Familial and Genetic Factors
Kathleen Ries Merikangas Departments of Epidemiology and Public Health, and Psychiatry Yale University School of Medicine
The Human Genome Project has enhanced dramatically our potential in genetic information ( Watson, 1990). Of 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 of major public health importance, ranging from adult chronic diseases, such as cancer and diabetes, to infectious and immunologic disorders, to diseases affecting the health of infants and children ( Khoury, 1997).
How can this information be applied to enhance our understanding of childhood psychopathology? Despite the advances in unraveling the genetic basis of several human diseases, there has been far less success than originally anticipated in identifying genes for complex disorders, or common diseases without simple Mendelian modes of inheritance such as diabetes, heart disease, and the psychiatric disorders. Failure to identify genes for these conditions can be attributed to the lack of validity of phenotypic definitions, complex modes of inheritance characterized by genetic heterogeneity, phenotypic heterogeneity, or both; strong environmental inputs; and gene-environment interaction, polygenic inheritance, or both.
This chapter will demonstrate how the application of the methods of the discipline of genetic epidemiology is ideally suited to address sources of complexity of chronic human diseases, particularly the psychiatric disorders. Evidence that a