Diagnosis of Huntington's Disease
Diagnosis is based on a thorough personal and family medical history, physical examination (including a neurological exam), and a series of laboratory tests. The physician will ask about recent changes in intellectual or emotional function, which may be early signs of Huntington's disease.
Genetic Testing and Huntington's Disease
Genetic testing involves taking a blood sample for DNA analysis to determine whether the distinct mutation for Huntington's disease has occurred in gene IT-15. A sample of DNA also may be required from a closely related affected relative, ideally a parent. This helps confirm the diagnosis of HD and is important if the family's history is in any way unclear, uncertain, or unusual. Persons who test positive and are considering pregnancy are advised to seek genetic counseling before they conceive.
Presymptomatic testing can be performed on adults, children, and even fetuses in the womb. Genetic testing of a fetus holds special challenges and risks, and some testing facilities choose not to do it.
At-risk couples wanting to have children may choose to undergo in vitro fertilization with preimplantation screening. In this procedure, embryos produced from the couple's sperm and eggs are screened to identify one that is free of the HD mutation, which is then implanted in the woman's uterus.
Testing GuidelinesA positive test result can have profound, unanticipated impacts on patients and their families. Anyone contemplating genetic testing should obtain testing guidelines from the testing center or from an organization devoted to the interests of Huntington's disease patients and their families. Guidelines recommend that testing centers follow these practices:
- Counseling should be provided before and after the test, and before the results are known.
- Test results should be strictly confidential and should be disclosed only in person, and only to the individual being tested, regardless of the outcome.
- To protect the interests of minors, including confidentiality, testing should not be conducted for persons under 18 without a compelling medical reason, such as the appearance of HD symptoms in a child.
Computed Tomography (CT scan) and Huntington's Disease
This painless diagnostic procedure produces computer-generated images of the brain's internal structures. Patients with HD often show shrinkage in two areas of the brain - the caudate nuclei and putamen - and enlargement of cavities within the brain called ventricles. The presence of these structural changes is not conclusive for Huntington's disease nor does their absence rule it out.
CT scans combined with other procedures such as magnetic resonance imaging (MRI scan) and/or positron emission tomography (PET scan) can be a helpful diagnostic tool, especially when evaluated in the context of family history and clinical symptoms.