Gene mapped for inherited hearing loss.

By studying deafness among the 500 descendants of a prosperous 18th century Costa Rican landowner, an international team of researchers has found a gene that they say could account for many inherited forms of hearing loss.

Geneticists Pedro E. Leon at the University of Costa Rica in San Jose, and Mary-Claire King at the University of California, Berkeley mapped a gene for deafness to the long arm of chromosome 5. At last week's Eighth International Congress of Human Genetics in Washington, D.C., they reported finding the gene in deaf descendants of Felix Monge, a Costa Rican aristocrat who became deaf as a young man.

Affected members of the Monge family lose the ability to hear low-frequency sounds around puberty, and usually become deaf by age 30. Because the gene is a dominant trait, each child in the family with one deaf parent faces a 50 percent chance of inheriting the gene and going deaf.

Leon and King determined that the new gene lies near one responsible for Treacher Collins' syndrome, whose victims suffer both deafness and severe deformities. They now want to isolate the newly mapped gene, and determine how it causes deafness. They are also looking for it among other families with many deaf members.

Roughly one in every 1,000 Americans is born deaf; researchers estimate that half of the cases result from a genetic cause, and the rest stem from injury or viral illness.