Pediatrics General b97903c8 Not true among the following is A Most common cause of Down's syndrome is Maternal meiotic disjunction. B Most Common inherited condition causing Intellectual disability in Fragile X Syndrome C The mandible in Down's child is smaller than usual D Isolated finding of simian crease in Down's in seen in almost 20% of Down's children. High-Yield Explanation Isolated finding of simian crease in Down's in seen in almost 1% of Down's children. So it is not a significant finding in a Down's child.