Mitochondrial tRNA(Leu(UUR)) mutation at position 3243 and symptomatic polyneuropathy in type 2 diabetes

Endocrine disorders in mitochondrial disease

Endocrine dysfunction in mitochondrial disease is commonplace, but predominantly restricted to disease of the endocrine pancreas resulting in diabetes mellitus. Other endocrine manifestations occur, but are relatively rare by comparison. In mitochondrial disease, neuromuscular symptoms often dominate the clinical phenotype, but it is of paramount importance to appreciate the multi-system nature of the disease, of which endocrine dysfunction may be a part. The numerous phenotypes attributable to pathogenic mutations in both the mitochondrial (mtDNA) and nuclear DNA creates a complex and heterogeneous catalogue of disease which can be difficult to navigate for novices and experts alike. In this article we provide an overview of the endocrine disorders associated with mitochondrial disease, the way in which the underlying mitochondrial disorder influences the clinical presentation, and how these factors influence subsequent management.

The heteroplasmic m.14709T>C mutation in the tRNA(Glu) gene in two Tunisian families with mitochondrial diabetes

Diabetes mellitus (DM) is a heterogeneous disorder characterized by the presence of chronic hyperglycemia. Genetic factors play an important role in the development of this disorder, and several studies reported mutations in nuclear genes implicated in the insulin function. Besides, DM can be maternally transmitted in some families, possibly due to the maternal mitochondrial inheritance. In fact, mitochondrial genes may be plausible causative agents for diabetes, since mitochondrial oxidative phosphorylation plays an important role in glucose-stimulated insulin secretion from beta cells.

MATERIALS AND METHODS

In this report, we screened two Tunisian families with mitochondrial diabetes for the m.3243A>G and the m.14709T>C mutations, respectively, in the tRNA(Leu(UUR)) and the tRNA(Glu) genes.

RESULTS

The polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and the sequence-specific primers by polymerase chain reaction (SSP-PCR) analysis in the leucocytes and the buccal mucosa in the members of the two families showed the absence of the m.3243A>G mutation and the presence of the heteroplasmic m.14709T>C mutation in the tRNA(Glu) gene in the two tested tissues.

CONCLUSIONS

We conclude that the m.14709T>C mutation in the tRNA(Glu) gene could be a cause of mitochondrial diabetes in Tunisian affected families. In addition, the heteroplasmic loads correlated with the severity and the onset of mitochondrial diabetes in one family but not in the other, suggesting the presence of environmental factors or nuclear modifier genes.

Clinical features, diagnosis and management of maternally inherited diabetes and deafness (MIDD) associated with the 3243A>G mitochondrial point mutation

Maternally inherited diabetes and deafness (MIDD) affects up to 1% of patients with diabetes but is often unrecognized by physicians. It is important to make an accurate genetic diagnosis, as there are implications for clinical investigation, diagnosis, management and genetic counselling. This review summarizes the range of clinical phenotypes associated with MIDD; outlines the advances in genetic diagnosis and pathogenesis of MIDD; summarizes the published prevalence data and provides guidance on the clinical management of these patients and their families.

Mutational analysis of the mitochondrial tRNALeu(UUR) gene in Tunisian patients with mitochondrial diseases

The mitochondrial tRNA(Leu(UUR)) gene (MTTL) is a hot spot for pathogenic mutations that are associated with mitochondrial diseases with various clinical features. Among these mutations, the A3243G mutation was associated with various types of mitochondrial multisystem disorders, such as MIDD, MELAS, MERRF, PEO, hypertrophic cardiomyopathy, and a subtype of Leigh syndrome. We screened 128 Tunisian patients for the A3243G mutation in the mitochondrial tRNA(Leu(UUR)) gene. This screening was carried out using PCR-RFLP with the restriction endonuclease ApaI. None of the 128 patients or the 100 controls tested were found to carry the mitochondrial A3243G mutation in the tRNA(Leu(UUR)) gene in homoplasmic or heteroplasmic form. After direct sequencing of the entire mitochondrial tRNA(Leu(UUR)) gene and a part of the mitochondrial NADH dehydrogenase 1, we found neither mutations nor polymorphisms in the MTTL1 gene in the tested patients and controls, and we confirmed the absence of the A3243G mutation in this gene. We also found a T3396C transition in the ND1 gene in one family with NSHL which was absent in the other patients and in 100 controls. Neither polymorphisms nor other mutations were found in the mitochondrial tRNA(Leu(UUR)) gene in the tested patients.