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New Study Reveals Environmental Factors in CF

March 27, 2007 A team photograph of the 2004 U.S. men Olympics gymnasts, in their stretch whites and laurel wreathes, elicits some chuckles at a recent Grand Rounds presentation. With a click of a mouse in his PowerPoint presentation, pediatrician Garry Cutting focuses in on two of the muscular young men—all-around gold medalist Paul Hamm and his identical twin brother, Morgan. The twins, Cutting says, have identical genes and training, yet one is the champion, the better athlete. Why the difference?

The same can be asked of homozygous twins with cystic fibrosis, the disease in which Cutting specializes. They, too, have the same genes, including the same defective cystic fibrosis transmembrane conductance regulator (CFTR) protein—a genetic mutation linked in 1989 to CF—and, as children, the same medical care and living environment. Separate them geographically and the manifestations and morbidity of their lung disease, for example, diverge.

What variables changed for these twins? Their environments, says Cutting, and chance factors. Whether it's a fiercer motivation to excel for one of the Hamms, or a decision to smoke for a twin with CF, individual choices, experiences and exposures help determine how genes and life will play out.

In Hopkins' fourth year of a national study of twins and siblings with CF, Cutting is on the trail of the environmental, as well as genetic, modifiers of CF. "Our intent in launching the national CF Twin and Sibling Study was to better understand the pathophysiology of the disease," says Cutting. "CF is a single cell defect with a lot of variability."

In a new joint study with the Bloomberg School of Public Health, Hopkins researchers are focusing on the larger study's finding of different outcomes for twins with CF who live together and then apart. Twins living together have the highest correlation of lung disease, for example, but when they live apart, the severity of their disease sharply diverges.

"Understanding the environmental factors in CF will give us the tools to help CF patients protect themselves," says Cutting. "These could include anything from preventing smoking to maintaining good health insurance to ensure proper medical care."

Sorting out the complex interactions of genes and environment that affect the course of CF, Cutting adds, should lead to new treatments tailored to the individual, not the disease, and better outcomes.