Predictive Testing for Huntington’s Disease

Distinguishable by a single gene, genetic testing for Huntington’s disease carries complex ethical issues.

Long before Angelina Jolie penned a New York Times editorial about her decision to undergo a preventive mastectomy because of her BRCA 1 status, patients with a family history of Huntington’s disease have been struggling with genetic testing.

Huntington’s disease is somewhat unique in that there’s one gene that was identified more than 20 years ago. At one end of the gene, a pattern of three DNA bases (CAG), or nucleotides, repeats itself in all cases. In normal individuals, this tri-nucleotide, or triplet, repeat occurs between 11 and 29 times. In people with Huntington’s disease, the repeat occurs over and over again, from 40 times to more than 80.

In between the normal range of repeats and the Huntington’s disease range lays an indeterminate gray area. Data continues to be collected in hopes of illuminating the significance of a repeat count in this gray area. Currently, a repeat count between 30 and 39 constitutes a non-informative result.

It has been shown that a weak correlation exists between the number of repeats and the age of onset, such that those having the very highest number of repeats develop the juvenile form of Huntington’s disease. Generally, however, this correlation is not tight and should not be used to attempt estimates of age of onset.

“Since the 90s, the only thing that’s improved is the accuracy of the test,” said Arik Johnson, PsyD, staff psychologist for patients with Huntington’s disease at UCLA’s movement disorders program and member of the Huntington’s Disease Society of America board of directors. “But there’s no cure and no way to slow progression. A fairly low percentage of the people living with risk of Huntington’s disease do the test because most people feel they’ll know when they develop symptoms and fear the result of a genetic test.”

Genetic testing always carries of host of psychological issues and these are often more magnified when there’s a possible risk of Huntington’s disease. The inherited disease causes the progressive breakdown (degeneration) of nerve cells in the brain. Huntington’s disease has a broad impact on a person’s functional abilities and usually results in movement, thinking (cognitive) and psychiatric disorders.

“It’s daunting because many people watch a parent living with this disease and their own future seems frightening,” shared Johnson. “This is a family disease and many people grow up in homes that have been disrupted by Huntington’s. Unlike cancer or even the BRCA gene, there’s no cure.”

Testing During Pregnancy

The multi-disciplinary patient care team for Huntington’s disease routinely screens for depression and suicide potential well before patients learn their genetic testing results.

When women request the screening during pregnancy, the ethical issues literally double and can resemble a Lifetime movie. A very common and problematic circumstance involves an at-risk woman who is pregnant and who undergoes pre-symptomatic and prenatal testing simultaneously. If the outcome is positive for both tests, the impact is overwhelmingly traumatic, according to the association.

“This woman has an additional layer of urgency because of the pregnancy,” added Johnson. “We try to avoid testing the fetus and, when we do, have a lot of counseling around making sound decisions with regard to terminating the pregnancy.”

Though he conceded individuals do have the right to genetic testing, issues of personal rights and accountability stemming from this test can be legally challenging as well.

“In this case, the family would have knowledge about an unborn child’s genetic status which could impact how the child is raised. It also takes away child’s right at age 18 to find out their gene status, or not find out. Genetic counselors will thoroughly investigate a pregnant woman’s intentions. Sometimes genetic counselors will say we’re not doing the testing because the pregnant patient is not psychiatrically sound.”

Sometimes, these patients are referred for psychiatric counseling. Others undergo the test but never return to learn their results.

Pre-Symptomatic Testing

Another sticky ethical issue surrounds pre-symptomatic testing of adults. Usually, this occurs when an adult child has a suspicion that a parent has Huntington’s. Here too, the family dynamic is very delicate and Johnson said best practices generally oppose performing the genetic test of anyone with a 25% risk when the risk parent is still living.

“After thorough investigation by a genetic counselor, there will be circumstances when we’ll offer the test to someone with a 25% risk but we try to take other approaches first,” he offered. “One example of an exception would be an adult child who has been estranged from her parent for 15 years. It’s different if someone comes in living with a parent suspected of Huntington’s. If you test someone for Huntington’s and the parent hasn’t found out, you’re also confirming the parent’s disease status when they’ve chosen not to undergo the test.”

When lab results are delivered 4-8 week post-test, the non-informative result between 30-39, aka the grey area, almost causes more anxiety for patients than a positive diagnosis.

“Every time they drop their key, they think the Huntington’s is starting,” shared Johnson.

All patients are encouraged to schedule a neurological evaluation after receiving their results. Many, especially those not yet displaying symptoms, neglect to take the next step. Johnson stresses compassion regardless of the result.

“It’s understandable to not want to face the disease, especially when there are not yet any symptoms,” he said. “Anything that makes them think about this disease is scary. Even a doctor’s appointment is something people worry about a week ahead of time.”