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    Cancer Genetics Overview (PDQ®): Genetics - Health Professional Information [NCI] - Introduction

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    Throughout this summary, the term "mutation" will be used to refer to a change in the usual DNA sequence of a particular gene. Mutations can have harmful, beneficial, neutral, or uncertain effects on health and may be inherited as autosomal dominant, autosomal recessive, or X-linked traits. Mutations that cause serious disability early in life are usually rare because of their adverse effect on life expectancy and reproduction. However, if the mutation is autosomal recessive-that is, if the health effect of the mutation is caused only when two copies (one from each parent) of the mutated gene are inherited-mutation carriers (healthy people carrying one copy of the altered gene) may be relatively common in the general population. "Common" in this context refers, by convention, to a prevalence of 1% or more. Mutations that cause health effects in middle and older age, including several mutations known to cause a predisposition to cancer, may also be relatively common. Many cancer-predisposing traits are inherited in an autosomal dominant fashion, that is, the cancer susceptibility occurs when only one copy of the altered gene is inherited. For autosomal dominant conditions, the term "carrier" is often used in a less formal manner to denote people who have inherited the genetic predisposition conferred by the mutation. Refer to individual PDQ summaries focused on the genetics of specific cancers for detailed information on known cancer-susceptibility syndromes.

    Increasingly, the public is turning to the Internet for information related both to familial and genetic susceptibility to cancer and to genetic risk assessment and testing. Direct-to-consumer marketing of genetic testing for hereditary breast and colon cancer is also taking place in some communities. This wider availability of information related to inherited cancer risk may raise concerns among persons previously unaware of the implications inherent in their family histories and may lead some of these individuals to consult their primary care physicians for management advice and recommendations. In many instances, the evaluation and advice will be relatively straightforward for physicians with a basic knowledge of familial cancer. In a subset of patients, the evaluation may be more complex, calling for referral to genetics professionals for further evaluation and counseling.

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