Genetic Counseling

The goal of the field of medical genetics is to detect and treat individuals with genetic disorders. There are numerous single gene and chromosome disorders, but genetics also contributes to common diseases such as cardiovascular disease, cancer, and diabetes. Genetic counseling is the process of helping people understand and adapt to the medical, psychological, and familial implications of genetic contributions to disease. This process, as defined by the National Society of Genetic Counselors’ Task Force, integrates the following

• Interpretation of family and medical histories to assess the chance of disease occurrence or recurrence
• Education about inheritance, testing, management, prevention, resources, and research
• Counseling to promote informed choices and adaptation to the risk or condition

Genetic diseases due to single gene defects, sometimes referred to as Mendelian disorders, are grouped into autosomal (encoded by genes on one of the 22 pairs of autosomes, or non–sex chromosomes) and X-linked (encoded mutant genes on the X chromosome, one of the two sex chromosomes). There are two modes of expression of mutant genes: dominant and recessive. Dominant refers to those conditions expressed in individuals having only one copy of a mutant allele. Recessive refers to those conditions that clinically manifest only in individuals who carry two copies of the abnormal gene. Of the 10,000 human phenotypes known to be inherited, more than one half is classified as autosomal dominant, about one third is autosomal recessive, and about one tenth is X-linked.

The patterns of inheritance of most Mendelian or single gene traits have been learned by observing the transmission of traits within families. An important reason for studying the pattern of inheritance of conditions within families is to advise members through genetic counseling about recurrence risks or the chance that the genetic disease would be passed on to their children. Generally, dominant conditions carry a 50% risk while recessive conditions carry a 25% risk.

The term genetic counseling was coined in the 1940s and, as practiced today, is a multidisciplinary activity involving the provision of services by clinical geneticists, genetic counselors, nurse practitioners, laboratorians, and other health care professionals. The components of a genetic counseling interaction include the following

• Information gathering
• Establishing or verifying the diagnosis
• Risk assessment
• Information giving
• Psychological counseling

Information gathering involves the collection of a family history from an individual knowledgeable about the family and health status of individuals within the family and is usually recorded in the form of a three-generation pedigree using conventional symbols to represent normal and affected males and females within and between generations and their relationships with other family members. The family history helps clarify relationships, identify other affected individuals, and records information of potential genetic significance (consanguinity or inbreeding, fertility problems, birth defects, ethnicity, mental disabilities). The person bringing the family to medical attention is referred to as the index case or proband.

Establishing or verifying the diagnosis is often accomplished by reviewing medical records before the family comes to the genetics clinic. Family photographs are often helpful. Sometimes, this requires physical examinations of other family members and/or laboratory testing.

Risk assessment is performed by analyzing the pedigree and the results of any laboratory testing. Mathematical calculations are often used to incorporate other information such as age of onset of the condition, population carrier frequencies, and number of affected individuals in the family. Information giving involves explaining to the family how the diagnosis was arrived at, what the implications are for the affected individual, what specialized services might be of help to the family, reproductive risks, options for prenatal diagnosis, and any treatment options.

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