Factors to consider before genetic testing

When is it time to order a genetic test for a patient? A Stanford University pediatric dermatologist says several factors should focus the minds of dermatologists.

Birthmarks, bumps on the face and skin tags in children should all be triggers for genetic testing, at least in certain cases, says Joyce Teng, M.D., Ph.D., clinical associate professor of Dermatology and Pediatrics at Stanford Medicine. She is also a pediatric dermatologist at Lucile Salter Packard Children's Hospital at Stanford.

She advises dermatologists to also be aware of two possible misconceptions. Contrary to assumptions, genetic tests may be cheaper than they expect, and a diagnosis can have value even without a successful treatment.
Dr. Teng spoke with Dermatology Times prior to her presentation about genetic testing at the summeer meeting of the American Academy of Dermatology in Boston.

Genetic conditions can affect the skin just like other organs in the body, she says, making it important for dermatologists to be aware of the possible role of genes in causing certain abnormal dermatologic conditions.

“I can think of 20-30 examples,” she says. For instance, “If I see a five-year-old with a tiny little red bump on the face, and I take a small skin biopsy and it turns out to be an angiofibroma, that’s pretty uncommon in children. Then the first thing that’s going to cross my mind is whether this child has tuberous sclerosis.”

That’s a rare genetic condition, also known as tuberous sclerosis complex, which causes benign tumors to appear in the brain and organs like the skin, heart, eyes and lungs. According to the National Institute of Neurological Disorders and Stroke, the condition “can be unrecognized or misdiagnosed for years.”

Skin tags around the neck in kids - they look like basal cell carcinoma - can also be a sign of the condition, Dr. Teng says.

Other kinds of ordinary skin conditions can be red flags if they appear at an unusual age, she says. “If you biopsy two or three carcinomas in an 18- or 17-year-old, instead of a 50-year-old, that should raise a red flag about a genetic condition, not just sun damage.”

What should dermatologists do when they are suspicious about a genetic link to a skin condition? Dr. Teng suggests trying an online search using two or three relevant keywords in order to narrow down possible diagnoses related to genes. That’s when testing comes into the picture.

“Dermatologists may think it’s expensive to get genetic tests,” she says, “and that it won’t tell them much if they get a negative test.” In fact, the tests are less expensive than in the past, she says, and some testing companies will do more than simply look for signs of one genetic disorder. Instead, she says, they’ll do an entire panel that searches for all genetic disorders linked to the patient’s skin condition.

As for the usefulness of a diagnosis, she says genetic tests can provide insight even if they don’t point to a cure. In some cases, “there are things that can be done for the patient from a health surveillance standpoint if we know that they have a possibility of developing other manifestations.”

A patient whose genetic condition puts them at higher risk of uterine tumors may wish to be monitored frequently by a gynecologist, she says. Or a patient with a spot in the eye, a possible sign of increased risk for ocular melanoma, may wish to wear sunglasses for protection.