Description: Tay Sachs disease is an autosomal recessive lysosomal storage disorder (LSD) caused by significantly reduced or absent activity of beta-hexosaminidase A. This deficiency results in accumulation of GM2 ganglioside which leads to the destruction of neurons in the brain and spinal cord. Although infants with Tay Sachs disease have normal developmental progress until the age of 3-6 months, regression becomes evident as the disorder progresses. Features of this condition include hypotonia, an increased startle reflex, inattentiveness, a retinal cherry-red spot, and loss of motor skills. Over time, seizures, hearing and vision loss, and spasticity develop, and most affected children die by the age of five. Tay Sachs disease occurs more frequently among specific groups including Ashkenazi Jewish, French Canadian, Pennsylvania Amish, and Louisiana Cajun populations.

Sandhoff disease is clinically indistinguishable from Tay Sachs disease, but it results from deficiencies in both beta-hexosaminidase A and hexosaminidase B. Higher frequencies of Sandhoff disease have been reported among individuals with backgrounds including Northern Argentina Creole, the Metis population in Saskatchewan, and Lebanese descent.

The following tests are available for diagnostic and carrier testing for Tay-Sachs and Sandhoff diseases.

Hexosaminidase total

< or =15 years: > or =20 nmol/min/mg

> or =16 years: 16.4-36.2 nmol/min/mg

Hexosaminidase percent A

< or =15 years: 20-80% of total

> or =16 years: 63-75% of total

Critical Value: A small percentage (<0.5%) of carriers may exhibit normal hexosaminidase A activity and will not be detected by this method.

Method of Analysis: Enzyme Assay-Fluorometry