Familial focal loss of cross striations

Summary Two patients, a brother and sister, both suffering from congenital generalized muscle weakness with a progressive course are reported. Muscle biopsy revealed areas with loss of cross striations in the muscle fibers, electronmicroscopically presenting complete disorganization of the myofibrils with streaming of the Z discs and absence of mitochondria. Vesicular nuclei with prominent nucleoli were present in these areas. There was a type I fiber prodominance in both cases. The mean diameter of the type I muscle fibers in one of the cases was too small. Motor endplate alterations in this patient gave no evidence of denervation but were suggestive of a delayed development of motor nerves.This study was supported by grants from the Prinses Beatrix Fonds, from the FRSM of Belgium and from the Free University of Brussels