Focus on Huntington Disease on Huntington Disease Awareness Day (May 15th)

When Laura first noticed the unusual movements her mother kept making, she was reminded of her grandfather, a man she only briefly met as a child. He was a difficult man, described in the family lore as an “alcoholic who drank himself to death”. But Laura’s mother does not drink. Her behaviour had also changed, she had become quiet and more distant in the past few years, something Laura chalked up to the divorce from Laura’s father. “She was never an openly loving parent, she was always strict” Laura tells her best friend, “but now she doesn’t even really want to talk to us or see us.” And she had forgotten Laura’s last birthday. After an internet search, Laura decided to bring her mother to a neurologist. After just a couple of sessions the neurologist is sure, Laura’s mother has Huntington’s disease. A genetic test confirms this.

Huntington disease (HD) is an inherited neurodegenerative disorder caused by a change in the HTT gene. It affects the brain over time and can lead to problems with movement, thinking, and mood. Symptoms often begin in adulthood, classically between the age of 30 and 60, though onset can vary. Common features include involuntary movements (chorea), difficulty with coordination, changes in memory and concentration, and psychiatric symptoms such as depression, irritability, or anxiety.

HD follows an autosomal dominant inheritance pattern. This means that a person who has the altered gene has a 50% chance of passing it on to each child. The condition is caused by an expansion of CAG repeats in the HTT gene. A higher number of repeats is associated with the disease, although the exact course and age of onset can differ from person to person.

Laura asks “so my brother and I have a 50% chance of getting this too?” The genetic counsellor confirms and tells Laura she can get testing now, or wait and see if symptoms develop over time.

Genetic testing for Huntington disease is available in two main settings: symptomatic testing and predictive testing. Symptomatic testing is used for people who already have signs or symptoms that suggest HD. In this setting, the test helps confirm whether the symptoms are due to Huntington disease and may support diagnosis, care planning, and family counseling.

Predictive testing is offered to adults who do not have symptoms but have a family history of HD and want to learn whether they inherited the altered gene. Because predictive testing can have major emotional, social, and practical implications, it is usually provided through a careful process that includes genetic counseling, informed consent, and psychological support. Testing is generally not recommended for minors unless there is a direct medical reason.

Laura has twin daughters, who are 10. The genetic counsellor tells her that while Laura can get testing, the girls will have to wait until adulthood. If Laura does not carry the gene expansion, then the girls are not at risk. Huntington’s disease cannot “jump a generation”.

While genetic testing can determine whether the HTT expansion is present, it cannot precisely predict when symptoms will begin or exactly how severe they will become. For many individuals and families, counseling before and after testing is an essential part of care, helping them understand the results, consider the impact, and make informed decisions.

Laura and her brother have one session with a psychologist and two sessions of genetic counselling before deciding whether to get testing. Laura’s brother decides to get the test, he got married last year and they are planning children soon, if he carries it, he can have preimplantation genetic testing (PGT) or prenatal testing to make sure his children do not get the disease.

Laura decides not to get testing. She has had her children, is planning no more. She does not want to live knowing that she carries it and especially does not want to live with the guilt of having potentially passed it on to her daughters. For now she is focused on caring for her mother and family. She knows testing is possible, if and when she is ready.

Author’s note: over 70% of people at 50% risk of Huntington’s disease decide against testing.