They were first diagnosed as having atypical spinal muscular atrophy and, subsequently, spinocerebellar ataxia, but, recently, the diagnosis of late-onset Tay-Sachs disease
[ncbi.nlm.nih.gov]
Other symptoms can include ataxia, progressive dementia, psychosis, a vegetative state in some cases, muscular atrophy, and muscular denervation.
[molecularbasisdisease.pbworks.com]