Genome-wide association study of pathological gambling

Background

Pathological gambling is a behavioural addiction with negative economic, social, and psychological consequences. Identification of contributing genes and pathways may improve understanding of aetiology and facilitate therapy and prevention. Here, we report the first genome-wide association study of pathological gambling. Our aims were to identify pathways involved in pathological gambling, and examine whether there is a genetic overlap between pathological gambling and alcohol dependence.

Methods

Four hundred and forty-five individuals with a diagnosis of pathological gambling according to the Diagnostic and Statistical Manual of Mental Disorders were recruited in Germany, and 986 controls were drawn from a German general population sample. A genome-wide association study of pathological gambling comprising single marker, gene-based, and pathway analyses, was performed. Polygenic risk scores were generated using data from a German genome-wide association study of alcohol dependence.

Results

No genome-wide significant association with pathological gambling was found for single markers or genes. Pathways for Huntington's disease (P-value = 6.63 × 10−3); 5′-adenosine monophosphate-activated protein kinase signalling (P-value = 9.57 × 10−3); and apoptosis (P-value = 1.75 × 10−2) were significant. Polygenic risk score analysis of the alcohol dependence dataset yielded a one-sided nominal significant P-value in subjects with pathological gambling, irrespective of comorbid alcohol dependence status.

Conclusions

The present results accord with previous quantitative formal genetic studies which showed genetic overlap between non-substance- and substance-related addictions. Furthermore, pathway analysis suggests shared pathology between Huntington's disease and pathological gambling. This finding is consistent with previous imaging studies.

The effect of 5-HTTLPR and a serotonergic multi-marker score on amygdala, prefrontal and anterior cingulate cortex reactivity and habituation in a large, healthy fMRI cohort

Major depressive disorder (MDD) is characterized by low mood for at least two weeks. Impaired emotion regulation has been suggested to be the consequence of dysfunctional serotonergic regulation of limbic and prefrontal regions, especially the amygdala, the anterior cingulate cortex (ACC) and the prefrontal cortex (PFC). The impact of genetic variation on brain function can be investigated with intermediate phenotypes. A suggested intermediate phenotype of MDD is emotion recognition: The 5-HTTLPR polymorphism of SLC6A4 as well as other serotonergic genes have been associated with amygdala and prefrontal function during emotion recognition. Previously, it has been suggested that habituation is a more reliable index of emotion recognition than functional activation. We examined the relationship of genes involved in serotonergic signaling with amygdala as well as prefrontal functional activation and habituation during an emotion recognition task in 171 healthy subjects. While effects of 5-HTTLPR and of a serotonergic multi-marker score (5-HTTLPR, TPH1(rs1800532), TPH2(rs4570625), HTR1A(rs6295) and HTR2A(rs6311)) on amygdala activation did not withstand correction for multiple regions of interest, we observed a strong correlation of the multi-marker score and habituation in the amygdala, DLPFC, and ACC. We replicated a well-studied intermediate phenotype for association with 5-HTTLPR and provided additional evidence for polygenic involvement. Furthermore, we showed that task habituation may be influenced by genetic variation in serotonergic signaling, particularly by a serotonergic multi-marker score. We provided preliminary evidence that PFC activation is an important intermediate phenotype of MDD. Future studies are needed to corroborate the results in larger samples.

Genome-wide association of mood-incongruent psychotic bipolar disorder

Mood-incongruent psychotic features (MICP) are familial symptoms of bipolar disorder (BP) that also occur in schizophrenia (SZ), and may represent manifestations of shared etiology between the major psychoses. In this study we have analyzed three large samples of BP with imputed genome-wide association data and have performed a meta-analysis of 2196 cases with MICP and 8148 controls. We found several regions with suggestive evidence of association (P<10(-6)), although no marker met genome-wide significance criteria. The top associations were on chromosomes: 6q14.2 within the PRSS35/SNAP91 gene complex (rs1171113, P=9.67 × 10(-8)); 3p22.2 downstream of TRANK/LBA1 (rs9834970, P=9.71 × 10(-8)); and 14q24.2 in an intron of NUMB (rs2333194, P=7.03 × 10(-7)). These associations were present in all three samples, and both rs1171113 and rs2333194 were found to be overrepresented in an analysis of MICP cases compared with all other BP cases. To test the relationship of MICP with SZ, we performed polygenic analysis using the Psychiatric GWAS Consortium SZ results and found evidence of association between SZ polygenes and the presence of MICP in BP cases (meta-analysis P=0.003). In summary, our analysis of the MICP phenotype in BP has provided suggestive evidence for association of common variants in several genes expressed in the nervous system. The results of our polygenic analysis provides support for a modest degree of genetic overlap between BP with MICP and SZ, highlighting that phenotypic correlations across syndromes may be due to the influence of polygenic risk factors.

Linkage disequilibrium mapping at DAT1, DRD5 and DBH narrows the search for ADHD susceptibility alleles at these loci

Abnormalities in dopaminergic neurotransmission are now accepted as factors in predisposing to ADHD. Evidence of associations between dopamine transporter gene polymorphism and ADHD was first reported by Cook et al. We confirmed the DAT1 association and also identified two additional susceptibility loci at the DRD5 and DBH. Notably, none of the associated variants at these three genes are known to be expressed. Other variants within or closely mapped to the associated alleles are likely to be relevant. In this investigation, we analyse additional markers creating a high-density map across and flanking these genes, and measure intermarker linkage disequilibrium (LD). None of the newly examined markers were more strongly associated with ADHD. At DAT1, the pattern of intermarker LD and haplotype association with the phenotype between exon 9 and the 3' of the gene suggests that the functional variant at DAT1 may be located to this region. For DRD5, three markers, covering a region of approximately 68 kb including the single DRD5 exon are all associated with disease, and thus do not provide localizing information. However, the data for DBH point to a region close to the centre of the gene. Correlation between D' and physical distance was observed between markers at DAT1 and DRD5 for distances less than 50 kb. This was not the case for DBH, where LD breakdown was observed between the intron 5 and intron 9 polymorphisms although they are only 9 kb apart. Further genetic analysis is unlikely to refine the location of susceptibility variants and functional assessment of variants within associated regions is required.

Analysis of the TSC2 gene in human medulloblastoma

Medulloblastoma (MB) represents the most frequent malignant brain tumor of childhood. Recent studies have shown that deregulation of developmental control genes may play an important role in its pathogenesis. Tuberous sclerosis is associated with hamartomas and cortical tubers, consisting of both glial and neuronal cellular components. MBs can also show markers of these lineages, raising the question of the potential involvement of TSC genes in these malignant tumors. Here we investigated tuberous sclerosis 2 (TSC2), one of the two genes responsible for tuberous sclerosis, in sporadic MBs. We analyzed MBs for allelic losses at the TSC2 locus and for the frequency of a polymorphism first described in gangliogliomas. Sixty-eight MBs were examined for this polymorphism located in intron 4, 3 base pairs 5' to the first coding nucleotide of exon 5. The distribution of the alleles was significantly different in MBs as compared to 208 control samples, (P=0.0017, Chi-square test). In MBs the frequency of the rare allele (A2) was 0.184 (18.4%), whereas in the control group it occurred in a frequency of 8.7%. Microsatellite analysis of the TSC2 region in 50 tumors did not identify allelic losses. TSC2 mRNA transcript was detectable via reverse transcription-PCR in all tumors as well as in normal cerebellum. Northern blot analysis of an MB cell line homozygous for the rare allele of the polymorphism and two other cell lines homozygous for the frequent allele revealed normal splicing patterns and normal expression levels of the TSC2 transcript. These findings may indicate that the presence of the rare TSC2 allele is associated with a predisposition for the development of MBs.

Tryptophan hydroxylase polymorphism and suicidality in unipolar and bipolar affective disorders: a multicenter association study

BACKGROUND

Being the rate-limiting enzyme in the biosynthesis of serotonin, the tryptophan hydroxylase gene (TPH) has been considered a possible candidate gene in bipolar and unipolar affective disorders (BPAD and UPAD). Several studies have investigated the possible role of TPH polymorphisms in affective disorders and suicidal behavior.

METHODS

The TPH A218C polymorphism has been investigated in 927 patients (527 BPAD and 400 UPAD) and their matched healthy control subjects collected within the European Collaborative Project on Affective Disorders.

RESULTS

No difference of genotype distribution or allele distribution was found in BPAD or UPAD. No statistically significant difference was observed for allele frequency and genotypes counts. In a genotype per genotype analysis in UPAD patients with a personal history of suicide attempt, the frequency of the C-C genotype (homozygosity for the short allele) was lower in UPAD patients (24%) than in control subjects (43%) (chi(2) = 4.67, p =.03). There was no difference in allele or genotype frequency between patients presenting violent suicidal behavior (n = 48) and their matched control subjects.

CONCLUSIONS

We failed to detect an association between the A218C polymorphism of the TPH gene and BPAD and UPAD in a large European sample. Homozygosity for the short allele is significantly less frequent in a subgroup of UPAD patients with a history of suicide attempt than in control subjects.

Schizophrenia and the serotonin transporter gene

A case control study was conducted among cases with schizophrenia (DSM IV criteria) and screened adult controls from three cohorts. Bi-allelic polymorphisms in the promoter region of the serotonin transporter gene (5-HTT) were examined in conjunction with those of the serotonin 5-HT2a receptor (HTR2). No significant association with 5-HTT was detected among US Caucasians (n = 207), African-Americans (n = 84) or Caucasians from Sweden (n = 221). However, survival analysis suggested an association with the age at onset among the Swedish cases. The association should be considered tentative as it was not evident in the smaller US samples. The following exploratory analyses among the US samples were also not significant: associations with subgroups of patients based on familiality or response to medications, or altered risk due to the joint effects of 5-HTT and HTR2 genotypes.

An association study of a neurotrophin-3 (NT-3) gene polymorphism with schizophrenia

Since abnormalities of brain development play a role in the aetiology of schizophrenia, growth factors, known to play a role in neurodevelopment, such as neurotrophin-3 (NT-3), are therefore candidate genes for this disorder. The A3/147 bp allele of a dinucleotide repeat polymorphism in the promoter region of the NT-3 gene has been reported as occurring more frequently in a sample of Japanese schizophrenics compared to controls. We have determined the frequency of alleles of this polymorphism in 175 Caucasian schizophrenic patients and 147 control subjects. The patient and control samples showed no significant deviation from Hardy-Weinberg equilibrium and, in a test of allalleles, the patients and controls did not differ significantly in allele frequencies. However, the male schizophrenics were more likely than male controls to have the A3/147 bp allele (P = 0.029).

Linkage studies of bipolar disorder in the region of the Darier's disease gene on chromosome 12q23-24.1

We have recently described a family in which there is cosegregation of major affective disorder with Darier's disease and have mapped this autosomal dominant skin disorder to 12q23-q24.1. This has provided an interesting candidate region for genetic studies of bipolar disorder. We have studied the segregation of seven markers spanning the Darier's disease locus in 45 bipolar disorder pedigrees and found modest evidence in support of linkage under heterogeneity for 5 of these markers. Nonparametric analyses were suggestive of linkage with a marker at the gene encoding a secretory form of phospholipase A2. Our sample has relatively low power to detect linkage under heterogeneity and independent researchers should examine markers from this region in further samples of bipolar pedigrees.

Desbuquois syndrome: three further cases and review of the literature

We report three further patients with similar clinical signs to those described by Desbuquois et al. (Desbuquois G, Grenier B, Michel J, Rossignol C (1966): Arch Fr Pédiatr 23; 573-587) Two of the patients were born to consanguineous parents, confirming autosomal recessive inheritance of this condition. The patients presented with micromelic short stature, flat midface, irregular ossification of the vertebral bodies and an advanced bone age.