NOVEL ASSOCIATION APPROACH FOR DETERMINING THE GENETIC PREDISPOSITIONTO SCHIZOPHRENIA - CASE-CONTROL RESOURCE AND TESTING OF A CANDIDATE GENE

We have developed a two-tiered approach to elucidating the genetic pre disposition to schizophrenia. The approach first involves the examinat ion of candidate genes in a subset of schizophrenic individuals to ide ntify DNA sequence variations of likely functional significance, i.e., that produce either structural alterations in the protein or affect t he level of gene expression. Once identified, the prevalence of the ab errant allele is examined in a large group of unrelated schizophrenic cases and controls to assess whether a true disease association exists . Herein, we describe the establishment of a DNA bank on nearly 200 un related schizophrenic cases defined by DSM-III-R criteria and on over 300 unrelated, ethnically similar controls. Characteristics of the stu dy sample are described. The study approach then is illustrated by tes ting known mutations in the phenylalanine hydroxylase gene, responsibl e for the autosomal recessive disease of phenylketonuria, in the case- control sample to determine if carriership of a mutant allele is assoc iated with an increased risk of schizophrenia. Using PCR amplification of specific alleles (PASA), we screened 190 schizophrenic cases and 3 36 controls for two common point mutations in the phenylalanine hydrox ylase gene. Two carriers were found among the controls, while none of the cases was shown to carry a mutant allele. Thus, carriership of eit her of two common mutations in the phenylalanine hydroxylase gene does not appear to be associated with an increased risk of schizophrenia. As additional candidate genes are tested in this case-control resource , adjustment for multiple comparisons will become crucial in order to reduce the chance of false positive findings. The ascertainment of aux illary groups of cases and controls with sequential hypothesis testing in these groups offers a technically feasible solution to the multipl e comparisons problem.