Which is M.C genetic cause of mental retardation -

Ans. is 'b' i.e., Fragile-x-syndrome Mental retardation :-IQ <70Mild MR= IQ between50-70Moderate= IQ between35-50Severe= IQ between20-35Profound MR= IQ between< 20Etiology :-Mild MR (IQ > 50) usually Environmental factor.Severe MR (IQ < 50) usually Biologic causes.Most common cause of Mild MR include genetic syndrome writh multiple minor congenital anomalis.In children with severe MR, biological cause (Most commonly prenatal can be identified in >75% of causes)Causes-include-chromosomal - Down syndromeCauses-include-genetic - Fragilex syndromeMost common genetic cause of mild MR = fragile xMost common genetic cause of moderate MR = down syndrome and in general population Mild MR > Moderate MR so overall M.C. genetic cause of MR is fragile-x-syndrome.Other features of fragile-x-syndromeo See in males > femaleso Autistic behaviorMacro orchidismLarge size facial feature.Long faceProminance jawrLearning disability'