Medical genetics: 3. An approach to the adult with a genetic disorder

Abstract

Many genetic disorders do not manifest themselves until the adult years. Such disorders often involve multiple genetic factors interacting with multiple environmental factors, over time, to produce a phenotype. This paper reviews the modes of inheritance of genetic disorders and describes the types of genetic testing that are currently available. It offers clues that should lead physicians to suspect that an adult patient might have a genetic disorder and raises issues that should be considered in counselling the patient about genetic testing. Resources for patients and their family physicians are also discussed.

Fig. 1: Drawing the patient's (P) pedigree. Note: 1. The slash in the relationship line indicates either divorce or separation. 2. This symbol indicates 4 siblings of unspecified sex. 3. The double line indicates consanguinity (in this case first cousins). 4. These siblings are monozygous twins. Dizygous twins are not joined by a horizontal line. If the type of twinning is unknown, a “?” replaces the horizontal line. 5. No children by choice or the reason is not known. 6. Infertility, indicate the reason if known. 7. Adopted into family. Children adopted out are drawn with a solid line of descent.