<Table> <Tr> <Th_colspan="2"> Tay--Sachs disease </Th> </Tr> <Tr> <Th> Synonyms </Th> <Td> GM2 gangliosidosis, hexosaminidase A deficiency </Td> </Tr> <Tr> <Td_colspan="2"> </Td> </Tr> <Tr> <Td_colspan="2"> Cherry - red spot as seen in the retina in Tay--Sachs disease . The fovea's center appears bright red because it is surrounded by a whiter than usual area . </Td> </Tr> <Tr> <Th> Specialty </Th> <Td> Medical genetics </Td> </Tr> <Tr> <Th> Symptoms </Th> <Td> Initially: Decreased ability to turn over, sit, or crawl Later: Seizures, hearing loss, inability to move </Td> </Tr> <Tr> <Th> Usual onset </Th> <Td> Three to six months of age </Td> </Tr> <Tr> <Th> Duration </Th> <Td> Long term </Td> </Tr> <Tr> <Th> Types </Th> <Td> Infantile, juvenile, late - onset </Td> </Tr> <Tr> <Th> Causes </Th> <Td> Genetic (autosomal recessive) </Td> </Tr> <Tr> <Th> Diagnostic method </Th> <Td> Testing blood hexosaminidase A levels, genetic testing </Td> </Tr> <Tr> <Th> Differential diagnosis </Th> <Td> Sandhoff disease, Leigh syndrome, neuronal ceroid lipofuscinoses </Td> </Tr> <Tr> <Th> Treatment </Th> <Td> Supportive care, psychosocial support </Td> </Tr> <Tr> <Th> Prognosis </Th> <Td> Death often occurs in early childhood </Td> </Tr> <Tr> <Th> Frequency </Th> <Td> Rare in the general population </Td> </Tr> </Table> <Tr> <Th_colspan="2"> Tay--Sachs disease </Th> </Tr>

What type of genetic disorder is tay sachs