Skip to 0 minutes and 16 secondsPeople who are concerned about their family history of cancer may be referred by their doctor to a genetics department to have their familial risk assessed by a genetic counsellor. Genetic counselling is defined as a communication process which deals with the human problems associated with the occurrence, or the risk of occurrence, of a genetic disorder in a family. The aims of genetic counselling are to help the individual or family understand the information about the genetic condition, appreciate the inheritance pattern, appreciate the risk of recurrence, understand the options available and make decisions appropriate to their personal and family situation. Cancer is a common disease which affects approximately one in three individuals at some point in their lifetime.
Skip to 1 minute and 6 secondsIt is not unusual to have a relative affected by cancer. The main risk factor in cancer is age. The older we become, the more likely we are to develop the disease. And the incidence of cancer starts to rise as people reach their late 40s and early 50s. Only 5% to 10% of families have a specific genetic mutation, also known as a gene fault or genetic alteration, which causes an inherited predisposition to cancer.
Skip to 1 minute and 38 secondsThe families who are most likely to have an inherited predisposition to cancer are those families where we see several close relatives affected by the same cancer, on the same side of the family, usually over three generations or families where we see several close relatives affected by cancer at a much younger age. At the genetics department, the genetic counsellor will obtain information by drawing a family tree and finding out who in the family has been affected by cancer, the age that they were diagnosed, and the types of cancer affecting family members.
Skip to 2 minutes and 15 secondsUsing this information, the counsellor is able to provide a familial risk assessment, advise on whether or not extra screening at a specialist clinic is required, and, when appropriate, offer genetic testing. Genetic testing is a two-step process. First of all, we obtain a blood sample from someone in the family who has been affected by cancer for DNA extraction, and mutation analysis of the relevant genes. This analysis is carried out in a molecular laboratory. Mutation analysis can have three possible outcomes. No pathogenic, that is disease-causing gene fault, is identified. This could mean that the cases of cancer have occurred sporadically or that the cases of cancer are due to a fault on another gene which has yet to be identified.
Skip to 3 minutes and 7 secondsA pathogenic, that is disease-causing gene fault, is identified. Or analysis shows a variant of unknown significance, which is a genetic change whose effect on the protein is undetermined. Further analysis of other affected family members may help to provide further information and determine the effect of the variant. Secondly, once a specific gene fault has been identified, we are then able to offer predictive testing to other family members. For the person, who has been affected by cancer, to provide a blood sample for mutation analysis requires careful consideration. If a specific gene fault is identified, then this would be the most likely cause of that person's cancer, which provides an answer for that person.
Skip to 3 minutes and 56 secondsBut along with that answer comes other information, which can be difficult to hear. To be told that they have a specific gene fault means that we would consider them to be at increased risk of recurrence of that cancer and at increased risk of developing another cancer. For an individual who has undergone surgery and possibly radiotherapy and chemotherapy, this information can be upsetting. However, there could be a targeted therapy, which would be more effective in treating the particular cancer caused by the specific gene faults. In most familial cancer syndromes, the pattern of inheritance is autosomal dominant. So someone only needs to inherit one faulty copy of a gene. In some cancer syndromes, the pattern of inheritance is autosomal recessive.
Skip to 4 minutes and 47 secondsSo two faulty copies would be necessary. If the pattern of inheritance is autosomal dominant, it can be difficult for a person who carries the gene fault to know that each of their children has a one in two chance of inheriting that gene fault. Equally, each child has a one in two chance of inheriting the normal copy of the gene. If a person inherits the normal copy of the gene, then they are not at increased risk for developing cancer. They do not require any extra screening for the disease and they cannot pass on the gene fault.
Skip to 5 minutes and 20 secondsIf a person inherits the faulty copy of the gene, we know that they are at significant increased risk for developing cancer and we would offer extra screening at a specialist clinic. This screening may be investigations such as breast x-rays or colonoscopy, depending on the familial risk. Some individuals who carry a specific gene fault decide to undergo risk-reducing surgery, that is, having healthy tissue removed to reduce their lifetime risk of developing cancer. Each individual makes a decision which is appropriate for them and genetic counsellors provide advice and support at each step of the process and continue with the support for each individual and their families.
Genetic counselling for inherited cancer (6.11)
Catherine Watt, a genetic counsellor specialising in inherited cancers, explains the her role and the options available for these patients. In this video you will see a pedigree or family tree. More information on drawing a family tree is given in steps 3.14-3.16.
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