Clinical Benefits of Genetic Research
At least with respect to highly heritable neurodevelopmental disorders such as autism, schizophrenia, and ADHD, the most important product of molecular genetic research is likely to be the lead provided for biological studies that could delineate the causal neural processes that constitute the biological underpinning of the disorders. Up to now, the findings from biological research in psychiatry have been singularly inconclusive on specifics (see Bailey. Phillips, & Rutter, 1996 for a discussion of this point with regard to autism; Harrison, 1997, regarding schizophrenia; and Tannock, 1998, regarding ADHD). Findings have been consistent in indicating abnormalities of brain structure or function. However, they have either been inconsistent on the details, or too general to be of much help in delineation of diagnosis- specific pathophysiology, or even nonspecific brain processes that truly mediate psychopathological risk, albeit risk that spans several diagnoses. The detection of susceptibility genes, alone, will not provide an answer. This notwithstanding. the determination of their function (through transgenics and proteomics) could do much to provide the leads that are needed to redirect biological studies. It will be appreciated that achieving the objective of determining causal neural processes will require a long and difficult research journey in which finding the genes (difficult though that has been) may prove to be the easiest step (Rutter. 2000b).
Pharmacogenetics
Related to the understanding of neural processes is the possibility of developing more effective pharmacological interventions. Of course, with respect to ADHD we already have drugs that make a real and worthwhile difference (MTA Cooperative Group, 1999a. b). Stimulants do much to alleviate key problems. There are. however, three limitations. First, the benefits are not diagnosis-specific and this must raise uncertainties over whether or not the medication addresses the basic underlying pathophysiology. Second, stimulants are not uniformly successful with respect to all the problems associated with ADHD. Third, not all children with ADHD respond dramatically to stimulant medication. Marked individual variability in response to drugs is a phenomenon that pervades medicine in its entirety. We know a good deal about which groups of drugs tend to benefit which groups of patients, but we know far less about what differentiates those within those groups who do and do not respond. Molecular genetic findings could help greatly in elucidating this, as well as providing leads on which new types of drugs might be useful— the growing field of pharmacogenetics (Evans & Relling, 1999).
