Specific combination of compound heterozygous mutations in 17β-hydroxysteroid dehydrogenase type 4 (HSD17B4) defines a new subtype of D-bifunctional protein deficiency

Table 2 Patient plasma and fibroblast biochemical analyses

Test	Units	Patient 1	Patient 2	Reference range
Plasma:
VLCFA concentration
C26:0 Hexacosanoic	μg/mL	0.220	0.270	0.23 ± 0.09*
C26/C22		0.021	0.012	0.01 ± 0.004*
C24/C22		0.918	0.967	0.84 ± 0.918*
Phytanic acid	μg/mL	1.260	0.810	< 3.0
Pristanic acid	μg/mL	0.140	0.060	< 0.3
Fibroblasts:
Catalase immunofluorescence		Near-normal	Normal	Normal
VLCFA concentration:
C26:0 concentration	μmol / g protein	0.20	0.20	0.18 - 0.38
C24:0 concentration	μmol / g protein	6.52	6.79	7.76 - 17.66
C22:0 concentration	μmol / g protein	3.00	3.23	3.84 - 10.20
Ratio C26:0 / C 22:0		0.07	0.06	0.03 - 0.07
Ratio C24:0 / C 22:0		2.18	2.10	1.55 - 2.30
Peroxisome function:
β-oxidation (of C16:0)	pmol / (mg protein / hour)	3876	5061	3330 - 7790
β-oxidation (of C26:0)	pmol / (mg protein / hour)	1290	1325	800 - 2040
β-oxidation (of pristanic acid)	pmol / (mg protein / hour)	157	248	790 - 1690
α-oxidation (of phytanic acid)	pmol / (mg protein / hour)	38	45	28 - 95
D-bifunctional protein activity:
Hydratase	pmol / (mg protein / min)	43	53	115 - 600
Dehydrogenase	pmol / (mg protein / min)	2	3	25 - 300
Immunoblotting:
DBP 79 kDa		Trace	Trace	Present
DBP 45 kDa		Absent	Absent	Present
DBP 35 kDa		±/−	±/−	Present

Plasma testing was performed at Kennedy-Krieger Institute (Baltimore, USA). Fibroblast testing was performed at the Laboratory Genetic Metabolic Diseases (Amsterdam, The Netherlands).
Bold and underlined values are abnormal; *Indicates mean +/− 1 standard deviation.

ISSN: 1750-1172