Type I GM2 Gangliosidosis:

An autosomal recessive inherited gangliosidosis characterized by the onset in the first 6 months of life of an exaggerated startle response, delay in psychomotor development, hypotonia (followed by spasticity), visual loss, and a macular cherry red spot. Hexosaminidase A (see BETA-N-ACETYLHEXOSAMINIDASE) is deficient, leading to the accumulation of GM2 ganglioside in neurons of the central nervous system and retina. This condition is strongly associated with Askenazic Jewish ancestory. (Menkes, Textbook of Pediatric Neurology, 5th ed pp89-96)