman E, Brochu P, Vohl MC, Labarge S, et al: Chylomicron retention disease: a long term study of two cohorts. Mol Genet Metab. 2009, 97: 136-142. 10.1016/j.ymgme.2009.02.003.View ArticlePubMedGoogle Scholar
- Bernard G, Panisset M, Sadikot AF, Chouinard S: Chylomicron retention disease: dystonia as a new clinical feature. Mov Disord. 2010, 25: 1755-1756. 10.1002/mds.23165.View ArticlePubMedGoogle Scholar
- Peretti N, Sassolas A, Roy CC, Deslandres C, Charcosset M, Castagnetti J, Pugnet-Chardon L, Moulin P, Labarge S, Bouthillier L, Lachaux A, Levy E: Guidelines for the diagnosis and management of chylomicron retention disease based on a review of the literature and the experience of two centers. Orphanet Journal of Rare Diseases. 2010, 5:24. 10.1186/1750-1172-5-24.PubMed CentralView ArticlePubMedGoogle Scholar
- Gurkan C, Stagg SM, Lapointe P, Balch WE: The COPII cage: unifying principles of vesicle coat assembly. Nat Rev Mol Cell Biol. 2006, 7: 727-738. 10.1038/nrm2025.View ArticlePubMedGoogle Scholar
- Fromme JC, Orci L, Schekman R: Coordination of COPII vesicle trafficking by Sec23. Trends Cell Biol. 2008, 18: 330-336. 10.1016/j.tcb.2008.04.006.View ArticlePubMedGoogle Scholar
- Stagg SM, LaPointe P, Razvi A, Gurkan C, Potter CS, Carragher B, Balch WE: Structural basis for cargo regulation of COPII coat assembly. Cell. 2008, 134: 474-484. 10.1016/j.cell.2008.06.024.PubMed CentralView ArticlePubMedGoogle Scholar
- Hughes H, Stephens DJ: Assembly, organization, and function of the COPII coat. Histochem Cell Biol. 2008, 129: 129-151. 10.1007/s00418-007-0363-x.PubMed CentralView ArticlePubMedGoogle Scholar
- Siddiqi SA, Gorelick FS, Mahan JT, Mansbach CM: COPII proteins are required for Golgi fusion but not for endoplasmic reticulum budding of the pre-chylomicron transport vesicle. J Cell Sci. 2003, 116: 415-427. 10.1242/jcs.00215.View ArticlePubMedGoogle Scholar
- Neeli I, Siddiqi SA, Siddiqi S, Mahan J, Lagakos WS, Binas B, Gheyi T, Storch J, Mansbach CM: Liver fatty acid-binding protein initiates budding of pre-chylomicron transport vesicles from intestinal endoplasmic reticulum. J Biol Chem. 2007, 282: 17974-17984. 10.1074/jbc.M610765200.View ArticlePubMedGoogle Scholar
- Siddiqi S, Saleem U, Abumrad N, Davidson N, Storch J, Siddiqi SA, Mansbach CM: A Novel Multi-protein Complex Is Required for the Generation of the Pre-chylomicron Transport Vesicle from Intestinal ER. J Lipid Res. 2010, 51: 1918-1928. 10.1194/jlr.M005611.PubMed CentralView ArticlePubMedGoogle Scholar
- Siddiqi S, Siddiqi SA, Mansbach CM: Sec24C is required for docking the prechylomicron transport vesicle with the Golgi. J Lipid Res. 2010, 51: 1093-1100. 10.1194/jlr.M002758.PubMed CentralView ArticlePubMedGoogle Scholar
- Mansbach CM, Siddiqi SA: The biogenesis of chylomicrons. Annu Rev Physiol. 2010, 72: 315-333. 10.1146/annurev-physiol-021909-135801.View ArticlePubMedGoogle Scholar
- Abifadel M, Varret M, Rabes JP, Allard D, Ouguerram K, Devillers M, Cruaud C, Benjannet S, Wickham L, Erlich D, et al: Mutations in PCSK9 cause autosomal dominant hypercholesterolemia. Nat Genet. 2003, 34: 154-156. 10.1038/ng1161.View ArticlePubMedGoogle Scholar
- Abifadel M, Rabes JP, Devillers M, Munnich A, Erlich D, Junien C, Varret M, Boileau C: Mutations and polymorphisms in the proprotein convertase subtilisin kexin 9 (PCSK9) gene in cholesterol metabolism and disease. Hum Mutat. 2009, 30: 520-529. 10.1002/humu.20882.View ArticlePubMedGoogle Scholar
- Horton JD, Cohen JC, Hobbs HH: PCSK9: a convertase that coordinates LDL catabolism. J Lipid Res. 2009, 50 (Suppl): S172-7. 10.1194/jlr.R800091-JLR200.PubMed CentralPubMedGoogle Scholar
- Lambert G, Charlton F, Rye KA, Piper DE: Molecular basis of PCSK9 function. Atherosclerosis. 2009, 203: 1-7. 10.1016/j.atherosclerosis.2008.06.010.View ArticlePubMedGoogle Scholar
- Allain CC, Poon LS, Chan CS, Richmond W, Fu PC: Enzymatic determination of total serum cholesterol. Clin Chem. 1974, 20: 470-475.PubMedGoogle Scholar
- Fossati P, Prencipe L: Serum triglycerides determined colorimetrically with an enzyme that produces hydrogen peroxide. Clin Chem. 1982, 28: 2077-2080.PubMedGoogle Scholar
- Egloff M, Leglise D, Duvillard L, Steinmetz J, Boyer MJ, Ruelland A, Agher R, Beucler I: Multicenter evaluation on different analyzers of three methods for direct HDL-cholesterol assay. Ann Biol Clin (Paris). 1999, 57: 561-572.Google Scholar
- Friedewald WT, Levy RI, Fredrickson DS: Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin Chem. 1972, 18: 499-502.PubMedGoogle Scholar
- Albers JJ, Marcovina SM, Kennedy H: International Federation of Clinical Chemistry standardization project for measurements of apolipoproteins A-I and B. II. Evaluation and selection of candidate reference materials. Clin Chem. 1992, 38: 658-662.PubMedGoogle Scholar
- Salmon S, Goldstein S, Pastier D, Theron L, Berthelier M, Ayrault-Jarrier M, Dubarry M, Rebourcet R, Pau B: Monoclonal antibodies to low density lipoprotein used for the study of low- and very-low-density lipoproteins, in "ELISA" and immunoprecipitation technics. Biochem Biophys Res Commun. 1984, 125: 704-711. 10.1016/0006-291X(84)90596-5.View ArticlePubMedGoogle Scholar
- Pease RJ, Milne RW, Jessup WK, Law A, Provost P, Fruchart JC, Roevens P: Use of bacterial expression cloning to localize the epitopes for a series of monoclonal antibodies against apolipoprotein B-100. J Biol Chem. 1990, 265: 553-568.PubMedGoogle Scholar
- Livak KJ, Schmittgen TD: Analysis of relative gene expression data using real-time quantitative PCR and the 2(-Delta Delta C(T)) Method. Methods. 2001, 25: 402-408. 10.1006/meth.2001.1262.View ArticlePubMedGoogle Scholar
- Patsch JR, Miesenbock G, Hopferwieser T, Muhlberger V, Knapp E, Dunn JK, Gotto AM, Patsch W: Relation of triglyceride metabolism and coronary artery disease. Studies in the postprandial state. Arterioscler Thromb. 1992, 12: 1336-1345.View ArticlePubMedGoogle Scholar
- Yue P, Averna M, Lin X, Schonfeld G: The c.43_44insCTG variation in PCSK9 is associated with low plasma LDL-cholesterol in a Caucasian population. Hum Mutat. 2006, 27: 460-466. 10.1002/humu.20316.View ArticlePubMedGoogle Scholar
- Su AI, Wiltshire T, Batalov S, Lapp H, Ching KA, Block D, Zhang J, Soden R, Hayakawa M, Kreiman G, et al: A gene atlas of the mouse and human protein-encoding transcriptomes. Proc Natl Acad Sci USA. 2004, 101: 6062-6067. 10.1073/pnas.0400782101.PubMed CentralView ArticlePubMedGoogle Scholar
- Gurkan C, Lapp H, Alory C, Su AI, Hogenesch JB, Balch WE: Large-scale profiling of Rab GTPase trafficking networks: the membrome. Mol Biol Cell. 2005, 16: 3847-3864. 10.1091/mbc.E05-01-0062.PubMed CentralView ArticlePubMedGoogle Scholar
- Jardim DL, da Cunha AF, Duarte Ada S, dos Santos CO, Saad ST, Costa FF: Expression of Sara2 human gene in erythroid progenitors. J Biochem Mol Biol. 2005, 38: 328-333.View ArticlePubMedGoogle Scholar
- Schwarz K, Iolascon A, Verissimo F, Trede NS, Horsley W, Chen W, Paw BH, Hopfner KP, Holzmann K, Russo R, et al: Mutations affecting the secretory COPII coat component SEC23B cause congenital dyserythropoietic anemia type II. Nat Genet. 2009, 41: 936-940. 10.1038/ng.405.View ArticlePubMedGoogle Scholar
- Berriot-Varoqueaux N, Aggerbeck LP, Samson-Bouma ME, Wetterau JR: The role of the Microsomal Triglyceride Transfer Protein in Abetalipoproteinemia. Annu Rev Nutr. 2000, 20: 663-697. 10.1146/annurev.nutr.20.1.663.View ArticlePubMedGoogle Scholar
- Cooper RA, Durocher JR, Leslie MH: Decreased fluidity of red cell membrane lipids in abetalipoproteinemia. J Clin Invest. 1977, 60: 115-121. 10.1172/JCI108747.PubMed CentralView ArticlePubMedGoogle Scholar
- Frézal J, Rey J, Polonovski J, Levy G, Lamy M: L'absence congénital de beta-lipoprotéines: étude de l'absorption des graisses après exsanguino-transfusion et mesure de la demi-vie des betalipoprotéines injectées. Rev Fr Clin Biol. 1961, 6: 677-683.PubMedGoogle Scholar
- Cooper RA, Gulbrandsen CL: The relationship between serum lipoproteins and red cell membranes in abetalipoproteinemia and deficiency of lecithin cholesterol acyl transferase. J Lab Clin Med. 1971, 78: 323-335.PubMedGoogle Scholar
- Schwartz JF, Rowland LP, Eder H, Marks PA, Osterman EF, Hirschberg E, Anderson H: Bassen-Kornzweig syndrome: Deficiency of serum β-Lipoprotein: A neuromuscular disorder resembling Friedreich's Ataxia, associated with steatorrhea, acanthocytosis, retinitis pigmentosa, and a disorder of lipid metabolism. Arch Neurol. 1963, 8: 438-454.View ArticleGoogle Scholar
- Perrin J, Georges A, Morali A, Vigneron C, Lecompte T, Lesesve JF: Acanthocytes and hypocholesterolemia. Ann Biol Clin Paris. 2008, 66: 569-572.PubMedGoogle Scholar
- Taneja TK, Mankouri J, Karnik R, Kannan S, Smith AJ, Munsey T, Christesen HB, Beech DJ, Sivaprasadarao A: Sar1-GTPase-dependent ER exit of KATP channels revealed by a mutation causing congenital hyperinsulinism. Hum Mol Genet. 2009, 18: 2400-2413. 10.1093/hmg/ddp179.View ArticlePubMedGoogle Scholar
- Rashid S, Curtis DE, Garuti R, Anderson NN, Bashmakov Y, Ho YK, Hammer RE, Moon YA, Horton JD: Decreased plasma cholesterol and hypersensitivity to statins in mice lacking Pcsk9. Proc Natl Acad Sci USA. 2005, 102: 5374-5379. 10.1073/pnas.0501652102.PubMed CentralView ArticlePubMedGoogle Scholar
- Zhang DW, Lagace TA, Garuti R, Zhao Z, McDonald M, Horton JD, Cohen JC, Hobbs HH: Binding of proprotein convertase subtilisin/kexin type 9 to epidermal growth factor-like repeat A of low density lipoprotein receptor decreases receptor recycling and increases degradation. J Biol Chem. 2007, 282: 18602-18612. 10.1074/jbc.M702027200.View ArticlePubMedGoogle Scholar
- Zhao Z, Tuakli-Wosornu Y, Lagace TA, Kinch L, Grishin NV, Horton JD, Cohen JC, Hobbs HH: Molecular characterization of loss-of-function mutations in PCSK9 and identification of a compound heterozygote. Am J Hum Genet. 2006, 79: 514-523. 10.1086/507488.PubMed CentralView ArticlePubMedGoogle Scholar
- Hooper AJ, Marais AD, Tanyanyiwa DM, Burnett JR: The C679X mutation in PCSK9 is present and lowers blood cholesterol in a Southern African population. Atherosclerosis. 2007, 193: 445-448. 10.1016/j.atherosclerosis.2006.08.039.View ArticlePubMedGoogle Scholar
- Leren TP, Berge KE: Identification of mutations in the apolipoprotein B-100 gene and in the PCSK9 gene as the cause of hypocholesterolemia. Clin Chim Acta. 2008, 397: 92-95. 10.1016/j.cca.2008.07.025.View ArticlePubMedGoogle Scholar
- Russell C, Stagg SM: New insights into the structural mechanisms of the COPII coat. Traffic. 2010, 11: 303-310. 10.1111/j.1600-0854.2009.01026.x.View ArticlePubMedGoogle Scholar
- Siddiqi SA, Mansbach CM: PKC zeta-mediated phosphorylation controls budding of the pre-chylomicron transport vesicle. J Cell Sci. 2008, 121: 2327-2338. 10.1242/jcs.022780.View ArticlePubMedGoogle Scholar
- Newberry EP, Xie Y, Kennedy SM, Luo J, Davidson NO: Protection against Western diet-induced obesity and hepatic steatosis in liver fatty acid-binding protein knockout mice. Hepatology. 2006, 44: 1191-1205. 10.1002/hep.21369.View ArticlePubMedGoogle Scholar
- Newberry EP, Kennedy SM, Xie Y, Luo J, Davidson NO: Diet-induced alterations in intestinal and extrahepatic lipid metabolism in liver fatty acid binding protein knockout mice. Mol Cell Biochem. 2009, 326: 79-86. 10.1007/s11010-008-0002-4.PubMed CentralView ArticlePubMedGoogle Scholar
- Siddiqi SA, Mahan J, Siddiqi S, Gorelick FS, Mansbach CM: Vesicle-associated membrane protein 7 is expressed in intestinal ER. J Cell Sci. 2006, 119: 943-950. 10.1242/jcs.02803.PubMed CentralView ArticlePubMedGoogle Scholar
- Siddiqi SA, Siddiqi S, Mahan J, Peggs K, Gorelick FS, Mansbach CM: The identification of a novel endoplasmic reticulum to Golgi SNARE complex used by the prechylomicron transport vesicle. J Biol Chem. 2006, 281: 20974-20982. 10.1074/jbc.M601401200.PubMed CentralView ArticlePubMedGoogle Scholar
- Boyadjiev SA, Fromme JC, Ben J, Chong SS, Nauta C, Hur DJ, Zhang G, Hamamoto S, Schekman R, Ravazzola M, et al: Cranio-lenticulo-sutural dysplasia is caused by a SEC23A mutation leading to abnormal endoplasmic-reticulum-to-Golgi trafficking. Nat Genet. 2006, 38: 1192-1197. 10.1038/ng1876.View ArticlePubMedGoogle Scholar
- Fromme JC, Ravazzola M, Hamamoto S, Al-Balwi M, Eyaid W, Boyadjiev SA, Cosson P, Schekman R, Orci L: The genetic basis of a craniofacial disease provides insight into COPII coat assembly. Dev Cell. 2007, 13: 623-634. 10.1016/j.devcel.2007.10.005.PubMed CentralView ArticlePubMedGoogle Scholar
- Merte J, Jensen D, Wright K, Sarsfield S, Wang Y, Schekman R, Ginty DD: Sec24b selectively sorts Vangl2 to regulate planar cell polarity during neural tube closure. Nat Cell Biol. 2010, 12: 41-46. 10.1038/ncb2002. sup pp 1-8.PubMed CentralView ArticlePubMedGoogle Scholar
- Fromme JC, Schekman R: COPII-coated vesicles: flexible enough for large cargo?. Curr Opin Cell Biol. 2005, 17: 345-352. 10.1016/j.ceb.2005.06.004.View ArticlePubMedGoogle Scholar
- Siddiqi SA: VLDL exits from the endoplasmic reticulum in a specialized vesicle, the VLDL transport vesicle, in rat primary hepatocytes. Biochem J. 2008, 413: 333-342. 10.1042/BJ20071469.View ArticlePubMedGoogle Scholar
- Siddiqi S, Mani AM, Siddiqi SA: The Identification of the SNARE-complex Required for the Fusion of VLDL Transport Vesicle with Hepatic cis-Golgi. Biochem J. 2010, 429: 391-401. 10.1042/BJ20100336.View ArticlePubMedGoogle Scholar
- Gusarova V, Brodsky JL, Fisher EA: Apolipoprotein B100 exit from the endoplasmic reticulum (ER) is COPII-dependent, and its lipidation to very low density lipoprotein occurs post-ER. J Biol Chem. 2003, 278: 48051-48058. 10.1074/jbc.M306898200.View ArticlePubMedGoogle Scholar
- Guilmeau S, Niot I, Laigneau JP, Devaud H, Petit V, Brousse N, Bouvier R, Ferkdadji L, Besmond C, Aggerbeck LP, et al: Decreased expression of Intestinal I- and L-FABP levels in rare human genetic lipid malabsorption syndromes. Histochem Cell Biol. 2007, 128: 115-123. 10.1007/s00418-007-0302-x.View ArticlePubMedGoogle Scholar
- Duluc I, Jost B, Freund JN: Multiple levels of control of the stage- and region-specific expression of rat intestinal lactase. J Cell Biol. 1993, 123: 1577-1586. 10.1083/jcb.123.6.1577.View ArticlePubMedGoogle Scholar
- Maiuri L, Rossi M, Raia V, Garipoli V, Hughes LA, Swallow D, Noren O, Sjostrom H, Auricchio S: Mosaic regulation of lactase in human adult-type hypolactasia. Gastroenterology. 1994, 107: 54-60.PubMedGoogle Scholar
- Wong MH, Saam JR, Stappenbeck TS, Rexer CH, Gordon JI: Genetic mosaic analysis based on Cre recombinase and navigated laser capture microdissection. Proc Natl Acad Sci USA. 2000, 97: 12601-12606. 10.1073/pnas.230237997.PubMed CentralView ArticlePubMedGoogle Scholar
- Rubin DC, Ong DE, Gordon JI: Cellular differentiation in the emerging fetal rat small intestinal epithelium: mosaic patterns of gene expression. Proc Natl Acad Sci USA. 1989, 86: 1278-1282. 10.1073/pnas.86.4.1278.PubMed CentralView ArticlePubMedGoogle Scholar
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