Congenital megaconial myopathy due to a novel defect in the choline kinase Beta gene.

To describe the first American patient with a congenital muscle dystrophy characterized by the presence in muscle of gigantic mitochondria displaced to the periphery of the fibers and to stress the potential origin and effects of the mitochondrial changes.,Case report and documentation of a novel mutation in the gene encoding choline kinase beta (CHKB).,Collaboration between 2 tertiary care academic institutions.,A 2-year-old African American boy with weakness and psychomotor delay.,Detailed clinical and laboratory studies, including muscle biopsy, biochemical analysis of the mitochondrial respiratory chain, and sequencing of the CHKB gene.,Definition of unique mitochondrial changes in muscle.,This patient had the same clinical and laboratory features reported in the first cohort of patients, but he harbored a novel CHKB mutation and had isolated cytochrome c oxidase deficiency in muscle.,Besides confirming the phenotype of CHKB mutations, we propose that this disorder affects the mitochondria-associated membrane and the impaired phospholipid metabolism in the mitochondria-associated membrane causes both the abnormal size and displacement of muscle mitochondria.