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: Pathology
[{'content': 'The most common chromosomal defect is: \nSelect and explain. \nA. Down’s, B. Turner, C. Edward, D. Patau', 'role': 'user'}, {'content': "Answer: A \nExplanation: Down’s syndrome is the most common of the chromosome disorders and a major cause of mental retardation.\nCytogenetic abnormality\nNon disjunction (MC) = 95%\nTranslocation (robertsonian) = 4 %\nMosaicism = 1%\nIncreased maternal age is the main risk factor .\nTranslocation carriers carry high recurrence risk.\nClinical features:\xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0Cardiac → endocardial cushion defect (MC)\nHypotonia\xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 GIT → duodenal atresia, TEF, IHPS, Hirschprung\nMental retardation\xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 disease, annular pancreas\nShort stature\xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 musculoskeletal system → atlantoaxial\nDislocation\nMicrocephaly/ brachycephaly\xa0 \xa0 \xa0 \xa0 \xa0 \xa0Respiratory → recurrent aspiration pneumonia\nOpen AF\xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0Endocrine → primary gonadal defect,\nHypothyroidism\nOblique palpebral fissure\xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0Haematopoietic → increased ALL and AML\nBushfield spot\xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0. But AML has a better\nDepressed nasal bridges\xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0prognosis than normal individuals\nLow set ears\xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 \xa0CNS Alzheimer's in patients older than 40 years\nShort neck\nSimian crease, clinodactyly\nSandal gap between 1st and 2nd\nToes\nKennedy crease", 'role': 'assistant'}]