Researchers Close In on Genetic Defect Causing Down’s Syndrome

Down’s syndrome has been linked to a defect on a tiny slice of one of the human chromosomes, an important step toward prevention and treatment of the disorder, researchers said Saturday.

In a separate report, researchers also reported progress in narrowing the search for the defect responsible for one, relatively uncommon form of Alzheimer’s disease.

In a week of intensive meetings and reviews of scientific reports, about 700 researchers from around the world announced the genetic “mapping” of about 400 new genes, 53 of them linked to specific diseases.

The reports were presented at the 10th International Workshop on Human Gene Mapping, held at Yale University.

The process of gene mapping, in which researchers determine where a particular gene lies on the 23 pairs of human chromosomes, is a necessary step toward isolating a gene and determining its role in human health.

“By mapping it, you can find it, isolate it and develop new means of therapy,” said Dr. Frank Ruddle of Yale, one of the organizers of the conference.

Down’s syndrome, marked by low IQ and facial abnormalities, is one of the most common genetic ailments. It occurs in people who mistakenly have an extra copy of chromosome 21.

Researchers reported Saturday that the condition is related to a tiny portion of that chromosome that could contain no more than a few thousand genes, probably fewer.

They can now begin to search that region for the precise genes responsible for the condition.

The work that led to the mapping of Down’s syndrome to that tiny region was done mostly by Dr. Pierre-Marie Sinet of the Necker Hospital for Sick Children in Paris and Dr. Julie Korenberg of Cedars-Sinai Medical Center in Los Angeles.

Researchers have determined that one uncommon form of Alzheimer’s disease is related to a defect on chromosome 21. They reported at the workshop that they have narrowed the location.