In Peutz–Jeghers syndrome

In Peutz–Jeghers syndrome hamartomatous gastrointestinal
polyps, which may bleed or cause intussusception, are
associated with pigmentation of the buccal mucosa and lips.
Malignant degeneration in the polyps occurs in up to 30–40%
of cases. Ovarian, breast and endometrial tumours also occur in
this dominant syndrome.
Mutations causing Peutz–Jehgers syndrome have been
detected in the serine/threonine protein kinase gene (STK11)
on chromosome