Identification of Novel GCK and HNF4α Gene Variants in Japanese Pediatric Patients with Onset of Diabetes before 17 Years of Age

Partial GCK gene deletion mutations causing maturity-onset diabetes of the young

AIMS

Maturity-onset diabetes of the young (MODY) is an autosomal dominant monogenic form of diabetes, and glucokinase-maturity-onset diabetes of the young (GCK-MODY), or MODY 2, being the most prevalent type. However, the presence of copy number variants (CNVs) may lead to misdiagnoses, as genetic testing for MODY is typically reliant on sequencing techniques. This study aimed to describe the process of diagnosis in a Chinese pedigree with an exon 8-10 deletion of the GCK gene.

METHODS

This study collected clinical data and medical history through direct interviews with the patient and reviewing relevant medical records. Sanger sequencing and whole exome sequencing (WES) were conducted over years of follow up. WES-based CNV sequencing technology was used to detect CNVs and the results were validated by multiplex ligation-dependent amplification dosage assay (MLPA). Additionally, we reviewed the previously reported cases caused by heterozygous exon deletion of the GCK gene.

RESULTS

WES-based CNV detection revealed a heterozygous exon 8-10 deletion in the GCK gene within this particular pedigree after Sanger sequencing and WES failed to find causal variants in single nucleotide variations (SNVs) and small indels. The deletion was considered pathogenic according to ACMG/AMP and ClinGen guidelines. Most of the previously reported cases caused by heterozygous exon deletion or whole gene deletion of the GCK gene present similarly to GCK-MODY caused by SNVs and small indels.

CONCLUSIONS

This study contributed to progress in our comprehension of the mutation spectrum of the GCK gene and underscored the significance of CNV detection in the genetic testing of MODY.

The use of precision diagnostics for monogenic diabetes: a systematic review and expert opinion

BACKGROUND

Monogenic diabetes presents opportunities for precision medicine but is underdiagnosed. This review systematically assessed the evidence for (1) clinical criteria and (2) methods for genetic testing for monogenic diabetes, summarized resources for (3) considering a gene or (4) variant as causal for monogenic diabetes, provided expert recommendations for (5) reporting of results; and reviewed (6) next steps after monogenic diabetes diagnosis and (7) challenges in precision medicine field.

METHODS

Pubmed and Embase databases were searched (1990-2022) using inclusion/exclusion criteria for studies that sequenced one or more monogenic diabetes genes in at least 100 probands (Question 1), evaluated a non-obsolete genetic testing method to diagnose monogenic diabetes (Question 2). The risk of bias was assessed using the revised QUADAS-2 tool. Existing guidelines were summarized for questions 3-5, and review of studies for questions 6-7, supplemented by expert recommendations. Results were summarized in tables and informed recommendations for clinical practice.

RESULTS

There are 100, 32, 36, and 14 studies included for questions 1, 2, 6, and 7 respectively. On this basis, four recommendations for who to test and five on how to test for monogenic diabetes are provided. Existing guidelines for variant curation and gene-disease validity curation are summarized. Reporting by gene names is recommended as an alternative to the term MODY. Key steps after making a genetic diagnosis and major gaps in our current knowledge are highlighted.

CONCLUSIONS

We provide a synthesis of current evidence and expert opinion on how to use precision diagnostics to identify individuals with monogenic diabetes.

Mutations in GCK May Lead to MODY2 by Reducing Glycogen Synthesis

Dysfunction of glucokinase (GCK) caused by mutations in the GCK gene is the main cause of maturity-onset diabetes of the young type-2 (MODY2, also known as GCK-MODY), which is usually present in adolescence or young adulthood. MODY2 is characterized by mild, stable fasting hyperglycemia that presents at birth, usually 5.4-8.3 mmol L^-1 , and rarely develops complications from diabetes. The treatment of MODY2 prefers a manageable diet rather than the use of insulin. Previous studies have identified GCK mutations only by online software prediction or enzyme kinetic analysis and thermolability assays which are complicated to be conducted. In this study, six mutations in the GCK gene, including four novel mutations and two mutations that are previously reported, are identified. All the six locations are highly conserved according to the sequencing alignment. Moreover, missense mutations are strongly predicted to be pathogenic using online programs. Functional studies show that mutations in GCK mutation do not affect insulin secretion but affect glycogen synthesis. These findings demonstrate that GCK mutations decrease glycogen synthesis, which leads to hyperglycemia in MODY2. Meanwhile, this study provides a new perspective and methods for identifying pathogenic mutations in GCK.