Adenylosuccinate Synthetase-Like 1-Related Distal Myopathy

A rare autosomal recessive distal myopathy characterized by slowly progressive diffuse muscle weakness in childhood, followed by predominantly distal muscle weakness in adolescence, and quadriceps muscle weakness in the fourth decade. Facial muscle weakness is commonly reported. Muscle biopsy shows fiber size variation, increased internal nuclei, fiber splitting, rimmed vacuoles, and focal endomysial fibrosis.