mucolipidosis II, III, IV, Salla disease), (3) defects of lysosomal enzymes or transport and activator proteins (sphingolipidoses: Gaucher disease, Niemann-Pick disease, Fabry disease, Faber disease, Krabbe disease) and (4) defects in degradation of gangliosides (GM I, GM II gangliosidosis, Tay Sachs disease, Sandhoff disease). The gene discussed is PPP1R3A; the disease is Tay-Sachs disease.