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Peutz-Jeghers syndrome follows an autosomal dominant pattern of inheritance, meaning a change in just one of the two copies of the STK11 gene is sufficient to cause the condition.
• The majority of people diagnosed with Peutz-Jeghers syndrome, roughly sixty to seventy-eight percent in large studies, have an affected parent.
• A meaningful proportion, estimated at somewhere between seventeen and forty-five percent depending on the study, appear to be the only affected person in their family. In some of these individuals the genetic change arose new, described as a de novo change, while in others a parent carries the change in only some of their cells or reproductive cells, a situation called mosaicism, which can be difficult to detect on routine testing.
• Everyone who has been found to carry a disease-causing change in STK11 has gone on to show at least some clinical feature of the condition, meaning penetrance is considered complete, although the specific features and their severity vary widely from person to person, even within the same family.
• If a parent is confirmed to be affected or to carry the family’s specific genetic change, each of that person’s children, including future children, has a fifty percent chance of inheriting the same change.
• If neither parent shows clinical features and the genetic change cannot be found in either parent’s blood sample, the chance of the condition recurring in future children is still slightly higher than in the general population, because of the possibility of undetected parental mosaicism.Because an apparently negative family history cannot be fully relied upon without proper clinical and genetic evaluation of both parents, referral for genetic counseling is strongly recommended for accurate, family-specific risk assessment and for discussion of reproductive options such as prenatal testing.
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