Nowhere is the need for caution more apparent than in predictive testing for psychiatric diseases. The most common psychiatric diseases are schizophrenia and manic depressive disorders. Based on extensive family, twin, and adoption studies, there is agreement that genetic factors play an important role in the causation of these diseases (Goldin et al., 1992; Hanson and Gottesman, 1992). However, the nature and number of the underlying genes are entirely unknown. Mendelian inheritance is rarely observed, and the mechanisms of transmission are generally obscure. There was much excitement when genetic linkage studies using anonymous DNA markers appeared to map specific genes in schizophrenia (Sherrington et al., 1988) and manic depressive disorders (Egeland et al., 1989), but repeated tests to replicate this work have, to date, yielded negative results (Kelsoe et al., 1989; Baron et al., 1993). Some other neuropsychiatric disorders in which genetic factors have been implicated include panic disorders (Crowe, 1992), Tourette syndrome, and certain types of alcoholism (Propping, 1992). However, no specific genes have been mapped or otherwise identified in any of these disorders.
It is likely that multiple genes, often interacting with yet poorly understood environmental factors, will be operative in many psychiatric disorders. As with other complex conditions, predictive testing in psychiatric diseases is unlikely to be as accurate as prediction in monogenic diseases. Prediction will always be more probabilistic, and there will be uncertainty regarding whether the disorder will ever manifest and, if so, at what age. The implications of predictive testing for mental disorders raise even more problems than those for other complex medical diseases, because of the heightened potential for stigmatization and discrimination.
The benefits of screening have been demonstrated in diseases such as PKU and congenital hypothyroidism, because of the overall benefit of early diagnosis of diseases for which effective treatment is available. Screening may offer no benefit if no treatment exists or services are not available. The committee recommends that newborn screening only take place (1) for conditions for which there are indications of clear benefit to the newborn, (2) when a system is in place for confirmatory diagnosis, and (3) when treatment and follow-up are available for affected newborns. The committee recommends that states with newborn screening programs for treatable disorders also have programs to ensure that necessary treatment and follow-up services are provided to affected children identified through newborn screening.