Molecular analysis of genetic diseases: an overview for clinicians

The identification of fetal genetic disease has, for the most part, relied on examination of an end product, such as analysis of factor VIII levels obtained from cord blood in fetuses at risk for hemophilia. Advances in molecular genetics have shifted our focus in prenatal diagnosis away from protein product analysis toward etiology, making new discoveries gleaned from the Human Genome Project relevant to clinicians. This review discusses the basic principles involved in gene-based diagnosis, highlighting the complexities of current approaches to molecular diagnosis of fetal genetic disease. Given an understanding of both the theory and practice of genetic analysis, the review covers the fundamental principles of molecular biology (structure, function, packaging, and regulation) and discusses recombinant DNA techniques presently used for the analysis of mutations. Clinical examples are presented to introduce the techniques most commonly employed in service laboratories: direct detection assays, where the specific mutation is recognized, and indirect detection assays, useful for the deduction of an inheritance pattern where the actual mutation or its gene is not known but may be closely linked to known DNA polymorphisms.