Maps To Medical Discovery Scientists At Children's Hospital Of Philadelphia Are Sifting Through The 1,000 To 2,000 Genes On Chromosome 22. What They Find Will Bring Clues To Hereditary Illness - And Perhaps New Treatments And Cures.

Four years into one of the biggest medical-research projects in the city, scientists at Children's Hospital of Philadelphia are rapidly unraveling the secrets of Chromosome 22.

They have just succeeded in "mapping" 70 percent of the chromosome and now know the precise locations of more than 100 of the genes that lie on it.

Their work is uncovering clues to cancer, heart abnormalities, and other birth defects, and perhaps even mental illness.

"We certainly had no idea that we would be so far along with the physical map as we are right now," said Beverly Emanuel, Children's chief of human genetics and molecular biology.

Emanuel heads a team involving several medical centers that is putting together a detailed picture of the genetic material along every stretch of Chromosome 22. The map should lead scientists to the estimated 1,000 to 2,000 genes believed to be on the chromosome.

"The technology has developed really quickly, and it has facilitated so many things," Emanuel said. Just two weeks ago, a consortium of gene-hunters informed Emanuel that they had identified as many as 43 additional genes on the chromosome.

The mapping of Chromosome 22, funded with a $10 million federal grant, is part of the Human Genome Project - an ambitious international effort to map all 23 pairs of human chromosomes by 2005. The hope is to eventually find all of the 80,000 to 100,000 genes that determine each person's individual makeup - everything from eye color to personality to whether the person enjoys a long healthy life or is faced with sickness.

Figuring out which genes do what could lead to better treatments, and even cures, for hundreds of human ailments.

Already, the work on Chromosome 22 is helping patients.

Alexa White, 3, of Monmouth Junction, N.J., who was born with a hole in her heart, has gotten medical attention for more than her heart because of the Chromosome 22 research.

Using a new genetic test, doctors determined that her heart problems were part of a larger syndrome caused by a defect of the chromosome. That diagnosis led to the discovery that she also had a defect in a muscle in the back of her mouth, which was causing the milk she was drinking to sometimes come out of her nose. The defect could cause serious speech problems as she grows. She will have surgery to correct the defect in April. It's not clear yet whether she'll also need heart surgery.

"When you see something in the laboratory and then take it back to the