Which are the causes of Huntingtons Disease?

Huntington's Disease is a hereditary neurodegenerative disorder caused by a specific genetic mutation in the HTT gene, which leads to the production of an abnormally long protein that damages brain cells. This condition is inherited in an autosomal dominant pattern, meaning a child of an affected parent has a 50% chance of inheriting the mutation. Because the underlying genetic cause is well-established, current research is focused on silencing this gene or modifying the resulting toxic proteins to slow disease progression.

What exactly causes Huntington's Disease?

The primary cause of Huntington's Disease is a mutation in the HTT gene located on chromosome 4. This gene provides instructions for making a protein called huntingtin. In individuals with Huntington's Disease, the gene contains an expanded "CAG trinucleotide repeat." Think of this as a stutter in the genetic code: while healthy individuals typically have 10 to 35 repeats, those with the disease have 40 or more. This expansion results in a "mutant" huntingtin protein that is abnormally long and unstable. Over time, these toxic protein fragments accumulate in neurons, particularly in the striatum and cerebral cortex, eventually leading to cell death and the clinical manifestations of Huntington's Disease.

Is Huntington's Disease hereditary?

Yes, Huntington's Disease is strictly hereditary. It follows an autosomal dominant inheritance pattern, which means that only one copy of the mutated gene from either parent is required to develop the condition. There are no known environmental triggers, infectious causes, or autoimmune mechanisms that cause the disease; it is entirely determined by the genetic code inherited at conception. While the genetic cause is fully understood, researchers are still investigating why the age of onset and the severity of symptoms vary significantly even among individuals with similar repeat lengths.

What is the difference between causes and risk factors?

In the context of Huntington's Disease, the distinction is clear-cut:

• The Cause: The specific expansion of CAG repeats in the HTT gene is the direct, singular cause of the disease. Without this mutation, an individual will not develop the condition.


• Risk Factors: There are no lifestyle or environmental "risk factors" that cause Huntington's Disease. However, the number of CAG repeats is a "modifying factor"—generally, a higher number of repeats is associated with an earlier onset of symptoms.

What does current research suggest about the etiology?

While the genetic etiology of Huntington's Disease is well-mapped, scientists are actively researching the downstream mechanisms of the disease. Current studies are focused on:

1. Gene Silencing: Developing therapies to "turn off" the HTT gene to prevent the production of the toxic protein.


2. Protein Clearance: Enhancing the body's natural ability to clear out the misfolded huntingtin protein fragments.


3. Neuroprotection: Finding ways to support and protect the neurons that are most vulnerable to the toxic effects of the mutation.

Currently, 39 people with Huntington's Disease have joined the DiseaseMaps community, sharing their lived experiences and helping researchers understand the real-world impact of these biological mechanisms.

Next steps

• Consult with a neurologist or a movement disorder specialist to discuss diagnostic testing and symptom management.


• Seek out a certified genetic counselor to discuss family planning and the implications of the hereditary nature of the disease.


• Connect with the 39 members of the DiseaseMaps community to share experiences and find emotional support.


• Visit the Huntington's Disease Society of America (HDSA) or similar patient foundations to learn about ongoing clinical trials and research opportunities.

Medical disclaimer: This content is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

References

• National Institutes of Health (NIH) Genetic and Rare Diseases Information Center (GARD): Huntington's Disease.


• Orphanet: Huntington's disease (ORPHA:399).


• Online Mendelian Inheritance in Man (OMIM): #143100 (Huntington Disease).


• Huntington's Disease Society of America (HDSA): Understanding the Science.