Making the Most of Family History Information, Single Gene Disorders and Mendelian Patterns of Inheritance, and When to Refer to a Genetic Specialist

Abstract

Family history is an essential tool for disease risk assessment, because it incorporates not only shared genetic susceptibilities but also shared environmental, behavioral and cultural factors. Family history data should be taken as part of routine patient care by all medical practitioners. This chapter discusses single-gene disorders, i.e. disorders for which there is a single cause, such as a gene mutation. Single-gene disorders cause the patterns of inheritance that obey the laws of segregation and independent assortment that Gregor Mendel first described (autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive and Y-linked). Because the laws that govern transmission of a single genetic factor are known, a physician or genetic counselor can give accurate estimates of the probability that other family members might possess the mutation. In this chapter we discuss the foundational principles that the reader must know to understand these principles, as well as guidelines on when to refer to a genetic specialist.