Correct Answer :
A. Trisomy 18
Many studies indicate that the risk of Alzheimer disease (AD) is significantly higher in women than in men. Some authorities have postulated that this difference is due to the loss of the neurotrophic effect of estrogen in postmenopausal women. The cause of AD is unknown. The prevalent notion is that most cases of AD are caused by converging risk factors that include advancing age (choice B), head injury (choice C), and lipoprotein E-epsilon 4 genotype, among other risk factors that appear to trigger a pathophysiologic cascade that, over decades, leads to dementia. Furthermore obesity (choice D), insulin resistance, vascular factors, dyslipidemia, and hypertension are also risk factors for Alzheimer-type dementia. Additional risk factors include low education level, smoking, Down's syndrome (Trisomy 21) and aluminum (still controversial). Familial forms of AD (choice E) account for less than 7% of all cases of AD, with most cases being sporadic (ie, not inherited).