Introduction

The identification and cloning of numerous genes associated with inherited disorders combined with the advancement and commercialization of molecular methods for the analysis of these genes in the clinical laboratory has had a significant impact on medical practice. These advancements have fuelled the rapid growth of molecular diagnostics. The field of molecular diagnostics takes the theories and principles of molecular genetics along with the technologies of molecular biology and applies them to the clinical laboratory (Amos & Patnaik, 2002). The outcome of such molecular tests can provide physicians and genetic counsellors with information that can improve their ability to offer optimal care for individuals affected with or at risk for genetic diseases. Molecular genetic diagnostic test results can be used to help confirm the diagnosis of inherited disorders in affected individuals and diagnose unaffected individuals prior to the onset of symptoms. In addition, molecular genetic testing can be used to identify individuals at increased risk for developing a disease and for prenatal or preimplantation diagnosis for couples at risk of having a child with a genetic condition.

One approach to the discovery of disease-associated genes has been research studies of families in which a particular disease afflicts multiple blood relatives (Fig. 6.1). Initially genomic regions or specific genes may be found to be linked to the disease of interest followed by the identification of specific molecular abnormalities or differences associated with a clinical phenotype (Hardy & Singleton, 2000).