Maturity Onset Diabetes of the Young (MODY) via the BLK Gene

Maturity onset diabetes of the young (MODY), a primary pancreatic beta-cell defect, is the most common type of monogenic diabetes, accounting for up to 5% of young adults diagnosed with diabetes (Owen 2013; McDonald et al. 2013). MODY typically presents in lean young adults before 25 years with an autosomal dominant family history. MODY patients have continued production of endogenous insulin, absence of beta-cell autoimmunity and absence of signs of insulin resistance. As this non-insulin dependent type of diabetes is frequently misdiagnosed as Type 1 or Type 2 diabetes, a timely and accurate molecular diagnosis of MODY is essential to treatment decisions, prognosis, family screening and obstetric management of gestational diabetes (Ellard et al. 2008). MODY has been conventionally classified into 11 types in terms of causative genes (Molven et al. 2011). Heterozygous BLK pathogenic variants are a rare cause of MODY.

MODY is inherited in an autosomal dominant manner. Proteins encoded by MODY-associated genes include nuclear transcription factors controlling pancreatic development (HNF1A, HNF4A, HNF1B, PDX1, KLF11, PAX4 and NEUROD1), glucokinase (a glucose sensor in pancreatic beta-cells) (GCK), insulin (INS), kinase stimulating insulin synthesis and secretion (BLK), the enzyme carboxyl ester lipase (CEL), and the ATP-sensitive potassium (KATP) channels (ABCC8 and KCNJ11) (Ellard et al. 2008; McDonald et al. 2013). The BLK gene (12 coding exons) encodes a beta-cell tyrosine kinase stimulating insulin synthesis and secretion. BLK pathogenic variants cause MODY11 (Borowiec et al. 2009). Genetic defects of BLK found in MODY so far only include a single missense variant found in one family (p.Alu71Thr) (Human Gene Mutation Database).

BLK pathogenic variants are a rare cause of MODY (Molven et al. 2011). Detection rates in a large cohort of patients are unknown because only one missense pathogenic variant has been reported in one family (Borowiec et al. 2009).

This test provides full coverage of all coding exons of the BLK gene plus 10 bases of flanking noncoding DNA in all available transcripts along with other non-coding regions in which pathogenic variants have been identified at PreventionGenetics or reported elsewhere. We define full coverage as >20X NGS reads or Sanger sequencing. PGnome panels typically provide slightly increased coverage over the PGxome equivalent. PGnome sequencing panels have the added benefit of additional analysis and reporting of deep intronic regions (where applicable).

Dependent on the sequencing backbone selected for this testing, discounted reflex testing to any other similar backbone-based test is available (i.e., PGxome panel to whole PGxome; PGnome panel to whole PGnome).