This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
[{'content': 'True about trisomies is - \nSelect and explain. \nA. Increased maternal age > 35 years, B. Downs causes MR, C. Most common trisomy is trisomy 21, D. All', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Trisomy 21 or Down syndrome is the most common of the chromosomal disorder.\nThe most common cause of trisomy and therefore of Down syndrome is meiotic nondisjunction (type II Meiosis error). a Maternal age has a strong influence on the incidence of trisomy 21.\nIt occurs once in 1550 live births in women under age 20 in contrast to 1 in 25 live births for mothers over age 45. The correlation with maternal age suggests that in most cases the meiotic nondisjunction of chromosome 21 occurs in the ovum.\nApproximately 40% of the patients with trisomies have associated congenital heart disease, most common defects of the endocardial cushion including.\nOstium premium atrial septal defects.\nA-V valve malformations and\nVSDS\nDown syndrome is an important cause of mental retardation in children', 'role': 'assistant'}]