Gangliosidosis is a lysosomal storage disease in which metabolic products, primarily GM1 ganglioside, build up in the cells due to a mutation of the GLB1 gene that codes for beta-galactosidase. Beta-galactosidase aids in the breakdown and recycling of various molecules, including GM1 ganglioside, to prevent their toxic accumulation within lysosomes and to allow for proper functioning of neurons in the brain and spinal cord. Because the mutation reduces activity of beta-galactosidase, toxic levels of the molecular by-products then accumulate in the organs and tissues, causing nerve destruction.

The disorder progressively damages neurons in the brain and spinal cord. The disease occurs in 1 of 200 000 newborns. Gangliosidoses are autosomal recessive disorders. There are infant, juvenile, and adult forms, but all 3 forms of the disease result from the same gene mutation. This condition is terminal and leads to premature death, with the exception of some adult cases.

A key sign in infants is that they appear floppy and develop seizures and spasticity as they grow. Extensive blue-gray spots / congenital dermal melanocytosis (covering the sacral to extrasacral area) have been described in infants with GM1 gangliosidosis type 1 but are typically an isolated finding. The vertebrae also become abnormally curved as scoliosis develops. Death usually occurs in early childhood.