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HUNTINGTON’S DISEASE: A rare genetic condition affecting the brain

Huntington’s disease (HD) is a fatal brain degenerative condition that causes mood and behavioral disturbances, a decline in cognition and uncontrolled movements. HD is hereditary which means that it is passed down from parent to child. Every child born to a HD parent has a 50/50 chance of suffering from HD. Currently there is no cure for HD but there are drugs that can alleviate the symptoms.

Symptoms usually appear after the age of 30 for adult-onset HD but could also appear earlier in life (in the case of juvenile HD). After the appearance of symptoms, they tend to decline over a 10-20 year period before individuals succumb to respiratory problems or heart disease.

The symptoms of HD can vary in severity and age at onset even for individuals in the same family.

Symptoms include:

  1. Behavioral, mood and personality changes
  2. Involuntary movements
  3. Eye movement abnormalities
  4. Forgetfulness and impaired judgement
  5. Slurred speech
  6. Difficulty swallowing
  7. Weight loss
  8. Loss of self-esteem
  9. Loss of sex drive

Different stages of Huntington’s disease Progression

After the onset of HD, the symptoms become progressively noticeable. At the different stages individuals face different challenges and concerns requiring attention from caregivers or professionals.

  1. Early Stage
    People suffer from a cognitive decline, subtle involuntary movements and a lack of coordination. At this point a formal diagnosis is needed. People can still maintain a fairly normal lifestyle and can work, drive and live independently.
  2. Early Intermediate Stage
    Individuals are employable but at a reduced capacity. They can still perform daily chores but with some difficulties.
  3. Late Intermediate Stage
    People are unable to manage household chores but are still fairly independent. They need help and supervision managing their finances and daily tasks.
  4. Early Advanced Stage
    Individuals lose their ability to perform tasks independently. They need to be cared for by family or professionals. They can still live at home with their families.
  5. Advanced stage
    People require complete support from a professional nursing home.

What causes HD?

HD is caused by a mutation in the gene coding for the protein molecule Huntingtin that is found in brain neuron cells. All of us carry a normal Huntingtin gene, however individuals with HD carry a CAG repeat expansion. These CAG repeat expansions influence the severity and age at onset of HD. With, most symptomatic cases of HD presenting with a CAG repeat expansion length that is greater than 40. With these 40 CAG repeats and above, it is predicted that individuals will be symptomatic in their lifetime. For 36-39 CAG repeats individuals will be symptomatic later in life. While 27-35 CAG repeats denote the genetically unstable intermediate zone and individuals here will not be symptomatic for HD but can transmit it to their children. The healthy population without HD has an average of 18 CAG repeats. Interestingly, studies have revealed that the length of CAG repeats correlates with age at onset of Huntington’s disease.

What is the scope of HD in Africa and beyond?

Currently, based on a small study in South Africa, it is estimated that 1/100,000 Africans suffer from huntington’s disease but the number could be higher. It has long been believed that HD has low prevalence in Africa. However large-scale studies to establish this have not been done. This lack of HD-epidemiological studies  results from lack of proper diagnosis, low numbers of neurologists and stigma related to traditional belief systems. HDA aims to support HD studies on the continent. Elsewhere, studies in populations of European ancestry show a higher prevalence of 5-10/100000, however it is not determined for Asian and Middle Eastern populations. Taken together HD is an incurable disease affecting all people groups in the world that requires concerted efforts to beat it.

Huntington’s disease look a likes among Sub-saharan South Africans

Most South Africans of Sub-saharan ancestry presenting with conventional Huntington’s disease-like symptoms lack the usual elongation mutation at the Huntingtin locus. In contrast they have mutations in genes coding for other proteins like Junctophilin 3 (JPH3) and Spino-cerebellar ataxias. This is interesting from a mechanistic perspective.