The Human Genome Project has enhanced dramatically our potential in genetic information (Watson, 1990). O f the estimated 100,000 human genes, more than 9,000 have been discovered, and more than 5,000 have been mapped to specific chromosomes (Guyer & Collins, 1995). Genetic testing for about 500 genes is now available in clinical practice. Gene variants have been identified that affect the risks of diseases o f major public health importance, ranging from adult chron­ ic diseases, such as cancer and diabetes, to infectious and immunologic disorders, to diseases affecting the health o f infants and children (Khoury, 1997).