Remodelling of skeletal muscle cells in children with SCO2 gene mutation - ultrastructural study

Mitochondrial protein coded by the SCO2 gene is involved in the process of assembly of mitochondrial cytochrome c oxidase (COX). Progressive cardiomyopathy, neuropathy and lactic acidosis are presented by infants with SCO2 gene mutations. Only a dozen patients with this gene mutation have been reported in the literature. Muscle ultrastructure is mentioned only in a few case reports. The aim of this study was to search for typical ultrastructural features in 11 skeletal muscle specimens from Polish patients bearing SCO2 gene mutations. Ultrastructural analysis confirms domination of atrophic and degenerative changes, including atrophic muscle fibres of irregular shape with folding of basal lamina and numerous papillary projections containing altered mitochondria, glycogen granules and degenerated organelles. Advanced disorganization of myofibrils and abnormalities of mitochondria were often found. Myeloid structures, vacuoles, and lipid accumulation were seen only sporadically. Those findings may be attributed to neurogenic atrophy visible in light microscopy. Our observations confirm that mutations in the SCO2 gene are frequently associated with the neurogenic pattern of skeletal muscle involvement accompanied by mitochondrial abnormalities. SCO2 gene mutation should be included in differential diagnosis in children with such a pattern; however, lack of neurogenic changes does not exclude SCO2 gene mutation.