Screening for HD includes a medical history, family history, neurological exam, psychiatric evaluation, brain imaging and function tests, laboratory tests and genetic tests. Individuals with a family member with HD have a 50 percent chance of inheriting the mutated form of the IT15 gene; this mutation can be detected through blood tests. However, there are some ethical concerns, especially considering that the genetic test will not indicate when symptoms will appear, how fast they will progress or how severe the condition will be. In addition, because there is neither a cure nor an effective treatment to slow the disease’s progress, patients whose blood tests are positive may require psychosocial counseling.
In the process of genetic counseling and testing, patients who are at risk of HD are advised about the nature of the disease and their probability of developing or transmitting it, as well as their options in managing the disease and family planning steps they can take to not pass the gene along. Once individuals who are at risk of HD are given this information, they can choose whether or not to receive genetic testing. A predictive genetic test for HD is usually not given to patients under the age of 18, though there are some exceptions. Parents who believe their child is at risk of HD can opt for prenatal genetic testing, though this too is fraught with ethical issues—for instance, what if the parents want to know the fetus’s status but not their own (a positive result would indicate that at least one parent has HD)?
While genetic tests can indicate the presence of the HD gene, other tests—including a complete physical and neurological assessment—and the presence of symptoms such as involuntary movements, progressive dementia and emotional problems are needed to confirm the disease’s onset. The neurological exam will evaluate the patient’s memory and thinking ability, as well as reflexes, balance and movement. Brain imaging tests such as a CT scan can detect changes in the brain in moderately advanced HD cases, and PET scans can show decreased glucose and oxygen metabolism in the brain, which, though they may be associated with other neurodegenerative disorders, can also support an HD diagnosis in patients with a family history.