Is cystic fibrosis inherited, and what is the chance my other children will be a

[Anonymous]

Is cystic fibrosis inherited, and what is the chance my other children will be affected?

[Genetic Counselor]

Yes. Cystic fibrosis is inherited in an autosomal recessive pattern. This means a person must inherit a disease-causing change in both copies of the CFTR gene, one from each parent, to have the condition.

A person with one changed copy and one working copy is called a carrier. Carriers are healthy and usually do not know their status until a relative is diagnosed or they are tested. When both parents are carriers, each pregnancy has:

• a 1-in-4 chance that the child inherits two changed copies and has cystic fibrosis
• a 1-in-2 chance that the child inherits one changed copy and is a healthy carrier
• a 1-in-4 chance that the child inherits two working copies and is neither affected nor a carrier

These chances apply to every pregnancy separately. Having one affected child does not mean the next three will be unaffected, much like tossing a coin does not “remember” the last toss.
Healthy brothers and sisters of a child with cystic fibrosis have a 2-in-3 chance of being carriers. This becomes important when they plan their own families. Aunts, uncles, and cousins may also be carriers, so testing is often offered to the wider family once the exact CFTR changes are known. This approach is called cascade testing.

Cystic fibrosis is most common among people of Northern European ancestry, where about 1 in 25 people is a carrier. It was long believed to be rare in India, but research now suggests it is underdiagnosed rather than truly rare. Estimates of how often it occurs among Indian births range widely, from about 1 in 2,500 to 1 in 40,000, largely because many affected children are never tested. The F508del change accounts for a much smaller share of disease-causing changes in Indian patients than in European patients, which is why full gene sequencing is preferred here.
For couples who are both known carriers, options include testing during pregnancy through chorionic villus sampling or amniocentesis, and preimplantation genetic testing alongside in vitro fertilization, which allows embryos to be tested before a pregnancy begins. Carrier screening before pregnancy is also offered to couples without a family history. A genetic counselor can explain which options suit a family’s situation and values.

[Author]

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