22 June 2022

By Sam Alexandra Rose

Sam guest blogs regularly for Bowel Research UK, sharing her experiences of bowel cancer and Lynch Syndrome

I’m willing to hazard a guess that you might not have heard of or previously come across CMMRD. It’s a rare condition that affects proportionately very few people, so I wouldn’t be surprised if what follows is something entirely new to you.

To explain what constitutional mismatch repair deficiency (CMMRD) is, we first need to talk about Lynch Syndrome. Lynch Syndrome increases a person’s risk of getting certain types of cancer in their lifetime, including bowel cancer, which is the most common cancer associated with this genetic condition.

What is Lynch Syndrome?

Lynch Syndrome affects genes called mismatch repair genes. They are genes responsible for correcting changes in genetic code when cells grow and divide. As the cells grow and make copies of their DNA, they can make mistakes, which mismatch repair genes rectify so that those errors don’t lead to cancer. So if these mismatch repair genes are abnormal or have a “mutation”, they may not repair those mistakes and cancer can occur. This is known as Lynch Syndrome. As well as bowel cancer, Lynch Syndrome raises the risks of gynaecological, pancreatic, prostate and brain cancer. The risks of each cancer can depend on which genes are affected, with the genes associated with Lynch Syndrome being MLH1, MSH2, MSH6, PMS2, and EPCAM.

How is Lynch Syndrome Inherited?

Each person has two copies of each gene – one inherited from their mother and one from their father.  If a parent has one mutated gene, the child has a fifty percent chance of inheriting it. But what happens if both parents have Lynch Syndrome, and you’re unlucky enough to inherit both of their mutated genes? Me. I’m what happens. And you, if you are also in the same situation.

What is CMMRD?

CMMRD, like Lynch Syndrome, is a genetic condition that makes it more likely for a person to get certain types of cancer, except this time it occurs when a child has inherited mutated genes from both parents, and the cancer risk is even higher. PMS2 is the most commonly affected gene in CMMRD.

To illustrate this: my mum has one “good” copy of the gene and one bad copy, so I could have inherited her good gene or her bad gene. And the same goes for my dad. My sister inherited both of their good copies, and therefore doesn’t have Lynch Syndrome or CMMRD, and neither do her children. Whereas I inherited both of their bad genes and therefore have CMMRD. We believe my brother, who passed away many years ago, also had Lynch Syndrome or CMMRD.

What are the Odds of Having CMMRD?

As many as 1 in every 300 people may have Lynch Syndrome, while the odds of having CMMRD are one in a million – or 0.0001%. Yes, I am literally one in a million – something I tell myself to feel a bit better about the whole thing. Something else I try to remember is that most people with CMMRD get cancer before the age of 18, and the average age is 7.5 years old. Whereas I had my diagnosis of bowel cancer at the age of 22, then duodenal and uterine cancer at the age of 30, and here I still am at the age of 34. I am lucky and very unlucky at the same time.

What’s it Like Having CMMRD?

Having CMMRD – and all of my previous cancers – means I have to have regular tests, such as annual gastroscopies, capsule endoscopies and brain and full body MRI scans. Regular tests means regular panic and regular worry about the cancer coming back. It means regular hospital trips, slightly less regular bad dreams, and wondering where on earth your good old regular life went.

CMMRD has changed my perspective on life, making me more grateful and much keener to do what I want right away instead of saying “one day”. It also makes me a lot more anxious. I’ve only recently been thinking about CMMRD, when previously I wouldn’t allow myself to and thought of myself as simply having Lynch Syndrome. Allowing myself to think about it now is like coming to terms with things all over again. But I know that the scans that make me so anxious are the things that are essential to managing my condition and finding and treating any new or recurring cancer as soon as possible.

With the introduction of capsule endoscopies in more and more hospitals, plus the possibility of a Lynch syndrome vaccine in our future, screening is getting better and a perhaps even a little more bearable for patients like me, so hope is on the horizon. By going to my regular scans and tests, I can only hope that cancer stays away – or if it returns, it’s early enough for it to be successfully treated.