Philip Gorwood

The A9 allele of the dopamine transporter gene is associated with delirium tremens and alcohol-withdrawal seizure

BACKGROUND The dopamine transporter (DAT) plays a key role in homeostatic regulation of dopaminergic neurotransmission and could thus be involved in the variability of two severe alcohol-withdrawal symptoms, alcohol-withdrawal seizure (AWS) and delirium tremens (DT). Interestingly, an association was found between the DAT gene (9-copy repeat) and the risk for these symptoms in two previous case-control studies. METHODS We reanalyzed the role of the DAT gene in the lifetime risk for AWS and DT in 120 alcohol-dependent patients, taking into account potentially confounding factors. RESULTS Alcohol-dependent patients with the A(9) allele had experienced AWS or DT at least once (odds ratio [OR] = 2.52, p =.03). This association persisted when excluding patients with antisocial personality comorbidity (OR = 3.48, p =.02) or limiting the analysis to older patients (OR = 8.3, p =.0008). CONCLUSIONS This study provides convergent data in favor of a significant role of the DAT gene in the risk for some severe withdrawal symptoms. If further replicated in larger samples, the DAT genetic polymorphism could be one of the factors to be analyzed to further assess the risk of some severe alcohol-withdrawal symptoms.

Association and excess of transmission of a DRD2 haplotype in a sample of French schizophrenic patients.

The gene which codes for dopamine receptor D2 (DRD2) is considered as one of the most relevant candidate genes in schizophrenia. Previous genetic studies focusing on this gene gave conflicting results, potentially because of the differences in methodology (linkage versus association studies), and the different loci analyzed (the DRD2 gene having many polymorphisms). We used a progressive strategy with three different approaches (case/control, haplotype relative risk and transmission disequilibrium test) and investigated two genetic polymorphisms (TaqI B1/B2 and TaqI A1/A2, spanning the coding region of the DRD2 gene) in 50 patients with DSM-IV diagnoses of schizophrenia, in their 100 parents and in 50 healthy, matched controls. Firstly, we found a significant excess of the two alleles (B2 and A2) in the schizophrenic group compared to unaffected controls. Secondly, we found an excess of transmission from the parents to their affected children, using the haplotype relative risk design applied to the B2A2 haplotype. Finally, the transmission disequilibrium test showed evidence for linkage between B2A2 haplotype and schizophrenia. The significant excess of the B2A2 haplotype in schizophrenic patients is specifically observed in a subsample of patients with a disease onset occurring after 20 years of age. As the haplotype contains nearly the entire DRD2 gene, we found convergent evidence in our sample for a significant role of the DRD2 gene in the risk for schizophrenia. This haplotype may be more specifically involved in the disorders onset at a later age in some patients, or, alternatively, may be implicated as a modifying factor acting on age of onset.

5-HT2A gene promoter polymorphism as a modifying rather than a vulnerability factor in anorexia nervosa

The A allele of the 5-HT(2A) gene (-1438A/G polymorphism) has been associated with anorexia nervosa in four studies, but not in three others. One possibility to explain such a discrepancy is that the A allele acts as a modifying rather than a vulnerability allele. To test this hypothesis, we increased our initial sample of 102 trios left open bracket Mol. Psychiatry 7 (2002) 90 right open bracket with 43 new patients with anorexia nervosa and 98 healthy controls. In addition to confirming the absence of association on the global sample of 145 patients, we found that patients with the A allele had a significantly later age at onset of the disease (P = 0.032). Furthermore, the A allele was also transmitted with an older age at onset (P = 0.023) using a quantitative-trait TDT approach. The A allele may thus act as a modifying factor (delaying onset), potentially explaining variations of allele frequency across samples, in which differences in average age at onset are not only possible, but also expected. Taking into account vulnerability genes, but also genes modifying the expression of the disorder, will help to disentangle the complexity of the etiological factors involved in anorexia nervosa.

Negative symptoms of schizophrenia could explain discrepant data on the association between the 5-HT2A receptor gene and response to antipsychotics.

Pharmacogenetic studies assessing the role of 5-HT(2A) receptor gene in antipsychotic efficacy yielded conflicting data. Phenotypical heterogeneity of schizophrenia might explain such discrepancies. For example, negative symptoms are known to reflect severity of illness and to restrain therapeutic response. On this basis, we re-assessed the possible influence of the -1438A/G polymorphism of the 5-HT(2A) receptor gene on the clinical efficacy of atypical antipsychotics with focus on several relevant dimensions. One hundred and sixteen French schizophrenic subjects treated for at least 1 month by atypical antipsychotics were screened for treatment response according to the May and Dencker scale. Gender, age at onset, duration and severity of illness, intensity of negative and positive symptoms at discharge were investigated. The intensity of negative symptoms at discharge was the only variable explaining May and Dencker score (p < 0.001), and was significantly associated with the AA genotype of the -1438A/G polymorphism of the 5-HT(2A) receptor gene (p = 0.03). However, the A allele was not independently associated with refractoriness to atypical antipsychotics. Accordingly, the score reached in the Scale for the Assessment of Negative Symptoms (SANS) appeared as a confounding factor between therapeutic response and the -1438A/G polymorphism of the 5-HT(2A) receptor gene, at least in our sample. This data indicate that negative symptoms are worth being systematically assessed in pharmacogenetic studies aimed at analysing candidate genes in schizophrenia.

The genetics of addiction: alcohol-dependence and D3 dopamine receptor gene.

Alcohol-dependence is a complex phenotype, with behavioral, psychological, pharmacological, medical and social dimensions. Aggregation studies, adoption and twin researches have demonstrated that the vulnerability to alcohol-dependence is at least in part linked to genetic factors, the genetic vulnerability to alcoholism being mainly not substance-specific. There are numerous candidate genes, but the D3 dopamine receptor is specifically located in the limbic area, and in particular in the nucleus accumbens, which are involved in reward and reinforcement behavior. Furthermore, a previous collaborative study showed that homozygosity for the Ball DRD3 locus was more frequently observed in opiate dependent patients with high sensation seeking scores. In this study, we analyzed the distribution of Ball DRD3 polymorphism in a new sample of 131 French male alcoholic-patients (DSM III-R criteria) and 68 healthy controls matched for sex and origins. Although we replicated the higher sensation seeking score in alcohol-dependent patients with comorbid dependence, we found no significant difference in the DRD3 gene polymorphism between controls and alcoholic patients, regardless of sensation seeking score, addictive or psychiatric comorbidity, alcoholism typology, and clinical specificities of alcoholism. There is good evidence that gene coding for the dopamine receptor D3 does not play a major role in the genetic vulnerability to alcoholism.

The DRD2 gene and the risk for alcohol dependence in bipolar patients

The high co-morbidity between bipolar disorder and alcohol dependence may have different explanations, one of them being the existence of common genetic factors for the two disorders. Several candidate genes may be involved but the genes acting in the dopaminergic pathway may be more specifically involved. We have thus tested the role of the gene encoding the D2 dopamine receptor (TaqI A1 allele) in the potentially shared vulnerability to alcohol dependence and bipolar disorder. One hundred and twenty-two French (for at least two generations) patients were recruited on the basis of hospital or outpatient files and were interviewed with the DIGS. The A1 allele frequencies were compared between four groups, namely, with bipolar patients and co-morbid alcohol dependence (N = 21), with bipolar patients without alcohol morbidity (N = 31), with alcohol dependence without mood disorder (N = 35) and unaffected controls (N = 35). The Hardy Weinberg equilibrium for the DRD2 Taq1 A1 genotypes was respected for the sample as a whole, and for each subsample. We observed that 42.9% of control subjects have at least one A1 allele, a frequency which is not significantly different from the one observed in the affected sample as a whole (39.1%), neither from patients with alcohol dependence (37.1%), patients with bipolar disorder (48.4%) nor patients with alcohol dependence and bipolar disorder (28.6%). The regression analysis based on the three variables (bipolar disorder, alcohol dependence and interaction between these two disorders) does not explain the presence of the A1 allele of the DRD2 gene. We thus found no evidence for a significant role of the A1 allele of the D2 dopamine receptor gene in the specific association between bipolar disorder and alcohol dependence in our sample.

Family-based association study of the 5-HT transporter gene and schizophrenia

The gene coding for the 5-HT transporter (5-HTT) is considered as a candidate gene for schizophrenia, because this transporter plays a key role in serotonin neurotransmission. Previous genetic studies focusing on this gene yielded conflicting results, presumably because of stratification biases linked to the case-control association study approach, and the potential genetic and phenotypic heterogeneity of schizophrenia. We investigated the 5-HTTLPR and 17-bp VNTR (variable number of tandem repeats) polymorphisms of this gene in 103 trios using the transmission disequilibrium test. No preferential transmission of either allele of the 17-bp VNTR was observed, but an excess of transmission of the L allele of the 5-HTTLPR polymorphism was detected (p = 0.03). As the haplotype analyses did not improve the strength of the association, our data provide convergent evidence for a significant role of the 5-HTTLPR promoter polymorphism of the 5-HTT gene in the vulnerability to schizophrenia.

Family‐based association study of the serotonin‐6 receptor gene (C267T polymorphism) in schizophrenia

The expression of serotonin type 6 receptor (5‐HT6) in limbic and cortical regions of the brain, and its high affinity for atypical antipsychotics suggest that its encoding gene may play a role in the pathogenesis of schizophrenia. We firstly performed a meta‐analysis of the C267T polymorphism of the 5‐HT6 gene in schizophrenia, based on four different case/control studies, and showed that the allelic distribution is not significantly different between patients and controls, even when taking into account the role of between samples heterogeneity. We then recruited 103 trios (patients with Diognostic and Statistical Manual Mental Disorders, 4th ed. (DSM‐IV) diagnosis of schizophrenia and their parents), and investigated the C267T polymorphism of the 5‐HT6 receptor gene with regard to family‐based association study approach (haplotype relative risk (HRR) and transmission disequilibrium test (TDT)). We found no excess of transmission of one allele from the parents to their affected children, using the HRR (P = 0.60), as well as no evidence for linkage between C267T polymorphism and schizophrenia, using the TDT (P = 0.71). Furthermore, the 267T allele frequency was comparable in the different subgroups defined on age at onset, family history of schizophrenia, treatment response, and subtypes of patients based on positive versus negative predominant symptoms. These data do not support the idea that the 5‐HT6 receptor gene plays a major role in the etiopathogenesis of schizophrenia.

Clinical characteristics of familial versus sporadic alcoholism in a sample of male and female patients.

Presence of a family history of alcoholism may predict clinical characteristics in affected subjects, such as an earlier age at onset. More frequent and severe social maladjustment and somatic complications are also regularly cited for familial alcoholism, although subject to many other confusing factors. We analysed the clinical specificities of 79 alcohol-dependent inpatients according to the absence versus presence of family history of alcoholism. Patients were evaluated for lifetime psychiatric morbidity with the Diagnostic Interview for Genetic Studies (DIGS), for somatic complications with a systematic screening list, and first-degree relatives (N = 428) were assessed with the Family Inventory Schedule and Criteria (FISC). Age at onset and social complications were predicting familial versus sporadic alcoholism, even when considering censored data and/or interaction between variables. But differences became non-significant when excluding patients with antisocial personality. If age at onset effectively appears to be the most informative characteristic for predicting familial versus sporadic alcoholism, it seems that it may be necessary in future studies to systematically take into account antisocial personality diagnosis, because of a probable contamination.

Schizophrénie et génétique : concepts et évidences

Resume La genetique a eu des rapports difficiles avec les sciences humaines, d’abord pressentie par les philosophes, elle fut utilisee en psychiatrie, non pour l’aide de patients reconnus comme vulnerables, mais dans l’idee d’un arret des degenerescences dans la population (theorie de Morel). La frilosite des psychiatres envers ce domaine de recherche peut donc bien se concevoir et s’entendre. Pourtant, la genetique est une voie d’abord puissante et originale dans l’approche de la souffrance psychique. Un certain nombre de malentendus expliquent que les psychiatres (francais notamment, et plus que les patients eux-memes), emettent des reserves sur la recherche en genetique des maladies mentales. Trois concepts souvent mal compris sont ici detailles (le determinisme genetique, l’heritabilite, l’agregation familiale) puis illustres pour la schizophrenie a travers une revue de la litterature des etudes familiales et de quelques genes candidats. Portees et limites de la genetique appliquee a la schizophrenie devraient ainsi etre mieux precises.