Two novel variants in DYRK1B causative of AOMS3: expanding the clinical spectrum

Updates on Rare Genetic Variants, Genetic Testing, and Gene Therapy in Individuals With Obesity

PURPOSE OF REVIEW

The goal of this paper is to aggregate information on monogenic contributions to obesity in the past five years and to provide guidance for genetic testing in clinical care.

RECENT FINDINGS

Advances in sequencing technologies, increasing awareness, access to testing, and new treatments have increased the utilization of genetics in clinical care. There is increasing recognition of the prevalence of rare genetic obesity from variants with mean allele frequency < 5% -new variants in known genes as well as identification of novel genes- causing monogenic obesity. While most of these genes are in the leptin melanocortin pathway, those in adipocytes may also contribute. Common variants may contribute either to higher lifetime tendency for weight gain or provide protection from monogenic obesity. While specific genetic mutations are rare, these segregate in individuals with early-onset severe obesity; thus, collectively genetic etiologies are not as rare. Some genetic conditions are amenable to targeted treatment. Research into the discovery of novel genetic causes as well as targeted treatment is growing over time. The utility of therapeutic strategies based on the genetic risk of obesity is an advancing frontier.

Functional characterization of two DYRK1B variants causative of AOMS3

BACKGROUND

Two new missense variants (K68Q and R252H) of the protein kinase DYRK1B were recently reported to cause a monogenetic form of metabolic syndrome with autosomal dominant inheritance (AOMS3).

RESULTS

Our in vitro functional analysis reveals that neither of these substitutions eliminates or enhances the catalytic activity of DYRK1B. DYRK1B-K68Q displays reduced nuclear translocation.

CONCLUSION

The pathogenicity of DYRK1B variants does not necessarily correlate with the gain or loss of catalytic activity, but can be due to altered non-enzymatic characteristics such as subcellular localization.

Pathogenic, Total Loss-of-Function DYRK1B Variants Cause Monogenic Obesity Associated With Type 2 Diabetes

OBJECTIVE

Rare variants in DYRK1B have been described in some patients with central obesity, type 2 diabetes, and early-onset coronary disease. Owing to the limited number of conducted studies, the broader impact of DYRK1B variants on a larger scale has yet to be investigated.

RESEARCH DESIGN AND METHODS

DYRK1B was sequenced in 9,353 participants from a case-control study for obesity and type 2 diabetes. Each DYRK1B variant was functionally assessed in vitro. Variant pathogenicity was determined using criteria from the American College of Medical Genetics and Genomics (ACMG). The effect of pathogenic or likely pathogenic (P/LP) variants on metabolic traits was assessed using adjusted mixed-effects score tests.

RESULTS

Sixty-five rare, heterozygous DYRK1B variants were identified and were not associated with obesity or type 2 diabetes. Following functional analyses, 20 P/LP variants were pinpointed, including 6 variants that exhibited a fully inhibitory effect (P/LP-null) on DYRK1B activity. P/LP and P/LP-null DYRK1B variants were associated with increased BMI and obesity risk; however, the impact was notably more pronounced for the P/LP-null variants (effect of 8.0 ± 3.2 and odds ratio of 7.9 [95% CI 1.2-155]). Furthermore, P/LP-null variants were associated with higher fasting glucose and type 2 diabetes risk (effect of 2.9 ± 1.0 and odds ratio of 4.8 [95% CI 0.85-37]), while P/LP variants had no effect on glucose homeostasis.

CONCLUSIONS

P/LP, total loss-of-function DYRK1B variants cause monogenic obesity associated with type 2 diabetes. This study underscores the significance of conducting functional assessments in order to accurately ascertain the tangible effects of P/LP DYRK1B variants.

Ancestry-dependent genetic structure of the Xq28 risk haplotype in the Mexican population and its association with childhood-onset systemic lupus erythematosus

Objective

Here we aimed to investigate the association of the Xq28 risk haplotype (H1) with susceptibility to childhood-onset systemic lupus erythematosus (SLE), and to compare its frequency and genetic structure in the Mexican population with those in other continental populations.

Methods

We genotyped 15 single-nucleotide variants (SNVs) that form the H1 haplotype, using TaqMan real-time PCR. The association analysis [case-control and transmission disequilibrium test (TDT)] included 376 cases and 400 adult controls, all of whom were mestizos (MEZ). To identify risk alleles in Mexican Indigenous individuals, SNVs were imputed from whole-exome sequencing data of 1,074 individuals. The allelic frequencies determined in MEZ and Indigenous individuals were compared with those of the continental populations from the 1,000 Genomes database phase 3. Linkage disequilibrium (LD) analysis of risk alleles was performed on all populations. Interleukin-1 receptor associated kinase 1 (IRAK1) and methyl CpG binding protein 2 (MECP2) mRNA levels were determined using real-time PCR.

Results

Case-control analysis revealed genetic association with childhood-onset SLE for all 15 SNVs (OR = 1.49-1.75; p = 0.0095 to 1.81 × 10^-4) and for the Xq28 risk haplotype (OR = 1.97, p = 4 × 10^-6). Comparing with individuals of European ancestry (0.14-0.16), the frequencies of the risk alleles were significantly higher in the MEZ individuals (0.55-0.68) and even higher in Indigenous individuals (0.57-0.83). LD analysis indicated a differential haplotype structure within the Indigenous groups, which was inherited to the MEZ population as a result of genetic admixture. Individuals homozygous for the Xq28 risk haplotype exhibited decreased levels of both MECP2A and B transcripts.

Conclusion

We found that the H1 risk haplotype differs in its conformation in the Mexican population. This difference could be attributed to positive selection within the Indigenous population, with its inheritance now having an autoimmune health impact in both the Mexican Indigenous and MEZ populations.

Analysis of DYRK1B, PPARG, and CEBPB Expression Patterns in Adipose-Derived Stem Cells from Patients Carrying DYRK1B R102C and Healthy Individuals During Adipogenesis

Background: Metabolic syndrome (MetS) is a group of signs and symptoms that are associated with a higher risk of type 2 diabetes mellitus and cardiovascular diseases. The major risk factor for developing MetS is abdominal obesity, which is caused by an increase in adipocyte size or quantity. Increased adipocyte quantity is a result of differentiation of stem cells into adipose tissue. Numerous studies have investigated the expression of key transcription factors, including PPARG and CEBPB during adipocyte differentiation in murine cells such as 3T3-L1 cell lines. To better understand the expression changes during the process of fat accumulation in adipose-derived stem cells (ASCs), we compared the expression of DYRK1B, PPARG, and ẟB in ASCs between the patient (harboring DYRK1B R102C) and control (healthy individuals) groups. Methods: Gene expression was evaluated on the eighth day before induction and days 1, 5, and 15 postinduction. The pluripotent capacity of ASCs and the potential for differentiation into adipocytes were confirmed by flow cytometry analysis of surface markers (CD34, CD44, CD105, and CD90), and Oil Red O staining, respectively. The Expression of DYRK1B, PPARG, and CEBPB were assessed by real-time-polymerase chain reaction in patients and normal individuals. The effects of AZ191, a potent small molecule inhibitor on DYRK1B and CEBPB expression in patients' samples were studied. Result: The expression of DYRK1B kinase and transcription factors (CEBPB and PPARG) are higher in ASCs harboring DYRK1B R102C compared with noncarriers on days 5 and 15 during adipocyte differentiation. These proteins may be helpful to elucidate the mechanisms underlying obesity and obesity-related disorders like MetS. Furthermore, the new compound AZ191 exhibited inhibitory activity toward DYRK1B and CEBPB. We suggest that AZ191 may be helpful in defining the potential roles of DYRK1B and CEBPB in adipogenesis.

DYRK1B haploinsufficiency in a family with metabolic syndrome and abnormal cognition

A family with DYRK1B LOF variant offering to expand the phenotype beyond the metabolic syndrome.