Genetic liability to schizophrenia in Oceanic Palau: a search in the affected and maternal generation

Association between polymorphism rs2421943 of the insulin-degrading enzyme and schizophrenia: Preliminary report

BACKGROUND

Insulin-degrading enzyme (IDE) is an important gene in studies of the pathophysiology of type 2 diabetes mellitus (T2DM). Recent studies have suggested a possible link between type 2 diabetes mellitus (T2DM) and the pathophysiology of schizophrenia (SZ). At the same time, significant changes in insulin-degrading enzyme (IDE) gene expression have been found in the brains of people with schizophrenia. These findings highlight the need to further investigate the role of IDE in schizophrenia pathogenesis.

METHODS

We enrolled 733 participants from the Czech Republic, including 383 patients with schizophrenia and 350 healthy controls. Our study focused on the single nucleotide polymorphism (SNP) rs2421943 in the IDE gene, which has previously been associated with the pathogenesis of Alzheimer's disease. The SNP was analyzed using the PCR-RFLP method.

RESULTS

The G allele of the rs2421943 polymorphism was found to significantly increase the risk of developing SZ (p < 0.01) when a gender-based analysis showed that both AG and GG genotypes were associated with a more than 1.55 times increased risk of SZ in females (p < 0.03) but not in males. Besides, we identified a potential binding site at the G allele locus for has-miR-7110-5p, providing a potential mechanism for the observed association.

CONCLUSION

Our results confirm the role of the IDE gene in schizophrenia pathogenesis and suggest that future research should investigate the relationship between miRNA and estrogen influence on IDE expression in schizophrenia pathogenesis.

Predicting risk and the emergence of schizophrenia

This article gives an overview of genetic and environmental risk factors for schizophrenia. The presence of certain molecular, biological, and psychosocial factors at certain points in the life span, has been linked to later development of schizophrenia. All need to be considered in the context of schizophrenia as a lifelong brain disorder. Research interest in schizophrenia is shifting to late childhood/early adolescence for screening and preventative measures. This article discusses those environmental risk factors for schizophrenia for which there is the largest evidence base.

Copy number variants for schizophrenia and related psychotic disorders in Oceanic Palau: risk and transmission in extended pedigrees

BACKGROUND

We report on copy number variants (CNVs) found in Palauan subjects ascertained for schizophrenia and related psychotic disorders in extended pedigrees in Palau. We compare CNVs found in this Oceanic population with those seen in other samples, typically of European ancestry. Assessing CNVs in Palauan extended pedigrees yields insight into the evolution of risk CNVs, such as how they arise, are transmitted, and are lost from populations by stochastic or selective processes, none of which are easily measured from case-control samples.

METHODS

DNA samples from 197 subjects affected with schizophrenia and related psychotic disorders, 185 of their relatives, and 159 control subjects were successfully characterized for CNVs using Affymetrix Genomewide Human SNP Array 5.0.

RESULTS

Copy number variants thought to be associated with risk for schizophrenia and related disorders also occur in affected individuals in Palau, specifically 15q11.2 and 1q21.1 deletions, partial duplication of IL1RAPL1 (Xp21.3), and chromosome X duplications (Klinefelter's syndrome). Partial duplication within A2BP1 appears to convey an eightfold increased risk in male subjects (95% confidence interval, .8-84.4) but not female subjects (odds ratio = .4, 95% confidence interval, .03-4.9). Affected-only linkage analysis using this variant yields a logarithm of the odds score of 3.5.

CONCLUSIONS

This study reveals CNVs that confer risk to schizophrenia and related psychotic disorders in Palau, most of which have been previously observed in samples of European ancestry. Only a few of these CNVs show evidence that they have existed for many generations, consistent with risk variants diminishing reproductive success.

Association between the Regulator of G-protein Signaling 9 Gene and Patients with Methamphetamine Use Disorder and Schizophrenia

The regulator of G-protein signaling (RGS) modulates the functioning of heterotrimeric G protein. RGS9-2 is highly expressed in the striatum and plays a role in modulating dopaminergic receptor-mediated signaling cascades. Previous studies suggested that the RGS9 gene might contribute to the susceptibility to psychotic diseases. Therefore, we investigated the association between the RGS9 gene and two related dopamine psychoses, schizophrenia and methamphetamine use disorders. The subjects comprised 487 patients of schizophrenia and 464 age- and sex-matched healthy controls and 220 patients of methamphetamine use disorder and 289 controls. We genotyped two nonsynonymous polymorphisms, rs12452285 (Leu225Ser) and rs34797451 (His498Arg), of the RGS9 gene. Rs34797451 showed monomorphism in the present Japanese population, but rs12452285 showed polymorphism. There were no significant differences in genotypic or allelic distributions of rs12452285 between patients with schizophrenia and the corresponding control or between patients with methamphetamine use disorder and the corresponding control. We also analyzed the clinical features of methamphetamine use disorder. We found a significant association in allelic distribution with the phenotypes of age at first consumption (p=0.047). The present study suggested that the RGS9 gene is unlikely to play a major role in schizophrenia and methamphetamine dependence liability and/or the development of methamphetamine induced psychosis, at least in a Japanese population.

The α7 nicotinic acetylcholine receptor and the acute stress response: maternal genotype determines offspring phenotype

α7 Nicotinic acetylcholine receptors (α7nAchRs) modulate immune activation by suppressing production of pro-inflammatory cytokines in peripheral immune cells. α7nAchRs also modulate inhibitory output in the hippocampus, which provides input to key circuits of the HPA axis. Therefore, the α7 nicotinic acetylcholine receptor gene (CHRNA7) may be associated with cortisol stress response. Polymorphisms in the CHRNA7 promoter decrease its expression and may dampen the cholinergic response, leading to an increase in inflammation. Increased inflammation may change the intrauterine environment, altering neuroendocrine development in the offspring. Maternal CHRNA7 genotype could affect an offspring's HPA regulation via reprogramming in utero. Patients with allergic disorders have a differential cortisol response to stress. This study utilized samples collected from a cohort of 198 adolescents in a previous study of atopic disorders, who demonstrated a disturbance in HPA response associated with atopy. Salivary cortisol samples collected from the adolescents after a series of laboratory procedures and DNA samples collected from the adolescents and their parents were used for further analysis. DNA samples were genotyped for allelic variation in the CHRNA7 promoter. Genetic association analyses with the cortisol levels were performed in the adolescents. Maternal genotype influences were investigated for the CHRNA7 gene. We also included maternal and child atopy diagnosis as covariates in determining cortisol levels and tested for association of CHRNA7 to atopy. Polymorphisms in the CHRNA7 promoter were associated with lower cortisol levels after a small laboratory stress. Our findings also show that although the child's CHRNA7 genotype affects stress response, the maternal genotype has a stronger influence on cortisol release after stress in male offspring. These effects were independent of atopy status.

Evidence for an interaction of schizophrenia susceptibility loci on chromosome 6q23.3 and 10q24.33-q26.13 in Arab Israeli families

A genome scan for schizophrenia related loci in Arab Israeli families by Lerer et al. [Lerer et al. (2003); Mol Psychiatry 8:488-498] detected significant evidence for linkage at chromosome 6q23. Subsequent fine mapping [Levi et al. (2005); Eur J Hum Genet 13:763-771], association [Amann-Zalcenstein et al. (2006); Eur J Hum Genet 14:1111-1119] and replication studies [Ingason et al. (2007); Eur J Hum Genet 15:988-991] identified AHI1 as a putative susceptibility gene. The same genome scan revealed suggestive evidence for a schizophrenia susceptibility locus in the 10q23-26 region. Genes at these two loci may act independently in the pathogenesis of the disease in our homogeneous sample of Arab Israeli families or may interact with each other and with other factors in a common biological pathway. The purpose of our current study was to test the hypothesis of genetic interaction between these two loci and to identify the type of interaction between them. The initial stage of our study focused on the 10q23-q26 region which has not been explored further in our sample. The second stage of the study included a test for possible genetic interaction between the 6q23.3 locus and the refined 10q24.33-q26.13 locus. A final candidate region of 19.9 Mb between markers D10S222 (105.3 Mb) and D10S587 (125.2 Mb) was found on chromosome 10 by non-parametric and parametric linkage analyses. These linkage findings are consistent with previous reports in the same chromosomal region. Two-locus multipoint linkage analysis under three complex disease inheritance models (heterogeneity, multiplicative, and additive models) yielded a best maximum LOD score of 7.45 under the multiplicative model suggesting overlapping function of the 6q23.3 and 10q24.33-q26.13 loci.

Reduced neuronal expression of insulin-degrading enzyme in the dorsolateral prefrontal cortex of patients with haloperidol-treated, chronic schizophrenia

Insulin-degrading enzyme (IDE) is a neutral thiol metalloprotease, which cleaves insulin with high specificity. Additionally, IDE hydrolyzes Abeta, glucagon, IGF I and II, and beta-endorphin. We studied the expression of IDE protein in postmortem brains of patients with schizophrenia and controls because: (1) the gene encoding IDE is located on chromosome 10q23-q25, a gene locus linked to schizophrenia; (2) insulin resistance with brain insulin receptor deficits/receptor dysfunction was reported in schizophrenia; (3) the enzyme cleaves IGF-I and IGF-II which are implicated in the pathophysiology of the disease; and (4) brain gamma-endorphin levels, liberated from beta-endorphin exclusively by IDE, have been reported to be altered in schizophrenia. We counted the number of IDE immunoreactive neurons in the dorsolateral prefrontal cortex, the hypothalamic paraventricular and supraoptic nuclei, and the basal nucleus of Meynert of 14 patients with schizophrenia and 14 matched control cases. Patients had long-term haloperidol treatment. In addition, relative concentrations of IDE protein in the dorsolateral prefrontal cortex were estimated by Western blot analysis. There was a significantly reduced number of IDE expressing neurons and IDE protein content in the left and right dorsolateral prefrontal cortex in schizophrenia compared with controls, but not in other brain areas investigated. Results of our studies on the influence of haloperidol on IDE mRNA expression in SHSY5Y neuroblastoma cells, as well as the effect of long-term treatment with haloperidol on the number of IDE immunoreactive neurons in rat brain, indicate that haloperidol per se, is not responsible for the decreased neuronal expression of the enzyme in schizophrenics. Haloperidol however, might exert some effect on IDE, through changes of the expression levels of its substrates IGF-I and II, insulin and beta-endorphin. Reduced cortical IDE expression might be part of the disturbed insulin signaling cascades found in schizophrenia. Furthermore, it might contribute to the altered metabolism of certain neuropeptides (IGF-I and IGF-II, beta-endorphin), in schizophrenia.

Convergent patterns of association between phenylalanine hydroxylase variants and schizophrenia in four independent samples

Recessive mutations in the phenylalanine hydroxylase (PAH) gene predispose to phenylketonuria (PKU) in conjunction with dietary exposure to phenylalanine. Previous studies have suggested PAH variations could confer risk for schizophrenia, but comprehensive follow-up has not been reported. We analyzed 15 common PAH "tag" SNPs and three exonic variations that are rare in Caucasians but common in African-Americans among four independent samples (total n = 5,414). The samples included two US Caucasian cohorts (260 trios, 230 independent cases, 474 controls), Bulgarian families (659 trios), and an African-American sample (464 families, 401 controls). Analyses of both US Caucasian samples revealed associations with five SNPs; most notably the common allele (G) of rs1522305 from case-control analyses (z = 2.99, P = 0.006). This SNP was independently replicated in the Bulgarian cohort (z = 2.39, P = 0.015). A non-significant trend was also observed among African-American families (z = 1.39, P = 0.165), and combined analyses of all four samples were significant (rs1522305: chi(2) = 23.28, 8 d.f., P = 0.003). Results for rs1522305 met our a priori criteria for statistical significance, namely an association that was robust to multiple testing correction in one sample, a replicated risk allele in multiple samples, and combined analyses that were nominally significant. Case-control results in African-Americans detected an association with L321L (P = 0.047, OR = 1.46). Our analyses suggest several associations at PAH, with consistent evidence for rs1522305. Further analyses, including additional variations and environmental influences such as phenylalanine exposure are warranted.

Population-based study of baseline ethanol consumption and risk of incident essential tremor

BACKGROUND

Recent postmortem studies have demonstrated pathological changes, including Purkinje cell loss, in the cerebellum in essential tremor (ET). Toxic exposures that compromise cerebellar tissue could lower the threshold for developing ET. Ethanol is a well-established cerebellar toxin, resulting in Purkinje cell loss.

OBJECTIVE

To test whether higher baseline ethanol consumption is a risk factor for the subsequent development of incident ET.

METHODS

Lifetime ethanol consumption was assessed at baseline (1994-1995) in a prospective, population-based study in central Spain of 3285 elderly participants, 76 of whom developed incident ET by follow-up (1997-1998).

RESULTS

In a Cox proportional hazards model adjusting for cigarette pack-years, depressive symptoms and community, the baseline number of drink-years was marginally associated with a higher risk of incident ET (relative risk, RR = 1.003, p = 0.059). In an adjusted Cox model, the highest baseline drink-year quartile doubled the risk of incident ET (RR = 2.29, p = 0.018), while other quartiles were associated with more modest elevations in risk (RR(3rd quartile) = 1.82 (p = 0.10), RR(2nd quartile) = 1.75 (p = 0.10), RR(1st quartile) = 1.43 (p = 0.34) vs non-drinkers (RR = 1.00)). With each higher drink-year quartile, the risk of incident ET increased an average of 23% (p = 0.01, test for trend).

CONCLUSIONS

Higher levels of chronic ethanol consumption increased the risk of developing ET. Ethanol is often used for symptomatic relief; studies should explore whether higher consumption levels are a continued source of underlying cerebellar neurotoxicity in patients who already manifest this disease.

Testing for association based on excess allele sharing in a sample of related cases and controls

Samples consisting of a mix of unrelated cases and controls, small pedigrees, and much larger pedigrees present a unique challenge for association studies. Few methods are available for efficient analysis of such a broad spectrum of data structures. In this paper we introduce a new matching statistic that is well suited to complex data structures and compare it with frequency-based methods available in the literature. To investigate and compare the power of these methods we simulate datasets based on complex pedigrees. We examine the influence of various levels of linkage disequilibrium (LD) of the disease allele with a marker allele (or equivalently a haplotype). For low frequency marker alleles/haplotypes, frequency-based statistics are more powerful in detecting association. In contrast, for high frequency marker alleles, the matching statistic has greater power. The highest power for frequency-based statistics occurs when the disease allele frequency closely matches the frequency of the linked marker allele. In contrast maximum power of the matching statistic always occurs for intermediate marker allele frequency regardless of the disease allele frequency. Moreover, the matching and frequency-based statistics exhibit little correlation. We conclude that these two approaches can be viewed as complementary in finding possible association between a disease and a marker for many different situations.