Ethnicity-independent genetic basis of functional psychoses: a genotype-to-phenotype approach

Case-control pharmacogenetic study of HCN1/HCN2 variants and genetic generalized epilepsies

Epilepsy is a common complex neurological disorder, and some forms are resistant to drug treatment. The HCN1/HCN2 genes encode hyperpolarization-activated cyclic nucleotide-gated channels, which play important roles in the electrophysiology of neurons. We investigated the association between HCN1/HCN2 variants and drug resistance or the risk of genetic generalized epilepsies (GGEs). We used matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to assess nine variants of HCN1/HCN2 in 284 healthy participants and 483 GGEs (279 drug-responsive, 204 drug-resistant). Frequencies of HCN2 rs7255568 and rs3752158 G alleles differed in GGEs and in controls (P = .039, P = .027, respectively). The frequency of HCN2 haplotype (CAC) was higher in patients than controls (P = .046). The frequency of the HCN1 rs10462087 CC+CT genotype was lower in patients with childhood absence epilepsy (CAE) than controls (P = .047). Rs7255568 was associated with the risk of CAE (P = .028) and juvenile myoclonic epilepsy (JME) (P = .02). Rs3752158 was associated with the risk of generalized tonic-clonic seizures, JME, and febrile seizures (all P < .05). The frequency of the HCN2 haplotype (CAC) was higher in patients with JME (P = .015) and in those with febrile seizures (P = .024) than in controls. No significant association was found between HCN1/HCN2 alleles, genotypes or haplotypes, and drug resistance in patients. After Bonferroni's multiple comparisons correction, only the HCN2 rs3752158 C allele and GC+CC genotype frequencies in patients with JME were higher than those in controls (19.2% vs 11.6%, odds ratio (OR) = 1.71, 95% CI = 1.18-2.32), P = .004 < 0.05/9; 36% vs 22.2%, OR = 1.62(1.18-2.23), P = .003 < 0.05/9). Our study suggests that HCN2 rs3752158 is involved in the susceptibility to JME.

Differential contribution of genetic variation in multiple brain nicotinic cholinergic receptors to nicotine dependence: recent progress and emerging open questions

Nicotine dependence (ND), a major public health challenge, is a complex, multifactorial behavior, in which both genetic and environmental factors have a role. Brain nicotinic acetylcholine receptor (nAChR)-encoding genes are among the most prominent candidate genes studied in the context of ND, because of their biological relevance as binding sites for nicotine. Until recently, most research on the role of nAChRs in ND has focused on two of these genes (encoding the alpha4- and beta2-subunits) and not much attention has been paid to the possible contribution of the other nine brain nAChR subunit genes (alpha2-alpha3, alpha5-alpha7, alpha9-alpha10, beta3-beta4) to the pathophysiology and genetics of ND. This situation has changed dramatically in the last 2 years during which intensive research had addressed the issue, mainly from the genetics perspective, and has shown the importance of the CHRNA5-CHRNA3-CHRNB4 and CHRNA6-CHRNB3 loci in ND-related phenotypes. In this review, we highlight recent findings regarding the contribution of non-alpha4/beta2-subunit containing nAChRs to ND, based on several lines of evidence: (1) human genetics studies (including linkage analysis, candidate-gene association studies and whole-genome association studies) of several ND-related phenotypes; (2) differential pharmacological and biochemical properties of receptors containing these subunits; (3) evidence from genetically manipulated mice; and (4) the contribution of nAChR genes to ND-related personality traits and neurocognitive profiles. Combining neurobiological genetic and behavioral perspectives, we suggest that genetic susceptibility to ND is not linked to one or two specific nAChR subtype genes but to several. In particular, the alpha3, alpha5-6 and beta3-4 nAChR subunit-encoding genes may play a much more pivotal role in the neurobiology and genetics of ND than was appreciated earlier. At the functional level, variants in these subunit genes (most likely regulatory) may have independent as well as interactive contributions to the ND phenotype spectrum. We address methodological challenges in the field, highlight open questions and suggest possible pathways for future research.

Modeling activation of inflammatory response system: a molecular-genetic neural network analysis

Significant alterations of T-cell function, along with activation of the inflammatory response system, appear to be linked not only to treatment-resistant schizophrenia, but also to functional psychoses and mood disorders. Because there is a relatively high comorbidity between rheumatoid arthritis (RA), schizophrenia and major depression, the question arises whether there is a common, genetically modulated inflammatory process involved in these disorders. On the basis of three family studies from the U.S. and Europe which were ascertained through an index case suffering from RA (599 nuclear families, 1868 subjects), we aimed to predict the inter-individual variation of autoantibody IgM levels, as an unspecific indicator of inflammatory processes, through molecular-genetic factors. In a three-stage strategy, we first used nonparametric linkage (NPL) analysis to construct an initial configuration of genomic loci showing a sufficiently high NPL score in all three populations. This initial configuration was then modified by iteratively adding or removing genomic loci such that genotype-phenotype correlations were improved. Finally, neural network analysis (NNA) was applied to derive classifiers that predicted the phenotype from the multidimensional genotype. Our analysis led to an activation model that predicted individual IgM levels from the subjects' multidimensional genotypes very reliably. This allowed us to use the activation model for an analysis of the DNA of an existing sample of 1003 psychiatric patients in order to test, in a first approach, whether a deviant, genetically modulated inflammatory process is involved in the pathogenesis of major psychiatric disorders.

Mutation analysis of the hyperpolarization-activated cyclic nucleotide-gated channels HCN1 and HCN2 in idiopathic generalized epilepsy

Hyperpolarization-activated cyclic nucleotide-gated (HCN1-4) channels play an important role in the regulation of neuronal rhythmicity. In the present study we describe the mutation analysis of HCN1 and HCN2 in 84 unrelated patients with idiopathic generalized epilepsy (IGE). Several functional variants were identified including the amino acid substitution R527Q in HCN2 exon 5. HCN2 channels containing the R527Q variant demonstrated a trend towards a decreased slope of the conductance-voltage relation. We also identified a variant in the splice donor site of HCN2 exon 5 that results in the formation of a cryptic splice donor. In HCN1, the amino acid substitution A881T was identified in one sporadic IGE patient but was not observed in 510 controls. Seven variants were examined further in a case-control association study consisting of a larger cohort of IGE patients. Further studies are warranted to more clearly establish the contribution of HCN1 and HCN2 dysfunction to the genetic variance of common IGE syndromes.

ADHS - Indikation für psychoanalytische Behandlungen? Einige klinische, konzeptuelle und empirische Überlegungen ausgehend von der Frankfurter Präventionsstudie

Based on clinical experiences, results of the Frankfurt Prevention Study and arguments taken from a current interdisciplinary dialogue between psychoanalysis and neurobiology the authors discuss that Attention Deficit Hyperactivity Disorder (ADHD) always has to be understood as a product of complex interactions of (mostly unconscious) idiosyncratic, biographical, relational, institutional, societal as well as neurobiological, neurophysiological, and genetical factors. This is one reason why the authors think that psychoanalysis with its unique conceptualizations to understand psychic realities as products of such a complex intertwining of unconscious and reality factors, taking into account biological as well as societal roots of human behavior, could be regarded as one of the best available psychotherapeutic approach nowadays which is capable to deal theoretically and therapeutically with children suffering from ADHD. Psychoanalysis offers an alternative (with longlasting positive results) to exclusive treatments with psychostimulants. This thesis is discussed by short case studies illustrating 7 subgroups of children with very different inner conflicts and fantasies all being subsumed under the ADHD diagnosis in DSM-IV.

Lack of evidence of an allelic association of a functional GABRB3 exon 1a promoter polymorphism with idiopathic generalized epilepsy

PURPOSE

Mutation screening and linkage disequilibrium mapping of the gene encoding the GABA(A) beta(3) subunit (GABRB3) identified a common genetic variant in the exon 1a promoter region (C-allele of rs4906902) which displayed a reduced transcriptional activity and showed a strong allelic association with childhood absence epilepsy (CAE). The present population-based association study tested whether the C-allele of rs4906902 confers susceptibility to CAE or other common syndromes of idiopathic generalized epilepsy (IGE) in a German sample.

METHODS

Seven hundred and eighty unrelated German IGE patients (250 CAE, 123 juvenile absence epilepsy, 303 juvenile myoclonic epilepsy (JME), 104 epilepsy with generalized tonic-clonic seizures on awakening) and 559 healthy population controls were genotyped for the single nucleotide polymorphism (SNP) rs4906902.

RESULTS

The frequency of the risk-conferring C-allele did not differ significantly between CAE patients (f(C)=0.190) and controls (f(C)=0.183; P=0.376, one-tailed). Similarly, no evidence for an allelic association was found for 373 patients with idiopathic absence epilepsy, 303 JME patients, and the entire IGE sample (P>0.77, two-tailed).

CONCLUSION

Our study failed to replicate an association of the common GABRB3 exon 1a promoter SNP rs4906902 with CAE. Moreover, the present results do not provide evidence that the common functional C-variant confers a substantial epileptogenic effect to a broad spectrum of IGE syndromes in the German population.

Allelic association of a truncation mutation of the KCNMB3 gene with idiopathic generalized epilepsy

The gene encoding the beta3-subunit regulatory subunit (KCNMB3) of large conductance calcium-sensitive potassium (BK) channels represents a positional and functional candidate gene for idiopathic generalized epilepsy (IGE). A single base pair deletion in exon 4 of KCNMB3 (delA750) alters/truncates the terminal 21 amino acids of the 3-subunit and affects channel inactivation of the beta3b-isoform. The present association study tested whether the KCNMB3 delA750 mutation confers susceptibility to common IGE syndromes. In total, 592 unrelated German IGE patients and 462 healthy population controls were genotyped for the delA750 truncation mutation. The frequency of the delA750 mutation was significantly increased in the IGE patients (7.9%) compared to that in the controls (5.5%; P = 0.016, one-sided; OR = 1.52; 95%-CI: 1.05-2.21). The increase of the delA750 frequency was accentuated in 312 patients exhibiting typical absence seizures (8.8%, P = 0.005, one-sided; OR = 1.72; 95%-CI: 1.13-2.62) relatively to that observed in the 237 patients with myoclonic seizures on awakening (7.2%; P = 0.11, one-sided; OR = 1.36; 95%-CI: 0.85-2.19), when compared with controls. The present results suggest that the functional KCNMB3 beta3b-truncation confers a common epileptogenic effect preferentially to the ictogenesis of typical absence seizures.

Confirmatory evidence for an association of the connexin-36 gene with juvenile myoclonic epilepsy

Juvenile myoclonic epilepsy (JME) is a genetically determined common subtype of idiopathic generalized epilepsy. Recently, linkage of JME to the chromosomal region 15q14, as well as an allelic and genotypic association between the synonymous coding single nucleotide polymorphism c.588C>T (dbSNP: rs3743123, S196S) of the positional candidate gene connexin-36 (CX36) and JME have been reported. The present replication study examined this tentative association in 247 German JME patients and 621 population controls. The frequency of the c.588T allele was significantly increased in the JME patients (35%) compared to controls (29.7%; P=0.016, one-tailed). Consistent to the original report, we also observed a significant increase of T/T homozygotes (13.4%) in the JME patients compared to controls (8.7%; P=0.019, one-tailed; OR(T/T+)=1.62; 95%-CI: 1.02-2.57). The present results provide confirmatory evidence for an allelic and genotypic association of the CX36 gene with JME.

Hidden population substructures in an apparently homogeneous population bias association studies

Linkage- and association-based approaches have been applied to attempt to unravel the genetic predisposition for complex diseases. However, studies often report contradictory results even when similar population backgrounds are investigated. Unrecognized population substructures could possibly explain these inconsistencies. In an apparently homogeneous German sample of 612 patients with type 2 diabetic and end-stage diabetic nephropathy and 214 healthy controls, we tested for hidden population substructures and their possible effects on association. Using a genetic vector space analysis of genotypes of 20 microsatellite markers, we identified four distinct subsets of cases and controls. The significance of these substructures was demonstrated by subsequent association analyses, using three genetic markers (UCSNP-43,-19,-63; intron 3 of the calpain-10 gene). In the undivided sample, we found no association between individual SNPs or any haplogenotypes (ie the genotype combination of two multilocus haplotypes) and type 2 diabetes. In contrast, when analyzing the four groups separately, we found that there was evidence for association of the common C allele of UCSNP-63 with the trait in the largest group (n=547 cases/101 controls; P=0.002). In this subset haplotype 112 was more frequent in controls than in cases (P=0.006; haplogenotype 112/121: odds ratio (OR)=0.27, 95% confidence intervals (CI)=0.13-0.57), indicating a protective effect against the development of type 2 diabetes. Our study demonstrates that unconsidered population substructures (ethnicity-dependent factors) can severely bias association studies.

Association of BRD2 polymorphisms with photoparoxysmal response

A trait locus for electroencephalographic photoparoxysmal response (PPR) has been mapped to the chromosomal region 6p21 near a susceptibility locus for juvenile myoclonic epilepsy (JME). Linkage disequilibrium mapping revealed strong associations between JME and polymorphisms of the gene encoding the bromodomain-containing protein 2 (BRD2). The present association study tested whether genetic variation of BRD2 confers also susceptibility to PPR. All study participants were of German descent, comprising 187 subjects exhibiting PPR (types I-IV) and 666 healthy controls. Genotypes of each study participant were assessed for seven single nucleotide polymorphisms and one dinucleotide repeat polymorphism, covering the genomic BRD2 sequence. Allelic and haplotypic associations were found between PPR and six BRD2 polymorphisms (P: 0.0075-0.035). Considering the strong neurobiological association of JME and PPR, the present results support evidence that PPR and JME share epileptogenic pathways, for which BRD2 might be an underlying susceptibility gene.

Candidate gene analysis of the succinic semialdehyde dehydrogenase gene (ALDH5A1) in patients with idiopathic generalized epilepsy and photosensitivity

Succinic semialdehyde dehydrogenase (SSADH) is involved in the degradation of the inhibitory neurotransmitter GABA and about 50% of patients with SSADH deficiency suffer from seizures. The gene encoding SSADH (gene symbol: ALDH5A1) maps in proximity to susceptibility loci for juvenile myoclonic epilepsy (JME) and photosensitivity on chromosome 6p22. The present study tested whether variation of the ALDH5A1 gene confers susceptibility to common syndromes of idiopathic generalized epilepsy (IGE) and an abnormal photoparoxysmal response (PPR). Mutation screening of the ALDH5A1 coding sequence of 35IGE/PPR patients and four healthy control subjects identified 17 sequence variants, of which three resulted in an exchange of amino acids (H180Y, P182L, A237S). Association analysis was carried out for six single nucleotide polymorphisms (SNPs) and one trinucleotide repeat polymorphism (TNR, intron 1), covering the genomic ALDH5A1 sequence. The study sample comprised 566 unrelated German IGE patients, including 218 JME and 95 photosensitive IGE patients, 78 PPR probands without IGE, and 662 German population controls. None of the investigated ALDH5H1 polymorphisms showed evidence for an allelic or genotypic association with either IGE, JME, or PPR, when corrected for multiple tests. A tentative haplotypic association of the two-marker haplotype (rs1883415-TNR) covering the 5'-regulatory region in IGE patients (chi2=11.65, d.f.=3, P=0.009) warrants further replication studies. The present results do not provide evidence that any ALDH5A1 missense variant itself contributes a common and substantial susceptibility effect (RR>2) to IGE syndromes or an increased liability to visually-induced cortical synchronization.

Association Analysis of Malic Enzyme 2 Gene Polymorphisms with Idiopathic Generalized Epilepsy

PURPOSE

Linkage disequilibrium mapping revealed allelic and haplotypic associations between single-nucleotide polymorphisms (SNPs) of the gene encoding the malic enzyme 2 (ME2) and adolescent-onset idiopathic generalized epilepsy (IGE). Homozygote carriers of the associated ME2 haplotype had a sixfold higher risk of IGE compared with any other genotype. The present population-based association study tested whether genetic variation of the ME2 gene confers susceptibility to common IGE syndromes in the German population.

METHODS

The study included 666 German healthy control subjects and 660 German IGE patients (IGE group), of which 416 patients had an age at onset in adolescence (IGEado group). Genotyping was performed for six SNPs and one dinucleotide repeat polymorphism, all located in the ME2 region.

RESULTS

Neither allele nor genotype frequencies of any ME2 polymorphism differed significantly between the controls and the IGE groups (p > 0.22). No hint of an association of the putative risk-conferring haplotype was seen, when present homozygously, in both IGE groups compared with controls (p > 0.18).

CONCLUSIONS

These results do not support previous evidence that genetic variation of the ME2 gene predisposes to common IGE syndromes. Thus if a recessively inherited ME2 mutation is present, then the size of the epileptogenic effect might be too small or not frequent enough to detect it in the present IGE sample.

Linkage disequilibrium analysis in the LOC93081-KDELC1-BIVM region on 13q in bipolar disorder

Genome-wide scans in bipolar disorder and a meta analysis on published data have provided evidence for linkage to chromosome 13q, although the reported peaks from various studies have not converged in a narrow region. Recently, single nucleotide polymorphisms (SNPs) at the G72/G30 locus have been shown to be associated with bipolar disorder suggesting its potential role in increasing disease risk. The proposed linkage region on 13q extends over a wide span, and could provide a clue to the existence of other susceptibility variants. In the present study, SNPs in the LOC93081-KDELC1-BIVM, a region proximal to G72, were interrogated in two bipolar family series. KDELC1 has a predicted filamin domain and BIVM contains an immunoglobulin-like motif. The small pedigree series yielded a nominally significant global P-value due to under-transmission of a rare haplotype but this finding was not supported by results from the larger series and in the case-control study that compared 278 cases and 277 controls.