The Mutations and Clinical Variability in Maternally Inherited Diabetes and Deafness: An Analysis of 161 Patients

AimsTo investigate the clinical features and mitochondrial mutations for maternally inherited diabetes and deafness.MethodsPubMed, Embase, Medline, Web of Science, the China National Knowledge Infrastructure, and Wanfang were searched with the following search terms: “Maternally inherited diabetes and deafness” OR “MIDD” OR “Mitochondrial diabetes”. The mutations and clinical features were analyzed. Correlation between the heteroplasmy levels of the m.3243A>G mutation in the peripheral blood and age at the onset of diabetes was conducted by Spearman test. The significance level was set as p < 0.05. Statistical analysis was performed using the Statistical Package for the Social Sciences version 26 for Windows.ResultsTotally 161 patients with 21 different mitochondrial mutations were enrolled. The most common mutation was the m.3243A>G mutation in 136 cases. Of 142 patients, 120 (84.51%) had family histories of diabetes or hearing loss. Hearing loss presented in 85.71% of the patients with mitochondrial mutations. Central nervous system diseases were found in 29.19%, myopathy in 22.98%, oculopathy in 23.60%, cardiac disease in 23.60%, and nephropathy in 13.66% of the patients. Forty-two of 101 (41.58%) patients were underweight. A significant negative correlation was found between the heteroplasmy levels of the m.3243A>G mutation in the peripheral blood and age at the onset of diabetes.ConclusionsThe young onset of diabetes with low or normal BMI, maternal inheritance, and presence of impairments of multiple systems should prompt a genetic testing in order to differentiate MIDD from other types of diabetes earlier.

The Role of Mitochondrial Mutations and Chronic Inflammation in Diabetes

Diabetes mellitus and related disorders significantly contribute to morbidity and mortality worldwide. Despite the advances in the current therapeutic methods, further development of anti-diabetic therapies is necessary. Mitochondrial dysfunction is known to be implicated in diabetes development. Moreover, specific types of mitochondrial diabetes have been discovered, such as MIDD (maternally inherited diabetes and deafness) and DAD (diabetes and Deafness). Hereditary mitochondrial disorders are caused by certain mutations in the mitochondrial DNA (mtDNA), which encodes for a substantial part of mitochondrial proteins and mitochondrial tRNA necessary for mitochondrial protein synthesis. Study of mtDNA mutations is challenging because the pathogenic phenotype associated with such mutations depends on the level of its heteroplasmy (proportion of mtDNA copies carrying the mutation) and can be tissue-specific. Nevertheless, modern sequencing methods have allowed describing and characterizing a number of mtDNA mutations associated with human disorders, and the list is constantly growing. In this review, we provide a list of mtDNA mutations associated with diabetes and related disorders and discuss the mechanisms of their involvement in the pathology development.

Mitochondrial diabetes and mitochondrial DNA mutation load in MELAS syndrome

Objective: Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome is a very rare condition; it encompasses a diverse group of disorders including diabetes. Phenotypic variability can be attributed to heteroplasmy along with varying proportions of mutant and WT mitochondrial DNA (mtDNA). To examine the clinical relationship between mitochondrial diabetes and mutational load, we analyzed the mtDNA of children and young adolescents with MELAS syndrome using next generation sequencing (NGS). Design and methods: Of 57 subjects with suspected MELAS syndrome, 32 children and young adolescents were diagnosed as MELAS syndrome with mtDNA A-to-G transition at nucleotide 3243. Mutation load studies and NGS were performed for 25 subjects. Results: The mean mutation load was 60.4 ± 18.4% (range: 22.5‒100). Of the 25 subjects with NGS results, 15 (60%) were diagnosed with DM and 2 (8%) were diagnosed with impaired glucose tolerance (IGT). The mutational load of subjects inversely correlated with first symptom onset, age at diagnosis of MELAS syndrome, and DM (P < 0.001). However, mutational load did not correlate with the clinical severity or progression of DM/IGT. There was no significant difference in insulin resistance or sensitivity indices between the low- and high-mutation load groups. During the 3.7 years of follow-up, insulin resistance indices were not significantly different between baseline and follow-up. Conclusions: We can infer that the mutation load in the MELAS syndrome is significantly associated with the onset of symptoms and associated diseases, including mitochondrial diabetes. However, it may not influence disease progression.

Monogenic Diabetes due to ABCC8/KCNJ11 Mutation: Case Study and Review of Literature

Monogenic diabetes arises due to mutation in a single-gene and is recognized by their striking familial inheritance pattern. This form of diabetes is inherited in an autosomal dominant or recessive fashion, unlike polygenic Type 1 (autoimmune) or type 2 diabetes caused by the combined action of more than one gene [1-11]. Monogenic diabetes is classified into three main groups: Neonatal diabetes mostly presents in the first six months of birth, maturity onset diabetes of the young (MODY) and maternally inherited mitochondrial diabetes. These mutations run in the family and have a predictable course. Most of the monogenic diabetes is treated with oral medications like sulfonylurea rather than insulin. ABCC8/KCNJ11 gene mutations also cause monogenic diabetes. This gene mutation has been found in ~50% of congenital hyperinsulinemia (CHI) patients. In such cases diabetes commonly presents in the neonatal period (transient or permanent) or at adolescence / early adulthood [1]. We present a 58-year-old diabetic lady, who was detected with ABCC8 mutation during the cascade testing [8]. She was diagnosed with diabetes at the age of 12 [8]. Her son had history of neonatal hypoglycaemia and developed diabetes at the age of 15. He was the index case who was found to have ABCC8 mutation. The family has several other members diagnosed with diabetes. The aim of the article is to increase awareness and understanding of monogenic diabetes among the medical practitioners in adult population with diabetes so that the genetic testing can be offered in a cost effective manner.