A 35-year old mentally retarded man died. His brain showed atrophy of the gyri and histologic features indistinguishable from those of Alzheimer disease. He had a chromosomal abnormality (trisomy 21). What was the most likely diagnosis?
A) Cerebral palsy
B) Duchene’s Muscular dystrophy
C) Mysthenia gravis
D) Myotonic dystrophy
E) Down syndrome