ABSTRACT
The impact of point mutations in mitochondrial tRNA genes on the amount and stability of respiratory chain complexes and ATP synthase (OXPHOS) has been broadly characterized in cultured skin fibroblasts, skeletal muscle samples, and mitochondrial cybrids. However, less is known about how these mutations affect other tissues, especially the brain. We have compared OXPHOS protein deficiency patterns in skeletal muscle mitochondria of patients with Leigh (8363G>A), MERRF (8344A>G), and MELAS (3243A>G) syndromes. Both mutations that affect mt-tRNA(Lys) (8363G>A, 8344A>G) resulted in severe combined deficiency of complexes I and IV, compared to an isolated severe defect of complex I in the 3243A>G sample (mt-tRNA(LeuUUR). Furthermore, we compared obtained patterns with those found in the heart, frontal cortex, and liver of 8363G>A and 3243A>G patients. In the frontal cortex mitochondria of both patients, the patterns of OXPHOS deficiencies differed substantially from those observed in other tissues, and this difference was particularly striking for ATP synthase. Surprisingly, in the frontal cortex of the 3243A>G patient, whose ATP synthase level was below the detection limit, the assembly of complex IV, as inferred from 2D-PAGE immunoblotting, appeared to be hindered by some factor other than the availability of mtDNA-encoded subunits.
Subject(s)
Brain/enzymology , Mitochondria/enzymology , Mitochondria/genetics , Mitochondrial Proton-Translocating ATPases/metabolism , Mutation/genetics , RNA, Transfer, Lys/genetics , Adolescent , Child , Electron Transport/genetics , Electrophoresis, Gel, Two-Dimensional , Fatal Outcome , Female , Humans , Immunoblotting , Infant, Newborn , Kinetics , Male , Muscle Fibers, Skeletal/enzymology , Muscle Fibers, Skeletal/pathology , Muscle, Skeletal/enzymology , Muscle, Skeletal/pathology , Organ Specificity , Oxidative Phosphorylation , Oxygen Consumption , Protein Subunits/metabolismABSTRACT
Ornithine transcarbamylase (OTC) deficiency, transmitted as an X-linked trait, is the most common disorder of the urea cycle. At least 3.5% out of more than 230 mutations consist of large gene deletions, involving one or more exons. Only in 78% of OTC patients the diagnosis was confirmed on DNA level. We analysed OTC intragenic polymorphisms and haplotypes, in an attempt to contribute to the clarification of unresolved cases, in three populations (Czech, Portuguese, and Mozambican) and identified six novel nucleotide changes, all of them occurring with frequency higher than 12.5% in Europeans. Five of these polymorphisms occur with a significant frequency also in Africans. The number and frequency of haplotypes defined with the newly reported markers differ in individual populations.
