Diagnosis of Huntington's disease

The great American folk singer and composer Woody Guthrie died on October 3, 1967, after suffering from Huntington's disease (HD) for 13 years. He had been misdiagnosed, considered an alcoholic, and shuttled in and out of mental institutions and hospitals for years before being properly diagnosed. His case, sadly, is not extraordinary, although the diagnosis can be made easily by experienced neurologists.

To establish a diagnosis, a neurologist will interview the individual intensively to obtain the medical history and rule out other conditions. A tool used by physicians to diagnose HD is to take the family history, sometimes called a pedigree or genealogy . It is extremely important for family members to be candid and truthful with a doctor who is taking a family history.

The doctor will also ask about recent intellectual or emotional problems, which may be indications of HD. He or she will test:

• Hearing
• Eye movements
• Strength
• Coordination
• Involuntary movements (chorea)
• Sensation
• Reflexes
• Balance
• Movement
• Mental status

A number of laboratory tests will probably be ordered as well. People with HD commonly have impairments in the way the eye follows or fixes on a moving target. Abnormalities of eye movements vary from person to person. These differences depend on the stage and duration of the illness.

There is a direct genetic test to make or confirm a diagnosis of HD in an individual who is exhibiting HD-like symptoms. Using a blood sample, the genetic test analyzes DNA for the HD mutation by counting the number of repeats in the HD gene region. Individuals who do not have HD usually have 28 or fewer CAG repeats. Individuals with HD usually have 40 or more repeats. A small percentage of individuals, however, have a number of repeats that fall within a borderline region.

Number of CAG repeats:

< 28; Outcome: Individual will not develop HD

29-34; Outcome: Individual will not develop HD but the next generation is at risk

35-39: Outcome: Some, but not all, individuals in this range will develop HD; next generation is also at risk

> 40; Outcome: Individual will develop HD

The physician may ask the individual to undergo a brain imaging test. Computed tomography (CT) and magnetic resonance imaging (MRI) provide excellent images of brain structures with little if any discomfort. Those with HD may show shrinkage of some parts of the brain-particularly two areas known as the caudate nuclei and putamen -and enlargement of fluid-filled cavities within the brain called ventricles . These changes do not definitely indicate HD, however, because they can also occur in other disorders.

In addition, a person can have early symptoms of HD and still have a normal CT scan. When used in conjunction with a family history and record of clinical symptoms, however, CT can be an important diagnostic tool. Another technology for brain imaging includes positron emission tomography (PET). PET is important in HD research efforts but is not often needed for diagnosis.