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Juvenile polyposis

Juvenile polyposis syndrome or JPS is a rare, inherited condition which leads to the development of juvenile (hamartomatous) polyps in the stomach, duodenum and large bowel.

Do the polyps only grow in childhood?

The term juvenile refers to the type of polyp and the way it appears under a microscope (histological appearance), rather than the age of the patient when the polyps develop. Most people with JPS have some polyps by the time they are 20 years old. Some may only develop a handful of polyps over their lifetime, while others may have hundreds.

What Causes JPS?

JPS is a genetic condition caused by an alteration in one of two genes: the SMAD4 gene on chromosome 18 and the BMPR1A gene on chromosome 10. In approximately 20% of patients with JPS, a genetic alteration cannot be found. When this happens a clinical diagnosis of JPS is made using the following criteria:

  • when a person has been found to have more than 5 juvenile polyps in the large bowel
  • juvenile polyps in other parts of the GI tract
  • any number of juvenile polyps in a person with a family history of juvenile polyposis

What is the chance of inheriting JPS?

JPS is inherited in a dominant way i.e. each child born to a person with JPS has a 50:50 chance of inheriting the altered gene that causes it.  Sometimes a person may be affected even though both parents have unaltered genes. This is because alterations can occasionally occur in the DNA during formation of the embryo. In a case where this has happened it is important that parents, brothers and sisters are screened to be sure. The children of a new person with JPS will have a 50:50 chance inheriting the altered gene as outlined above.

How would you know if you have JPS?

Juvenile polyps often bleed and if left untreated may cause anaemia (iron deficiency in the blood). A person may be diagnosed after a blood test has shown they are anaemic and a colonoscopy has revealed juvenile polyps. Some people do not have any signs or symptoms so it is important that those who think they might be at risk see their GP and ask for a referral to St Mark’s Hospital or their local genetics service.

There are two ways of determining if a person has JPS:

  • DNA analysis
  • Bowel screening with histological confirmation

If a person is found to have an alteration in the SMAD4 or BMPR1A genes then other individuals in that family can be tested to see if they have the same genetic alteration (predictive testing). In some families, the genetic alteration cannot be found, as mentioned earlier. In this case, predictive genetic testing is not possible and family members will need bowel screening to see if they too have juvenile polyps.

How is JPS treated?

The aim of treatment is to identify and remove polyps before they become too numerous or large enough to cause problems or become cancerous.

Polyps can be monitored by regular endoscopy: OGD to check the stomach and duodenum and colonoscopy to check the large bowel. This is usually carried out 1-3 yearly depending on how many polyps a patient develops over time. Polyps are removed at endoscopy if they are becoming too large.

Very occasionally, patients develop too many polyps in their stomach or large bowel and when this happens they may be advised to have an operation. This is rare in a rare condition and if it should be necessary, the surgeon would discuss the options and provide detailed information to the patient.

Can a person with JPS have any other problems?

People who have JPS caused by an alteration in the SMAD4 gene, have been found to be more likely to develop Hereditary Haemorrhagic Telangectasia (HHT). People with HHT have a tendency to nose bleeds and they are also more likely to have abnormal blood vessels. If surgery is to take place, it is important that the doctors are informed about JPS so that various tests such as chest x-ray and ECG are performed prior to the general anaesthetic.