Metachromatic Leukodystrophy Due to Saposin B Deficiency, also known as metachromatic leukodystrophy due to cerebroside sulfatase activator deficiency, is related to gm2-gangliosidosis, ab variant and metachromatic leukodystrophy, and has symptoms including muscle spasticity, seizures and gait ataxia. An important gene associated with Metachromatic Leukodystrophy Due to Saposin B Deficiency is PSAP (Prosaposin). Affiliated tissues include spinal cord and brain, and related phenotypes are hypotonia and muscle weakness