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Huntington’s Disease: The Degeneration of Nerve Cells

Huntington's disease is a disorder that causes the brain nerve cells to breakdown / Photo by Getty Images

 

Huntington’s disease is a fatal genetic disorder that causes the progressive breakdown of nerve cells in the brain. In a webpost by Genetics Home Reference, they mentioned that this disease usually appears when the person is on their thirties or forties. The symptoms of this disease include emotional instability, mental health issues, lack of proper motor skills and having poor cognitive functions. People who suffer from Huntington's disease usually experience involuntary jerking or twitching movements that they are unaware of and this is usually called chorea. These movement problems are occurring more frequently as the person with Huntington’s Disease ages while walking and other ordinary movements could also be very difficult for them.

This disease has a broad impact on a person’s functional abilities and usually results in movement, thinking, and psychiatric disorders. Most people with Huntington’s disease develop signs and symptoms in their 30s or 40s but the disease may emerge earlier or later in their life. Careflex also mentioned on their website that Huntington’s disease could be inherited since it is caused by a gene that damages the brain eventually. The disease is caused by an autosomal dominant mutation in either of an individual’s two copies of the gene called Huntingtin.

The weakened individual succumbs to pneumonia, heart failure or other complications. Everyone has the gene that causes Huntington’s disease, but only those that inherit the expansion of the gene will develop Huntington’s disease and perhaps pass it on to each of their children. Every person who inherits the expanded Huntington disease gene will eventually develop the disease

Juvenile Huntington’s Disease

Every child of a parent with Huntington’s disease has a 50/50 chance of inheriting the expanded gene that causes the disease. If the child has not inherited this expanded gene, he or she will never develop the disease and cannot pass it on their children. Likewise, Huntington’s Disease News reported that Huntington’s disease could also affect people who are younger than 30 years old.

Juvenile Huntington’s disease is a less common, early-onset form of Huntington disease that begins in childhood or adolescence. It is also a progressive disorder that causes the breakdown of brain cells in certain areas of the brain. Approximately 1 in 7000 Canadians have been diagnosed with Huntington’s disease and about 10% of these cases are classified under juvenile Huntington’s disease. Most often, children with juvenile Huntington's disease inherit the mutation repeat from their fathers, although on occasion they inherit from their mothers.

Few studies have attempted to assess the population-based prevalence of juvenile Huntington’s disease. A 2013 study in the UK found that the average annual prevalence of juvenile Huntington's disease was 6.77 per million. Whether onset occurs during adolescence or adulthood, behavioral and psychiatric manifestations are very common. Presentation of juvenile Huntington’s disease includes changes in personality, coordination, behavior, speech or ability to learn. Physical changes include rigidity, leg stiffness, clumsiness, slowness of movement, tremors or myoclonus. In comparison with adult Huntington’s disease, seizures and rigidity are common, and chorea is uncommon.

The Genetics of Huntington’s Disease

All humans have two copies of the Huntingtin gene, which codes for the protein Huntingtin. The gene is also called HD and IT15, which stands for ‘interesting transcript 15’. Part of this gene is a repeated section called a trinucleotide repeat, which varies in length between individuals and may change length between generations. The Huntingtin protein interacts with over 100 other proteins and appears to have multiple biological functions.

Since Huntington’s disease is inherited in an autosomal dominant manner, the mutation in only one of the two copies of the HTT gene is enough to cause the condition. When a person with Huntington’s disease has children, each child has a 50% chance in inheriting the mutated gene and develop the condition too. The family history can sometimes appear negative for various reasons even though a parent carries, or carried, a mutation in the HTT gene.

People at-risk for the disease face a difficult choice about genetic testing for Huntington's disease, given the current absence of an effective treatment or cure. Many people see no benefit in knowing that they will someday develop the disease and others may want an end to uncertainty so that they can make informed choices about the future. The decision on whether to test or not is intensely personal and there is no right answer.

Huntington’s disease is caused by a genetic defect on chromosome 4. The defect causes a part of DNA to occur many more times than it is supposed to. This defect is called a CAG repeat. Normally, this section of DNA is repeated 10 to 28 times. But in persons with Huntington’s disease, it is repeated 36 to 120 times. As gene is passed down through families, the number of repeats tend to get larger. The larger the number of repeats, the higher a person’s chance of developing symptoms at an earlier age.

 

Huntington's diseases causes a weak person to succumb to pneumonia / Photo by Kateryna Kon via Shutterstock

 

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