Ultrastructural and histochemical abnormalities of skeletal muscle in a patient with a new variant (type Homburg) of glucosephosphate isomerase (GPI) deficiency.

: Ultrastructural and enzyme histochemical muscle abnormalities are described in a case with a new variant (type Homburg) of glucosephosphate isomerase (GPI) deficiency, associated with congenital nonspherocytic hemolytic anemia and muscle weakness. The enzyme is thermostable in contrast to other described variants. The muscle fibers showed decreased GPI activity, ultrastructural abnormalities, including giant mitochondria, and a diffuse increase of glycogen. The functional alteration of muscle tissue is due to a stable enzyme protein with decreased specific activity.