Huntington's disease, a genetically linked disorder, progressively destroys nerve cells and results in damage to specific areas of the brain. As a rule, genes code for the construction of proteins. and the gene involved in the development of Huntington's disease is HTT, also known as the IT15 or HD gene. According to "Adams and Victor's Principles of Neurology" by Drs. Allan Ropper and Martin Samuels, the name of the protein made by this gene is called huntingtin. Diagnoses and treatments for diseases should be made with the consultation of a healthcare professional.
Cause
Genes are made from sequences of four chemicals, called bases. These are abbreviated A, T, C and G. Different sequences code for the construction of different proteins by the cell. The proteins are made of amino acids, and each sequence of three bases codes for an amino acid. The HTT gene has a section with the chemical sequence CAG repeated over and over, resulting in inserting the amino acid glutamine into the protein over and over as noted by "Harrison's Principles of Internal Medicine" by Anthony Fauci, M.D. These excessive repetitions cause the protein to be dysfunctional and results in death to certain nerve cells in the brain. The more repetitions there are, the more severe the disease is and the earlier it develops, with most cases beginning in middle age and progressing for about 10 years. The repetitions can be expanded in the children of those with the disease, so that successive generations have more severe disease; this process is called anticipation.
Inheritance
Huntington's disease is genetically heritable. In the majority of cases, if a parent has the disease, there is a 50 percent chance of a child inheriting the gene and therefore developing the disease, as noted by the National Institutes of Health.
Symptoms and Signs
One of the most prominent symptoms of the disease is a rhythmic dance-like movement of the head, limbs and trunk. Early symptoms include depression, irritability, mood swings and cognitive difficulties such as trouble learning new facts, remembering things, planning and making decisions. As the disease progresses, these tasks become more difficult, and the movement problems result in a person having difficulty eating and swallowing. Other common problems include trouble maintaining weight and coordinating eye movements.
Diagnosis
The first step to diagnosis is a thorough medical history. The family history is particularly important, though 1 to 3 percent of persons with the disease may have no history of the disease, according to the National Institutes of Health. Genetic tests are very good at detecting the disease. Brain scans such as MRI are usually not used to establish the diagnosis, but may be done to see if any other disease is responsible for the symptoms.
Treatment
There is no cure for Huntington's disease. However, some treatments can be given to help with the symptoms. Movement disorders can be addressed with medications that block or deplete the actions of dopamine, such as antipsychotic medications and the drug tetrabenazine. Mood disorders and depression may be addressed with various antipsychotic medications and antidepressants, such as the selective serotonin inhibitors, including fluoxetine or Prozac. A number of drugs and other interventions are presently being researched, such as deep brain stimulation, but none has been shown to significantly modify the course of the disease.
References
- "Adams and Victor's Principles of Neurology"; Allan Ropper and Martin Samuels; 9th Ed 2009
- "Harrison's Principles of Medicine"; Anthony S Fauci et al; 17th Ed 2008
- National Institutes of Health; NINDS Huntington's Disease Information Page
