INTRODUCTION HISTORY DISEASE DIAGNOSIS SYMPTOMS CAUSES PREVALENCE WORLDWIDE TREATMENT AND MANAGEMENT FUTURE PERSPECTIVE REFERENCES
Huntington’s Disease is an inherited disease characterized by progressive brain disorder caused by a single defective gene on chromosome 4, this leads to degeneration of certain nerve cells in the brain. This disease has a broad impact on a person’s functional abilities and usually results in movement, cognitive and psychiatric disorders. Most people with this disease develop signs and symptoms in their 30s or 40s, but the onset is usually earlier or later in life.
When HD onset begins before the age of 20, the condition is called juvenile Huntington’s Disease. Earlier onset often result in a somewhat different presentation of symptoms and faster disease progression.
HD has been recognized as a disorder since at least the middle age, but the cause was unknown until fairly recently. It was originally called “chorea” for the jerky dancelike movement associated with the disease. In 1846, Charles Gorman observed how higher prevalence seemed to occur in localized region. The first thorough description of the disease was by George Huntington in 1872
Huntington examined the combined medical history of several generations of a family exhibiting similar symptoms, he realized their conditions must be linked; he presented his detailed and accurate definition of the disease as his first paper. Huntington described the exact pattern of inheritance of autosomal dominant disease years before the rediscovery by scientists of Mendelian inheritance Sir William Osler was interested in HD and chorea in general and was impressed with Huntington’s paper
Osler’s continued interest in HD coupled with his influence in the field of medicine, helped to rapidly spread awareness and knowledge of the disorder throughout the medical community. During the rediscovery of Medelian inheritance at the turn of the 20 th century, HD was used as an example of autosomal dominant inheritance The English Biologist William Bateson used the pedigrees of affected families to establish that HD had an autosomal dominant inheritance pattern.
Diagnosis of HD is based primarily on general physical examinations including examinations like: Examination on motor symptoms e.g. reflexes, muscle tone, coordination, balance e.t.c. Examination on sensory symptoms e.g. sense of touch, vision and eye movement. Examination on psychiatric symptoms e.g. mental status, mood. Neuropsychological testing e.g. memory, reasoning, language function.
Other means of diagnosis includes; Brain imaging and function via MRI and CT Scan. Scientists identified the defective gene that causes HD in 1993. A diagnostic genetic test is now available. Genetic counseling and testing. Predictive genetic test via family history.
Symptoms usually develops between ages 30 & 50, but they can appear as early as age 2 or as late as 80. These symptoms include ; Uncontrolled movement of the arms, legs, head, face and upper body. Declined thinking and reasoning skills including memory, concentration, judgment and ability to plan and organize. Alteration in mood including depression, anxiety, uncharacteristic anger and irritability. Obsessive-compulsive behavior (OCD). Changes in speech- trouble learning new information, or loss of previous learnt skills.
This disease is caused by an inherited defect in a single gene. It is an autosomal dominant mutation in either of an individual’s two copies of a gene called Huntingtin. Everyone has the HD gene, but in some families an abnormal copy of the gene gets passed from parent to children. Every child in the family with the history of HD has a 50% chance of inheriting the gene that causes the genetic disorder.
The worldwide prevalence of HD is 5-10 cases per 100,000 persons, but varies greatly geographically as a result of ethnicity, local migration and past immigration patterns. Prevalence is similar for both men and women. The rate of occurrence is highest in people of Western Europe descent, averaging around 7 per 100,000 people and is lower in the rest of the world. Increased prevalence in some cases occurs due to local founder effect, a historical migration of carriers into an area of geographical isolation.
There is no cure. Medications can help manage some of the symptoms, but cannot slow down or stop the progression of the disease. Treatments focusing on management of symptoms includes: Chorea(involuntary movement): some experts begin treatment with an atypical antipsychotic drug. Irritability: For severe anger and threatening behavior, experts agree that an atypical antipsychotic drug is also the best first-line approach.
Obsessive-compulsive thoughts and action. Nutritional support- ranges from using special utensils to focusing on nutrient-dense foods to supplementing with tube feeding in later stages. Exercise may be very helpful. Therapies includes: Psychotherapy, speech therapy, physical therapy, occupational therapy.
With the knowledge about the HD gene, scientists have been able to learn a great deal about how the disease affects the brain. More importantly, this discovery may help pave the way for future treatment. 3 broad approaches are under study to attempt to slow the progression of Huntington’s disease. They includes: Reducing production of the mutant protein. Improving cells’ ability to survive its diverse harmful effects and replacing lost neurons.
Large observational studies involving human volunteers have revealed insights into the pathobiology of HD and supplied outcome measures for future clinical trials.