Question: Is it possible to predict at what age a person could get infected by a hereditary disease just by looking their ancestors? If not is it possible to predict any hereditary diseases?

Elaine Duncan answered on 17 Jun 2020:

Hi Diego, this is a really interesting question!

Some diseases have a very clear genetic link (eg colour blindness or sickle cell anemia) so if you know what genes your parents have, it’s possible to predict the likelihood that the offspring will have the same condition. Many of these diseases affect a person for their whole life, so there’s no “age of onset”.

However, most diseases are caused by a complex mix of genetic and environmental factors. If someone has inherited a specific set of genes (eg mutated BRCA1 for breast cancer), it becomes more likely that they will suffer from the disease but it is not guaranteed. It is very difficult to predict whether a person will get the disease or not, and even harder to know at what age these will set in. In some cases it is similar to a person’s ancestors since these people typically have similar genetics and share similar environmental factors, but this would be an approximation at best.

One really interesting example is Huntington’s disease. This is caused by a repeating CAG motif in the DNA – the more repeats that are present, the more severe the disease symptoms. There is some evidence that as number of repeats increases, the age of onset gets lower. Again, it’s not fixed in stone and can only be used as a rough estimate.

I hope this answers your question!