Huntington's disease: genetic causes, symptoms, and clinical diagnosis

Huntington's disease, also known as HD, is an uncommon degenerative disorder that greatly impacts the central nervous system of the individual. It is often characterized by surplus and unneeded choreatic movements, unusual behavioral patterns, disturbances in the mental level and dementia. (Sheth 2013) As far as the Caucasian population is concerned, the Huntington's disease is prevalent in one out of ten thousand persons. The symptoms start to appear when the individual is thirty to fifty years of age. In a few cases, adolescents start to show symptoms of HD (known as JHD or Juvenile Huntington's disease) before the age of twenty by demonstrating behavioral disorders and learning difficulties at school. However, chorea is the major sign of the onset of HD that spreads to all muscles with the passage of time. The affected individual becomes severely retarded as the psychomotor processes are affected gradually. he/she also suffers decline of cognitive skills and starts experiencing mental disorder symptoms (Roos 2010).

If described in medical language, Huntington's Disease is "an autosomal dominant inherited disease caused by an elongated CAG repeat (36 repeats or more) on the short arm of chromosome 4p16.3 in the Huntingtin gene" (Roos 2010). The symptoms begin to show as early as elongated the CAG repeat is. In adolescents that suffer from Juvenile Huntington's disease, the repeat frequently goes beyond 55. The signs and clinical symptoms lay the basis for diagnosis, especially for individuals who have a parent with confirmed Huntington's disease. The diagnosis is confirmed with the determination of DNA. Several types of diagnosis may be conducted including pre-manifest diagnosis, prenatal diagnosis and pre-implantation diagnosis. Although, there is still no cure for the mentioned disease, the quality of life of the patients can be improved with the help of care (both medical and non-medical) and other available treatments. The individual with Huntington's disease becomes completely dependent as the disease progresses and is not able to carry out even the day-to-day tasks. This situation ends up in full time care and then death. Death is most commonly caused by pneumonia seconded by successful suicidal attempts (Roos 2010).

The above chromosome map clearly shows there is a mutation in the Huntington's disease.

Causes and Risks

All Huntington's disease cases are found to be caused by the defective gene that was identified by the medical scientists in the year 1993. The huntingtin gene imperfection is consisted of an additional particular chemical code repeat in a minute part of chromosome 4. Normally, the huntingtin gene has a total of more or less twenty repetitions of this specific chemical code among the total codes that number three thousand approximately. The Huntington's disease is caused by the chromosomal defect in which there are more than forty repetitions. For the genetic tests of the Huntington's disease, these number of chemical codes repetitions that are present in the huntingtin protein gene of the patients are measured (Knowles 2007).

The actual function of the hungtin protein/gene is still not known to the scientists. They still don't know about the process due to which dozens of surplus repeats in its genetic design cause the destructive indicators of Huntington's disease. This is the reason why scientific researchers are making endeavors for the resolution of the unanswered Huntington's mysteries. Any advancement and solution would be advantageous for the getting insights of psychological disorders for instance Alzheimer's, Parkinson's disease etc. (Knowles 2007).

Symptoms

The symptoms of this disease may vary from person to person. There are cases when within the same family the symptoms differed from the other family member. In some cases, emotional and behavioral symptoms are more prominent. For others, the emotional and behavioral symptoms may be less obvious as compared to the symptoms of involuntary movements (Lemiere 2004). Following are some of the most common symptoms of Huntington's disease.

Emotional/Behavioral Symptoms

Some of the symptoms which are commonly encountered in the Huntington's disease are anxiety, irritability, depression and apathy. Some people suffer from depression for a longer period which may be months or even a year, before its recognition to be a symptom of HD. Social withdrawal, several occurrences of mood swings and impulsiveness with aggression are the behavioral changes that may show up. Existing personality traits can also get intense by Huntington's disease. There are also very less chances of schizophrenia and other psychiatric problems in Huntington's disease (Lemiere 2004).

Cognitive/Intellectual Symptoms

The very first signs of cognitive disturbance often are the slight changes in intellectual capacity. These signs may be the reduced ability to handle new situations and the organization of the routine matters as well. Long-term memory stays well but short-term memory loss is a symptom too. The daily routine work/tasks become extremely difficult to perform (Lemiere 2004).

Motor Symptoms

Excessive restlessness, fidgeting, twitching are the nervous activities that are initial physical symptoms. There may be a change in the hand writing of the person. Routine activities like driving and cooking, which involve concentration and coordination, become difficult. Facial grimaces can appear as well. All these initial symptoms may develop with time into some involuntary movements of head and limbs. As a result, these may lead to walking problem and balance maintenance. During rest and taking sleep, movements decrease and the movement in stress or excitement may increase during voluntary effort (Lemiere 2004).

Diagnosis

Only a comprehensive and detailed examination of Huntington's disease can make sure the completion of an accurate clinical diagnosis. The examinations to diagnose Huntington's disease consist of numerous neurological and psychological exams. Family history is also checked in detail. In some cases, diagnosis also involves MRI (magnetic response imaging)/CT scans (computerized tomography). However, the findings from such processes do not provide enough information with the help of which a proper diagnosis may be formed. In the similar manner, Huntington's disease may also be diagnosed by conducting the genetic test of the individual, the results of which may help in the confirmation, ruling out or identification of Huntington's disease development (DiMaio, Fox & Mahoney 2010).

It is extremely important to mention here that if the HD gene is identified after a positive test result, this finding may not be helpful for the confirmation of HD diagnosis without a neurological examination. This is the reason why it is excessively significant to get checked up by a neurologist who is well-known with the Huntington's disease. The efficiency of the neurologist counts a lot as HD symptoms are similar to symptoms of Parkinson's disease, alcoholism etc. Therefore, it is really essential "to confirm that at least one affected member of the family has had the clinical diagnosis confirmed by molecular testing to provide the most accurate genetic counseling, especially if the husband would be considering molecular testing of his own Huntington disease genes" (DiMaio, Fox & Mahoney 2010).

The HD diagnosis may prove to be a relief for some people. They consider it a blessing to know that their lack of memory is a problem and the mystery of why they keep forgetting things is finally resolved. For others, the news regarding HD diagnosis comes as an upsetting shock. A majority of people tend to deny that they have HD even after positive results as it is rather disturbing for them to accept that they have such a rare disease. For such people, the best way to cope up with the reality is to engage in discussions regarding their emotional status. They may share their feelings with a closed one, support group member or therapist.

Genetic Testing

A test was developed soon after the discovery of the Huntington's disease gene in the year 1993. This test made it possible for people to get confirmed whether they carry the HD-causing gene or not. In the initial phases, the linkage analysis process was used to test people and this needed the family members to get their blood samples tested. However, with the passage of time, new tests were introduced out of which the "direct gene test" is regarded as the most appropriate and authentic. This genetic test only requires the individual who takes the test for the detection of HD gene to give his/her blood sample (Knowles 2007).

Thus, the tests findings revealed that the Huntington disease gene consists of a particular expanded section only found in people who have HD. On the other hand, others who do not suffer from HD have a "tri-nucleotide repeats" section in their DNA. DNA is composed of building blocks i.e. nucleotides which are represented by the alphabets C, A, G and T. As already mentioned, the CAG pattern is repeated forty times or more in people who have Huntington's disease. The genetic test is used for the analysis of an individual's DNA whereby the CAG numbers in his/her DNA is counted. The results of the genetic test then make it possible to tell whether there are chances of HD development or not. However, the onset of HD cannot be predicted by genetic testing. It is surprising to know that the genetic disease for Huntington's disease offer results that are more or less ninety-nine percent accurate all the time (Kirby 1998).

It is an entirely personal matter to decide about undergoing genetic testing, a decision that must not be taken with a light heart. It is required of the family members to not enforce an at-risk individual to go for genetic testing. The process of testing consists of a number of sessions with several professionals. At least one session is meant for having genetic counseling, conducting a neurological exam, an interview with a psychologist, results' discussion with the individual and family members and follow-up. The genetic test is only a blood test after which diagnosis is made.

Treatment

There are many ways to treat Huntington's disease although there is still no cure for it. At the same time as no current treatments can be helpful in altering the progression of the Huntington's disease, there are numerous medications that can be useful in the treatment of common HD symptoms like anxiety, irritation and frustration. Moreover, medications can also help in the lessening of involuntary movements. It is important to mention that a number of drugs can have disturbing side effects. This is the reason why it is the responsibility of the physician to explain them to the patient and his/her family before the beginning of the treatment.

Most of the give drug prescriptions to the patients for treating HD symptoms even when there is no need of it. In majority of cases, it has been observed that people who do not take drugs or take minimal drugs did better than those who took drugs in heavy doses. It happens a lot of time that drugs are helpful at one stage while they stop to have any effect on the patient's condition at other stages. For such factors, it is often preferable for patients and their families to look for an experienced Huntington's disease neurologist as not all of them are well-acquainted with it. It is also a good thing to keep the family physician involved in the continuing treatment. A critical role is played by both the HD patients and their families for the monitoring and assessment of the treatment effectiveness.

The treatment also involves physical and speech therapies so it is a good thing if both physical therapist and speech therapist are consulted. Such strategies can turn out to be really helpful in giving a positive influence to the patient and making his/her quality of life improved. In addition, the HD patients need a very well balanced diet as nutrition may have a lasting impact on their physical condition. An exceptional number of calories are needed by the HD patients for the maintenance of their body weight so the importance of diet can never be underestimated in this regard. Patients who are experiencing the last stages of HD find it really helpful to have a really good diet in order to reduce the involuntary movements (by both gaining and losing weight; depending on their physical condition). Nutritional supplements are also suggested by the nutritionists.

Research

Research in finding a cure for Huntington's disease is the key. A number of ground-breaking theories have been propounded regarding the HD. The gene discovery in 1993 was the main highlight. Since that time, medical scientists have been able to discover certain brain proteins related to huntingtin protein. Currently, research is conducted for finding out the process with which the mentioned proteins combine for producing HD-causing symptoms. Scientists are also keen to find out a way to stop the proteins' interaction as a main treatment method.