What is HNPCC

.....and how is it inherited

What is HNPCC

HNPCC is a rare condition that runs in some families. Conditions that run in families are known as familial or hereditary.

HNPCC is the most common cause of hereditary bowel cancer. Just less than 5 in 100 (5%) of all bowel cancers are linked to HNPCC. Women with HNPCC also have an increased risk of developing womb (endometrial) cancer. There is also a slight increase in risk of developing cancer of the ovaries.

People with HNPCC also have an increased risk of stomach, pancreas, biliary, bladder and transitional cell cancers.

Knowing about risk and having regular screening may help prevent some cancers and detect others in the early stages when they're curable.

So how is HNPCC inherited

Our genes carry the information that is passed on (inherited) from our parents. Genes determine things like the colour of our eyes and affect the way our bodies grow, work and look.

HNPCC is caused by a fault in one of the genes known as the 'mismatch repair' genes. These particular genes normally work to help prevent you getting cancer.

HNPCC may be suspected in families with close blood relatives who have developed bowel, womb and ovarian cancer over several generations. They may have inherited a faulty copy of one of the mismatch repair genes.

Three of the mismatch repair genes (known as MLH1, MSH2 and MSH6) are responsible for most cases of HNPCC. So, if a person inherits a faulty copy of one of these genes, it increases their risk of developing bowel cancer and the other types of cancer.

We have two copies of each gene – one from each of our parents. If someone has HNPCC it means they have a healthy gene but also one that's faulty.

If that person has a child there is a fifty–fifty chance that they will pass on the faulty gene (only one copy of a gene is passed on from each parent).

HNPCC is more likely if there are lots of cases of bowel and womb cancer on one side of the family and if they were diagnosed at an early age.

(However, not everyone with HNPCC has a family history of it. This is because some people may be the first in their family to get it.)

HNPCC may be suspected if:

  • at least two relatives on the same side of the family have had bowel cancer
  • a family member developed bowel cancer at a young age (under 45)
  • there are cases of bowel and womb cancer on the same side of the family
  • three or more relatives on the same side of the family have had one HNPCC-type cancer (not necessarily the same kind of cancer).

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