Huntington’s disease, or also known as Huntington’s Chorea, is an incurable hereditary brain disorder, which causes nerve cells to become damaged, resulting in various parts of the brain deteriorating. Huntington’s disease was recognized by George Huntington in 1872. Huntington’s disease had been acknowledged as a disease entity previously, several people before 1872 reported having and describing movement disorders that later would be connected to Huntington’s disease.
The disease now bares Huntington’s name because of a paper he wrote called On Chorea which was later published and the disorder he talked about became known as Huntington’s Chorea. More than a quarter of a million Americans have HD or are at risk of inheriting the disease from an affected parent. Each child of a person with HD has a 50/50 chance of inheriting the fatal gene. Any person who carries the gene for HD will develop the disease eventually.
One out of every 10,000 Americans has HD and there is no known cure. Symptoms of Huntington’s disease start to become noticeable slowly and are different for each individual and vary between emotional and physical symptoms such as motor skill impairment. In time, the person impacted by HD will need full-time care. Some examples of behavioral symptoms are: irritability, aggressive outbursts, depression, and social withdrawal. Irritability means easily annoyed or made angry.
For example if you are chewing with your mouth open might irritate the impacted person and the might get angry, which leads into the next symptom mentioned, aggressive outbursts. At random time the person may get aggressive and may lead to violence such as trying to punch or kick someone for no reason. People affected by HD may also show signs of depression or social withdrawal, not wanting to go anywhere or talk to anyone. They want to be by themselves and want to be alone.
Other symptoms are categorized as lack of motor skills such as, fidgety behavior, incoordination, involuntary behavior and difficulties with things like speech, swallowing, balance and walking. The diseased person would not be able to sit in one place for a long time and would constantly be moving around in their seat. Also the person would become very clumsy and would maybe for example bump into things or trip over their own feet. The patient would also show signs of muscle spasms or other involuntary movements.
Almost all HD patients develop short-term memory loss, and have problems with concentrating. It is impossible to predict exactly when the disease with start to show in its victims but most start to show symptoms between the ages of 30-50 years old. In rare cases, children as young as two and individuals as old as 80 have exhibited symptoms of HD. To determine if you have HD or not, your doctor may order tests such as a Brain-imaging test or an Electroencephalogram (EEG).
A Brain-imaging test shows images of the brain that could be affected by Huntington’s disease and helps to rule out any possibilities of the symptoms. The other option is an Electroencephalogram (EEG), which records electrical impulses from the nerves in the head. These impulses are the way nerves talk to each other and get information from the brain to the rest of the body. At this point in time there is no known cure for HD and there is no way to stop or reverse it. Since there is no cure, HD leads to death in 10-25 years of diagnosis.
People with the disease usually die from symptoms such as choking, infection or heart failure, rather than the disease itself. Huntington’s disease is caused by a mutation of the HTT gene. The HTT gene gives direction on making a protein called huntingtin. It is unknown what the protein actually does but it seems to have an important role in nerve cells in the brain. The HTT mutation that causes Huntington disease is because of a DNA section known as CAG trinucleotide (made of the three bases cytosine, adenine and guanine) which repeats. In a normal gene, the CAG segment repeats 10 to 35 times, however in a person with HD, the segment is repeated 36 to 120 times.
Because this person has more than the needed amount of CAG repeats, it leads to an irregular size of the huntingtin protein. This causes disruption in the nerve cells in the brain and causes death of the cells causing the symptoms of Huntington’s disease. As the gene is inherited from one generation to another, the number of CAG repeats increases in size. A larger number of repeats of the CAG segment results in developing the disease earlier in life. People with 40-50 CAG repeats in the
HTT gene usually see signs of the disease later on in life, while people with more than 50 repeats tend to see it earlier. Huntington’s disease is inherited in an autosomal dominant pattern, which means that only one parent has to have the disease for it to get passed down to an offspring. The gene that causes HD is the HTT gene. The gene is located on chromosome 4 between base pairs 3,074,680 to 3,243,959. Each parent has two copies of every chromosome but gives only one copy to each child.
Each child of an HD parent has a 50-50 chance of inheriting the HD gene, if the offspring does not inherit the disease than they will not develop it and cannot pass it down to their children. HD is a dominant disease, which means that if you carry the gene for HD, you have the disease. Other disease, are recessive, which means you could be carrying the gene and never even know it because it is hidden under the dominant trait.
This Punnett square above shows the possibility of passing down HD to your child if you have the disease. On the top of the square it shows the alleles of parent with HD, and to the left of the square, the alleles of a parent without HD. Each parent passes down one allele and one goes into each box. The capital H represents HD, and capital letters are dominant, while the lowercase h’s are recessive and represent no HD. In the square the capital H goes in front of the lowercase h’s.
As shown in the Punnett square, if a parent with Huntington’s disease and a parent without Huntington’s disease have a baby, then there is a 50% chance that the child will have Huntington’s disease. Huntington’s disease, a terrible incurable hereditary brain disorder, not only impacts the life of its victim’s but their loved ones and everyone around them. Even though there is no known cure for HD at this time, scientists are working hard to try and find one.
Ever since 1993 when the gene that caused HD was found, people are trying new things for finding a cure. Since 1999, the Huntington’s Disease Society of America (HDSA) has committed more than $18 million to fund research with the goal of finding effective treatments to slow Huntington’s disease. Hopefully in the near future a new cure will be discovered to put an end to Huntington’s disease.