Q&A: I have cystic fibrosis but still want to have a baby.

Cystic fibrosis is quite common in the US where about one in 2,500 children are born affected. Each of us possesses a gene located near the end of the long arm of chromosome 7, of which we have two—one from each parent. This gene makes a protein called CFTR; its function is to assist in the movement of various salts, minerals, and water across cell walls. This function is important wherever mucus is made in the body. Consequently, when there is a defect in this gene contributed by each parent, this protein is ineffective and the mucus becomes extremely sticky and difficult to cough up. As a result, infection settles into the lungs and they become damaged progressively over years. With good care, antibiotics, and physical therapy, you can take care of the recurrent infections, but eventually the vast majority of survivors will need to consider a lung transplant.

Over 900 different gene defects (mutations) have been described thus far in the rather large cystic fibrosis gene. Among caucasians, analysis of the most common 30-50 mutations enables precise detection of 85 to 90 percent of all carriers. The rest are much rarer.

Your random likelihood of also carrying any cystic fibrosis mutation is probably about one in 50. In the US, one in 25 caucasians carry a cystic fibrosis gene mutation. So, your risks of having a child with cystic fibrosis are approximately one in 400.