Principles of Genetic Counseling



Although there have been many attempts to define what it means to provide genetic counseling, the provision of genetic counseling is a process that needs to vary depending on the specific clinical circumstances. In the case of a patient seeking genetic counseling because of a cousin with cystic fibrosis, the components of the session likely will include a discussion of the natural history of cystic fibrosis, an explanation of autosomal recessive inheritance, the risk the patient and her partner are carriers of the gene, and finally a summary of available testing to determine their exact carrier status. Prior to providing them in depth information, a complete medical, family, and social history would be obtained to determine if there are other factors that could impact a future pregnancy.1 Counseling in this circumstance should be nondirective; that is, the counselor provides the information necessary for the individual or couple to make informed decisions. This type of counseling is important, especially in a circumstance where both members of the couple are subsequently found to be carriers of the cystic fibrosis gene. The reproductive options available to them should be explained to them fully, and without bias. These options will range from not having children to preimplantation genetic diagnosis. The role of the counselor (whether that is a trained genetics professional or a general obstetrician-gynecologist) is to provide an explanation of each option, including the risks and benefits of each approach. There is no place for the provision of “recommendation.”

On the other hand, providing genetic counseling to a 35-year-old woman that has just been found to carry a BRCA-1 mutation is likely to include precise information on current recommendations regarding prophylactic mastectomy and oophorectomy. The role of the counselor is to recognize when there are clear evidence-based guidelines, and when the options presented to the patient allow her to make a decision based on having balanced and complete information.

The following cases outline the importance of obtaining a complete family history, understanding patterns of inheritance, and using that information to calculate the risks involved, and knowing the various testing options available to the individual or couple.

Case 1: At the time of her annual visit your 26-year-old nulligravida patient tells you that she and her husband have decided they want to start their family. However, she is concerned because her first cousin died at age 3 of Tay-Sachs disease.

The key to providing appropriate counseling to patients regarding their risk for genetic disorders is obtaining a complete family history, and using that information to assess the potential risk to the patient or her offspring.2 Although there are many ways to obtain family history information, the most effective approach for both obtaining the information and assessing the risk is a three-generation pedigree, as depicted in Figure 5-1. As noted in Chapter 4, a simple pedigree uses the following symbols: squares for males, circles for females, and by small filled in circles for miscarriages. Individuals with a genetic disease have their square or circle filled in, and a slash through the symbol indicates the person has died. Spouses are connected by a horizontal line and children connected to their parents by vertical lines. Ages can be added if that information is key to interpretation (eg, early-onset breast cancer). Ethnic backgrounds of both sides of the family should be documented.


Pedigree for Case 1.

In Figure 5-1 we have used the question mark to represent a potential future pregnancy. Your patient, known as the proband, is designated by the arrow. The first step in the analysis of risk is to ascertain the inheritance of the disease within the family. In this case scenario Tay-Sachs is an autosomal recessive disease, one that occurs because the affected individual has two copies of the mutated gene, one copy inherited from each of his parents. His parents, who carry one mutated gene and one normal gene, are described as “carriers.” Because the patient’s uncle is a carrier of the Tay-Sachs mutation, one of his parents also must be a carrier. Therefore, your patient’s mother could have received either the mutated gene or the normal gene from that parent, giving her a 50% chance of being a carrier. Likewise, if she did receive the Tay-Sachs gene, she has a 50% chance of passing it to her daughter, giving your patient a one in four chance (25%) that she carries the Tay-Sachs gene. Table 5-1 provides the risk figures for various relationships when dealing with autosomal recessive disorders.

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Jan 12, 2019 | Posted by in OBSTETRICS | Comments Off on Principles of Genetic Counseling
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