Norbert Dahmen

Genome-wide Association Study of Alcohol Dependence

CONTEXT Alcohol dependence is a serious and common public health problem. It is well established that genetic factors play a major role in the development of this disorder. Identification of genes that contribute to alcohol dependence will improve our understanding of the mechanisms that underlie this disorder. OBJECTIVE To identify susceptibility genes for alcohol dependence through a genome-wide association study (GWAS) and a follow-up study in a population of German male inpatients with an early age at onset. DESIGN The GWAS tested 524,396 single-nucleotide polymorphisms (SNPs). All SNPs with P < 10(-4) were subjected to the follow-up study. In addition, nominally significant SNPs from genes that had also shown expression changes in rat brains after long-term alcohol consumption were selected for the follow-up step. SETTING Five university hospitals in southern and central Germany. PARTICIPANTS The GWAS included 487 male inpatients with alcohol dependence as defined by the DSM-IV and an age at onset younger than 28 years and 1358 population-based control individuals. The follow-up study included 1024 male inpatients and 996 age-matched male controls. All the participants were of German descent. MAIN OUTCOME MEASURES Significant association findings in the GWAS and follow-up study with the same alleles. RESULTS The GWAS produced 121 SNPs with nominal P < 10(-4). These, together with 19 additional SNPs from homologues of rat genes showing differential expression, were genotyped in the follow-up sample. Fifteen SNPs showed significant association with the same allele as in the GWAS. In the combined analysis, 2 closely linked intergenic SNPs met genome-wide significance (rs7590720, P = 9.72 x 10(-9); rs1344694, P = 1.69 x 10(-8)). They are located on chromosome region 2q35, which has been implicated in linkage studies for alcohol phenotypes. Nine SNPs were located in genes, including the CDH13 and ADH1C genes, that have been reported to be associated with alcohol dependence. CONCLUSIONS This is the first GWAS and follow-up study to identify a genome-wide significant association in alcohol dependence. Further independent studies are required to confirm these findings.

Differences between Human Plasma and Serum Metabolite Profiles

Background Human plasma and serum are widely used matrices in clinical and biological studies. However, different collecting procedures and the coagulation cascade influence concentrations of both proteins and metabolites in these matrices. The effects on metabolite concentration profiles have not been fully characterized. Methodology/Principal Findings We analyzed the concentrations of 163 metabolites in plasma and serum samples collected simultaneously from 377 fasting individuals. To ensure data quality, 41 metabolites with low measurement stability were excluded from further analysis. In addition, plasma and corresponding serum samples from 83 individuals were re-measured in the same plates and mean correlation coefficients (r) of all metabolites between the duplicates were 0.83 and 0.80 in plasma and serum, respectively, indicating significantly better stability of plasma compared to serum (p = 0.01). Metabolite profiles from plasma and serum were clearly distinct with 104 metabolites showing significantly higher concentrations in serum. In particular, 9 metabolites showed relative concentration differences larger than 20%. Despite differences in absolute concentration between the two matrices, for most metabolites the overall correlation was high (mean r = 0.81±0.10), which reflects a proportional change in concentration. Furthermore, when two groups of individuals with different phenotypes were compared with each other using both matrices, more metabolites with significantly different concentrations could be identified in serum than in plasma. For example, when 51 type 2 diabetes (T2D) patients were compared with 326 non-T2D individuals, 15 more significantly different metabolites were found in serum, in addition to the 25 common to both matrices. Conclusions/Significance Our study shows that reproducibility was good in both plasma and serum, and better in plasma. Furthermore, as long as the same blood preparation procedure is used, either matrix should generate similar results in clinical and biological studies. The higher metabolite concentrations in serum, however, make it possible to provide more sensitive results in biomarker detection.

The catechol-O-methyltransferase Val108/158Met polymorphism affects short-term treatment response to mirtazapine, but not to paroxetine in major depression.

The catechol-O-methyltransferase (COMT) is a major degrading enzyme in the metabolic pathways of catecholaminergic neurotransmitters such as dopamine and norepinephrine. This study investigated whether the functionally relevant Val108/158Met gene variant is associated with differential antidepressant response to mirtazapine and/or paroxetine in 102 patients with major depression (DSM-IV criteria) participating in a randomized clinical trial with both drugs. In patients treated with mirtazapine, but not paroxetine, allelic variations in the COMT gene were associated with differential response. COMTVAL/VAL and COMTVAL/MET genotype carriers showed a better response than COMTMET/MET-bearing patients in the mirtazapine group. Moreover, carriers of the COMTVAL/VAL or COMTVAL/MET genotype had significantly greater HAMD-17 (Hamilton Rating Scale for Depression 17 item version) score reductions than COMTMET/MET homozygotes from week 2 to 6, respectively, in the mirtazapine group. Time course of response and antidepressant efficacy of mirtazapine, but not paroxetine, seem to be influenced in a clinically relevant manner by this allelic variation within the COMT gene.

Detection Times for Urinary Ethyl Glucuronide and Ethyl Sulfate in Heavy Drinkers during Alcohol Detoxification

AIMS Ethyl glucuronide (EtG) and ethyl sulfate (EtS) are conjugated ethanol metabolites formed in low amounts after alcohol consumption. Compared with ethanol, EtG and EtS are excreted in urine for a prolonged time, making them useful as sensitive alcohol biomarkers. This study determined the detection times for EtG and EtS in alcoholic patients undergoing alcohol detoxification. METHODS Alcohol-dependent patients (n = 32) with an initial alcohol concentration >or=1 g/L based on breath testing were followed during detoxification. Urine samples for determination of EtG, EtS, ethanol and creatinine were collected on admission to the hospital and thereafter once daily for several days. EtG and EtS measurements were performed by liquid chromatography-mass spectrometry (LC-MS) and EtG also using an immunochemical assay (DRI-EtG EIA, ThermoFisher/Microgenics). RESULTS The detection time for urinary EtG was weakly correlated (r = 0.434, P = 0.013) with the initial alcohol concentration (range 1.0-3.4 g/L). For EtG, the individual time range until return to below the applied cut-off limit (<0.5 mg/L) was approximately 40-130 h (median 78) with a similar time course observed for EtS. After correction for urine dilution, the time until an EtG/creatinine ratio <0.5 mg/g was approximately 40- 90 h (median 65). The detection times after an estimated zero ethanol concentration were approximately 30-110 h (median 66) for EtG and approximately 30- 70 h (median 56) for EtG/creatinine. The EtG results by LC-MS and the immunoassay were in good agreement. CONCLUSIONS During alcohol detoxification, EtG and EtS remained detectable in urine for several days. The detection times showed wide inter-individual variations, also after adjusting values for urine dilution and to the estimated times for a completed ethanol elimination.

Increased prevalence of obesity in narcoleptic patients and relatives

Abstract Increased Body Mass Indices (BMIs), increased prevalences of non insulin-dependent diabetes and sleep apnoe syndrome have been reported to be associated with narcolepsy. Our objective was to explore and possibly confirm the association of narcolepsy and increased BMI. In addition, we addressed the question whether increased BMIs also occur in relatives of narcoleptic patients. Together with narcolepsy-related clinical parameters we measured body weight and height of 132 narcoleptic patients who agreed to participate in our narcolepsy research program. In addition, 52 first degree relatives of 22 index patients, mostly from multiplex families, were included in the study. Data were compared to published general population surveys, recently conducted in Germany and Switzerland as well as to collective of 104 psychiatric inpatients. Narcoleptic patients had significantly increased BMIs in comparison to general populations or psychiatric controls. BMIs of first degree relatives were lower than those of index patients but significantly higher than those found in the general population. BMIs were not related to symptom severity or to medication status. Thus, the elevated BMIs appeared not to be secondary to behavioral consequences of narcolepsy but may reflect a trait at least partially common to index patients and relatives.

Association of a MAOA gene variant with generalized anxiety disorder, but not with panic disorder or major depression

This study was conducted to detect a possible association of a T941G single nucleotide polymorphism (SNP) in the monoamine oxidase A (MAOA) gene with generalized anxiety disorder (GAD), panic disorder (PD), or major depression (MD). Fifty GAD patients (34 females and 16 males), 38 PD patients (21 females and 17 males), and 108 MD patients (80 females and 28 males) were included. The comparison group consisted of 276 (132 females and 144 males) unrelated healthy individuals. The 941T allele was over‐represented in patients suffering from GAD (χ2 = 6.757; df = 1; P < 0.01, not corrected for multiple testing) when compared to healthy volunteers. No association was observed in MD or PD. This is the first study specifically analyzing the MAOA G941T polymorphism in GAD and thus needs to be replicated in an independent sample. However, the results are in line with previous data suggesting an association between the MAOA locus and regulation of complex human behavior.

Systematic Analysis of Glutamatergic Neurotransmission Genes in Alcohol Dependence and Adolescent Risky Drinking Behavior

CONTEXT Glutamatergic neurotransmission is implicated in alcohol-drinking behavior in animal models. OBJECTIVE To investigate whether genetic variations in glutamatergic neurotransmission genes, which are known to alter alcohol effects in rodents, contribute to the genetic basis of alcoholism in humans. DESIGN Association analysis of alcohol dependence and haplotype-tagging single nucleotide polymorphisms (SNPs) covering 10 glutamatergic genes. Resequencing of functional domains of these genes identified 204 SNPs. Haplotypes with a frequency of 5% or greater could be discriminated by 21 haplotype-tagging SNPs analyzed for association in 2 independent samples of alcohol-dependent adult patients and controls as well as adolescent trios. SETTING Four university medical centers in the south of Germany. PARTICIPANTS One thousand three hundred thirty-seven patients and 1555 controls (study 1: 544 patients, 553 controls; study 2: 793 patients, 1002 controls). One hundred forty-four trios of 15-year-old adolescents assessed for risky drinking behavior. MAIN OUTCOME MEASURES Genotype profiles for GLAST; N-methyl-d-aspartate-receptor subunits NR1, NR2A, and NR2B; MGLUR5; NNOS; PRKG2; CAMK4; the regulatory subunit of PI3K; and CREB were analyzed for association with alcohol dependence using multivariate statistical analysis. Risky adolescent drinking was tested using the transmission disequilibrium test. RESULTS Analysis of study 1 revealed that NR2A and MGLUR5 have the greatest relevance for human alcohol dependence among the genes selected with odds ratios of 2.35 and 1.69, respectively. Replication analysis in study 2 confirmed an association of alcohol dependence with NR2A (odds ratio, 2.01) but showed no association with MGLUR5. Combined analysis of study 1 and study 2 exhibited a more significant association on the Cochran-Mantel-Haenszel test (P < .001) for NR2A; NR2A was associated with positive family history, early onset of alcoholism, and maximum number of drinks in adults as well as risky drinking patterns in adolescents. CONCLUSION Genetic variations in NR2A have the greatest relevance for human alcohol dependence among the glutamatergic genes selected for their known alteration of alcohol effects in animal models.

Metabolic Profiling Reveals Distinct Variations Linked to Nicotine Consumption in Humans — First Results from the KORA Study

Exposure to nicotine during smoking causes a multitude of metabolic changes that are poorly understood. We quantified and analyzed 198 metabolites in 283 serum samples from the human cohort KORA (Cooperative Health Research in the Region of Augsburg). Multivariate analysis of metabolic profiles revealed that the group of smokers could be clearly differentiated from the groups of former smokers and non-smokers. Moreover, 23 lipid metabolites were identified as nicotine-dependent biomarkers. The levels of these biomarkers are all up-regulated in smokers compared to those in former and non-smokers, except for three acyl-alkyl-phosphatidylcholines (e.g. plasmalogens). Consistently significant results were further found for the ratios of plasmalogens to diacyl-phosphatidylcolines, which are reduced in smokers and regulated by the enzyme alkylglycerone phosphate synthase (alkyl-DHAP) in both ether lipid and glycerophospholipid pathways. Notably, our metabolite profiles are consistent with the strong down-regulation of the gene for alkyl-DHAP (AGPS) in smokers that has been found in a study analyzing gene expression in human lung tissues. Our data suggest that smoking is associated with plasmalogen-deficiency disorders, caused by reduced or lack of activity of the peroxisomal enzyme alkyl-DHAP. Our findings provide new insight into the pathophysiology of smoking addiction. Activation of the enzyme alkyl-DHAP by small molecules may provide novel routes for therapy.

The HTR1B 861G>C receptor polymorphism among patients suffering from alcoholism, major depression, anxiety disorders and narcolepsy

The HTR1B receptor gene has been linked to antisocial alcoholism in a Finnish population and an American Indian tribe [Lappalainen et al. , Arch. Gen. Psychiatry, 55 (1998) 989]. Using a candidate gene approach, we genotyped 209 patients with alcoholism, 108 patients with major depression, 32 patients with panic disorder, 50 patients with generalized anxiety disorder, 58 patients with narcolepsy and 74 healthy volunteers for the HTR1B 861G>C polymorphism. There was a higher frequency of the HTR1B 861G alleles among the alcohol-dependent patients as compared to the control subjects (chi(2)=4.02, d.f.=2, P=0.04). However, the association resulted from higher frequencies of the opposite alleles (HTR1B 861G), as originally reported by Lappalainen et al. (1998). Although the association in our study might be due to a type I error, the higher degree of HTR1B allele sharing within both populations could also argue for another alcoholism-relevant gene within the proximity of the HTR1B gene on human chromosome 6.

Increased frequency of migraine in narcoleptic patients: a confirmatory study

Previously we have reported an increased prevalence of migraine in narcoleptic patients. Because of the theoretical and clinical implications of this finding we recruited an independent new study sample of 100 patients with proven narcolepsy and conducted a structured 26-item interview based on the international diagnostic criteria for headache disorders, the Kiel Headache Questionnaire. Narcolepsy symptoms were measured by means of the Stanford Centre for Narcolepsy Sleep Inventory. Migraine prevalence was twofold to fourfold increased in the narcoleptic patients and amounted to 44.4% in women and 28.3% in men. The onset of narcolepsy symptoms was 12.3 ± 11.4 years before the onset of migraine symptoms. The results might be regarded as indicative of a common pathophysiological pathway relevant to both of the two disorders.