A 35-year-old man with Down syndrome dies of acute lymphoblastic leukemia. Gross examination of the patient's brain at autopsy shows mild microcephaly and underdevelopment of the superior temporal gyri. Histologic examination would most likely show which of the following neuropathologic changes?

One of the most intriguing neurologic features of Down syndrome (trisomy 21) 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 include granulovacuolar degeneration, neurofibrillary tangles, senile (neuritic) plaques, and loss of neurons. The gene for amyloid precursor protein (APP) is located on chromosome 21, and the additional dose of the gene product in patients with trisomy 21 may predispose to precocious accumulation of Ab. Some patients with the familial form of Alzheimer disease harbor mutations in APP or presenilin genes. These mutations lead to increased production of Ab--the amyloidogenic fragment of APP. None of the other choices are associated with the pathogenesis of Down syndrome or Alzheimer disease.Diagnosis: Down syndrome, amyloidosis