Model for Integration of Monogenic Diabetes Diagnosis Into Routine Care: The Personalized Diabetes Medicine Program

Phenotypic features, prevalence of KCNJ11-MODY in Chinese patients with early-onset diabetes and a literature review

OBJECTIVE

Gain-of-function (GOF) variants of KCNJ11 cause neonate diabetes and maturity-onset diabetes of the young (KCNJ11-MODY), while loss-of-function (LOF) variants lead to hyperinsulinemia hypoglycemia and subsequent diabetes. Given the limited research of KCNJ11-MODY, we aimed to analyse its phenotypic features and prevalence in Chinese patients with early-onset type 2 diabetes (EOD).

DESIGN, PATIENTS AND MEASUREMENTS

We performed next-generation sequencing on 679 Chinese EOD patients to screen for KCNJ11 exons variants. Bioinformatics prediction and the American College of Medical Genetics and Genomics guidelines was used to determine the pathogenicity and diagnosed KCNJ11-MODY. A literature review was conducted to investigate the phenotypic features of KCNJ11-MODY.

RESULTS

We identified six predicted deleterious rare variants in six EOD patients (0.88%). They were classified as uncertain significance (variant of uncertain significance [VUS]), but more common in this EOD cohort than a general Chinese population database, however, without significant difference (53/10,588, 0.50%) (p = .268). Among 80 previously reported patients with KCNJ11-MODY, 23.8% (19/80) carried 9 (32.1%) LOF variants, who had significantly older age at diagnosis, higher birthweight and higher fasting C-peptide compared to patients with GOF variants. Many patients carrying VUS were not correctly diagnosed.

CONCLUSIONS

Some rare variants of KCNJ11 might contribute to the development of Chinese EOD, although available evidence has not enough power to support them as cause of KCNJ11-MODY. The clinical features of LOF variants were different from GOF variants in KCNJ11-MODY patients. It is necessary to evaluate the pathogenicity of VUS through function experiments.

In Vitro Functional Analysis Can Aid Precision Diagnostics of HNF1B-MODY

Precision medicine relies on accurate and consistent classification of sequence variants. A correct diagnosis of hepatocyte nuclear factor (HNF) 1B maturity-onset diabetes of the young, caused by pathogenic variants in the HNF1B gene, is important for optimal disease management and prognosis, and it has implications for genetic counseling and follow-up of at-risk family members. We hypothesized that the functional characterization could provide valuable information to assist the interpretation of pathogenicity of HNF1B variants. Using different in vitro functional assays, variants identified among 313 individuals, suspected to have monogenic diabetes with or without kidney disease, were characterized. The data from the functional assays were subsequently conjugated with obtained clinical, biochemical, and in silico data. Two variants (p.A167P, p.H336Pfs∗22) showed severe loss of function due to impaired transactivation, reduced DNA binding (p.A167P), and mRNA instability (p.A167P). Although both these variant carriers were diagnosed with diabetes, the p.H336Pfs∗22 carrier also had congenital absence of a kidney, which is a characteristic trait for HNF1B maturity-onset diabetes of the young. Functional analysis of the p.A167P variant revealed damaging effects on HNF-1B protein function, which may warrant imaging of the kidneys and/or pancreas. In addition, the current study has generated important data, including evidence supporting the benign functional impact of five variants (p.D82N, p.T88A, p.N394D, p.V458G, and p.T544A), and piloting new approaches that will prove critical for the growth of HNF1B-diabetes diagnosis.

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.

Genetically transitional disease: a new concept in genomic medicine

Traditional classification of genetic diseases as monogenic and polygenic has lagged far behind scientific progress. In this opinion article, we propose and define a new terminology, genetically transitional disease (GTD), referring to cases where a large-effect mutation is necessary, but not sufficient, to cause disease. This leads to a working disease nosology based on gradients of four types of genetic architecture: monogenic, polygenic, GTD, and mixed. We present four scenarios under which GTD may occur; namely, subsets of traditionally Mendelian disease, modifiable Tier 1 monogenic conditions, variable penetrance, and situations where a genetic mutational spectrum produces qualitatively divergent pathologies. The implications of the new nosology in precision medicine are discussed, in which therapeutic options may target the molecular cause or the disease phenotype.

Enrollment of underrepresented racial and ethnic groups in the Rare and Atypical Diabetes Network (RADIANT)

Introduction

Diabetes mellitus in underrepresented racial and ethnic groups (URG) is rapidly increasing in incidence and has worse outcomes than diabetes in non-Hispanic White individuals. Rare and Atypical Diabetes Network (RADIANT) established recruitment targets based on the racial and ethnic distribution of the USA to enroll a diverse study population. We examined participation of URG across RADIANT study stages and described strategies to enhance recruitment and retention of URG.

Materials and Methods

RADIANT is a multicenter NIH-funded study of people with uncharacterized forms of atypical diabetes. RADIANT participants consent online and progress through three sequential study stages, as eligible.

Results

We enrolled 601 participants with mean age 44 ± 16.8 years, 64.4% female. At Stage 1, 80.6% were White, 7.2% African American (AA), 12.2% other/more than one race, and 8.4% Hispanic. Enrollment of URG was significantly below preset targets across most stages. Referral sources differed by race (p < 0.001) but not ethnicity (p = 0.15). Most AA participants were referred by RADIANT investigators (58.5% vs. 24.5% in Whites), whereas flyers, news, social media, and family or friends were more frequent referral sources for White individuals (26.4% vs. 12.2% in AA). Ongoing initiatives to increase enrollment of URG in RADIANT include engaging with clinics/hospitals serving URG, screening electronic medical records, and providing culturally competent study coordination and targeted advertisement.

Conclusions

There is low participation of URG in RADIANT, potentially limiting the generalizability of its discoveries. Investigations into barriers and facilitators for recruitment and retention of URG in RADIANT, with implications for other studies, are ongoing.