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What is Hereditary Mixed Polyposis Syndrome (HMPS)?

Hereditary mixed polyposis syndrome (HMPS) as the name suggests is a hereditary medical condition that is linked with a high risk of developing mixed polyps in the digestive tract, most often in the colon and/or rectum. Polyps are small, protruding abnormal tissue growths on a mucous membrane. Individuals with HMPS have been noted to be at higher risk of developing colorectal cancer as some of these polyps may transform into cancer over a period of time if they are not removed. Some of the types of polyps that may be noted in hereditary mixed polyposis syndrome include:

  • Hyperplastic polyps: These polyps in most cases do not have the potential to transform into cancer.
  • Adenomatous polyps or adenomas: These polyps have the potential to transform into cancer if they are not removed.
  • Juvenile polyps or hamartomatous: These polyps may have the potential to transform into cancer.
  • Serrated polyps: These polyps may also have the potential to transform into cancer.

Causes of Hereditary Mixed Polyposis Syndrome (HMPS)

HMPS is a genetic medical condition that predisposes an individual to a high risk of developing polyps and cancer. As it is a genetic condition, it can be passed down from generation to generation in a family. The condition is caused by the duplication of a small part of the end of the SCG5 gene found on chromosome 15 which is deemed to trigger overproduction of an adjacent gene called GREM1. For the majority of families with HMPS, the particular gene mutation triggering this syndrome may not be established, even though some families may have an inherited mutation in the GREM1 gene, although seldom.

How is Hereditary Mixed Polyposis Syndrome (HMPS) Inherited?

Usually, all cells have two copies of each gene: one inherited from the father and one inherited from the mother. If a parent has HMPS, they have a normal copy of the gene and a mutated (altered) copy of the gene. When the affected parents have children, they are likely to pass down either the normal copy or mutated copy of the gene to their children. Hence, the children have a fifty per cent (one in two) chance of inheriting the altered gene from their parent.

Seldom, a family with HMPS is noted to have a mutation in the GREM1 gene. In such families, genetic testing can play a key role to find out which person is at risk of developing polyps and/or cancer and which person is not. For families of HMPS without a detectable genetic mutation, all persons must go through a screening test to detect potential polyps and/or cancer.

Diagnosis of Hereditary Mixed Polyposis Syndrome (HMPS)

No specific diagnostic criteria are available for HMPS. The condition is suspected in families and individuals who have a history of colon polyps of different types. Presently, bowel screening with colonoscopy for patients at risk of developing HMPS is started generally at the age of twenty-five years as the polyps are not noted to occur at a specific age. The findings on the first colonoscopy will determine the interval of screening by your doctor. If the polyps are noted on screening, they can be quickly removed and the chance of developing cancer is significantly reduced. Family members who have not inherited the mutated gene are not at heightened risk of developing polyps and do not need any additional bowel screening.

Your doctor may order one or more of the following tests to diagnose colorectal polyps:

  • Colonoscopy and Sigmoidoscopy: These procedures use a camera attached to a thin tube called an endoscope. The tube is flexible which makes it comfortable to be threaded through the anus. Colonoscopy can be used to view the colon and rectum whereas sigmoidoscopy views only the lower colon and rectum.
  • CT Colonography: Computer Tomography (CT) technique is used to obtain 3D images of the colon and rectum. A polyp or ulcer or a mass is visible in the images obtained.
  • Barium enema: Your lab technician injects Barium (liquid) in your colon and uses a special x-ray to obtain images. Polyps, if present, appear dark and the colon appears white.
  • Stool Test: Your stool sample is tested for the presence of blood cells.

Treatment for Hereditary Mixed Polyposis Syndrome (HMPS)

Your doctor may prescribe medications to reduce pain and other symptoms. The best way to get rid of polyps is removing them. Your doctor may remove the polyps using sterile forceps during colonoscopy. If polyps are large, then your doctor may suggest laparoscopic surgery to remove them.

Eating a healthy diet consisting of low fat and high-fibre foods with a large amount of fruits and vegetables, restricting alcohol consumption, refraining from smoking, and participating in regular exercise are helpful in averting the development of cancer. Developing awareness about bowel health and visiting your doctor for regular check-ups and screening is strongly recommended for better management of HMPS.

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