Question: Two of my siblings have autism, but me and my youngest sister don't. Why is that?

Emma Meaburn answered on 8 Jan 2019:

This is a really great question, and one that scientists are working hard to figure out. I think it is fair to say that at present scientists don’t have a simple explanation for this. We know that the combination of genes (unique to you) that you inherit from your parents play an important role in increasing (or decreasing) risk for autism, as do non-genetic (i.e., environmental) factors. A lot of progress has been made in identifying specific genes linked to autism and understanding how it alters neurobiology and brain development, but we are still unsure how genetic and non-genetic factors act and interact over the course of development to result in autism – or indeed why some individuals who are seemingly at high risk of autism develop typically.