A 42-year-old woman gives birth to a neonate with multiple congenital abnormalities. Physical findings included a flat facial profile, slanted eyes, epicanthal folds, Brushfield spots, short nose, short neck, dysplastic ears, clinodactyly, a large protruding tongue, and a pronounced heart murmur. As an adult, the brain of the patient will show histopathologic changes that are seen in patients with which of the following neurologic diseases?

One of the most intriguing neurologic features of Down syndrome is its association with Alzheimer disease. The morphologic lesions characteristic of Alzheimer disease progress in all patients with Down syndrome and are universally demonstrable by age 35 years. These changes in the brain include (1) granulovacuolar degeneration, (2) neurofibrillary tangles, (3) senile plaques, and (4) loss of neurons. The senile plaques and cerebral blood vessels of both Alzheimer disease and Down syndrome always contain an amyloid composed of the same fibrillar protein (b-amyloid protein). The other choices are unrelated to Down syndrome.Diagnosis: Down syndrome