Genetic mutations

We all have variations in the genetic code which is why we are all unique. Most variations are harmless. However, variations to the genetic information can sometimes make the gene faulty which means that a particular protein is not produced properly, produced in the wrong amounts or not produced at all.

Variations that make the gene faulty are called mutations.

For example: If “The cat ate the rat” is a genetic code and a mutation causes one letter to be missing, “Thc ata tet her at” has lost all meaning.

 

Genetic damage causes cancer

Cancer is caused by changes to genes that control the way cells function, grow and divide.  As part of the aging process, DNA gets damaged and the cell either repairs the damage or the cell dies. In cancer cells, the damaged DNA is not repaired and the cell does not die and continues to grow and form new, abnormal cells. These cancer cells can also invade (grow into) other tissues, something that normal cells cannot do.

The factors that are associated with an increased risk of cancer cause this DNA damage.  Most cancers occur in older people and are part of the aging process. However smoking, alcohol, ultraviolet light damage and an unhealthy diet will also result in damage to our DNA.

Chromosomes and DNA

Every cell in our body contains a nucleus, the control centre for the cell.  The nucleus contains most of the cell's genetic material or DNA which form pairs of long chains called chromosomes. We have 23 pairs of chromosomes and in each pair, one chromosome comes from our mother and one from our father.

The genetic information contained in the DNA is in the form of a genetic code, which is like a recipe with instructions for the cell to make proteins and control how the genes work. The genetic code is made up of very long chains of combinations of just four chemical ‘letters’: Adenine (A), Guanine (G), Thymine (T) and Cytosine (C).  In the code, each ‘word’ is a combination of three of these four chemical ‘letters’ A, G, C and T.  Each three-letter word (triplet) tells the cell to produce a particular amino acid, the building blocks of proteins.

Hereditary cancer

Breast cancer is a common cancer but one in every five women diagnosed with breast cancer will have a close relative who has also had breast or ovarian cancer.  In just 5% of cancers, the cancer is related to a BRCA1 or BRCA2 mutation.

We all have BRCA1 and BRCA2 tumour suppressor genes that work to prevent cells turning into cancer cells.  We do not fully understand why BRCA1 and BRCA2 gene mutations result in a high risk of breast, ovarian and prostate cancers rather than other types of cancer.

 

Inheritance of mutations

Our chromosomes are arranged in pairs so we each have two BRCA1 and two BRCA2 genes.  One has been inherited from our mum and one from our dad.  Having one faulty (mutated) copy is enough for that person to have the increased risk of developing breast, ovarian and prostate cancer, even though the other copy of the gene, which they inherited from their other parent, works normally.

If a person carries a BRCA mutation there is a 1 in 2 or 50% chance they will pass the faulty copy of the gene to each of their children.

The faulty gene cannot skip a generation. Not all individuals with a BRCA mutation  will develop cancer, especially men, so it may look as if the mutation has skipped a generation in some families.

 

BRCA mutations in men

There are just as many men with BRCA1 and BRCA2 mutations as women but they are much less likely to develop cancer. Men with these mutations do have higher risk of breast and prostate cancer than men without the mutations.  A man can also pass the mutation on to his children and each child has a 50% chance of having the faulty gene irrespective as to whether their mother or father had the mutation.

The greatest risk factor for breast and ovarian cancer is inheritance of a mutation in one of the breast cancer susceptibility genes, BRCA1 & BRCA2.