Down’s Syndrome, Alzheimer’s Disease Show Similar Brain Abnormalities
NEW YORK (AP) _ Studying some people with the Down’s syndrome, which is present from birth, could tell scientists about a lethal condition at the other end of the human lifetime: Alzheimer’s disease, an expert says.
Not only are people with Down’s syndrome at increased risk of developing Alzheimer’s, but by middle age they develop concentrations of brain abnormalities that are characteristic of Alzheimer’s, even if they don’t show outward symptoms of that disease, said Dr. Charles Epstein.
That means people in their 30s and 40′s who have Down’s syndrome are ″an excellent population to study″ for clues to development of Alzheimer’s, Epstein, chief of the division of medical genetics at the University of California in San Francisco, said Thursday at a meeting on Down’s syndrome.
Approximately 5,000 American children are born annually with Down’s syndrome, which produces varying degrees of mental retardation and added risks for heart disease, leukemia and Alzheimer’s. The syndrome’s cause lies in the chromosomes, threadlike bodies within cells that carry the genes, the basic unit of heredity. Chromosomes usually come in pairs, but a third copy of the chromosome designated 21 causes Down’s syndrome.
No cause has been pinpointed for Alzheimer’s disease, which strikes mostly the elderly and afflicts an estimated 2.5 million Americans. The progressive illness, which kills an estimated 150,000 Americans annually, includes impairment of learning and memory, and personality changes.
Virtually all people with Down’s syndrome who have reached reach age 40 have developed brain abnormalities seen in Alzheimer’s, although only about a quarter of them show the outward symptoms of Alzheimer’s itself, Epstein said. The brain abnormalities include unusually high concentrations of fine, tangled nerve fibers and degenerating bits of nerve cells, called plaques.
Dr. Melvyn Ball, neuropathologist at the University of Western Ontario, presented a study of five Down’s syndrome brains that showed abnormalities in the same places that similar studies had found them in brains of Alzheimer’s victims.
One Down’s syndrome brain, from a man who had shown Alzheimer’s-like decline for three years before dying at age 48, contained an extensive amount of the abnormalities and major brain cell loss in an area called the hippocampus, he said. If that finding is duplicated in other Down’s syndrome brains, it would suport the idea that the declines in functioning are ″somehow very closely related to these lesions,″ he said.
The hippocampus, which plays a role in some kinds of learning and abstract thinking, typically shows abnormalities in Alzheimer’s disease and Down’s syndrome, said Lynn Nadel, professor of cognitive science at the University of Arizona in Tucson.
Much of the growth of the hippocampus takes place after birth, which raises the possibility of interventions to help fight the effects of Down’s syndrome, he said. Studies show that exposing rats to stimulating environments early in life can increase the size of the hippocampus and the number of connections between brain cells, he said.
But nobody knows how much such a strategy could accomplish, or whether it would help in a brain already weakened by the effects of Down’s syndrome, he said.