A polymorphism in the OPRM1 3'-untranslated region is associated with methadone efficacy in treating opioid dependence

The mu-opioid receptor (MOR) is the primary target of methadone and buprenorphine. The primary neuronal transcript of the OPRM1 gene, MOR-1, contains a ~13kb 3′ untranslated region with five common haplotypes in European-Americans. We analyzed the effects of these haplotypes on the percentage of opioid positive urine tests in European-Americans (n = 582) during a 24-week, randomized, open-label trial of methadone or buprenorphine/naloxone (Suboxone) for the treatment of opioid dependence. A single haplotype, tagged by rs10485058, was significantly associated with patient urinalysis data in the methadone treatment group. Methadone patients with the A/A genotype at rs10485058 were less likely to have opioid-positive urine drug screens than those in the combined A/G and G/G genotypes group (Relative Risk = 0.76, 95% confidence intervals = 0.73–0.80, p = 0.0064). Genotype at rs10485058 also predicted self-reported relapse rates in an independent population of Australian patients of European descent (n = 1215) who were receiving opioid substitution therapy (p = 0.003). In silico analysis predicted that miR-95-3p would interact with the G, but not the A allele of rs10485058. Luciferase assays indicated miR-95-3p decreased reporter activity of constructs containing the G, but not the A allele of rs10485058, suggesting a potential mechanism for the observed pharmacogenetic effect. These findings suggest that selection of a medication for opioid dependence based on rs10485058 genotype might improve outcomes in this ethnic group.

A genome-wide association study of anorexia nervosa

Anorexia nervosa (AN) is a complex and heritable eating disorder characterized by dangerously low body weight. Neither candidate gene studies nor an initial genome-wide association study (GWAS) have yielded significant and replicated results. We performed a GWAS in 2907 cases with AN from 14 countries (15 sites) and 14 860 ancestrally matched controls as part of the Genetic Consortium for AN (GCAN) and the Wellcome Trust Case Control Consortium 3 (WTCCC3). Individual association analyses were conducted in each stratum and meta-analyzed across all 15 discovery data sets. Seventy-six (72 independent) single nucleotide polymorphisms were taken forward for in silico (two data sets) or de novo (13 data sets) replication genotyping in 2677 independent AN cases and 8629 European ancestry controls along with 458 AN cases and 421 controls from Japan. The final global meta-analysis across discovery and replication data sets comprised 5551 AN cases and 21 080 controls. AN subtype analyses (1606 AN restricting; 1445 AN binge-purge) were performed. No findings reached genome-wide significance. Two intronic variants were suggestively associated: rs9839776 (P=3.01 × 10(-7)) in SOX2OT and rs17030795 (P=5.84 × 10(-6)) in PPP3CA. Two additional signals were specific to Europeans: rs1523921 (P=5.76 × 10(-)(6)) between CUL3 and FAM124B and rs1886797 (P=8.05 × 10(-)(6)) near SPATA13. Comparing discovery with replication results, 76% of the effects were in the same direction, an observation highly unlikely to be due to chance (P=4 × 10(-6)), strongly suggesting that true findings exist but our sample, the largest yet reported, was underpowered for their detection. The accrual of large genotyped AN case-control samples should be an immediate priority for the field.

Analysis of candidate genes for morphine preference quantitative trait locus Mop2

Compared to DBA/2J (D2), C57BL/6J (B6) inbred mice exhibit strong morphine preference when tested using a two-bottle choice drinking paradigm. A morphine preference quantitative trait locus (QTL), Mop2, was originally mapped to proximal chromosome (Chr) 10 using a B6xD2 F2 intercross population, confirmed with reciprocal congenic strains and fine mapped with recombinant congenic strains. These efforts identified a ∼ 10-Million base pair (Mbp) interval, underlying Mop2, containing 35 genes. To further reduce the interval, mice from the D2.B6-Mop2-P1 congenic strain were backcrossed to parental D2 mice and two new recombinant strains of interest were generated: D2.B6-Mop2-P1.pD.dB and D2.B6-Mop2-P1.pD.dD. Results obtained from testing these strains in the two-bottle choice drinking paradigm suggest that the gene(s) responsible for the Mop2 QTL is one or more of 22 remaining within the newly defined interval (∼ 7.6 Mbp) which includes Oprm1 and several other genes related to opioid pharmacology. Real-time qRT-PCR analysis of Oprm1 and opioid-related genes Rgs17, Ppp1r14c, Vip, and Iyd revealed both between-strain and within-strain expression differences in comparisons of saline- and morphine-treated B6 and D2 mice. Analysis of Rgs17 protein levels also revealed both between-strain and within-strain differences in comparisons of saline- and morphine-treated B6 and D2 mice. Results suggest that the Mop2 QTL represents the combined influence of multiple genetic variants on morphine preference in these two strains. Relative contributions of each variant remain to be determined.

Enrichment of cis-regulatory gene expression SNPs and methylation quantitative trait loci among bipolar disorder susceptibility variants

We conducted a systematic study of top susceptibility variants from a genome-wide association (GWA) study of bipolar disorder to gain insight into the functional consequences of genetic variation influencing disease risk. We report here the results of experiments to explore the effects of these susceptibility variants on DNA methylation and mRNA expression in human cerebellum samples. Among the top susceptibility variants, we identified an enrichment of cis regulatory loci on mRNA expression (eQTLs), and a significant excess of quantitative trait loci for DNA CpG methylation, hereafter referred to as methylation quantitative trait loci (mQTLs). Bipolar disorder susceptibility variants that cis regulate both cerebellar expression and methylation of the same gene are a very small proportion of bipolar disorder susceptibility variants. This finding suggests that mQTLs and eQTLs provide orthogonal ways of functionally annotating genetic variation within the context of studies of pathophysiology in brain. No lymphocyte mQTL enrichment was found, suggesting that mQTL enrichment was specific to the cerebellum, in contrast to eQTLs. Separately, we found that using mQTL information to restrict the number of single-nucleotide polymorphisms studied enhances our ability to detect a significant association. With this restriction a priori informed by the observed functional enrichment, we identified a significant association (rs12618769, P(bonferroni)<0.05) from two other GWA studies (TGen+GAIN; 2191 cases and 1434 controls) of bipolar disorder, which we replicated in an independent GWA study (WTCCC). Collectively, our findings highlight the importance of integrating functional annotation of genetic variants for gene expression and DNA methylation to advance the biological understanding of bipolar disorder.

Case-control association analysis of polymorphisms in the δ-opioid receptor, OPRD1, with cocaine and opioid addicted populations

BACKGROUND

Addiction susceptibility and treatment responsiveness are greatly influenced by genetic factors. Sequence variation in genes involved in the mechanisms of drug action have the potential to influence addiction risk and treatment outcome. The opioid receptor system is involved in mediating the rewarding effects of cocaine and opioids. The μ-opioid receptor (MOR) has traditionally been considered the primary target for opioid addiction. The MOR, however, interacts with and is regulated by many known MOR interacting proteins (MORIPs), including the δ-opioid receptor (DOR).

METHODS

The present study evaluated the contribution of OPRD1, the gene encoding the DOR, to the risk of addiction to opioids and cocaine. The association of OPRD1 polymorphisms with both opioid addiction (OA) and cocaine addiction (CA) was analyzed in African American (OA n=336, CA n=503) and European American (OA n=1007, CA n=336) populations.

RESULTS

The primary finding of this study is an association of rs678849 with cocaine addiction in African Americans (allelic p=0.0086). For replication purposes, this SNP was analyzed in a larger independent population of cocaine addicted African Americans and controls and the association was confirmed (allelic p=4.53 × 10(-5); n=993). By performing a meta-analysis on the expanded populations, the statistical evidence for an association was substantially increased (allelic p=8.5 × 10(-7)) (p-values non-FDR corrected).

CONCLUSION

The present study suggests that polymorphisms in OPRD1 are relevant for cocaine addiction in the African American population and provides additional support for a broad role for OPRD1 variants in drug dependence.

Molecular linkage studies of bipolar disorder

Linkage studies have defined at least five bipolar (BP) disorder susceptibility loci that meet suggested guidelines for initial identification and subsequent confirmation. These loci, found on 18p11, 18q22, 21q21, 4p16, and Xq26, are targets for BP candidate gene investigations. Molecular dissection of expressed sequences for these regions is likely to yield specific BP susceptibility alleles in most cases, in all probability, these BP susceptibility alleles will be common in the general population, and, individually, will be neither necessary nor sufficient for manifestation syndrome. Additive or multiplicative oligogenic models involving several susceptibility loci appear most reasonable at present, it is hoped thai these BP susceptibility genes will increase understanding of many mysteries surrounding these disorders, including drug response, cycling patterns, age-of-onset, and modes of transmission.

The CHRNA5-A3-B4 gene cluster in nicotine addiction

Nicotine addiction (NA) is a common and devastating disease, such that the annual number of deaths (world-wide) from tobacco-related diseases will double from 5 million in the year 2000 to 10 million in 2020. Nicotine is the only substance in tobacco which animals and humans will self-administer. NA, as a lifetime diagnosis, has been assessed in various approaches, including the concept of cigarettes per day (CPD). Other assessments of NA are somewhat more comprehensive, such as the Fagerstrom Test for Nicotine Dependence or the American Psychiatric Association's Diagnostic and Statistical Manual (fourth edition) diagnosis of nicotine dependence. These different measures have moderate agreement with one another. Twin, family and adoption studies have shown that these different assessments of NA have substantial heritability (that fraction of risk attributable to genetic factors). The heritability of NA has been estimated at 50-75%, depending on the definition and the population under study. DNA-based studies of NA have been somewhat successful in identifying a common haplotype, which increases risk for NA among European-origin populations. This haplotype explains a small amount of variance, accounting for ∼1 CPD, and it includes the α5 and the α3 nicotinic receptor subunit genes (CHRNA5 and CHRNA3). The review will focus on this implicated region. In this risk region, there is a common (among European-origin people) mis-sense single-nucleotide polymorphism in the CHRNA5 gene (D398N), which changes a conserved amino acid from aspartic acid to asparagine. The risk allele (398N) confers decreased calcium permeability and more extensive desensitization, according to in vitro cellular studies, raising the possibility that a positive allosteric modulator of the (α4β2)(2)α5 type of nicotinic receptor might have therapeutic potential in NA. There are other genetic influences on NA in this region, apart from the mis-sense variant, and additional biological experiments must be done to understand them.

Genetic association analyses of PDYN polymorphisms with heroin and cocaine addiction

Genetic factors are believed to account for 30-50% of the risk for cocaine and heroin addiction. Dynorphin peptides, derived from the prodynorphin (PDYN) precursor, bind to opioid receptors, preferentially the kappa-opioid receptor, and may mediate the aversive effects of drugs of abuse. Dynorphin peptides produce place aversion in animals and produce dysphoria in humans. Cocaine and heroin have both been shown to increase expression of PDYN in brain regions relevant for drug reward and use. Polymorphisms in PDYN are therefore hypothesized to increase risk for addiction to drugs of abuse. In this study, 3 polymorphisms in PDYN (rs1022563, rs910080 and rs1997794) were genotyped in opioid-addicted [248 African Americans (AAs) and 1040 European Americans (EAs)], cocaine-addicted (1248 AAs and 336 EAs) and control individuals (674 AAs and 656 EAs). Sex-specific analyses were also performed as a previous study identified PDYN polymorphisms to be more significantly associated with female opioid addicts. We found rs1022563 to be significantly associated with opioid addiction in EAs [P = 0.03, odds ratio (OR) = 1.31; false discovery rate (FDR) corrected q-value]; however, when we performed female-specific association analyses, the OR increased from 1.31 to 1.51. Increased ORs were observed for rs910080 and rs199774 in female opioid addicts also in EAs. No statistically significant associations were observed with cocaine or opioid addiction in AAs. These data show that polymorphisms in PDYN are associated with opioid addiction in EAs and provide further evidence that these risk variants may be more relevant in females.

Opiate agonist-induced re-distribution of Wntless, a mu-opioid receptor interacting protein, in rat striatal neurons

Wntless (WLS), a mu-opioid receptor (MOR) interacting protein, mediates Wnt protein secretion that is critical for neuronal development. We investigated whether MOR agonists induce re-distribution of WLS within rat striatal neurons. Adult male rats received either saline, morphine or [d-Ala2, N-Me-Phe4, Gly-ol5]-enkephalin (DAMGO) directly into the lateral ventricles. Following thirty minutes, brains were extracted and tissue sections were processed for immunogold silver detection of WLS. In saline-treated rats, WLS was distributed along the plasma membrane and within the cytoplasmic compartment of striatal dendrites as previously described. The ratio of cytoplasmic to total dendritic WLS labeling was 0.70±0.03 in saline-treated striatal tissue. Morphine treatment decreased this ratio to 0.48±0.03 indicating a shift of WLS from the intracellular compartment to the plasma membrane. However, following DAMGO treatment, the ratio was 0.85±0.05 indicating a greater distribution of WLS intracellularly. The difference in the re-distribution of the WLS following different agonist exposure may be related to DAMGO's well known ability to induce internalization of MOR in contrast to morphine, which is less effective in producing receptor internalization. Furthermore, these data are consistent with our hypothesis that MOR agonists promote dimerization of WLS and MOR, thereby preventing WLS from mediating Wnt secretion. In summary, our findings indicate differential agonist-induced trafficking of WLS in striatal neurons following distinct agonist exposure. Adaptations in WLS trafficking may represent a novel pharmacological target in the treatment of opiate addiction and/or pain.

Quantitative trait loci for electrical seizure threshold mapped in C57BLKS/J and C57BL/10SnJ mice

We mapped the quantitative trait loci (QTL) that contribute to the robust difference in maximal electroshock seizure threshold (MEST) between C57BLKS/J (BKS) and C57BL10S/J (B10S) mice. BKS, B10S, BKS × B10S F1 and BKS × B10S F2 intercross mice were tested for MEST at 8-9 weeks of age. Results of F2 testing showed that, in this cross, MEST is a continuously distributed trait determined by polygenic inheritance. Mice from the extremes of the trait distribution were genotyped using microarray technology. MEST correlated significantly with body weight and sex; however, because of the high correlation between these factors, the QTL mapping was conditioned on sex alone. A sequential series of statistical analyses was used to map QTLs including single-point, multipoint and multilocus methods. Two QTLs reached genome-wide levels of significance based upon an empirically determined permutation threshold: chromosome 6 (LOD = 6.0 at ∼69 cM) and chromosome 8 (LOD = 5.7 at ∼27 cM). Two additional QTLs were retained in a multilocus regression model: chromosome 3 (LOD = 2.1 at ∼68 cM) and chromosome 5 (LOD = 2.7 at ∼73 cM). Together the four QTLs explain one third of the total phenotypic variance in the mapping population. Lack of overlap between the major MEST QTLs mapped here in BKS and B10S mice and those mapped previously in C57BL/6J and DBA/2J mice (strains that are closely related to BKS and B10S) suggest that BKS and B10S represent a new polygenic mouse model for investigating susceptibility to seizures.

Confirmation of multiple seizure susceptibility QTLs on chromosome 15 in C57BL/6J and DBA/2J inbred mice

To confirm seizure susceptibility (SZS) quantitative trait loci (QTLs) on chromosome (chr) 15 identified previously using C57BL/6J (B6) and DBA/2J (D2) mice and to refine their genomic map position, we studied a set of three congenic strains in which overlapping segments of chr 15 from D2 were transferred onto the B6 background. We measured thresholds for generalized electroshock seizure (GEST) and maximal electroshock seizure (MEST) in congenic strains and B6-like littermates and also tested their responses to kainic acid (KA) and pentylenetetrazol (PTZ). Results document that MEST is significantly lower in strains 15M and 15D, which harbor medial and distal (telomeric) segments of chr 15 (respectively) from D2, compared with strain 15P, which harbors the proximal (acromeric) segment of chr 15 from D2, and with control littermates. Congenic strains 15P and 15M exhibited greater KA SZS compared with strain 15D and B6-like controls. All congenic strains were similar to controls with regard to PTZ SZS. Taken together, results suggest there are multiple SZS QTLs on chr 15 and that two QTLs harbor gene variants that affect MEST and KA SZS independently. The MEST QTL is refined to a 19 Mb region flanked by rs13482630 and D15Mit159. This interval contains 350 genes, 183 of which reside in areas where the polymorphism rate between B6 and D2 is high. The KA QTL interval spans a 65 Mb region flanked by markers D15Mit13 and rs31271969. It harbors 83 genes in highly polymorphic areas, 310 genes in all. Complete dissection of these loci will lead to identification of genetic variants that influence SZS in mice and provide a better understanding of seizure biology.

Anorexia nervosa trios: behavioral profiles of individuals with anorexia nervosa and their parents

BACKGROUND

Anorexia nervosa (AN) is associated with behavioral traits that predate the onset of AN and persist after recovery. We identified patterns of behavioral traits in AN trios (proband plus two biological parents).

METHOD

A total of 433 complete trios were collected in the Price Foundation Genetic Study of AN using standardized instruments for eating disorder (ED) symptoms, anxiety, perfectionism, and temperament. We used latent profile analysis and ANOVA to identify and validate patterns of behavioral traits.

RESULTS

We distinguished three classes with medium to large effect sizes by mothers' and probands' drive for thinness, body dissatisfaction, perfectionism, neuroticism, trait anxiety, and harm avoidance. Fathers did not differ significantly across classes. Classes were distinguished by degree of symptomatology rather than qualitative differences. Class 1 (approximately 33%) comprised low symptom probands and mothers with scores in the healthy range. Class 2 ( approximately 43%) included probands with marked elevations in drive for thinness, body dissatisfaction, neuroticism, trait anxiety, and harm avoidance and mothers with mild anxious/perfectionistic traits. Class 3 (approximately 24%) included probands and mothers with elevations on ED and anxious/perfectionistic traits. Mother-daughter symptom severity was related in classes 1 and 3 only. Trio profiles did not differ significantly by proband clinical status or subtype.

CONCLUSIONS

A key finding is the importance of mother and daughter traits in the identification of temperament and personality patterns in families affected by AN. Mother-daughter pairs with severe ED and anxious/perfectionistic traits may represent a more homogeneous and familial variant of AN that could be of value in genetic studies.

Beta-adrenoceptor function in human adult skin fibroblasts: a study of manic-depressive illness

Catecholamine theories of affective illness provide a rationale for the study of beta-adrenoceptor function in these disorders. Skin fibroblasts were grown in tissue culture from skin biopsies of normal volunteers and manic-depressive subjects for measurement of isoprenaline-stimulated production of cyclic AMP. Monolayers of fibroblasts in wells were incubated for 3 min with or without 0.5 microM-isoprenaline. The cyclic AMP was isolated by ion-exchange chromatography and quantitated by radioimmunoassay. The isoprenaline-stimulated levels of cyclic AMP in manic-depressive subjects (n = 12) were no different from those in normal volunteers (n = 13). Thus, no evidence was found for abnormal beta-adrenoceptor function in manic-depressive illness.

Association of OPRM1 A118G variant with the relative reinforcing value of nicotine

RATIONALE

The endogenous opioid system has been implicated in substance abuse and response to pharmacotherapies for nicotine and alcohol addiction. We examined (1) the association of the functional OPRM1 A118G variant with the relative reinforcing value of nicotine and (2) the main and interacting effects of the mu-opioid receptor antagonist naltrexone on nicotine reinforcement.

METHODS

In a within-subject, double-blind human laboratory study, 30 smokers of each OPRM1 genotype (A/A vs. A/G or G/G) participated in two experimental sessions following 4 days of orally administered naltrexone 50 mg or placebo. Participants completed a validated assessment of the relative reinforcing value of nicotine. This cigarette choice paradigm assesses self-administration of 0.6 mg nicotine vs. 0.05 mg (denicotinized) cigarettes after a brief period of nicotine abstinence.

RESULTS

The relative reinforcing value of nicotine (number of nicotine cigarette puffs) was predicted by a significant OPRM1 by gender interaction. Among women, the low-activity G allele (A/G and G/G) was associated with a reduced reinforcing value of nicotine; among male smokers, there was no association with genotype. Smokers carrying a G allele were also significantly less likely to differentiate the nicotine vs. denicotinized cigarettes by subjective ratings of satisfaction and strength. No evidence for an effect of naltrexone on nicotine reinforcement was found in the overall sample or in the genotype or gender subgroups.

CONCLUSIONS

This study provides initial evidence for an association of the OPRM1 A118G variant with nicotine reinforcement in women.

Interaction between variation in the D2 dopamine receptor (DRD2) and the neuronal calcium sensor-1 (FREQ) genes in predicting response to nicotine replacement therapy for tobacco dependence

We have previously demonstrated that a functional dopamine D2 receptor promoter variant (DRD2 -141 Ins/Del) predicts response to nicotine replacement therapy (NRT). The present study extends this finding in the same population of 363 NRT-treated subjects, by examining variation in the gene encoding the neuronal calcium sensor-1 protein (FREQ), which functions to regulate D2 receptor desensitization. The results indicate a statistically significant interaction effect of DRD2-141 and FREQ genotypes on abstinence at the end of the NRT treatment phase; 62% of the smokers with at least one copy of the DRD2 -141 Del allele and two copies of the FREQ rs1054879 A allele were abstinent from smoking, compared to 29-38% abstinence rates for other smokers in the trial. This result suggests that the interaction between variation in the DRD2 and FREQ genes, which both encode components of the D2 dopamine receptor signal transduction pathway, impacts the efficacy of NRT.

Confirmation of association between the Val66Met polymorphism in the brain-derived neurotrophic factor (BDNF) gene and bipolar I disorder

Recent studies have indicated that the brain-derived neurotrophic factor (BDNF) gene is involved in the etiology of bipolar disorder (BPD). Two family-based association studies showed that the Val allele of the functional polymorphism Val66Met in the BDNF gene is associated with BPD; however, others could not confirm the results. Here we performed a replication study in an independent sample and tested the hypothesis that the Val66 allele in the BDNF gene confers susceptibility to bipolar I disorder (BPI). Six hundred twenty-one patients with BPI and 998 control subjects were genotyped for the Val66Met polymorphism. All cases and controls were of European descent. All BPI patients had a positive family history of affective disorder. The frequency of the Val allele was significantly increased in BPI patient when compared to controls (chi2 = 4.8; df = 1; P = 0.028; two-sided; OR = 1.22; 95% CI: 1.02-1.47). Results confirm previous findings and suggest that the Val allele increases risk for BPI in patients of European descent. Further studies are necessary to elucidate the involvement of the BDNF gene in the pathophysiology of BPD.

Alternative transcripts and evidence of imprinting of GNAL on 18p11.2

Genetic studies implicating the region of human chromosome 18p11.2 in susceptibility to bipolar disorder and schizophrenia have observed parent-of-origin effects that may be explained by genomic imprinting. We have identified a transcriptional variant of the GNAL gene in this region, employing an alternative first exon that is 5' to the originally identified start site. This alternative GNAL transcript encodes a longer functional variant of the stimulatory G-protein alpha subunit, Golf. The isoforms of Golf display different expression patterns in the CNS and functionally couple to the dopamine D1 receptor when heterologously expressed in Sf9 cells. In addition, there are CpG islands in the vicinity of both first exons that are differentially methylated, a hallmark of genomic imprinting. These results suggest that GNAL, and possibly other genes in the region, is subject to epigenetic regulation and strengthen the case for a susceptibility gene in this region.

The functional mu opioid receptor (OPRM1) Asn40Asp variant predicts short-term response to nicotine replacement therapy in a clinical trial

To determine whether the functional mu-opioid receptor (OPRM1) Asn40Asp variant predicts the comparative efficacy of different forms of NRT, we conducted a clinical trial of transdermal nicotine (TN) vs nicotine nasal spray (NS) in 320 smokers of European ancestry. Smokers carrying the OPRM1 Asp40 variant (n=82) were significantly more likely than those homozygous for the Asn40 variant (n=238) to be abstinent at the end of treatment, and reported less mood disturbance and weight gain. The genotype effect on treatment outcome was most pronounced among smokers receiving TN, particularly during the 21 mg dose phase. Smokers who carry the OPRM1 Asp40 variant are likely to have a favorable response to TN and may benefit from extended therapy with the 21 mg dose.

Association between variation in the human KCNJ10 potassium ion channel gene and seizure susceptibility

PURPOSE

Our research program uses genetic linkage and association analysis to identify human seizure sensitivity and resistance alleles. Quantitative trait loci mapping in mice led to identification of genetic variation in the potassium ion channel gene Kcnj10, implicating it as a putative seizure susceptibility gene. The purpose of this work was to translate these animal model data to a human genetic association study.

METHODS

We used single stranded conformation polymorphism (SSCP) electrophoresis, DNA sequencing and database searching (NCBI) to identify variation in the human KCNJ10 gene. Restriction fragment length polymorphism (RFLP) analysis, SSCP and Pyrosequencing were used to genotype a single nucleotide polymorphism (SNP, dbSNP rs#1130183) in KCNJ10 in epilepsy patients (n = 407) and unrelated controls (n = 284). The epilepsy group was comprised of patients with refractory mesial temporal lobe epilepsy (n = 153), childhood absence (n = 84), juvenile myoclonic (n = 111) and idiopathic generalized epilepsy not otherwise specified (IGE-NOS, n = 59) and all were of European ancestry.

RESULTS

SNP rs#1130183 (C > T) alters amino acid 271 (of 379) from an arginine to a cysteine (R271C). The C allele (Arg) is common with conversion to the T allele (Cys) occurring twice as often in controls compared to epilepsy patients. Contingency analysis documented a statistically significant association between seizure resistance and allele frequency, Mantel-Haenszel chi square = 5.65, d.f. = 1, P = 0.017, odds ratio 0.52, 95% CI 0.33-0.82.

CONCLUSION

The T allele of SNP rs#1130183 is associated with seizure resistance when common forms of focal and generalized epilepsy are analyzed as a group. These data suggest that this missense variation in KCNJ10 (or a nearby variation) is related to general seizure susceptibility in humans.

Candidate genes for anorexia nervosa in the 1p33-36 linkage region: serotonin 1D and delta opioid receptor loci exhibit significant association to anorexia nervosa

Serotonergic and opioidergic neurotransmitter system alterations have been observed in people with eating disorders; the genes for the serotonin 1D receptor (HTR1D) and the opioid delta receptor (OPRD1) are found on chr1p36.3-34.3, a region identified by our group in a linkage analysis of anorexia nervosa (AN). These candidate genes were evaluated for sequence variation and for linkage and association of this sequence variation to AN in family and case : control data sets. Resequencing of the HTR1D locus and a portion of the OPRD1 locus identified novel SNPs and confirmed existing SNPs. Genotype assay development and genotyping of nine SNPs (four at HTR1D and five at OPRD1) was performed on 191 unrelated individuals fulfilling DSM-IV criteria (w/o amenorrhea criterion) for AN, 442 relatives of AN probands and 98 psychiatrically screened controls. Linkage analysis of these candidate gene SNPs with 33 microsatellite markers in families including relative pairs concordantly affected with restricting AN (N=37) substantially increased the evidence for linkage of this region to restricting AN to an NPL score of 3.91. Statistically significant genotypic, allelic, and haplotypic association to AN in the case : control design was observed at HTR1D and OPRD1 with effect sizes for individual SNPs of 2.63 (95% CI=1.21-5.75) for HTR1D and 1.61 (95% CI=1.11-2.44) for OPRD1. Using genotype data on parents and AN probands, three SNPs at HTR1D were found to exhibit significant transmission disequilibrium (P&<0.05). The combined statistical genetic evidence suggests that HTR1D and OPRD1 or linked genes may be involved in the etiology of AN.

Candidate gene analysis of the Price Foundation anorexia nervosa affected relative pair dataset

The eating disorders are severe psychiatric illnesses with significant morbidity and mortality that exhibit statistically significant familial risk and heritability, providing support for a molecular genetic approach toward defining etiological factors. An emerging candidate gene literature has concentrated on serotinergic and dopaminergic candidates. With the financial support of the Price Foundation, a group of investigators initiated an international multi-center collaboration (Price Foundation Collaborative Group) in 1995 to study the genetics of anorexia and bulimia nervosa by collecting and analyzing phenotypes and genotypes of individuals and their relatives affected with eating disorders. The first sample of families collected by this collaborative group, known as the Price Foundation Anorexia Nervosa Affected Relative Pair (AN-ARP) dataset, was ascertained on an proband affected with Anorexia Nervosa (AN), with relative pairs affected with the eating disorders AN, Bulimia Nervosa or Eating Disorders Not Otherwise Specified [1]. Biognosis U.S., Inc. was founded to identify and characterize candidate susceptibility genes for anorexia and bulimia nervosa phenotypes in the Price Foundation eating disorder datasets. During 2000-2001, Biognosis U.S., Inc. developed and implemented a research program with a focus on the analysis of candidate genes nominated by neurochemical characteristics of eating disorder patients [2], serotonergic and dopaminergic candidate gene polymorphisms [3], neuroendocrine regulation of appetite [4], and by a positional hypothesis from a linkage analysis of the AN-ARP dataset [5]. This report reviews the anorexia nervosa candidate gene literature through 2001, the candidate gene research program implemented at Biognosis U.S., Inc. and selected candidate gene findings in the AN-ARP dataset derived from that research program.

Evidence for a susceptibility gene for anorexia nervosa on chromosome 1

Eating disorders, such as anorexia nervosa (AN), have a significant genetic component. In the current study, a genomewide linkage analysis of 192 families with at least one affected relative pair with AN and related eating disorders, including bulimia nervosa, was performed, resulting in only modest evidence for linkage, with the highest nonparametric linkage (NPL) score, 1.80, at marker D4S2367 on chromosome 4. Since the reduction of sample heterogeneity would increase power to detect linkage, we performed linkage analysis in a subset (n=37) of families in which at least two affected relatives had diagnoses of restricting AN, a clinically defined subtype of AN characterized by severe limitation of food intake without the presence of binge-eating or purging behavior. When we limited the linkage analysis to this clinically more homogeneous subgroup, the highest multipoint NPL score observed was 3.03, at marker D1S3721 on chromosome 1p. The genotyping of additional markers in this region led to a peak multipoint NPL score of 3.45, thereby providing suggestive evidence for the presence of an AN-susceptibility locus on chromosome 1p.

Molecular linkage studies of bipolar disorders

OBJECTIVES

To review the reports of linkage findings for bipolar disorder.

METHODS

Literature review of published linkage findings in bipolar disorder.

RESULTS

There are several regions of the human genome that have been implicated repeatedly by independent investigators. These include 4p16, 12q24, 18q22, 18p11, 21q21 and 22q11. Two of these regions (18p11 and 22q11) are also implicated in genome scans of schizophrenia, suggesting that these two distinct nosological categories may share some genetic susceptibility. This hypothesis can only be tested when the underlying genes are identified.

Effects of strain, behavior and age on the self-administration of ethanol, nicotine, cocaine and morphine by two rat strains

Two genetically different strains, Brown Norway rats (BNR) and Wistar Kyoto rats (WKR), with the latter showing higher emotionality and lower plasma stress catecholamine responses, were compared for their voluntary intake of ethanol, nicotine, cocaine and morphine. Younger BNR self-administered the same amounts of all 4 substances as did the younger WKR suggesting a similar genetic basis for all drugs at this age. Older BNR consumed less ethanol and nicotine but equal amounts of cocaine and morphine as compared to older WKR, and older BNR were more sensitive to the effects of ethanol than WKR suggesting a different genetic basis for different drugs at an older age. Forcing both strains to consume one of the drugs did not affect a subsequent voluntary consumption of ethanol and morphine but reduced nicotine intake in WKR and decreased cocaine intake in both strains suggesting that drug use is determined by individual preferences and not drug exposure per se. The behavioral characteristics of both strains coincide only with the self-administration of ethanol and nicotine supporting a possible genetic linkage between anxiety/stress and ethanol and nicotine use.