Hereditary mixed polyposis syndrome

What it is

From: Orphanet

Hereditary mixed polyposis syndrome (HMPS) describes an autosomal dominantly inherited large-bowel disease characterized by the presence of a mixture of hyperplastic, atypical juvenile and adenomatous polyps that are associated with an increased risk of developing colorectal cancer if left untreated.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abnormal bleeding · Very frequent (99-80%)

An abnormal susceptibility to bleeding, often referred to as a bleeding diathesis. A bleeding diathesis may be related to vascular, platelet and coagulation defects.

Hematochezia · Very frequent (99-80%)

The passage of fresh (red) blood per anus, usually in or with stools. Most rectal bleeding comes from the colon, rectum, or anus.

Hyperplastic colonic polyposis · Very frequent (99-80%)

Presence of multiple hyperplastic polyps in the colon. Hyperplastic polyps are generally about 5 mm in size and show hyperplastic mucosal proliferation.

Adenomatous colonic polyposis · Frequent (79-30%)

Presence of multiple adenomatous polyps in the colon.

Colorectal polyposis · Frequent (79-30%)

Multiple abnormal growths that arise from the lining of the large intestine (colon or rectum) and protrude into the intestinal lumen.

Juvenile colonic polyposis · Frequent (79-30%)

The presence of more than 5 juvenile polyps of the colon. The term juvenile polyps refer to a special histopathology and not the age of onset as the polyp might be diagnosed at all ages. The juvenile polyp has a spherical appearance and is microscopically characterized by overgrowth of an oedematous lamina propria with inflammatory cells and cystic glands.

Neoplasm of the gastrointestinal tract · Frequent (79-30%)

A tumor (abnormal growth of tissue) of the gastrointestinal tract.

Rectal polyposis · Frequent (79-30%)

The presence of multiple rectal hyperplastic/adenomatous polyps.

Colon cancer · Frequent (79-30%)

Refractory anemia · Frequent (79-30%)

Intussusception · Occasional (29-5%)

An abnormality of the intestine in which part of the intestine invaginates (telescopes) into another part of the intestine.

Adenocarcinoma of the colon · Occasional (29-5%)

Neoplasm of the rectum · Occasional (29-5%)

Desmoid tumors · Very rare (<4-1%)

Benign, slow-growing tumors without any metastatic potential. Despite their benign nature, they can damage nearby structures causing organ dysfunction. Histologically they resemble low-grade fibrosarcomas, but they are very locally aggressive and tend to recur even after complete resection. There is a tendency for recurrence in the setting of prior surgery and the most common localisation of these tumors is intraabdominal from smooth muscle cells of the instestine.

Other findings in the same source

From: Orphanet

Additional reported features include Duodenal adenocarcinoma (Very rare (<4-1%)); Endometrial carcinoma (Very rare (<4-1%)); Prostate cancer (Very rare (<4-1%)); Thyroid carcinoma (Very rare (<4-1%)). This is a selected summary, not a complete description of the condition.

When it may begin

From: Orphanet

Childhood

Inheritance in the source

From: Orphanet

Autosomal dominant

Frequency and the population described

From: Orphanet

Reported case(s): 15.0; Worldwide. This is a published case count, not prevalence. Point prevalence: <1 / 1 000 000; Worldwide; Class only.

Understanding the inheritance label

From: MedlinePlus Genetics

An autosomal dominant pattern means that one altered copy of a relevant gene can be sufficient for the condition. Some affected people inherit the change; others have a new change without an affected parent. The precise finding, family history and condition determine what this means for relatives.

Which doctor should you see?

The suggested department for discussing Hereditary mixed polyposis syndrome is Gastroenterology, with a gastroenterologist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Which digestive symptoms or nutritional changes matter most?
• What question would an endoscopy, scan or laboratory test answer if one is proposed?
• How should persistent pain, bleeding or difficulty eating be followed up?

Treatment discussions and follow-up

Where the source describes treatments, these are an overview of possible care, not a prescription for an individual. Ask which option applies to the confirmed diagnosis, what benefit is expected, what adverse effects to watch for and how progress will be assessed. Availability, approvals and local practice can differ from the country described in the source.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.