Everybody has repeats, but the normal range is from 7 to 27. Someone with 27-35 repeats doesn't have Huntington's symptoms but may pass it on to a child because repeats in this range are unstable. At 36-39 repeats, some people will develop Huntington's and some won't. Again, their children are at risk.

Huntington's symptoms are very likely to appear at 40 or more CAG repeats, if a person lives long enough.

Researchers believe the severity of symptoms and age of onset are linked to the number of repeats. But what form the disease will take — and what symptoms will appear — simply can't be predicted. Roberts points out that's he's seen people with very mild symptoms of the disease, even late in life.

The testing itself is a multistage affair. There's genetic counseling, a neurological exam and some psychological assessment before any blood is even drawn. The assessment will determine whether someone is even considered stable enough emotionally to get the results of such a test.

It takes three to four weeks to get the results, which are supposed to be delivered in person, with a psychiatrist or psychologist and genetic counselor both present. Follow-up counseling is suggested, no matter what the outcome. And if the patient doesn't seem stable, he or she won't be given the results.

The patient can also change his or her mind at any time. Until the results are given, it's never too late to back out.

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Lael Askew learned one truth in 1995. People are anxious to have genetic testing only so they will know they don't have a disease. And they don't talk much about the testing, even to their siblings or their mother.

A genetic counselor explained it this way to the Boston Globe two years ago: Before testing is done, brothers and sisters are all in the same boat together. Once the testing's completed, some are standing safe on the island and others are swimming with sharks.

In April, the results of John's test came back. He definitely had Huntington's disease. That meant all six of their children were at risk.

Individuals have to decide for themselves whether they want to get genetic testing. Since the advent of testing for the disease, experts have expressed some surprise that not as many people get the test as they had expected.