Genetic testing in clinical practice.

In the practice of internal medicine, the value of genetic testing in common (mono)genetic diseases such as familial hemochromatosis, hypercholesterolemia, Mediterranean fever, and thrombophilia is limited. The genotype insufficiently predicts the phenotype because of the powerful effects of other modifying genes, environmental influences, and lifestyle factors. Many common diseases, including diabetes mellitus, osteoporosis, and cardiovascular disease, have strong genetic influences but are called complex genetic traits. The underlying genetic factors are currently investigated using new molecular tools such as genome-wide association studies, analyzing up to 500,000 markers in huge numbers of patients. Many new (often unexpected) markers have been identified, and in many instances their functional significance is unknown. Genomic profiles play a rapidly growing role in the field of pharmacogenomics. A number of recently identified pharmacogenomic biomarkers are helpful to predict drug-related toxic effects.