Huntington's Disease

It may start with a slight tremor. You are probably just tired. Or maybe it was a dropped glass. Accidents happen. Or maybe you find it hard to remember new things. Just a part of aging! So what if you are feeling a little depressed and your spouse is complaining that you have been irritable… It’s just a mid-life crisis… Right?... While seemingly innocuous, all of these symptoms may be early signs of a devastating neurological condition: Huntington’s Disease.

What is Huntington’s Disease?

Huntington’s Disease (HD) is a progressive and ultimately fatal brain disease that causes neurons to deteriorate affecting movement, emotions, and cognitive ability. HD is caused by an autosomal dominant mutation to the huntingtin protein gene. This means that an affected individual will have a 50/50 chance of passing on the condition to his or her child. There are currently around 30,000 affected individuals in the U.S. and another 200,000 at risk of developing the disease. Huntington’s Disease symptoms typically begin between the ages of 30 to 50 and worsen over time, ultimately resulting in death 10 to 25 years after onset of the disease. While rare, a juvenile form of HD also exists with age of onset beginning before the age of 20. Juvenile HD typically progresses more rapidly than adult-onset. There is no cure for HD and treatment options are limited to palliative care.

What are the symptoms of HD?

Huntington’s Disease can vary from individual to individual, but in general follows three stages:

Early Stage

In the early stage of the disease affected individuals may notice changes in coordination, involuntary twitches in their extremities and face, and difficulty performing complex motions. Even if physical symptoms are mild, cognitive and behavioral symptoms can be significant. People often experience trouble organizing and processing new information, poor attention, impulsivity, anxiety, depression, and irritability. These symptoms often make it difficult for the affected individual to function normally at work or in social situations.

Middle Stage

As the disease progresses to the middle stage, symptoms become more debilitating. Chorea, the involuntary jerking or swaying motions which are the hallmark of the disease, becomes pronounced and individuals have trouble controlling voluntary movements making walking, speaking, and eating difficult. Cognitive ability declines and people have difficulty thinking clearly. At the middle stage of the disease, affected individuals are still able to eat, dress, and take care of their own hygiene, but may require assistance from a caregiver.

Late Stage

As the disease progresses into the late stage, individuals become completely dependent upon their caregivers. Chorea typically stops, and movements instead become slow and stiff. Affected individuals eventually become bedridden and unable to speak, but are still able to understand speech and recognize loved ones. Swallowing becomes extremely difficult leading to increased risk of choking and severe weight loss. Death typically occurs as a result of complications of the disease such as aspirational pneumonia caused when the individual accidentally inhales food into their lungs resulting in infection.

What causes HD?

While scientists are not certain what function the huntingtin protein normally plays in the body, the etiology, or disease-causing mechanism, of HD is clearly established. All proteins are made up of chains of amino acids which are coded for by a sequence of three nucleotides called a “codon.” In some proteins, codons may be repeated several times in a sequence. In the normal huntingtin protein the codon “CAG” is repeated 10 to 35 times. In an individual with adult-onset Huntington’s Disease, the CAG repeat has expanded to 40 or more repeats. In the case of Juvenile Huntington’s Disease, the CAG repeat expands to 50 or more repeats. The additional codons result in an elongated amino acid chain which produces a toxic form of the huntingtin protein that accumulates in neurons, disrupting their normal function and ultimately leading to cell death.

HD’s effect on the family

While the mutation in the huntingtin protein can occur randomly with no prior family history, most cases of Huntington’s Disease run in families. This can result in a severe psychological and financial burden for affected families. The disease typically strikes when people are in their prime working years and after they have had children. As an autosomal dominant trait, affected individuals have a 50/50 chance of passing on the condition to their children. This means that caregivers of the affected individual might also become affected with the disease. Seeing the devastating effect of the disease on their loved one and grappling with their own disease risk can lead to a high level of anxiety, fear, and depression in unaffected family members. Diagnostic tests exist to determine whether an individual carries the mutated gene, but the decision to get tested is not easy. For some, living with uncertainty would cause more stress than a positive result. For others, not knowing means there is always hope that they are unaffected. Family planning can also be a difficult decision. For some individuals, preimplantation genetic diagnosis (PGD) can be done in conjunction with invitro fertilization (IVF) to selectively screen for unaffected embryos without revealing the carrier status of the parents.

The following video was created by the Huntington’s Disease Society of America (HDSA) San Diego chapter to offer people insight into the effect HD has on families:

For more information on Huntington’s Disease, please visit the Huntington’s Disease Society of America website and if you are financially able, please consider donating to the cause.