The syndrome is associated with malfunction of serine-threonine kinase 11 or STK 11 gene, and has a 2% to 10% increase in risk of developing cancer of the intestinal tract. The syndrome also causes increased risk of extraintestinal cancer such as that involving breast, ovary, cervix, fallopian tubes, thyroid, lung, gallbladder, bile ducts, pancreas, and testicles. The polyps often bleeds and may cause obstruction that would require surgery. Any polyps larger than 1.5 cm needs removal and patients should be monitored closely and screen every 2 years for malignancy. Juvenile polyposis syndrome
Juvenile polyposis syndrome is an autosomal dominant syndrome characterized by increased risk of cancer of intestinal tract and extraintestinal cancer. It often presents with bleeding and obstruction of the intestinal tract along with low serum albumin due to protein loss in the intestine. The syndrome is linked to malfunction of SMAD4 a tumor suppression gene that is seen in 50% of cases. Individuals with multiple juvenile polyps have at least 10% chance of developing malignancy and should undergo abdominal colectomy with ileorectal anastomosis, and close monitoring via endoscopy of rectum. For individuals with few juvenile polyps, patients should undergo endoscopic polypectomy. Types
Colorectal polyps can broadly be classified as follows:

hyperplastic,
neoplastic (adenomatous & malignant),
hamartomatous and,
inflammatory. Comparison table
Hyperplastic polyp
Most hyperplastic polyps are found in the distal colon and rectum. They have no malignant potential, which means that they are no more likely than normal tissue to eventually become a cancer. Neoplastic polyp
A neoplasm is a tissue whose cells have lost normal differentiation.
It was later further studied by Henry Lynch who recognized an autosomal dominant transmission pattern with those affected having relatively early onset of cancer (mean age 44 years), greater occurrence of proximal lesions, mostly mucinous or poorly differentiated adenocarcinoma, greater number of synchronous and metachronous cancer cells, and good outcome after surgical intervention. The Amsterdam Criteria was initially used to define Lynch syndrome before the underlying genetic mechanism had been worked out. The Criteria required that the patient has three family members all first-degree relatives with colorectal cancer that involves at least two generations with at least one affected person being younger than 50 years of age when the diagnosis was made. The Amsterdam Criteria is too restrictive and was later expanded to include cancers of endometrial, ovarian, gastric, pancreatic, small intestinal, ureteral, and renal pelvic origin. The increased risk of cancer seen in patients with by the syndrome is associated with dysfunction of DNA repair mechanism. Molecular biologists have linked the syndrome to specific genes such as hMSH2, hMSH1, hMSH6, and hPMS2. Peutz–Jeghers syndrome
Peutz–Jeghers syndrome is an autosomal dominant syndrome that presents with hamartomatous polyps, which are disorganized growth of tissues of the intestinal tract, and hyperpigmentation of the interlining of the mouth, lips and fingers. The syndrome was first noted in 1896 by Hutchinson, and later separately described by Peutz, and then again in 1940 by Jeghers.