Over the past few years, there have been many attempts to gain more insight into the genetic factors involved in metabolic diseases [7,8,9]. Multiple genetic variants have been shown to participate in the pathogenesis of each of the traits of metabolic syndrome. The polygenic nature of these conditions implies that the effect of the majority of genetic variants in these disorders is small . However, families in which autosomal dominant inheritance is present have been used to search for rare mutations in genes with a strong contribution [10, 11]. The availability of exome sequencing is leading to the rapid identification of new players in the pathogenesis of metabolic diseases. This is the case for DYRK1B mutations, which cause a rare monogenic form of MetS known as AOMS3 . This syndrome has been described as the presence of abdominal obesity, type 2 diabetes, hypertension, and early-onset coronary artery disease . Pathological DYRK1B variants result in the enhanced expression of transcription factors C/EBPalpha and PPARgamma, leading to increased adipogenesis. In addition, DYRK1B increases glucose-6-phosphatase, which is strongly associated with insulin resistance, explaining the metabolic phenotypes characterizing AOMS3 [2, 3].
The participation of DYRK1B in MetS is poorly studied. Six years after DYRK1B was associated with AOMS3, only a few carriers have been reported . Furthermore, only two missense DYRK1B mutations (p.Arg102Cys and p.His90Pro) have been identified in these individuals . It is possible for rare diseases that mimic symptoms of common diseases to be confused with them. The prevalence of metabolic diseases in Mexico is one of the highest in the world [12, 13], and rare metabolic diseases are often hidden behind them; therefore, families with rare monogenic forms can remain unnoticed.
Next generation sequencing technologies have greatly improved the possibility of identifying rare pathogenic variants involved in monogenic diseases [4, 11]. In this study, after analyzing the sequence of all DYRK1B exons in a sample of 968 adult, including 509 with type 2 diabetes (SIGMA-ExAC) , we found 29 variants. SIFT and PolyPhen predicted that four of them (p.Leu28Pro, p.Asp436Asn, p.Arg252His, and p.Lys68Gln) have a deleterious and damaging effect. The p.Leu28Pro variant was described previously as having a protective effect against type 2 diabetes in a phenome-wide association study . In this study, we found five heterozygotes individuals with neither type 2 diabetes nor AOMS3, but we were not able to recruit the familial relatives to confirm its protective effect. The p.Asp436Asn variant was found in a male heterozygote, who was 98 years old and metabolically healthy. However, p.Arg252His and p.Lys68Gln exhibited co-segregation with the AOMS3 phenotype with classic dominant autosomal inheritance and full penetrance. Both variants were absent in the 1000 Genomes database , and the gnomAD database reports eight individuals with p.Arg252His variant and five with p.Lys68Gln variant, including the ones we report here. In Latinos, these variants were found with a frequency of 0.00008677 and 0.00005783, respectively .
MD structural analyses predicted that, when DYRK1B-252His was present, the formation of three hydrogen bonds was impaired, with instability in the N- and C-terminal regions. In contrast, the p.Lys68Gln variant did not produce any significant changes in the protein structure, although the NLS motif could be affected, in accordance with Kosugi et al., who showed that the N-terminal basic pattern “Lys68Arg69” is required for a strong NLS activity . More over, the effect of these variants could be similar to those documenting that DYRK1B-102Cys and DYRK1B-90Pro variants cause changes to the structure and perinuclear aggregation but barely affect the kinase activity . We classified p.Arg252His and p.Lys68Gln as causative of AOMS3, in agreement with the American College of Medical Genetics and Genomics standards and guidelines .
Compared to non-carriers of pathogenic variants, we found that carriers had higher BMI, and FG and triglyceride levels. Furthermore, pulse wave velocity was increased in all carriers, even in the absence of arterial hypertension, explaining the high cardiovascular risk found in this condition. Insulin action was decreased in all but one case, but the insulinogenic index was significantly decreased in all carriers, even in normoglycemic individuals, suggesting that the remarkable severity of hyperglycemia found in this condition results from a combination of moderate insulin resistance and a moderate to severe defect in insulin secretion. This could be supported by recent findings showing that DYRK1A and DYRK1B play an important role in human β cells proliferation .
Notably, we are describing additional features of the disease and manifestations that develop throughout life. Our findings exhibit age-dependent variance in expressivity in all patients, with some clinical features apparent at a very early age and other manifestations appearing later in life. Central obesity and insulin resistance started during childhood and then progressed rapidly to morbid obesity and labile type 2 diabetes. They also had severe hypertriglyceridemia with onset as a teenager. Similarly, AOMS3 patients developed hypertension in the fifth decade of life, and both families had a history of premature death due to cardiovascular events. Another interesting finding was that p.Lys68Gln carriers had a higher BMI, hypoinsulinemia, worse diabetes control and an increased urine albumin/creatinine ratio compared to the p.Arg252His carriers, suggesting an allelic heterogeneity.
Remarkably, none of the non-carriers had diabetes; only a 49-year-old woman (II.2 in family 2) had glucose serum levels of 109 mg/dl, along with obesity and hypertension. Other non-carrier individuals also had low levels of HDL or obesity, however, none of them met all the AOMS3 clinical features. These manifestations could be a reflection of the high prevalence of metabolic diseases in our population [12, 13].