Dr. Hana Neibur: CGD is a genetic disease, which means it’s passed down from parents to children. There are few different ways that can happen. Sometimes, it’s mothers passing down the gene to sons and daughters. Now, because this can be an X-linked disease, and girls have two X chromosomes, girls end up being carriers. The normal chromosome or the normal expression of the gene allows them to have enough function that they don’t usually have the same problems as a child who’s affected.

But boys get their X chromosome from their mother and their Y chromosome from their father, and so they don’t have that second X chromosome that gives them a normal gene. They only have the gene that causes the problem. So this is why boys are generally affected and girls are generally carriers. There are also autosomal recessive forms of CGD, but it’s carried on a different chromosome, and since you get one copy from each parent, each parent has a bad copy. The parent is not affected. But when a child happens to have the bad luck of getting two bad copies, the child actually has the disease, as opposed to, if they get one bad copy and they’re a carrier, or no bad copies and they’re not affected at all.