An autosomal recessive neurodegenerative disorder characterized by an accumulation of G(M2) GANGLIOSIDE in neurons and other tissues. It is caused by mutation in the common beta subunit of hexosaminidase a and hexosaminidase b. Thus this disease is also known as the O variant since both hexosaminidase a and B are missing. Clinically, it is indistinguishable from tay-sachs disease.