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Testing for genetic mutations within ethnic groups

August 17, 2009|Shari Roan

Sean Delshad, 19, probably could have found more enjoyable things to do on a breezy Sunday afternoon. But instead he was waiting his turn at Sinai Temple -- along with dozens of other members of Los Angeles' large Persian Jewish community -- to undergo genetic testing.

The UCLA student deposited a few drops of saliva in a tube handed to him by a doctor and, in four to six weeks, he'll learn whether he carries gene mutations for four disorders that are especially prevalent among Persian Jews. Three are easy to treat -- provided a person knows he or she is afflicted. The fourth is incurable.

The screening program, conducted by the Cedars-Sinai Medical Genetics Institute, is a unique attempt to make broad-scale genetic testing more efficient by targeting ethnicity, a concept called ethnogenetics. Organizers hope to test at least 10,000 of the 30,000 Persian Jews in Southern California.

"The bottom line is, it's good to know. You can see what steps you need to take to be better prepared," Delshad said.

The program grew out of the institute because its director, Dr. David L. Rimoin, was one of the pioneers of genetic screening for Tay-Sachs disease in the Ashkenazi Jewish population more than 40 years ago.

Since that time, the mapping of the human genome has revealed many gene mutations that appear more frequently in certain ethnic groups. Recent discoveries on several mutations found in Persian Jews, plus their large numbers in Los Angeles, made this group a prime target for the launch of the program.

Every ethnic and racial group has five to 10 gene mutations that increase the risk for specific conditions, Rimoin says. Such traits are more easily identifiable -- because they're more common -- in groups with a strong tradition of intermarriage.

For Persian Jews, this tradition began in 586 BC, during an era of captivity in Babylon, which is now Iran. For centuries, Persian Jews were isolated from other Jewish and non-Jewish communities by geography and reproductive practices. In the late 1970s, many migrated to the United States.

But, Rimoin says, "no one group has more mutations than another."

As scientists continue to find genes linked to specific diseases, and as treatments emerge, doctors hope more institutions and medical centers will offer screenings.

Dr. Michael Kaback, a professor of pediatrics and reproductive medicine at UC San Diego, points out that people of Cajun ethnicity also have higher rates for Tay-Sachs disease. African Americans have higher rates of sickle cell disorder; Vietnamese, thalassemia; Finns, congenital nephrosis; and Northern Europeans, cystic fibrosis.

Screenings usually target disorders that are treatable, says Kaback, who pioneered the use of Tay-Sachs screening in Ashkenazi Jews in the 1970s with Rimoin. But the Persian Jewish program also tests for hereditary inclusion body myopathy, a devastating condition that causes progressive weakness of the arms and legs.

People who learn they are carriers can undergo in vitro fertilization -- with preimplantation genetic diagnosis -- should they choose to have children. Choosing not to implant embryos with the defect would ensure the trait isn't passed to offspring. One in 20 Persian Jews is a carrier of the mutation.

Nahid Talassazan, 50, attended the screening because of the incidence of hereditary inclusion body myopathy in her family. One of her uncles married a cousin, and three of the couple's four children -- Talassazan's cousins -- have the disorder. "These things are worrisome," she says. "But I am very pro-science. I'd rather know than not know."

The other conditions associated with Persian Jewish heritage are:

* Pseudocholinesterase deficiency, which causes a sensitivity to anesthesia. One in 10 Persian Jews carry one copy of the gene.

* Congenital hypoaldosteronism, which makes the body lose salt and can result in dehydration, shock, short stature, blood pressure problems and salt craving. One in 30 Persian Jews is a carrier.

* Polyglandular deficiency, in which the body is deficient in multiple hormones. One in 50 Persian Jews is a carrier.

The symptoms of hereditary inclusion body myopathy develop in early adulthood, but many people are unaware they are at risk for other conditions that could be easily treated, preventing serious health consequences, Rimoin says.

All four illnesses are autosomal recessive disorders, meaning that they occur only when both parents carry the mutation. Children of parents who both carry a gene for such recessive traits have a 25% chance of inheriting the disorder, a 25% chance of not carrying the gene mutation and a 50% chance of carrying one copy of the mutation.

About 100 people attended the Aug. 3 event, which pleased organizers, who worried that people might fear the results of testing or feel stigmatized by it.

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