What are polyposis syndromes?
Polyposis syndromes are inherited diseases associated with the development of small tissue growths called polyps in the gastrointestinal tract. Usually, polyps form in the colon, but they can also appear in other places like the small bowel or stomach.
Many children are first diagnosed with a polyposis syndrome after discovering a polyp that protrudes from the rectum, bleeding from the rectum or having blood in their stool, although it may not be visible.
Sometimes children also have anemia, or low numbers of red blood cells. Later in life, affected individuals may have an increased risk of cancer, benign tumors and other conditions that involve the gastrointestinal tract, as well as other body parts.
What are the types of polyposis syndromes?
The most common types of polyposis syndromes manifesting in childhood are:
- Juvenile polyposis syndrome (JPS)
- Peutz-Jegher syndrome (PJS)
- Familial adenomatous polyposis or Gardner syndrome (FAP)
There are other very rare, polyposis syndromes including PTEN Hamartoma tumor syndrome, ataxia telangiectasia, and neurofibromatosis.
What causes polyposis syndromes?
Because these are inherited conditions, screening of family members is often recommended. Although a cure is not currently available, screenings for diagnosis and monitoring programs for early detection and treatment are important to prevent more severe problems from developing. Screenings may begin before age 5 for some polyposis conditions.
Who gets polyposis syndromes?
Children of every gender, race and ethnicity can develop inherited polyposis syndromes. These conditions may affect children and adolescents as well as adults.
JPS, PJS, and most forms of FAP are inherited in an autosomal dominant fashion. This means a child may develop the condition if just one parent passes on the genes for polyposis. If a person is affected, each of his or her offspring has a 50% chance of getting the disease. However, many genes may be involved in each of the different conditions below. Some people do not have affected family members; they have new mutations.
Juvenile polyposis syndrome
Researchers have identified two genes, BMPR1A and SMAD4, which cause nearly 40 % of JPS. However, for more than 60 % of children with JPS, the exact cause is still unknown. In the majority of cases, faulty genes are passed down from a parent, but in 25 % of cases a new mutation has developed for the first time in a family. About 1 in 100,000 children may develop JPS.
Both the BMPR1A and SMAD4 genes contain the blueprint for tumor suppressors. These proteins keep the body’s cells from growing and dividing too quickly, and promote cell death, an important part of keeping the body’s tissues healthy. When these genes are altered, cells can grow too fast or divide too much, which may cause tumors or polyps to form.
Between 1 in 30,000 and 1 in 300,000 kids may develop PJS. Mutations in the STK11 gene, another tumor suppressor gene, cause PJS. This mutation leads to the development of non-cancerous and cancerous tumors. One copy of the altered gene in each cell is sufficient to develop PJS. In over half of cases, it is inherited from an affected family member; but in about half, there are no affected family members and a new mutation is suspected.
Familial adenomatous polyposis
FAP is the most common polyposis syndrome, affecting 1 in 10,000 children. The classic and attenuated forms of FAP are caused by mutations in the APC (adenomatous polyposis coli) gene. A third form of the disease, called the recessive form, is caused by a mutation in the MUTYH (mutY homolog) gene. This is also called MYH-associated polyposis. The MUTYH gene mutation affects the ability to repair mistakes made in the DNA as cells copy their genetic material and then divide.