This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Pediatrics, environment and nutrition, Subject name: Pathology
Deficinecy of enzyme hexosaminidase, subunit causes - 
Select and explain. 
A. Tay - Sach's disease, B. Hurler's syndrome, C. Fabry disease, D. Pompe disease
A: Tay - Sach's disease
Answer: A: Tay - Sach's disease 
Explanation: Tay-Sachs Disease (GM2 Gangliosidosis: Deficiency in Hexosaminidase b Subunit) Gangliosidoses are characterized by accumulation of gangliosides, principally in the brain, as a result of a deficiency of a catabolic lysosomal enzyme. Depending on the ganglioside involved, these disorders are subclassified into GM1 and GM2 categories. Tay-Sachs disease, by far the most common of all gangliosidoses, is characterized by a mutation in and consequent deficiency of the b subunit of enzyme hexosaminidase A, which is necessary for the degradation of GM2. More than 100 mutations have been described; most affect protein folding or intracellular transpo. Referense:Robbins basic pathology pg no:229,230