Assessing your chance of developing a genetic disorder or passing one on to your children
You may have noticed that some diseases seem to “run in your family”. These disorders may have a genetic basis or be due to lifestyle factors or a combination of the two. You can create a record of the disorders that have affected your family by making a medical family tree, which may help you to assess your own risk of disease.
Information on your parents, brothers, and sisters is the most important, but you can provide a fuller picture by finding out about as many generations as possible, including your uncles, aunts, and grandparents. It is also helpful to know something about your relatives’ lifestyles to help you and your doctor to assess whether any diseases were largely due to behaviour or inheritance.
You may want to find out about your medical family tree out of curiosity, but you will find this information useful whenever a doctor needs to ask questions about illnesses in your family. You are likely to be asked about your family medical history when you first see a new doctor; you are expecting a baby; if you are admitted to hospital; and if you develop symptoms of a disorder with a genetic component, such as asthma.
Assessing the information
You may be able to come to some conclusions about your risk of disease by looking at your medical family tree. If your investigation suggests that a particular disease has affected more than one member of your family, you should consult your doctor. In some cases, you may be referred for genetic counselling to assess your chance of developing a disorder or passing it on to your children.
Drawing your own conclusions
Longevity runs in families, and, if many of your relatives lived beyond the age of 80, you have a good chance of doing the same, especially if you adopt a healthy lifestyle. If many of your relatives died young, you should try to find out the causes of death. You may be susceptible to disorders that have occurred more than once in your family.
You should suspect an inherited disorder if more than one child in your family was stillborn or died in childhood; if more than one adult died from heart disease or cancer before the age of 60; if more than two people in the family had a long-term disorder, such as arthritis; or if more than one family member had the same disabling or fatal disease. Deaths before the age of 60 are especially relevant, unless they were caused by accidents or by an infection, such as tuberculosis, that occurred before effective treatment was available.
Genetic counsellors are trained to interpret genetic family histories, to assess your risk of genetic disease, and to determine whether you are a carrier of an altered gene that causes a genetic disorder. Carriers do not show signs of the disorder because the altered gene is masked by a normal gene, but children of carriers can inherit the altered gene. The counsellor will try to find out whether a high frequency of a disease in your family is due more to genetics or to environmental factors, such as lifestyle. For example, in some families where there are several people with colorectal cancer, this could be due more to environmental factors, such as diet, whereas in other families there may be an inherited predisposition to the disease.
Considering the options
Your family medical history may suggest that you have a higher than average probability of having an inherited disorder. In this case, the counsellor will tell you whether a specific gene alteration for the disorder has been identified and whether there is a test to see if you have the altered gene. If a test is available, the counsellor can pro-vide information that will help you decide whether or not to have the test.
Some people decide not to proceed with genetic tests for a variety of reasons. Prospective parents may feel there is no point in worrying about a disorder that would not necessarily affect them or their child, or they may choose to carry on with a pregnancy even if there is an increased probability of their child being affected by a genetic disease. They may also be concerned by the stigma associated with “labelling” someone as having or being a carrier of a disorder. Other people want to know the results of a test even if they would not act on them. Bear in mind that the test result for one family member may have implications for other family members who may not want to know the outcome.
Members of some groups of the population are susceptible to particular genetic disorders, and individuals may be offered a screening test based on this fact alone. For example, 1 in 10 black people carries the gene for sickle-cell disease, a disorder of red blood cells. If you are Jewish, a genetic counsellor may recommend that you consider a screening test for the metabolic disorder Tay–Sachs disease because 1 in 25 Ashkenazi Jews, compared with only 1 in 250 of the general population, carries the altered gene that causes the disease.
What you can do
If tests show that you have an altered gene, your course of action will depend on whether you already have the symptoms of a genetic disorder or whether you are at high risk of developing the disorder. If you carry an altered gene and you are planning a family, there are several options to consider.
People with a genetic disorder
Certain genetic disorders can be treated. For example, a person who has inherited a tendency to high levels of cholesterol in the blood (see Inherited hyperlipidaemias) may be treated with a low-fat diet and lipid-lowering drugs. Children with the genetic disorder haemophilia may be given regular transfusions of Factor VIII, a protein that helps the blood to clot.
People at risk
If you find that you have an altered gene that predisposes you to a particular disorder, such as breast cancer, you may be offered regular screening to detect signs of the disorder at an early stage. You may also be able to make lifestyle changes to help to reduce the likelihood of developing a disease. For example, if your family history suggests that you are at increased risk of developing diabetes mellitus, you should keep your weight within the normal range.
If you and your partner are both carriers of an altered gene for the same condition, you may decide not to have children or may consider various family planning options, such as adoption or artificial insemination. You may be able to take advantage of advances in assisted conception, in which fertilization is carried out in the laboratory and the embryo is tested for the altered gene. Only an embryo that does not have the genetic condition is then implanted into the uterus. If you are already expecting a baby and find that your baby is affected by a genetic disorder, options you may want to consider include terminating the pregnancy.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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