<unk>  is typically first noticed in infants around 6 months old displaying an abnormally strong response to sudden noises or other stimuli, known as the "startle response". There may also be listlessness or muscle stiffness (hypertonia). The disease is classified into several forms, which are differentiated based on the onset age of neurological symptoms. Infantile Infants with<unk>  appear to develop normally for the first six months after birth. Then, as neurons become distended with GM2 gangliosides, a relentless deterioration of mental and physical abilities begins. The child may become blind, deaf, unable to swallow, atrophied, and paralytic. Death usually occurs before the age of four. Juvenile Juvenile<unk>  is rarer than other forms of<unk><unk> , and usually is initially seen in children between two and ten years old. People with<unk>  experience cognitive and motor skill deterioration, dysarthria, dysphagia, ataxia, and spasticity. Death usually occurs between the ages of five and fifteen years. Late-onset A rare form of this disease, known as Adult-Onset or Late-Onset<unk> , usually has its first symptoms during the 30s or 40s. In contrast to the other forms, late-onset<unk>  is usually not fatal as the effects can stop progressing. It is frequently misdiagnosed. It is characterized by unsteadiness of gait and progressive neurological deterioration. Symptoms of late-onset<unk><unk>  – which typically begin to be seen in adolescence or early adulthood – include speech and swallowing difficulties, unsteadiness of gait, spasticity, cognitive decline, and psychiatric illness, particularly a schizophrenia-like psychosis. People with late-onset<unk><unk>  may become full-time wheelchair users in adulthood. Until the 1970s and 1980s, when the disease's molecular genetics became known, the juvenile and adult forms of the disease were not always recognized as variants of<unk> . Post-infantile<unk><unk>  was often misdiagnosed as another neurological disorder, such as Friedreich's ataxia.
Tay–Sachs disease
Sandhoff disease
Fox–Fordyce disease
Leigh syndrome
Bietti's crystalline dystrophy
Neuronal ceroid lipofuscinosis
Akureyri disease
Dejerine–Sottas disease