Megalencephaly is commonly seen in ______

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