This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Growth and development, Subject name: Pediatrics
[{'content': "Megalencephaly is commonly seen in ______ \nSelect and explain. \nA. Down syndrome, B. Tay-Sach's disease, C. Turner syndrome, D. Intauterine infection", 'role': 'user'}, {'content': 'Answer: B \nExplanation: Tay sachs disease:- Autosomal recessive. Low serum beta-hexosaminidase level is the characteristic metabolic defect. As a result GM2 ganglioside accumulates in the neurons. Initially milestones are delayed. Later there is regression of development and death occurs by 2-4 years. The baby has an abnormal stale to response. Convulsions, rigidity of extensor group of muscles and blindness supervene after the first year. A cherry red spot seen over the macular region of retina. The head size increases. Liver and spleen not enlarged. Reference: GHAI essential Paediatrics', 'role': 'assistant'}]