I am 55 and my father had Huntington's. What is my chance now?

Well below 50%, but not zero. Most of the usual window has passed, and every year without symptoms counts as evidence. How far below depends on the usual ages for this disease and on how old your father was when his symptoms started.

Does Huntington's disease skip a generation?

Essentially no. Someone who inherits a full-length repeat will develop it if they live long enough. A generation that looks skipped usually means a relative who died of something else first, a borderline repeat length, or a diagnosis that was never made or never talked about.

Can it be inherited from my mother?

Yes, exactly as easily. The gene is not on a sex chromosome. Which parent passed it on matters for a different reason: the repeat tends to lengthen more when it comes from the father, which is why very early-onset cases are more often inherited that way.

My grandparent had it and my parent has never been tested. What is my chance?

Twenty-five per cent as a starting point — and lower if your parent is now past the usual age of onset and still well, because their own chance has fallen too.

Are there early signs I should be watching for?

Small changes in movement, mood or thinking can come years before a diagnosis, which is exactly why watching yourself is unreliable. Ordinary clumsiness and ordinary low mood are very common, and worrying about them is not a symptom. A neurologist can answer that question; introspection cannot.

My Parent Has Huntington's: What Are My Chances?

Why the starting number is 50%

Autosomal dominant — affected people in every generation, in a line, men and women alike, and a father can pass it to a son. □ male · ○ female · filled = affected · centre dot = carrier

Huntington’s disease is caused by a stretch of DNA in one gene that is repeated too many times. One affected copy is enough to cause the disease, which makes it a dominant condition.

Your affected parent has one affected copy and one normal copy. Which one ended up in the egg or sperm that made you was a coin toss — and the toss was independent for each child. Two affected brothers or sisters does not make the third one safe.

What the CAG numbers on a report mean

If anyone in your family has been tested, the report gives a number: how many times a short piece of DNA called CAG is repeated.

CAG repeats	What it means
26 or fewer	Normal. Does not cause the disease, and stays stable when passed on.
27 – 35	In between. This person will not develop Huntington’s from it, but the repeat can grow when passed on — mainly from a father — so a child could inherit a longer one.
36 – 39	Borderline. Some people in this range develop the disease and some never do.
40 or more	Will cause the disease in anyone who lives long enough.

Longer repeats generally mean earlier symptoms, but the link is loose. A result of 42 tells you the disease will come. It does not tell you when, and no honest report will claim otherwise.

Why symptoms can start earlier in each generation

The repeat is unstable when sperm are made, so it tends to grow longer when passed from a father rather than a mother. That is why symptoms sometimes start earlier in each successive generation, and why childhood-onset Huntington’s is nearly always inherited from the father.

This does not change your 50%. It changes the range of ages you should be measuring yourself against.

Your chance today is not your chance at birth

This is the part most information pages leave out.

Huntington’s can start at almost any point in adult life, but most diagnoses come in the thirties, forties and fifties. Every year you live without symptoms is a piece of evidence, and evidence changes the odds.

In plain terms: a 25-year-old at risk is still close to 50%, because almost nobody has developed it by 25 — so being well tells you very little. A 60-year-old at risk is much lower, because if they had inherited it, the odds are it would have shown itself by now.

Two other things move the number, and neither of them needs a test:

How old your affected parent was when it started. Repeat lengths run in families, so a parent who became ill at 62 implies something different for you than a parent who became ill at 38.
The ages of your brothers and sisters who are still well. They say something about the family, though much less about you than your own age does.

If it was your grandparent rather than your parent

Your starting point is 25% — your parent’s 50%, halved.

But if your parent has never been tested, is well, and is now past the usual age of onset, their own chance has dropped below 50%, and yours drops with it. This two-step adjustment is where doing it in your head goes wrong most often: the intuitive answer sits at 25% long after the real one has fallen well below.

What predictive testing involves

The test itself is simple — a laboratory counts the repeat. What follows is not, which is why long-standing international guidance puts it inside a counselling process: appointments beforehand to talk through what each possible result would mean, a gap to think, and support afterwards whichever way it goes.

It is offered to adults only. Children are not tested while they are well, because the decision belongs to the person whose result it is.

Most people at risk choose not to be tested, and that is a recognised and respected choice rather than avoidance. Things people weigh up:

There is no treatment yet proven to delay or prevent it, though gene-targeting treatments are in clinical trials.
A result cannot be un-known, and it says something about your brothers, sisters, children and parents, who may not have chosen to know.
Insurance and employment consequences vary a lot depending on where you live. That is worth checking before testing, not after.
Planning a family is the commonest reason people decide to go ahead.

If you are thinking about children

Testing during pregnancy and testing embryos created through IVF are both possible.

So is something called exclusion testing, which works out whether a pregnancy inherited a chromosome from the affected grandparent without revealing whether you yourself carry the repeat. It exists precisely for people who want to protect a pregnancy without finding out their own status.