Racial differences in tumor disorder.

Two people with an identical genetic defect may suffer widely different medical problems. In the case of neurofibromatosis, researchers from Washington, D.C., and Ohio have found that whites are more likely than blacks to suffer from benign, yet potentially dangerous, optic nerve tumors.

"What this tells us is that single-gene disorders manifest themselves with respect to the other genes in individual carriers," says Howard M. Saal of the Children's Hospital Medical Center in Cincinnati.

Saal and colleagues at the Children's National Medical Center in Washington, D.C., studied 372 children with neurofibromatosis, a disease marked by tumors of the skin and central nervous system and skin pigmentation known as cafe au lait spots. Using magnetic resonance imaging (MRI), the team found optic nerve tumors, which can cause blindness and pituitary problems, in roughly 1 out of 5 white children but in only 1 out of 62 black children.

Saal says the finding illustrates how differences in other genes can affect neurofibromatosis. However, he recommends MRI scans for all children with the disease, because 7 to 10 percent suffer from malignant brain tumors regardless of race.