Genetic Counseling
Empirical data for genetic counseling are summarized in Table 6-10. Some illnesses have fairly narrow age-at-onset distributions in the general population. For example, first episodes of bipolar illness almost always occur before age 50. Fully 50% of bipolar individuals develop an initial episode (either depressive or manic) before age 25. Age at onset should be considered in a general way when assessing risk. For example, an unaffected 40-year-old son of a parent with bipolar disorder has already passed through most of the age at risk; thus his risk of developing bipolar disorder is substantially less than 9%. An estimate of approximately 2% would be more accurate in this case.
Risk estimates should be provided in a psychotherapeutic meaning for the individual should be explored carefully. A pedigree diagram should be constructed. Empirical risk information should be provided (at this point no specific biological tests are indicated in the great majority of cases). Finally, the subject’s response to the information provided should be explored, with support and further counseling offered as appropriate.
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Conclusion
Major psychiatric disorders are substantially heritable; however, with few exceptions their inheritance patterns are complex and suggest multiple genes. As a result, linkage studies have been difficult to carry out, although multiple studies are implicating certain chromosomal areas (including some common areas for bipolar disorder and schizophrenia). Identification of specific genes is expected to proceed over the upcoming decade and should enable the development of more specifically targeted strategies for treatment and prevention of psychiatric disorders.
