from St. Jude:
What is constitutional mismatch repair deficiency syndrome (CMMRD)*?
Constitutional mismatch repair deficiency syndrome is a rare condition that makes a child more likely to develop the following:
- Brain tumors
- Cancers in blood and lymph systems
- Polyps (abnormal growths in the the intestinal tract) and cancers in the gastrointestinal tract
- Cancers in the female reproductive organs (for example, the uterus and ovaries)
- Certain skin or physical findings, for example café au lait spots (flat brown colored areas on the skin) or patches of skin that are lighter than the overall skin tone
- Other rare pediatric cancers
- A child with constitutional mismatch repair deficiency syndrome can develop more than one type of cancer at a time or more than one cancer during the person’s lifetime.
What causes constitutional mismatch repair deficiency syndrome?
Constitutional mismatch repair deficiency syndrome is related to changes in the genes MLH1, MSH2, MSH6, or PMS2 and rarely in a gene called EPCAM. Genes carry information telling cells within the body how to function. The MLH1, MSH2, MSH6 and PMS2 genes help to repair a specific type of DNA damage through a process called “mismatch repair” or MMR. It is harder for people with constitutional mismatch repair deficiency syndrome to repair the damage that naturally occurs in their genes. This can lead to the growth of polyps and tumors at an early age.
Most people have two working copies of each of the MMR genes in their cells. One copy is inherited from the mother and one from the father. A change in the gene that causes it to not work properly is called a mutation. When someone inherits an MMR gene mutation from the mother and another mutation in the same MMR gene from the father, they have constitutional mismatch repair deficiency syndrome. In other words, this person has a mutation affecting each of the 2 copies of an MMR gene.
Most children with constitutional mismatch repair deficiency syndrome inherit the MMR gene mutations from their parents. Parents of a child with constitutional mismatch repair deficiency syndrome have a 25% or 1 in 4 chance for each pregnancy of having a child with the same syndrome.
All children of a person with constitutional mismatch repair deficiency syndrome will inherit one MMR mutation. To understand the chances of having a child with this syndrome, the partner of a person with the syndrome might consider genetic testing to see if he or she also carries an MMR gene mutation.
Note: Please see below for information regarding Lynch syndrome. This is a condition where people have one MMR gene mutation.
What is the cancer risk for children with constitutional mismatch repair deficiency syndrome?
For people with this syndrome the exact risk of developing cancer during their lifetime is not known at this time. It is expected to be very high in these people. Because constitutional mismatch repair deficiency syndrome can cause a wide variety of cancers, it is hard to predict what type of cancer a child with this condition may develop and when that cancer will occur.
How are people with constitutional mismatch repair deficiency syndrome screened for cancer?
In general, tumor screening involves undergoing certain tests to check for tumors before symptoms occur. The goal is to detect tumors at the earliest and most treatable stage. Currently, no common screening guidelines exist for people with this syndrome. The tumor screening tests should be discussed with a doctor who knows this syndrome well.
Screening tests may include the following:
- Annual or semi-annual full physical exams
- Gastrointestinal tract screening, including colonoscopy, esophagogastroduodenoscopy (EGD) and video capsule endoscopy (VCE)
- MRI exam of the brain
- Abdominal imaging
- Chest X-rays
- Routine blood tests, such as complete blood count
How is genetic testing done for constitutional mismatch repair deficiency syndrome?
The doctor may suspect this syndrome after looking at a person’s medical history, physical findings and family history. In most cases, a doctor or genetic counselor will ask questions about a person’s health and physical findings and the health of other family members.
The genetic counselor or doctor will record which family members have developed tumors, what types of tumors and at what ages tumors occurred. From this information they will create a family tree. Doctors and genetic counselors will look at the family tree to find out the following:
- If there are more cancers than normal
- If cancers occurred at younger-than-expected ages
- If the types of tumors match up with what might be seen in those with MMR mutations
Please note, it is not uncommon for a patient with constitutional mismatch repair deficiency syndrome to not have many cases of cancer in the family.
Are there other special health care needs for a patient with constitutional mismatch repair deficiency syndrome?
Children with constitutional mismatch repair deficiency syndrome are at risk of developing multiple types of cancer during their lifetimes. They should monitor their health and adopt healthful habits throughout life. It is important to continue to have regular physical checkups and screenings. That way, any cancer can be found early at the most treatable stage.
People with this syndrome should watch closely for general signs or symptoms that could signal cancer:
- Unexplained weight loss
- Tiredness
- Fever that does not go away
- Night sweats
- Loss of appetite
- Aches, pains, lumps or swelling that cannot be explained
- Headaches, vomiting, changes in vision or nerve function that do not go away
- Swollen glands
- Trouble breathing
- Blood in the stool
- Pain in the abdomen
Lynch Syndrome: Inheritance and Healthcare Considerations
If a person has one working copy and one non-working copy of an MMR gene, they have a condition known as hereditary non-polyposis colorectal cancer or Lynch syndrome. Generally, when a child has constitutional mismatch repair deficiency, both parents are assumed to have Lynch syndrome.
People with Lynch syndrome are more likely to develop colon polyps and certain types of cancer, such as colon, uterine, ovarian and small bowel cancer, most commonly as adults.
A person with Lynch syndrome will need to be followed closely by a doctor (a gastroenterologist who knows the condition well would be best). There are well-established cancer screening guidelines for Lynch syndrome. Starting in adulthood, regular screening exams, known as colonoscopies, are recommended to look for and remove any polyps and to detect colon cancer if it is present. Women with Lynch syndrome can consider screening of the reproductive organs. Screening for other cancers may be considered depending on the gene involved and the family history.
*Constitutional Mismatch Repair Deficiency (CMMRD) is synonymous with Biallelic Mismatch Repair Deficiency (BMMRD).