My grandfather had Huntington's. What's the chance I get it?

I'm sorry you're carrying this question. Let me give you the math, then the harder part.

Huntington's disease is autosomal dominant, which means a person with the affected gene variant has the condition. It is not skipped. If your grandfather had Huntington's, the genetics work like this:

- If your grandfather had Huntington's, he had one copy of the affected gene.

- Each of his children (including your parent) had a 50% chance of inheriting that copy.

- If your parent inherited it, your parent has - or will develop - Huntington's. The condition usually appears between ages 30 and 50, sometimes later.

- If your parent inherited the variant, you have a 50% chance of having it too.

So your risk depends on whether your parent inherited the variant. If your parent is older than 50 and has shown no symptoms, the chance they inherited it is lower than 50% (because they would likely have shown symptoms by now). But "lower than 50%" is not "zero."

The harder part: this is one of the conditions where many people choose not to test, because the result tells you for certain what is or isn't coming, and there is no effective preventive treatment. A genetic counsellor can walk you through what testing would and would not give you, and what the testing process itself looks like. I'd strongly encourage that conversation before you make any decision.

Please be gentle with yourself. This is a heavy thing to think about.

I'm not a Huntington's specialist, but I want to add one practical note.

The decision of whether to test for a late-onset, currently incurable condition is one of the most personally weighty calls in clinical genetics. People choose differently. Some want to know so they can plan, have children before symptoms appear, or use IVF with embryo screening to avoid passing it on. Others choose not to know because the uncertainty is more bearable than a confirmed positive.

There is no right answer. There is the right answer for you. Take the time. Talk to people who have been through this.