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OBJECTIVES: Susceptibility to heroin dependence is strongly influenced by genetic factors with heritability estimates as high as 0.7. A number of genes, as well as environmental factors, are likely to contribute to its etiology. Not all individuals who have ever tried heroin at some stage during their lifetime become dependent on heroin. It has been suggested that genetic factors might be more important in the transition stage to heroin dependence rather than in environmental exposures and experimenting with heroin. As the features of substance dependence and memory formation have been found to be strikingly similar, we have focused on a key enzyme involved in long-term potentiation and synaptic plasticity, namely the calcium-dependent/calmodulin-dependent protein kinase IIα (CAMKIIa). We hypothesized, that CamK2A genetic variation may play a role in the transition from occasional to regular heroin use. MATERIALS AND METHODS: Using quantitative trait association analysis, we addressed this hypothesis by correlating the self-reported time interval between occasional and regular heroin use with the frequency of 12 single nucleotide polymorphisms located within the genomic region of the CamK2A gene. A sample of 570 Caucasian patients was available for analysis. RESULTS: Single marker association analysis (rs10066581, P=0.007), as well as haplotype analysis (global P=0.005), suggested an association with the quantitative trait 'time interval from occasional to regular heroin use CONCLUSION: Our results propose that genetic variants located in the genomic region of the CamK2A gene may be involved in transition time from occasional to regular heroin use. Refereed/Peer-reviewed

Two intronic polymorphisms of the human alpha subunit of the olfactory G-protein (G(olf)) are described. They were detected with single-stranded conformational polymorphism (SSCP) methods and confirmed by sequencing both strands. These single base pair (bp) substitutions occur in introns 3 (an A/G at 35 bp 3' from the exon 3/intron 3 5' splice site) and 10 (an T/G at 7 bp 5' from the 3' splice site). Both polymorphisms are relatively common, with minor allele frequencies of 31% (intron 3) and 16% (intron 10). The intron 3 variant shows no linkage disequilibrium with an intron 5 (CA)n microsatellite located approximately 50 kb 3' from the intron 3 variant, among a small group of German individuals with schizophrenia. The intron 3 variant is interesting because it may create an 'in-frame' cryptic splice site which, if activated, would add 12 residues to exon 3. The intron 10 variant is interesting because a purine is substituted for a pyrimidine in the 'polypyrimidine' tract of the 3' splice site, a single base substitution of the type which has been associated with aberrant splicing in the androgen receptor gene.

Single nucleotide polymorphisms (SNPs) in the trace amine associated receptor trace amine associated receptor 6 gene and 3' flanking region have been shown to be associated with schizophrenia. To replicate these findings, we conducted a family-based association study with the five most significant SNPs in our sample of 79 sib-pair families (56/79 sib-pair families showed linkage to 6q23) and 125 triads. No evidence for association was obtained between these SNPs and schizophrenia in our sample, even when limited to the 56 linked families (P>0.2). We conclude that trace amine associated receptor 6 is not important for the development of schizophrenia in our family samples.

OBJECTIVES Recent studies investigating the association of DNA variants in the metabotropic glutamate receptor gene (GRM3) with schizophrenia susceptibility revealed conflicting results. In this study, we focused on DNA sequence variants, for which association was reported and attempted to replicate association with schizophrenia or with cognitive deficits known to be present in patients with schizophrenia. METHODS A sample of 242 families with affected offspring and five single nucleotide markers located in the genomic region of GRM3 has been used to replicate association with schizophrenia. In addition, results of neuropsychological tests, trail making test B and the Stroop color-naming task were available for a subgroup of these families (N=88) and an independent sample of 148 patients with schizophrenia. Correlation of these measurements with genotypic data was performed using analysis of variance. RESULTS No statistical evidence for association with schizophrenia or correlation with cognitive deficits as measured by the trail making test B or the Stroop color-naming task and the five DNA sequence variants could be detected. A trend towards association with schizophrenia was revealed for a single marker (rs2237562, P=0.056) and for 2-marker and 3-marker haplotypes containing this variant. CONCLUSIONS Our study of DNA sequence variants in the GRM3 gene did not provide further support for genetic association with schizophrenia or for correlation with cognitive deficits.