Infants with type I disease are usually hypotonic from birth but develop spasticity, psychomotor retardation, and hyperreflexia within 6 months. Early death from cardiopulmonary disease or infection is common. Hepatomegaly, coarse facial features, brachydactyly, and cardiomyopathy with valvular dysfunction are common. Dermal melanocytosis has also been described in infants in a pattern some have called Mongolian spots. Skeletal dysplasia is a feature and often leads to vertebral deformities and scoliosis. The ears are often large and low-set, the nasal bridge is depressed, the tongue is enlarged and frontal bossing is often striking. Hirsutism, coarse skin, short digits, and inguinal hernias are common.
The juvenile form, type II, has a later onset with psychomotor deterioration, seizures and skeletal changes apparent between 7 and 36 months and death in childhood. Visceral involvement and cherry-red spots are usually not present.
Type III, or adult form, is manifest later in the first decade or even sometime by the 4th decade. Symptoms and signs are more localized. Neurological signs are evident as dystonia or speech and gait difficulties. Dementia, parkinsonian signs, and extrapyramidal disease are late features. No hepatosplenomegaly, facial dysmorphism, or cherry red spots are present in most individuals. Lifespan may be normal in this type.