Muscle & nerve. Supplement最新文献

Extrapolating the figures from a previous study on FSHD in a province of The Netherlands to the entire Dutch population suggests that at present a nearly complete overview is obtained of all symptomatic kindred. In 139 families, dominant inheritance was observed in 97, a pattern compatible with germline mosaicism in 6, while sporadic cases were found in 36 families. A mutation frequency of 9.6% was calculated. Mental retardation and severe retinal vasculopathy were reported in low frequencies (1%). Early onset was seen more frequently in sporadic cases. Chromosome 4 linkage appeared excluded in 3 of 22 autosomal-dominant families. The clinical pictures in the linked and nonlinked families were identical.

Pearson syndrome is a fatal disorder involving the hematopoietic system and exocrine pancreas. Mitochondrial respiratory chain deficiencies and/or rearrangements of the mitochondrial DNA were consistently observed in all patients. We report here on the variant phenotypic expression of mitochondrial genotypes in cultured cells from a patient with Pearson syndrome. Skin fibroblasts and lymphocytes harbored, respectively, 60% and 80% of deleted mtDNA molecules initially and displayed defective respiratory chain activities. In both cases, there was a progressive recovery of respiratory chain activities during in vitro cell proliferation due to the loss of deleted mtDNA molecules in cultured skin fibroblasts and to an increase in the mtRNA translation efficiency in Epstein-Barr virus-transformed lymphocytes. The present study suggests that various cellular responses to abnormal mitochondrial genotypes might contribute to the tissue-specific expression of mitochondrial disorders in vivo.

Japanese diabetic patients whose mothers were also diabetic were screened, using peripheral leukocytes, for an A to G transition at nucleotide pair 3243 of the mitochondrial gene, a tRNA(Leu)(UUR) mutation. This mutation was identified in four pedigrees from among 300 unrelated patients. Diabetes mellitus cosegretated with the mutation, except in 1 young subject, and was maternally inherited. Long-term follow-up revealed that the underlying disorder in affected members is a progressive impairment of insulin secretion. In accord with this finding, this mutation was found to be highly prevalent in a subset of diabetes mellitus called slowly progressive IDDM; the mutation was identified in 3 of 27 Japanese patients enrolled in the prospective study of islet cell antibody (ICA)-positive, initially non-insulin-dependent diabetic patients, who are very likely to become insulin dependent in several years. The histologic characteristics of slowly progressive IDDM include loss, though incomplete, of pancreatic beta-cells. Mitochondrial gene defects in beta-cells could therefore cause glucose-induced signaling defects as well as beta-cell loss, which explains the wide range of diabetic phenotypes, from NIDDM phenotype to IDDM, in patients with this mitochondrial gene mutation.

Phosphoglycerate kinase (PGK; EC 2.7.2.3) is a glycolytic enzyme encoded by a single gene on the X chromosome and ubiquitously expressed. Hereditary PGK deficiency can cause hemolytic anemia, central nervous system dysfunction, and/or myopathy characterized by exercise intolerance, cramps, and myoglobinuria. So far, 20 PGK variants with reduced PGK activity have been identified, 8 of them in patients with myopathy. Six missense mutations and one splice-junction mutation have been identified in 7 patients, 2 of whom had myopathy. However, the biochemical and molecular bases for clinical heterogeneity in PGK deficiency remain unknown.

The association of muscle glycogenosis with hyperuricemia led to the identification of a unique purine disorder. Myogenic hyperuricemia is ascribed to excessive degradation of muscle purine nucleotides, secondary to impaired ATP generation. Although this pathophysiological condition has been observed not only in glycolytic defects but also in mitochondrial diseases affecting lipid and carbohydrate oxidation, it is most common and prominent in muscle phosphofructokinase deficiency, in which neither glycogen nor glucose can be used as metabolic fuels. The first key reaction of muscle purine degradation is catalysis by AMP deaminase. Numerous studies have indicated that AMP deaminase may play an important role in energy metabolism in contracting muscle. Arguments against this hypothesis have emerged through analyses on muscle AMP deaminase deficiency. According to a recent study, the mutant allele is extremely frequent among Caucasians and African-Americans, suggesting that many individuals with this enzyme defect may be clinically asymptomatic. Further study is required to explain the significance of muscle purine degradation in energy metabolism.