ABCC8 variants in MODY12: Review of the literature and report of a case with severe complications

The Elusive Nature of ABCC8-related Maturity-Onset Diabetes of the Young (ABCC8-MODY). A Review of the Literature and Case Discussion

PURPOSE OF REVIEW

Maturity-onset diabetes of the young (MODY) are monogenic forms of diabetes resulting from genetic defects, usually transmitted in an autosomal dominant fashion, leading to β-cell dysfunction. Due to the lack of homogeneous clinical features and univocal diagnostic criteria, MODY is often misdiagnosed as type 1 or type 2 diabetes, hence its diagnosis relies mostly on genetic testing. Fourteen subtypes of MODY have been described to date. Here, we review ABCC8-MODY pathophysiology, genetic and clinical features, and current therapeutic options.

RECENT FINDINGS

ABCC8-MODY is caused by mutations in the adenosine triphosphate (ATP)-binding cassette transporter subfamily C member 8 (ABCC8) gene, involved in the regulation of insulin secretion. The complexity of ABCC8-MODY genetic picture is mirrored by a variety of clinical manifestations, encompassing a wide spectrum of disease severity. Such inconsistency of genotype-phenotype correlation has not been fully understood. A correct diagnosis is crucial for the choice of adequate treatment and outcome improvement. By targeting the defective gene product, sulfonylureas are the preferred medications in ABCC8-MODY, although efficacy vary substantially. We illustrate three case reports in whom a diagnosis of ABCC8-MODY was suspected after the identification of novel ABCC8 variants that turned out to be of unknown significance. We discuss that careful interpretation of genetic testing is needed even on the background of a suggestive clinical context. We highlight the need for further research to unravel ABCC8-MODY disease mechanisms, as well as to clarify the pathogenicity of identified ABCC8 variants and their influence on clinical presentation and response to therapy.

Co-inheritance of Rare Variants of Maturity-Onset Diabetes of the Young (MODY): A Case Report and Review of the Literature

Maturity onset diabetes of the young (MODY) is a rare, monogenic autosomal dominant form of diabetes that is characterized by early-onset, non-insulin-dependent hyperglycemia, strong family history, and is often misdiagnosed as type 1 or type 2 diabetes. Co-inheritance of multiple MODY genes, however, is rare. We describe here a case of MODY involving co-inherited rare variants in the ABCC8 and B-lymphocyte kinase (BLK) genes. A 55-year-old non-obese man with a past medical history of dyslipidemia and premature ischemic heart disease was initially misdiagnosed with type 2 diabetes for more than 18 years. He is a smoker with a strong family history of diabetes affecting both of his parents and most of his siblings. Despite treatment with different oral antihyperglycemics, his diabetes remained uncontrolled with glycated hemoglobin (HBA1c) between 8 and 10% until the addition of gliclazide, which improved his HBA1c to 5.7%. Based on all the previous information, MODY was suspected, and genetic testing was done, which showed rare variants in the BLK and ABCC8 genes and suggested a co-occurrence of MODY11 and MODY12. This case highlights the importance of accurate genetic testing, which is crucial for proper MODY subtyping, enabling tailored treatment strategies and potentially improving patient outcomes. Moreover, the consistent presence of the BLK gene variant in limited cases of co-inheritance raises questions about its causative role in MODY, suggesting a need for further investigation into its clinical significance.

MODY Only Monogenic? A Narrative Review of the Novel Rare and Low-Penetrant Variants

Maturity-onset diabetes of the young (MODY) represents the most frequent form of monogenic diabetes mellitus (DM), currently classified in 14 distinct subtypes according to single gene mutations involved in the differentiation and function of pancreatic β-cells. A significant proportion of MODY has unknown etiology, suggesting that the genetic landscape is still to be explored. Recently, novel potentially MODY-causal genes, involved in the differentiation and function of β-cells, have been identified, such as RFX6, NKX2.2, NKX6.1, WFS1, PCBD1, MTOR, TBC1D4, CACNA1E, MNX1, AKT2, NEUROG3, EIF2AK3, GLIS3, HADH, and PTF1A. Genetic and clinical features of MODY variants remain highly heterogeneous, with no direct genotype-phenotype correlation, especially in the low-penetrant subtypes. This is a narrative review of the literature aimed at describing the current state-of-the-art of the novel likely MODY-associated variants. For a deeper understanding of MODY complexity, we also report some related controversies concerning the etiological role of some of the well-known pathological genes and MODY inheritance pattern, as well as the rare association of MODY with autoimmune diabetes. Due to the limited data available, the assessment of MODY-related genes pathogenicity remains challenging, especially in the setting of rare and low-penetrant subtypes. In consideration of the crucial importance of an accurate diagnosis, prognosis and management of MODY, more studies are warranted to further investigate its genetic landscape and the genotype-phenotype correlation, as well as the pathogenetic contribution of the nongenetic modifiers in this cohort of patients.

Insulin Secretion Defect in Children and Adolescents with Obesity: Clinical and Molecular Genetic Characterization

Introduction

Childhood obesity is increasing worldwide and presents as a global health issue due to multiple metabolic comorbidities. About 1% of adolescents with obesity develop type 2 diabetes (T2D); however, little is known about the genetic and pathophysiological background at young age. The objective of this study was to assess the prevalence of impaired glucose regulation (IGR) in a large cohort of children and adolescents with obesity and to characterize insulin sensitivity and insulin secretion. We also wanted to investigate adolescents with insulin secretion disorder more closely and analyze possible candidate genes of diabetes in a subcohort.

Methods

We included children and adolescents with obesity who completed an oral glucose tolerance test (OGTT, glucose + insulin) in the outpatient clinic. We calculated Matsuda index, the area under the curve (AUC (Ins/Glu)), and an oral disposition index (ISSI-2) to estimate insulin resistance and beta-cell function. We identified patients with IGR and low insulin secretion (maximum insulin during OGTT < 200 mU/l) and tested a subgroup using next generation sequencing to identify possible mutations in 103 candidate genes.

Results

The total group consisted of 903 children and adolescents with obesity. 4.5% showed impaired fasting glucose, 9.4% impaired glucose tolerance, and 1.2% T2D. Matsuda index and Total AUC (Ins/Glu) showed a hyperbolic relationship. Out of 39 patients with low insulin secretion, we performed genetic testing on 12 patients. We found five monogenetic defects (ABCC8 (n = 3), GCK (n = 1), and GLI2/PTF1A (n = 1)).

Conclusion

Using surrogate parameters of beta-cell function and insulin resistance can help identify patients with insulin secretion disorder. A prevalence of 40% mutations of known diabetes genes in the subgroup with low insulin secretion suggests that at least 1.7% of patients with adolescent obesity have monogenic diabetes. A successful molecular genetic diagnosis can help to improve individual therapy.

Genome-wide survey reveals the genetic background of Xinjiang Brown cattle in China

Introduction: Xinjiang Brown cattle are a famous dual-purpose (dairy-beef) cultivated breed in China that occupy a pivotal position within the cattle breeding industry in Xinjiang, China. However, little information is available on the genetic background of this breed. To fill this research gap, we conducted a whole-genome screen using specific-locus amplified fragment sequencing to examine the genetic structure and diversity of 130 Xinjiang Brown cattle-grazing type (XBG, traditional type) cattle. Methods: A subsequent joint analysis incorporating two ancestral breeds, specifically 19 Brown Swiss (BS) foreign and nine Kazakh (KZ) Chinese cattle, as well as 20 Xinjiang Brown cattle-housing type (XBH) cattle, was used to explore the genetic background of the Xinjiang Brown cattle. Results: The results showed that, after nearly a century of crossbreeding, XBG cattle formed a single population with a stable genetic performance. The genetic structure, genetic diversity, and selection signature analysis of the two ancestral types showed highly different results compared to that of XBH cattle. Local ancestry inference showed that the average proportions of XGB cattle within the BS and KZ cattle lineages were 37.22% and 62.78%, respectively, whereas the average proportions of XBH cattle within the BS and KZ cattle lineages were 95.14% and 4.86%, respectively. Thus, XGB cattle are more representative of all Xinjiang Brown cattle, in line with their breeding history, which involves crossbreeding. Two complementary approaches, fixation index and mean nucleotide diversity, were used to detect selection signals in the four aforementioned cattle breeds. Finally, the analysis of 26 candidate genes in Xinjiang Brown cattle revealed significant enrichment in 19 Gene Ontology terms, and seven candidate genes were enriched in three pathways related to disease resistance (CDH4, SIRPB1, and SIRPα) and the endocrine system (ADCY5, ABCC8, KCNJ11, and KCNMA1). Finally, development of the core SNPs in XBG cattle yielded 8,379 loci. Conclusion: The results of this study detail the evolutionary process of crossbreeding in Xinjiang Brown cattle and provide guidance for selecting and breeding new strains of this species.

ABCC8-Related Monogenic Diabetes Presenting Like Type 1 Diabetes in an Adolescent

Background

Identifying cases of diabetes caused by single gene mutations between the more common type 1 diabetes (T1D) and type 2 diabetes (T2D) is a difficult but important task. We report the diagnosis of ATP-binding cassette transporter sub-family C member 8 (ABCC8)-related monogenic diabetes in a 35-year-old woman with a protective human leukocyte antigen (HLA) allele who was originally diagnosed with T1D at 18 years of age.

Case Report

Patient A presented with polyuria, polydipsia, and hypertension at the age of 18 years and was found to have a blood glucose > 500 mg/dL (70-199 mg/dL) and an HbA1C (hemoglobin A1C) >14% (4%-5.6%). She had an unmeasurable C-peptide but no urine ketones. She was diagnosed with T1D and started on insulin therapy. Antibody testing was negative. She required low doses of insulin and later had persistence of low but detectable C-peptide. At the age of 35 years, she was found to have a protective HLA allele, and genetic testing revealed a pathogenic mutation in the ABCC8 gene. The patient was then successfully transitioned to sulfonylurea therapy.

Discussion

Monogenic diabetes diagnosed in adolescence typically presents with mild to moderate hyperglycemia, positive family history and, in some cases, other organ findings or dysfunction. The patient in this report presented with very high blood glucose, prompting the diagnosis of T1D. When she was found to have a protective HLA allele, further investigation revealed the mutation in the sulfonylurea receptor gene, ABCC8.

Conclusion

Patients suspected of having T1D but with atypical clinical characteristics such as negative autoantibodies, low insulin requirements, and persistence of C-peptide should undergo genetic testing for monogenic diabetes.

Severe nephrotic syndrome and early end-stage diabetic kidney disease in ABCC8-MODY12: A case report

A 24-year-old man with diabetes mellitus presented with advanced kidney disease and severe proteinuria. Genetic testing revealed ABCC8-MODY12 (OMIM 600509), and a kidney biopsy showed nodular glomerulosclerosis. He commenced dialysis shortly thereafter, and glycemic control improved on treatment with a sulfonylurea. Diabetic end-stage kidney disease in patients with ABCC8-MODY12 has not been reported until now. Thus, our case highlights the risk for early-onset and severe diabetic kidney disease in patients with ABCC8-MODY12 and the importance of timely genetic diagnosis in unusual cases of diabetes to allow for proper treatment and prevention of late sequelae of diabetes.

A case report of maturity-onset diabetes of the young (MODY12) in a Chinese Han patient with a novel ABCC8 gene mutation

RATIONALE

Maturity onset diabetes of the young (MODY) is the most common type of monogenic diabetes, characterized by autosomal dominant inheritance, the age of onset is often <25 years old, and the clinical manifestations are atypical. MODY12 is caused by a rare missense mutation of adenosine triphosphate (ATP)-binding cassette transporter subfamily C member 8 (ABCC8) gene and more than 50 ABCC8 variants were associated with MODY12.

PATIENT CONCERNS

The patient was a 30-year-old Chinese Han man. He was overweight with a poor control of blood glucose.

DIAGNOSES

The patient was diagnosed with MODY12.

INTERVENTIONS

The patient was given glimepiride (4 mg/d) with diet and exercise therapy to reduce blood glucose and weight.

OUTCOMES

The level of fasting blood glucose and C-peptide was improved after 1 year treatment as well as body weight.

LESSONS

A Chinese Han adult with a heterozygous missense mutation c.3976G > A (p.Glu1326Lys) was diagnosed with MODY12, which was the new pathogenic mutation for the disease. This report expands the spectrum of variants causing MODY12 and reduces misdiagnosis.

An effective preselection criterion for MODY with an increasingly positive genetic testing rate by NGS: results from two cohorts of Chinese children

The purpose of this study was to determine the frequency of maturity-onset diabetes of the young (MODY) in two selected cohorts of Chinese children with diabetes and clinically suspected MODY, using next-generation sequencing (NGS). Ninety-three children who met the comprehensive criteria of suspected MODY were enrolled in two cohorts. A custom NGS panel or a whole exon group was used for sequencing. We identified 55/93 (59.1%) children with pathogenic and likely pathogenic MODY variants. Forty-two (76.3%) were confirmed to have the GCK (MODY2) mutation. Additionally, five had the HNF1A (MODY3), two the HNF1B (MODY5), one the 17q12 microdeletion (MODY5), two the HNF4A (MODY1), two the ABCC8 (MODY12), and one the PDX1 mutation (MODY4). Of these, 13 novel variants were detected in different genes. By comparing the gene-positive with gene-negative children, we found that discriminatory factors for MODY at diagnosis included lower HbA1c [7.4% vs. 10.2% (53 vs. 86 mmol/mol); P = 0.002], lower body mass index z score (0.2 vs. 1.0; P = 0.01), lower onset age (8.1 vs. 11.2 years; P = 0.001), and lower C-peptide (1.4 vs. 2.5 ng/mL; P = 0.02). In conclusion, the criteria used in this study for screening MODY are effective, and MODY2 is the most common subtype (76%), followed by MODY3 and MODY5. Some rare MODY subtypes have been reported in Chinese children.NEW & NOTEWORTHY We proved the clinical suspicion of maturity-onset diabetes of the young (MODY) according to the comprehensive criterion for next-generation sequencing testing, which helps to identify both common and rare MODYs, leading to accurate diagnosis and personalized treatment.

Maturity-Onset Diabetes of the Young: Mutations, Physiological Consequences, and Treatment Options

Maturity-Onset Diabetes of the Young (MODY) is a rare form of diabetes which affects between 1% and 5% of diagnosed diabetes cases. Clinical characterizations of MODY include onset of diabetes at an early age (before the age of 30), autosomal dominant inheritance pattern, impaired glucose-induced secretion of insulin, and hyperglycemia. Presently, 14 MODY subtypes have been identified. Within these subtypes are several mutations which contribute to the different MODY phenotypes. Despite the identification of these 14 subtypes, MODY is often misdiagnosed as type 1 or type 2 diabetes mellitus due to an overlap in clinical features, high cost and limited availability of genetic testing, and unfamiliarity with MODY outside of the medical profession. The primary aim of this review is to investigate the genetic characterization of the MODY subtypes. Additionally, this review will elucidate the link between the genetics, function, and clinical manifestations of MODY in each of the 14 subtypes. In providing this knowledge, we hope to assist in the accurate diagnosis of MODY patients and, subsequently, in ensuring they receive appropriate treatment.