Familiar familial questions

Based on my own experience I expect many GPs have had similar consultations involving an anxious relative (or relatives) wanting to know if they need genetic testing for their risk of cancer as they have a family history.

I remember a few of these. My patients attended during stressful times – for example during bereavement. I’m sure these kinds of consultations will increase in frequency – gene mapping is still a relatively young area. The media and cancer charities are keen to inform people about genes “responsible” for causing cancer.

I was pleased to find a recent BMJ learning article very helpful.

• 5-10% of cancers are thought to be caused by genetic factors.
• Cancer genes can greatly increase the risk of a person developing cancer.
• The genes that predispose to cancer are not on the X or Y chromosomes. They are passed on through autosomal dominant inheritance: this means that you only need to inherit a mutation from one parent in order to inherit the increased risk of developing cancer.
• The family history is the most reliable way of assessing the familial risk of developing cancer.

Mutations in genes can lead to an increased risk of developing certain cancers. Some mutations have a low chance of  achieving this, others a higher chance. This chance is called penetrance.

 A high index of suspicion is warranted in cases of bilateral breast cancer, breast cancer in a man, sarcoma in a patient under the age of 45, glioma or childhood carcinoma of the adrenal cortex and multiple family members who have had unusual cancers.

The ideal family history is to map three generations of first and second degree relatives and include the specific type of cancer affected members have/had and at what age the cancer developed.

First degree relatives: mother, father, daughter, son, sister, brother.

Second degree relatives: grandparent, grandchild, aunt, uncle, niece, nephew, half sister, and half brother.

Third degree relatives: first cousins.

The key relatives are:

• Parents
• Siblings
• Aunts and uncles
• Grandparents
• Children.

Factors in the family history suggestive of an increased risk of developing cancer include; two or more closely related people who have the same type of cancer, unusual combinations of cancer within a family or in one individual (such as the combination of breast and ovarian cancer, or colorectal and endometrial cancer), the same type of cancer occurring in successive generations or cancer occurring at unusually young ages (such as colorectal or breast cancer under the age of 40).

The first step in the testing process is to identify the specific mutation that is responsible for cancers in the family. This is expensive and time consuming. Once a mutation is found in a family, the predictive tests are much cheaper and quicker.

The DoH and the Association of British Insurers have reached a voluntary agreement which ensures that the results of predictive genetic tests for cancer genes will not be taken into consideration in insurance applications

 http://www.geneticseducation.nhs.uk/

I’d like 45 minutes to an hour to map the family history well.