Huntington's Disease

Also called Huntington's chorea, hereditary chorea, chronic progressive chorea, and adult chorea, Huntington's disease is a hereditary disease in which degeneration in the cerebral cortex and basal ganglia causes chronic progressive chorea (involuntary and irregular movements) and cognitive deterioration, ending in dementia.

Huntington's disease usually strikes people between ages 25 and 55 (the average age is 35); however, 2% of cases occur in children, and 5%, as late as age 60. Death usually results 10 to 15 years after onset from suicide, heart failure, or pneumonia.

Causes

Huntington's disease is an inherited condition caused by a single abnormal gene. Doctors refer to the illness as an autosomal dominant disorder because only one copy of the defective gene, inherited from either parent, is necessary to produce the disease. If one parent has the single faulty gene, the chance that an offspring will have the defect is 50 percent. Because signs and symptoms typically appear in middle age, some parents may not know they carry the gene until they've already had children and possibly passed on the trait.

If your child doesn't inherit the faulty gene, he or she won't develop Huntington's disease and can't pass it on to the next generation. Everyone who has the gene eventually develops Huntington's disease, if he or she lives long enough.

Signs and symptoms

People usually have symptoms for up to 10 years before they find out they have Huntington's disease. Most people are diagnosed between the ages of 30 and 50, although this can happen much earlier or later. Symptoms are often overlooked, as they are mild and commonly experienced by well people. They include:

• mild tremor
• clumsiness
• lack of concentration
• difficulty remembering things
• mood changes, including depression
• sometimes, aggressive antisocial behavior

As the disease continues, the symptoms become progressively worse, and lead to incapacitation.

Symptoms fall into three categories:

Physical symptoms include chorea (involuntary movements of the limbs, face and body). Chorea may lead to difficulty walking, speaking and swallowing. Choking is a particular hazard, due to reduced ability to control the muscles of the tongue, neck and diaphragm. People often lose weight because they have difficulty eating and burn more calories due to the continuous movement.

Cognitive manifestations : Dementia is an early indication of the disease and is subcortical in nature. Unlike patients with Alzheimer's disease, Huntington patients have no significant impairment of immediate memory. When problems with recent memory occur, they may be due to retrieval rather than encoding problems. Comprehension of information is preserved. Because the disease primarily affects the frontal lobes, deficits of executive function (planning, organizing, regulating, and programming) are common. Impulse control is also impaired, whereas insight into loss of cognitive function is retained.

Psychiatric manifestations : Psychiatric symptoms may precede movement alteration by several years. Depression is the earliest symptom. Other common personality changes include irritability, liability, impulsiveness, and aggressive behavior. Depression may also have a manic component. Psychosis and obsessive-compulsive behavior are not common.

Diagnosis

Tests for Huntington's disease are offered to individuals with a history of the disease in the family, although this must be accompanied by counseling to help such individuals come to terms with the future. A great deal of anxiety can be caused when those living in the shadow of Huntington's disease spend time looking for the symptoms and anticipating their onset. Prenatal tests for Huntington's disease are also available, although the prospect of terminating a pregnancy because the child may develop a disease in middle age raises considerable ethical concerns.

A computed tomography scan and magnetic resonance imaging demonstrate brain atrophy. Molecular genetics may detect the gene for Huntington's disease in people at risk while they're still asymptomatic.

Treatment

Because Huntington's disease has no known cure, treatment is supportive, protective, and aimed at relieving symptoms. Tranquilizers as well as chlorpromazine, haloperidol, and imipramine help control choreic movements, but they can't stop mental deterioration.They also alleviate discomfort and depression, making the patient easier to manage. However, tranquilizers increase patient rigidity.

To control choreic movements without rigidity, choline may be prescribed. Institutionalization is often necessary because of mental deterioration.

Prevention

Genetic counseling is advised if there is a family history of Huntington's disease. This may include DNA analysis of multiple family members. Since the odds that the child of a person with Huntington's disease will be affected are so high, people with the disorder may wish to consider adoption or forms of assisted reproduction that can reduce the chance that the disease will be passed on to their children.