Major manifestations include abnormal pigmentation of the lips, buccal mucosa, face and fingers, and hamartomatous polyps of the small bowel. The pigmentation generally appears as brown spots or "black freckles." It is usually not present at birth, but appears during infancy and early childhood and fades as the patient ages. The lips and buccal mucosa are the sites most commonly affected. The polyps are typically found in the jejunum and ileum, but may occur anywhere in the gastrointestinal tract. Symptoms secondary to the polyp rarely occur in infancy and usually present in puberty and adolescence. They may act as a lead point for the formation of an intussusception, which accounts for the most common clinical symptom, abdominal pain. The second most frequent finding is gastrointestinal bleeding from the polyps. It is generally believed that the polyps are benign but malignant degeneration has been reported.
It is important to differentiate this syndrome
Gellis SS, Feingold M, Bachman RP. Picture of the Month. Am J Dis Child. 1973;125(1):77-78. doi:10.1001/archpedi.1973.04160010049011