Therefore, our first aim was to investigate the enzyme activities of arylsulfatase A (ARSA, indicative for MLD) [17], β-galactosidase (β-Gal, indicative for GM1-gangliosidosis), β-hexosaminidase A (HEX A, indicative for GM2-gangliosidosis variant B (Tay Sachs disease)) and β-hexosaminidase A and B (HEX A+B, indicative for GM2-Gangliosidosis variant 0 (Sandhoff disease)) [18,19] in separated leukocyte fractions. The gene discussed is HHEX; the disease is Tay-Sachs disease.