Steps in the Predictive Testing Program
The testing program usually involves several sessions. The following components are usually included:
- An initial phone contact and a pre-screen interview with the at-risk individual.
- At least three pre-test, in-person sessions for genetic and psychological counseling, neurological and neuropsychological evaluations. Additional sessions may be necessary if issues emerge that should be resolved before proceeding with the test. A blood sample for DNA testing may be drawn at the third visit or a subsequent visit.
- The next session is for disclosure of results. It takes about three to four weeks to get the results once the blood is drawn.
- Post-test counseling sessions.
The time between each visit will depend both on the number of people who request testing at our center and on the length of time you choose between visits. The length of time needed to complete the protocol from the first visit to receiving results is commonly three to four months.
The same kind of predictive testing described above can be used in prenatal testing (testing of a pregnancy). There are three different situations in which prenatal testing for HD may be done:
- The expectant parent has HD.
- The expectant parent has had presymptomatic testing and has inherited gene for HD.
- The expectant parent is at risk and asymptomatic and does not wish to have predictive testing for himself/herself. "Exclusion" prenatal testing may be offered to determine if the fetus is "excluded" as a gene carrier or if the fetus has the same risk as the parent (50%).
The purpose of the neurological examination is to make certain that the individual at risk for HD is not showing symptoms of the disease and actually is "presymptomatic." A person for whom a positive clinical diagnosis has been made may feel that he or she does not need testing. Another individual may want confirmatory testing. Similarly, an individual who shows no clinical signs of HD may decide to defer the genetic testing.
A person with subtle dysfunctions may be at increased risk of being a gene-carrier or may be relatively close to more overt symptomatology. The neurological exam can provide the HD team with information about how closely an individual may need to be followed after learning the test outcome. For completely asymptomatic people who later find that they have inherited the gene for HD, the neurological evaluation also serves as a starting point for long-term follow-up and care.
Psychological screening, including neuropsychological testing, is part of the protocol. If significant psychological problems are identified, it may be appropriate to delay testing and address these psychological issues first.
The risk of an adverse emotional response remains the single greatest risk of the test. It is important that the psychological evaluation of emotional stability not be viewed as a hurdle to be jumped in order to qualify for testing, but rather as a method of identifying persons likely to need greater emotional support in follow-up. In some instances, such as overt risk for suicide and/or major depressive symptoms, it is appropriate to delay testing, initiate psychiatric treatment, and become emotionally stabilized before proceeding with the test.
Regularly scheduled follow-up is a necessary and important part of testing. The psychological impact of a test result -- a good or a bad result -- varies considerably and it is difficult to predict what your response might be. The testing center works with the local counselor to provide the assistance needed.