Exploring Huntington disease

As part of this year’s Jeans for Genes day, The Guardian has published one family’s story of their experience of the devastating condition, Huntington disease.

Huntington disease (HD) is an incurable ‘autosomal dominant condition’. All of us inherit our genes from our parents and the genes are bundled together on long, discrete pieces of DNA called chromosomes. There are 22 pairs of ‘autosomes’ and 1 one pair of sex chromosomes; 23 pairs (46) of chromosomes altogether. One set of chromosomes (22 autosomes and one sex chromosome) is inherited from each of our parents.

Because our chromosomes come in pairs, our genes also come in pairs – one of each pair comes from our mother, the other from our father.

Autosomal dominant conditions refer to conditions that occur when there is a change in (at least) one copy of a particular gene.

In HD, the huntingtin (or simply ‘htt‘) gene is affected. Every version of the htt gene contains a repetitive stretch of three letters of DNA; these three letters are ‘CAG’. People without HD have 35, or fewer CAG repeats; inheriting just one copy of the htt gene with 36 or more CAG repeats will cause HD. The greater the number of CAG repeats, the more severe the symptoms of the disease are and the earlier in life they begin.

Because only one changed copy of the gene is required to cause the condition, if an adult with the changed version htt has children, there is a 50/50 chance they will pass that changed version on to each child they have.

Today it is relatively easy to check if an individual carries a changed version of their htt gene. People not at risk of HD tend to assume that those who are at risk (people who have a parent with HD) would prefer to know whether they have inherited a changed version of the gene or not. The rationale is that by knowing, people can plan their lives in advance, and not knowing is tantamount to living in hear. However, the majority of people at risk of HD prefer not to take the test – the disease is so devastating that knowing you are going to develop it can feel like a death sentence.

HD is currently incurable. It is possible to relieve some of the symptoms of the condition, but people with a changed htt gene will develop the condition in later life. Because it is caused by a genetic change, HD is a potential candidate for gene therapy. The idea is that the damaging effects of the changed version of htt can be prevented by silencing that changed version so that only the ‘healthy’ version is active. Such a treatment is likely a long time away, but researchers continue to work hard to find ways of curing both the symptoms and the underlying cause of Huntington’s disease.

Watch Luke’s story; Luke’s mum is affected by HD.

More information about HD is available from the following sources: