Huntington’s disease is a disease of the brain cells. As of the moment of writing, it is not curable and is always fatal, though a patient can live as long as 25 years after they are first diagnosed. Huntington’s disease affects 30,000 people in the United States and about 200,000 people are at risk of contracting it. This article describes the disease, its symptoms and its treatment.
What Is Huntington’s Disease?
Huntington’s disease is a rare, inherited, progressive, degenerative disease. People who have it start seeing symptoms between 30 and 50 years old. However, about 10 percent of the patients are children or teenagers. This is called Juvenile HD, and it progresses more rapidly than the more common type of the disease.
Signs and Symptoms of Huntington’s Disease
The signs and symptoms of Huntington’s disease are gradual and include the involuntary, jerky or slow movements or tics of the muscles in the hands, face, feet and body. The patient may be clumsy and their eyes may move in an abnormal way. They have trouble speaking and swallowing.
As the disease progresses, it affects the person’s cognitive abilities and their memory, resulting in dementia in the final stages. Patients find that they can no longer focus on tasks, have little impulse control, have trouble learning and become inflexible in their habits. Patients with advanced disease need round-the-clock care and are unable speak, though they are probably able to understand what is being said to them and are aware of their surroundings. Their deaths are usually caused by infections, accidents or choking. The disease itself usually does not kill them.
Eventualy, the involuntary movement, or chorea subsides and the patient may not be able to move at all. Being bedridden is why so many are at risk of life-threatening infections such as pneumonia.
Causes of Huntington’s Disease
Huntington’s disease is the result of a mutation of a gene known as huntingtin. The gene is found on the short arm of the person’s fourth chromosome, and everyone has it. The mutation causes errors in the gene’s nucleotide bases that manifest as abnormally long chains of repeating cytosine, adenine and guanine nucleotides, or CAG. People without Huntington’s disease have around 20 repeats of CAG in their gene, but people with the disorder can have over 39. This causes neurons, or nerve cells in the patient’s brain to deteriorate.
The length of the chains of these nucleotides can determine the age at which the patient starts experiencing symptoms. Not only that, the repetitive CAG chains can expand, which can cause a child with Huntington’s disease to start having symptoms at an earlier age than their parent. This kind of expansion seems to be more often inherited from the patient’s father.
The disease is an autosomal dominant trait. This means that a single copy of the mutated huntingtin gene from one parent dominates the normal gene of the other parent. Therefore, the chances of inheriting Huntington’s disease is about 50 percent for every pregnancy. Both males and females can get Huntington’s disease.
The huntingtin gene carries a protein also called huntingtin, but scientists do not know what the function of this protein is. However, the mutation attacks the brain and particularly strikes the cerebral cortex and basal ganglia. The former is responsible for cognition, and the latter controls movement.
Genetic testing is available to diagnose Huntington’s disease. Still, some patients may not want to know, seeing that the disease is incurable and fatal. If a couple is having a child through in vitro fertilization or IVF, an embryo can be chosen that does not have the mutated gene before it is implanted in the woman’s uterus. A pregnant woman can have her fetus tested for the gene though amniocentesis or a chorionic villus biopsy.
Treatment of Huntington’s Disease
The Food and Drug administration approved a drug called tetrabenazine to treat the chorea of Huntington’s disease in 2008. As of 2017, it is the only treatment for the disease approved by the FDA. Other than this, treatment is supportive and consists of making the patient comfortable and trying to alleviate the symptoms, though temporarily.
The patient can be given drugs to treat epilepsy to calm their chorea. These drugs tend to work somewhat in the early stages of the disease. Doctors also prescribe anti-depressants to help the patient’s mood, and some nutritionists recommend a high calorie diet to help the patient keep their weight up and specially cooked foods that lower the risk of choking.
Clinical trials are always being held to find a drug or other treatment for Huntington’s disease. These trials include Co-Enzyme Q10 and Remacemide trial, which was sponsored by the National Institute of Health from 1997 to 2002, a study investigating the amino acid creatine, which was sponsored by Huntington’s Disease Society of America from 1999 to 2004 and another group sponsored by the NIH and the FDA Orphan Products Division that returned to study the safety and effectiveness of creatine in 2007 to 2013. Other studies sponsored by the FDA, Medivation and NeuroSearch Sweden studied the effects of medications such minocycline, dimebon, phenylbutyrate, SD-809 Extended Release and pridopidine on Huntington’s disease.
In 2017, an experimental drug that was injected into the cerebrospinal fluid of patients with Huntington’s disease at the Leonard Wolfson Experimental Neurology Centre in London, UK seemed to lower the load of dangerous proteins in test subjects’ brains. The drug works by destroying the messenger RNA that tells cells to create the damaged huntingtin protein. The drug seemed to be well tolerated by the 46 patients, but more study is needed.
Though the disease is admittedly grim, the prospects for treating or even correcting Huntington’s disease look brighter than they were a few years ago. Clinical trials point toward drugs that can alleviate the distressing symptoms of the disorder or even destroy the instructions that cause the mutated protein to attack the nerve cells in the brain.