Genetic Defect in Alzheimer’s Found in Down’s Chromosome
The genetic defect that causes an inherited form of Alzheimer’s disease has been traced to the same chromosome responsible for Down’s syndrome, a finding that researchers say suggests the same genes may be involved in both conditions.
Scientists from Harvard Medical School and Massachusetts General Hospital, working with colleagues from other institutions, say that their results should help in isolating the culprit Alzheimer’s gene and determining what goes wrong.
In addition, the genetic tags used to trace the whereabouts of the gene one day might be used to diagnose inherited Alzheimer’s in individuals belonging to families prone to the malady long before any symptoms arise, they said.
Links to Protein Buildup
There is a possibility that the cause of the inherited Alzheimer’s disease is the same gene responsible for proteins that clog the brain of those suffering this condition, the scientists said.
Alzheimer’s disease is a degenerative condition of unknown origin that results in a buildup of tangled fibers within nerve cells of the brain and scaly plaques in between. The condition normally strikes people over age 60 and robs them of memory and physical mobility.
In a report to be published today in the journal Science, doctors Peter St. George-Hyslop, Rudolph Tanzi and James Gusella of Harvard, along with 19 other authors from institutions around the world, said that the two types of Alzheimer’s have almost identical pathology.
Anything learned about the inherited form of the disease also should be applicable to the so-called sporadic Alzheimer’s seen in the majority of patients, St. George-Hyslop and Gusella said Thursday at a briefing in Boston.
“Our discovery is the first definitive lead to an actual cause of Alzheimer’s disease,” St. George-Hyslop said.
Genes are small pieces of DNA, or deoxyribonucleic acid, the basic substance of heredity. Strands of DNA containing genes make up the 23 pairs of rod-shaped chromosomes within cells that pass on their characteristics to subsequent generations.
Focus on Chromosome 21
Finding Alzheimer’s genes on chromosome 21 is important because this genetic bank is implicated in some inherited diseases, such as Down’s syndrome, researchers said. Adults with Down’s develop the buildup of brain proteins characteristic of Alzheimer’s, and scientists have suspected there must be a link between the two diseases.
Down’s syndrome, a disabling condition that is the leading cause of mental retardation, afflicts about 5,000 newborns in the United States each year. It develops when a person has the normal complement of 23 pairs of chromosomes plus an extra copy of one of them, chromosome 21.
