Osnat Karni

Why do young women smoke? I. Direct and interactive effects of environment, psychological characteristics and nicotinic cholinergic receptor genes.

Despite the health hazards, cigarette smoking is disproportionately frequent among young women. A significant contribution of genetic factors to smoking phenotypes is well established. Efforts to identify susceptibility genes do not generally take into account possible interaction with environment, life experience and psychological characteristics. We recruited 501 female Israeli students aged 20–30 years, obtained comprehensive background data and details of cigarette smoking and administered a battery of psychological instruments. Smoking initiators (n=242) were divided into subgroups with high (n=127) and low (n=115) levels of nicotine dependence based on their scores on the Fagerstrom Tolerance Questionnaire and genotyped with noninitiators (n=142) for single nucleotide polymorphisms (SNPs) in 11 nicotinic cholinergic receptor genes. We found nominally significant (P<0.05) allelic and genotypic association with smoking initiation of SNP rs2072660 and multilocus haplotypes (P<0.007–0.05) in CHRNB2 and nominal (P<0.05) allelic or genotypic association of SNPs in CHRNA7 (rs1909884), CHRNA9 (rs4861065) and CHRNB3 (rs9298629) with nicotine dependence. Employing logistic regression and controlling for known risk factors, the best-fitting model for smoking initiation encompassed a 5 SNP haplotype in CHRNB2, neuroticism and novelty seeking (P=5.9 × 10−14, Nagelkerke r2=0.30). For severity of nicotine dependence, two SNPs in CHRNA7 (rs1909884 and rs883473), one SNP in CHRNA5 (rs680244) and the interaction of a SNP in CHRNA7 (rs2337980) with neuroticism, were included in the model (P=2.24 × 10−7, Nagelkerke r2=0.40). These findings indicate that background factors, psychological characteristics and genetic variation in nicotinic cholinergic receptors contribute independently or interactively to smoking initiation and to severity of nicotine dependence in young women.

Genome scan of Arab Israeli families maps a schizophrenia susceptibility gene to chromosome 6q23 and supports a locus at chromosome 10q24

Schizophrenia is a complex neuropsychiatric disorder to which an as-yet-unknown number of genes contribute, interacting with each other and the environment. Linkage analyses have implicated several chromosomal regions as harboring schizophrenia susceptibility loci although rarely at levels commensurate with proposed thresholds for genome-wide significance. We systematically recruited Arab Israeli families multiply affected with schizophrenia from the catchment area of a Regional Mental Health Center. Clinical diagnoses were established by semistructured interviews and all other available sources of information under narrow, core and broad categories. Using 350 microsatellite markers, spaced at an average of 10.3 cM, we performed an autosomal scan in 155 subjects from 21 families. Linkage analysis employed affects only, multipoint, nonparametric (model-free) and also parametric (dominant and recessive) approaches. We detected significant evidence for a schizophrenia susceptibility gene at chromosome 6q23 with a nonparametric LOD score (NPL) of 4.60 (P=0.000004) under the broad diagnostic category and a parametric LOD score of 3.33 (dominant model). Under the core diagnostic category the NPL was 4.29 (P=0.00001) and the LOD score 4.16 (dominant model). We also detected suggestive evidence for linkage at chromosome 10q24 under the broad diagnostic category (NPL 3.24, P=0.0008; heterogeneity LOD score, dominant model 2.65, α=0.82). Additionally, NPL scores >2.0 were observed at chromosome 2q37, 4p15–16, 7p22, 9q21–22 and 14q11.1–11.2. The linkage we detected at chromosome 6q23 fulfills the criteria for genome-wide significance and is located approximately midway between loci suggested by a previous significant report at chromosome 6q25 and findings located more centromerically at 6q21–22.

Association study of cannabinoid receptor gene (CNR1) alleles and anorexia nervosa: Differences between restricting and bingeing/purging subtypes

Anorexia nervosa (AN) is a severe and disabling psychiatric disorder, characterized by profound weight loss and body image disturbance. Family and twin studies indicate a significant genetic contribution to this disorder although no genetic mutation has yet been identified. The endocannabinoid system has recently been implicated in many physiological functions including appetite regulation. We, therefore, undertook a family based study to test the hypothesis whether a polymorphism of the CNR1 gene, which encodes human CB1 receptor, a subclass of the central cannabinoid receptor, contributes to the susceptibility to AN. Fifty two families (parents with one or two affected siblings) were genotyped for the (AAT) trinucleotide repeat of CNR1 gene. Using the haplotype relative risk (HRR) method, the distribution of alleles transmitted to the patients was not found to be significantly different from the non‐transmitted parental alleles. However, upon dividing the samples to restricting and bingeing/purging subtypes of AN, the extended transmission disequilibrium test (ETDT) revealed that there is preferential transmission of different alleles in each of the subtypes. The 14 repeat allele was preferentially transmitted in the bingeing/purging AN group (P = 0.05) but not in the restricting AN group, whereas the 13 repeat allele was preferentially transmitted in the restricting AN group (almost significant, P = 0.07) but not in the bingeing/purging AN group. Our study suggests that restricting AN and bingeing/purging AN may be associated with different alleles of the CNR1 gene.

AHI1 , a pivotal neurodevelopmental gene, and C6orf217 are associated with susceptibility to schizophrenia

Schizophrenia, a severe neuropsychiatric disorder, is believed to involve multiple genetic factors. A significant body of evidence supports a pivotal role for abnormalities of brain development in the disorder. Linkage signals for schizophrenia map to human chromosome 6q. To obtain a finer localization, we genotyped 180 single nucleotide polymorphisms (SNPs) in a young, inbred Arab-Israeli family sample with a limited number of founders. The SNPs were mostly within a ∼7 Mb region around the strong linkage peak at 136.2 Mb that we had previously mapped. The most significant genetic association with schizophrenia for single SNPs and haplotypes was within a 500 kb genomic region of high linkage disequilibrium (LD) at 135.85 Mb. In a different, outbred, nuclear family sample that was not appropriate for linkage analysis, under-transmitted haplotypes incorporating the same SNPs (but not the individual SNPs) were significantly associated with schizophrenia. The implicated genomic region harbors the Abelson Helper Integration Site 1 (AHI1) gene, which showed the strongest association signal, and an adjacent, primate-specific gene, C6orf217. Mutations in human AHI1 underlie the autosomal recessive Joubert Syndrome with brain malformation and mental retardation. Previous comparative genomic analysis has suggested accelerated evolution of AHI1 in the human lineage. C6orf217 has multiple splice isoforms and is expressed in brain but does not seem to encode a functional protein. The two genes appear in opposite orientations and their regulatory upstream regions overlap, which might affect their expression. Both, AHI1 and C6orf217 appear to be highly relevant candidate genes for schizophrenia.

Why do young women smoke? III. Attention and impulsivity as neurocognitive predisposing factors

Since nicotine has been shown to facilitate sustained attention and control of impulsivity, impairment in these domains may influence individuals who initiate smoking for various reasons to continue to smoke cigarettes. The purpose of this study was to determine whether young women who smoke regularly but are not abstinent at the time of testing, differ in their cognitive functioning from non-smokers and whether they resemble women who smoked in the past but quit. Female undergraduate students aged 20-30 years were recruited by advertisement from institutes of higher education in the Jerusalem area. The study sample consisted of 91 current smokers (CS), 40 past smokers (PS) and 151 non-smokers (NS). 46 occasional smokers (OS) were also tested. Confounding by withdrawal state was neutralized by including only CS and OS who smoked their last cigarette less than 90 min before testing. Subjects performed a computerized neurocognitive battery, which tests the domains of attention, memory, impulsivity, planning, information processing and motor performance. Analyses were controlled for age. The results showed that CS made significantly more errors than NS on the Continuous Performance Task (CPT), Matching Familiar Figures Test (MFFT) and Tower of London (TOL) test. PS were significantly worse than NS on the MFFT and TOL test. PS did not differ significantly from CS on any test. No association was found between duration of smoking and performance. These findings suggest that a neurocognitive profile characterized by impairments in sustained attention and control of impulsivity may be one of the factors that predispose young women who initiate cigarette smoking to maintain the habit.

Linkage disequlibrium in the DTNBP1 (dysbindin) gene region and on chromosome 1p36 among psychotic patients from a genetic isolate in Israel: findings from identity by descent haplotype sharing analysis.

Several genes have been reported recently to be associated with schizophrenia and bipolar disorder. Because of the complexity of the inheritance of these disorders, there is an urgent need to replicate these findings and to search for additional candidate genes. The study of genetic isolates is a powerful technique that may overcome some of the obstacles caused by genetic heterogeneity and ambiguity of phenotype definition. Identity by descent (IBD) haplotype sharing analysis in these populations may be used to detect mutations within shared haplotypes in smaller samples of affected individuals. In this study, we used IBD haplotype sharing analysis to replicate positive linkage and association findings in psychotic disorders, and to identify other regions of interest. Fifty‐two patients with major psychiatric disorders from a genetically isolated village in Israel were studied. By studying eight Y chromosome markers, we were able to confirm the oral tradition of members of this isolate regarding a common paternal origin. Three hundred fifty nine microsatellite markers on 9 candidate chromosomes were genotyped, and haplotypes were reconstructed using information from family members. Two highly significant (P < 0.0001) peaks of haplotype sharing were found. One was for psychotic patients with any diagnosis at the location of dysbindin, a gene previously associated with schizophrenia. The other peak was for patients with schizophrenia on chromosome 1p36. Thus, this study both replicates an earlier finding and points to a novel region of interest, which might be unique to this population.

Association of the RGS2 gene with extrapyramidal symptoms induced by treatment with antipsychotic medication.

Objectives To investigate the role of genes encoding regulators of G protein signaling in early therapeutic response to antipsychotic drugs and in susceptibility to drug-induced extrapyramidal symptoms. As regulators of G protein signaling and regulators of G protein signaling-like proteins play a pivotal role in dopamine receptor signaling, genetically based, functional variation could contribute to interindividual variability in therapeutic and adverse effects. Methods Consecutively hospitalized, psychotic patients with Diagnostic and Statistical Manual of Mental Disorder-IV schizophrenia (n=121) were included in the study if they received treatment with typical antipsychotic medication (n=72) or typical antipsychotic drugs and risperidone (n=49) for at least 2 weeks. Clinical state and adverse effects were rated at baseline and after 2 weeks. Twenty-four single nucleotide polymorphisms were genotyped in five regulators of G protein signaling genes. Results None of the single nucleotide polymorphisms were related to clinical response to antipsychotic treatment at 2 weeks. Five out of six single nucleotide polymorphisms within or flanking the RGS2 gene were nominally associated with development or worsening of parkinsonian symptoms (PARK+) as measured by the Simpson Angus Scale, one of them after correction for multiple testing (rs4606, P=0.002). A GCCTG haplotype encompassing tagging single nucleotide polymorphisms within and flanking RGS2 was significantly overrepresented among PARK+ compared with PARK− patients (0.23 vs. 0.08, P=0.003). A second, ‘protective’, GTGCA haplotype was significantly overrepresented in PARK− patients (0.13 vs. 0.30, P=0.009). Both haplotype associations survive correction for multiple testing. Conclusions Subject to replication, these findings suggest that genetic variation in the RGS2 gene is associated with susceptibility to extrapyramidal symptoms induced by antipsychotic drugs.

Why do young women smoke? II. Role of traumatic life experience, psychological characteristics and serotonergic genes.

Cigarette smoking is a complex behavioral phenotype to which environmental, psychological and genetic factors contribute. The purpose of this study was to investigate these multifactorial effects with a specific focus on young women and on genes that encode serotonin (5-HT) receptors and the 5-HT transporter. A case–control sample of female Israeli college students provided comprehensive background data and details of cigarette smoking and completed a battery of psychological instruments. They were divided into smoking initiators (SI, n=242) or non-initiators (NI, n=148); SI were further subdivided into high (HND, n=127) and low nicotine-dependent smokers (LND, n=115) on the basis of their scores on the Fagerstrom Tolerance Questionnaire (FTQ). Single-nucleotide polymorphisms (SNPs) in five serotonin receptor genes (HTR1A, HTR1B, HTR2A, HTR2C and HTR6) and the 5-HT transporter-linked polymorphic region (5-HTTLPR) were genotyped. In a logistic regression model for SI (χ2=117.90, P=1.6 × 10−19, Nagelkerke R2=0.42), novelty seeking (odds ratio (OR)=1.134, P=0.00009) was a significant risk factor. A five SNP CACCC haplotype in HTR6 was a strong protective factor against SI (OR=0.26; P=0.007). The interaction of HTR6-C276T genotype and lifetime traumatic experience contributed strongly to the risk of SI (OR=13.88, P=0.0001). Specifically, subjects homozygous for the HTR6-C276T C allele showed significantly increased risk of SI if they had experienced trauma. Although significant (χ2=42.85, P=1.00 × 10−7), the best-fitting model for ND was less predictive than the model for SI (Nagelkerke R2=0.24). HTR1B-G861C GG genotype (OR=2.29, P=0.01) was a significant risk factor for HND. Further studies should consider the interactive contribution of life events and relevant gene variants to cigarette smoking and other complex behavioral traits.

Fine mapping of a schizophrenia susceptibility locus at chromosome 6q23: increased evidence for linkage and reduced linkage interval

We previously reported an autosomal scan for schizophrenia susceptibility loci in a systematically recruited sample of Arab Israeli families. The scan detected significant evidence for linkage at chromosome 6q23 with a nonparametric LOD score (NPL) of 4.60 (P=0.000004) and a multipoint parametric LOD score of 4.16. In order to refine this finding we typed 42 additional microsatellite markers on chromosome 6q between D6S1570 (99.01 cM from the pter) and D6S281 (190.14 from the pter) in the same sample (average intermarker distance ∼1.7 cM). In the 23 cM region between D6S1715 and D6S311, markers were more closely spaced (∼1.1 cM). Multipoint nonparametric and parametric and single point linkage analyses were performed. The peak NPL rose to 4.98 (P=0.00000058) at D6S1626 (136.97 cM), immediately adjacent to D6S292 (NPL 4.98, P=0.00000068), the marker that gave the highest NPL in the original genome scan, under the broad diagnostic category. The putative susceptibility region (NPL-1) was reduced from 12.0 to 4.96 cM. The peak multipoint parametric LOD score was 4.63 at D6S1626 under a dominant genetic model, core diagnostic category and the LOD-1 interval was 2.10 cM. The maximum single point LOD score (3.55, θ=0.01) was also at D6S1626 (dominant model, core diagnostic category). Increased evidence for linkage in the same sample as in the original genome scan and consistent localization of the linkage peak add further support for the presence of a schizophrenia susceptibility locus at chromosome 6q23. Moreover, the markedly reduced linkage interval greatly improves prospects for identifying a schizophrenia susceptibility gene within the implicated region.

Association of the dopamine receptor interacting protein gene, NEF3, with early response to antipsychotic medication

Genetic variation in antipsychotic drug targets could underlie variability among patients in the time required for antipsychotic effects to be elicited. In a clinical, pharmacogenetic study we focused on the dopamine receptor interacting protein (DRIP) gene family. DRIPs are pivotally involved in regulating dopamine receptor signal transduction. Consecutively hospitalized, acutely psychotic patients with DSM-IV schizophrenia (n=121) were included in the study if they received treatment with typical antipsychotic medication (TYP, n=72) or TYP plus risperidone (TYP-R, n=49) for at least 2 wk. Clinical state and adverse effects were rated at baseline and after 2 wk. Patients improved significantly on both TYP and TYP-R with no significant difference between them. Early responders were defined as patients whose PANSS change scores were greater than the median. Twenty-two single nucleotide polymorphisms (SNPs) were analysed in five DRIP-encoding genes. Two SNPs in NEF3, which encodes the DRIP, neurofilament-medium (NF-M), were associated with early response (rs1457266, p=0.01; rs1379357, p=0.006). A 5 SNP haplotype spanning NEF3 was over-represented in early responders (p=0.015), in the combined patient group and in the TYP group alone. These findings suggest that variation in NEF3, most likely functional variants that are in linkage disequilibrium with the SNPs that we studied, influences rate of response to TYP. Since NEF3 is primarily associated with dopamine D1 receptor function, the evidence for a complementary role of dopamine D1 receptors in antipsychotic effects is considered. The findings reported here open an interesting research avenue in the pharmacogenetics of antipsychotic effects but require replication in larger samples treated in a controlled context.