GM1-gangliosidosis type I (generalised GM1-gangliosidosis) typically presents within weeks or months of birth with apathy, laboured breathing, feeding difficulties and delay in motor development. Hepatosplenomegaly, a coarse facies and, in some cases, dorsolumbar kyphosis and macular cherry-red spots occur. There is a progressive deteriorating course similar to that in Tay-Sachs disease, with death usually occurring within two years. In the juvenile and adult variants there is a later onset, slower course and less skeletal and visceral involvement.
Deficiency of lysosomal b -galactosidase activity is the primary defect in GM1-gangliosidosis.