GM2-gangliosidosis, AB variant is a rare, autosomal recessive metabolic disorder that causes progressive destruction of nerve cells in the brain and spinal cord.

AB variant is caused by a failure in the gene that makes an enzyme cofactor for beta-hexosaminidase, called the GM2 activator.

[2][3] Signs and symptoms of GM2-gangliosidosis, AB variant are identical with those of infantile Tay–Sachs disease, except that enzyme assay testing shows normal levels of hexosaminidase A.

As the disease progresses, infants develop seizures, vision and hearing loss, mental retardation, and paralysis.

This protein is required for the normal function of beta-hexosaminidase A, a critical enzyme in the nervous system that breaks down a lipid called GM2 ganglioside.

Because AB variant is so rarely diagnosed, it is likely that most mutations of GM2A are fatal at the embryonic or fetal stage of development in homozygotes and genetic compounds, and thus are never observed clinically.