My mom got HD without anyone in her family having it
HDYO has more information about HD available for young people, parents and professionals on our site:
Q. No one in my family had HD, but some how my mom got it. Is there any way to developer this disease without it being passed down?
Jasmine, Young Adult, USA
A. Dear Jasmine
Thank you for contacting HDYO with your question. Most people with HD have inherited the gene from a parent who also has it (following what is known as ‘autosomal dominant’ inheritance, see link below for more info). However, in rare cases the gene change that causes HD happens for the first time in an individual, in which case there would not be a family history in the parents/extended family. In some cases this is because a parent carries an HD gene with an ‘intermediate’ size – which may mean that they will not develop symptoms but their children may be at increased risk. This HDYO article gives more information about this. In other cases, we occasionally see people with HD who have no family history of the condition, but one of their parents perhaps died young of something else so it is possible that they may have carried the gene but had not started to show signs yet. The age at onset of symptoms can also be quite variable. Alternatively, it may be that because in the past HD was often less well known, sometimes people further back in a family were not diagnosed even if they had symptoms, or the symptoms may have been wrongly called something else (such as Parkinson’s disease, Alzheimer’s or dementia).
So, the short answer to your question is that although most people with HD have a family history of the condition, sometimes it can happen ‘out of the blue’ in a family. I hope this helps answer your question and please get back in touch if you have any other queries.