Analysis of Human Clinical Mutations of Mitochondrial ND1 in a Bacterial Model System for Complex I.

The most common causes of mitochondrial dysfunction and disease include mutations in subunits and assembly factors of Complex I. Numerous mutations in the mitochondrial gene ND1 have been identified in humans. Currently, a bacterial model system provides the only method for rapid construction and analysis of mutations in homologs of human ND1. In this report, we have identified nine mutations in human ND1 that are reported to be pathogenic and are located at subunit interfaces. Our hypothesis was that these mutations would disrupt Complex I assembly. Seventeen mutations were constructed in the homologous nuoH gene in an E. coli model system. In addition to the clinical mutations, alanine substitutions were constructed in order to distinguish between a deleterious effect from the introduction of the mutant residue and the loss of the original residue. The mutations were moved to an expression vector containing all thirteen genes of the E. coli nuo operon coding for Complex I. Membrane vesicles were prepared and rates of deamino-NADH oxidase activity and proton translocation were measured. Samples were also tested for assembly by native gel electrophoresis and for expression of NuoH by immunoblotting. A range of outcomes was observed: Mutations at four of the sites allow normal assembly with moderate activity (50−76% of wild type). Mutations at the other sites disrupt assembly and/or activity, and in some cases the outcomes depend upon the amino acid introduced. In general, the outcomes are consistent with the proposed pathogenicity in humans.

Analysis of Human Mutations in the Supernumerary Subunits of Complex I.

Complex I is the largest member of the electron transport chain in human mitochondria. It comprises 45 subunits and requires at least 15 assembly factors. The subunits can be divided into 14 "core" subunits that carry out oxidation-reduction reactions and proton translocation, as well as 31 additional supernumerary (or accessory) subunits whose functions are less well known. Diminished levels of complex I activity are seen in many mitochondrial disease states. This review seeks to tabulate mutations in the supernumerary subunits of humans that appear to cause disease. Mutations in 20 of the supernumerary subunits have been identified. The mutations were analyzed in light of the tertiary and quaternary structure of human complex I (PDB id = 5xtd). Mutations were found that might disrupt the folding of that subunit or that would weaken binding to another subunit. In some cases, it appeared that no protein was made or, at least, could not be detected. A very common outcome is the lack of assembly of complex I when supernumerary subunits are mutated or missing. We suggest that poor assembly is the result of disrupting the large network of subunit interactions that the supernumerary subunits typically engage in.

Prevalence of Diabetes and Prediabetes among Children Aged 11-14 Years Old in Vietnam.

AIM: Diabetes in children is becoming more prevalent in some countries. However, in most countries, little is known about the epidemiology of this disease. This study is aimed at estimating the prevalence of type 1 and type 2 diabetes and prediabetes among children in Vietnam and examining factors associated with the conditions. METHODS: A total of 2880 students aged 11-14 years old were recruited for the survey, using a school-based and nationally representative sampling frame. Capillary blood samples of participants were collected to measure fasting glucose level, using glucose meter OneTouch Verio Pro+. Diabetes and impaired fasting plasma glucose were initially diagnosed based on the cut-off points of the American Diabetes Association criteria. Diabetes status and type of diabetes of participants were confirmed at a hospital. Additionally, anthropometric and blood pressure measurements were conducted following a standardized procedure. Multivariate logistic regression was used to examine the association between outcome and independent variables. RESULTS: The overall prevalence of diabetes among the participants was 1.04‰ (three cases), with 2 cases (0.75‰) diagnosed with type 1 diabetes (one known and one newly diagnosed) and 1 case newly diagnosed with type 2 diabetes (0.35‰). The prevalence of impaired fasting glucose was 6.1%. Body mass index, place of residence, and age were found to be significantly associated with the impaired fasting glucose condition in participants. CONCLUSION: The prevalence of type 1 and type 2 diabetes in children in Vietnam is lower than that in some other countries reported recently. However, there is a high prevalence in impaired fasting glucose, requiring attention from policymakers to take action to prevent the occurrence of the epidemic of type 2 diabetes in children in the future.