Alternative transcripts and evidence of imprinting of GNAL on 18p11.2

Mutational spectrum of GNAL, THAP1 and TOR1A genes in isolated dystonia: study in a population from Spain and systematic literature review

OBJECTIVE

We aimed to investigate the prevalence of TOR1A, GNAL and THAP1 variants as the cause of dystonia in a cohort of Spanish patients with isolated dystonia and in the literature.

METHODS

A population of 2028 subjects (including 1053 patients with different subtypes of isolated dystonia and 975 healthy controls) from southern and central Spain was included. The genes TOR1A, THAP1 and GNAL were screened using a combination of high-resolution melting analysis and direct DNA resequencing. In addition, an extensive literature search to identify original articles (published before 10 August 2020) reporting mutations in TOR1A, THAP1 or GNAL associated to dystonia was performed.

RESULTS

Pathogenic or likely pathogenic variants in TOR1A, THAP1 and GNAL were identified in 0.48%, 0.57% and 0.29% of our patients, respectively. Five patients carried the variation p.Glu303del in TOR1A. A very rare variant in GNAL (p.Ser238Asn) was found as a putative risk factor for dystonia. In the literature, variations in TOR1A, THAP1 and GNAL accounted for about 6%, 1.8% and 1.1% of published dystonia patients, respectively.

CONCLUSIONS

There is a different genetic contribution to dystonia of these three genes in our patients (about 1.3% of patients) and in the literature (about 3.6% of patients), probably due the high proportion of adult-onset cases in our cohort. As regards age at onset, site of dystonia onset, and final distribution, in our population there is a clear differentiation between DYT-TOR1A and DYT-GNAL, with DYT-THAP1 likely to be an intermediate phenotype.

Inherited dystonias: clinical features and molecular pathways

Recent decades have witnessed dramatic increases in understanding of the genetics of dystonia - a movement disorder characterized by involuntary twisting and abnormal posture. Hampered by a lack of overt neuropathology, researchers are investigating isolated monogenic causes to pinpoint common molecular mechanisms in this heterogeneous disease. Evidence from imaging, cellular, and murine work implicates deficiencies in dopamine neurotransmission, transcriptional dysregulation, and selective vulnerability of distinct neuronal populations to disease mutations. Studies of genetic forms of dystonia are also illuminating the developmental dependence of disease symptoms that is typical of many forms of the disease. As understanding of monogenic forms of dystonia grows, a clearer picture will develop of the abnormal motor circuitry behind this relatively common phenomenology. This chapter focuses on the current data covering the etiology and epidemiology, clinical presentation, and pathogenesis of four monogenic forms of isolated dystonia: DYT-TOR1A, DYT-THAP1, DYT-GCH1, and DYT-GNAL.

Development of novel biosensors to study receptor-mediated activation of the G-protein α subunits Gs and Golf

Gαs (Gs) and Gαolf (Golf) are highly homologous G-protein α subunits that activate adenylate cyclase, thereby serving as crucial mediators of intracellular signaling. Because of their dramatically different brain expression patterns, we studied similarities and differences between their activation processes with the aim of comparing their receptor coupling mechanisms. We engineered novel luciferase- and Venus-fused Gα constructs that can be used in bioluminescence resonance energy transfer assays. In conjunction with molecular simulations, these novel biosensors were used to determine receptor activation-induced changes in conformation. Relative movements in Gs were consistent with the crystal structure of β2 adrenergic receptor in complex with Gs Conformational changes in Golf activation are shown to be similar to those in Gs Overall the current study reveals general similarities between Gs and Golf activation at the molecular level and provides a novel set of tools to search for Gs- and Golf-specific receptor pharmacology. In view of the wide functional and pharmacological roles of Gs- and Golf-coupled dopamine D1 receptor and adenosine A2A receptor in the brain and other organs, elucidating their differential structure-function relationships with Gs and Golf might provide new approaches for the treatment of a variety of neuropsychiatric disorders. In particular, these novel biosensors can be used to reveal potentially therapeutic dopamine D1 receptor and adenosine A2A receptor ligands with functionally selective properties between Gs and Golf signaling.

High-resolution chromosome ideogram representation of recognized genes for bipolar disorder

Bipolar disorder (BPD) is genetically heterogeneous with a growing list of BPD associated genes reported in recent years resulting from increased genetic testing using advanced genetic technology, expanded genomic databases, and better awareness of the disorder. We compiled a master list of recognized susceptibility and genes associated with BPD identified from peer-reviewed medical literature sources using PubMed and by searching online databases, such as OMIM. Searched keywords were related to bipolar disorder and genetics. Our compiled list consisted of 290 genes with gene names arranged in alphabetical order in tabular form with source documents and their chromosome location and gene symbols plotted on high-resolution human chromosome ideograms. The identified genes impacted a broad range of biological pathways and processes including cellular signaling pathways particularly cAMP and calcium (e.g., CACNA1C, CAMK2A, CAMK2D, ADCY1, ADCY2); glutamatergic (e.g., GRIK1, GRM3, GRM7), dopaminergic (e.g., DRD2, DRD4, COMT, MAOA) and serotonergic (e.g., HTR1A, HTR2A, HTR3B) neurotransmission; molecular transporters (e.g., SLC39A3, SLC6A3, SLC8A1); and neuronal growth (e.g., BDNF, IGFBP1, NRG1, NRG3). The increasing prevalence of BPD calls for better understanding of the genetic etiology of this disorder and associations between the observed BPD phenotype and genes. Visual representation of genes for bipolar disorder becomes a tool enabling clinical and laboratory geneticists, genetic counselors, and other health care providers and researchers easy access to the location and distribution of currently recognized BPD associated genes. Our study may also help inform diagnosis and advance treatment developments for those affected with this disorder and improve genetic counseling for families.

Identification of genomic locus responsible for experimentally induced testicular teratoma 1 (ett1) on mouse Chr 18

Spontaneous testicular teratomas (STTs) composed by various kinds of tissues are derived from primordial germ cells (PGCs) in the fetal testes of the mouse. In contrast, intra-testicular grafts of the mouse strain (129/Sv-Ter (+/+)) fetal testes possessed the ability to develop the experimental testicular teratomas (ETTs), indistinguishable from the STTs at a morphological level. In this study, linkage analysis was performed for exploration of possible candidate genes involving in ETT development using F2 intercross fetuses derived from [LTXBJ × 129/Sv-Ter (+/+)] F1 hybrids. Linkage analysis with selected simple sequence length polymorphisms along chromosomes 18 and 19, which have been expected to contain ETT-susceptibility loci, demonstrated that a novel recessive candidate gene responsible for ETT development is located in 1.1 Mb region between the SSLP markers D18Mit81 and D18Mit184 on chromosome 18 in the 129/Sv-Ter (+/+) genetic background. Since this locus is different from the previously known loci (including Ter, pgct1, and Tgct1) for STT development, we named this novel gene "experimental testicular teratoma 1 (ett1)". To resolve the location of ett1 independently from other susceptibility loci, ett1 loci was introduced in a congenic strain in which the distal segment of chromosome 18 in LTXBJ strain mice had been replaced by a 1.99 Mbp genomic segment of the 129/Sv-Ter (+/+) mice. Congenic males homozygous for the ett1 loci were confirmed to have the ability to form ETTs, indicating that this locus contain the gene responsible for ETTs. We listed candidate genes included in this region, and discussed about their possible involvement in induction of ETTs.

Mutations in GNAL: a novel cause of craniocervical dystonia

IMPORTANCE

Mutations in the GNAL gene have recently been shown to cause primary torsion dystonia. The GNAL-encoded protein (Gαolf) is important for dopamine D1 receptor function and odorant signal transduction. We sequenced all 12 exons of GNAL in 461 patients from Germany, Serbia, and Japan, including 318 patients with dystonia (190 with cervical dystonia), 51 with hyposmia and Parkinson disease, and 92 with tardive dyskinesia or acute dystonic reactions.

OBSERVATIONS

We identified the following two novel heterozygous putative mutations in GNAL: p.Gly213Ser in a German patient and p.Ala353Thr in a Japanese patient. These variants were predicted to be pathogenic in silico, were absent in ethnically matched control individuals, and impaired Gαolf coupling to D1 receptors in a bioluminescence energy transfer (BRET) assay. Two additional variants appeared to be benign because they behaved like wild-type samples in the BRET assay (p.Ala311Thr) or were detected in ethnically matched controls (p.Thr92Ala). Both patients with likely pathogenic mutations had craniocervical dystonia with onset in the fifth decade of life. No pathogenic mutations were detected in the patients with hyposmia and Parkinson disease, tardive dyskinesias, or acute dystonic reactions.

CONCLUSIONS AND RELEVANCE

Mutations in GNAL can cause craniocervical dystonia in different ethnicities. The BRET assay may be a useful tool to support the pathogenicity of identified variants in the GNAL gene.

Recurrent proximal 18p monosomy and 18q trisomy in a family due to a pericentric inversion

Here, we report on a family with pericentric inversion of chromosome 18 [inv(18)(p11.2q21)] and two recombinants with a duplication of q21 → qter and a deletion of p11.2 → pter regions in a four-generation family. This chromosomal abnormality was inherited in our first patient from the father, while it was transmitted to the second patient from the mother. Array-CGH analysis were used to better characterize duplicated and deleted chromosomal regions and showed no genomic copy number variation (CNV) differences between these two relatives. We discussed genotype-phenotype correlations including previously reported.

Plasma total homocysteine is associated with DNA methylation in patients with schizophrenia

Schizophrenia (SCZ) is a devastating psychiatric disorder with a median lifetime prevalence rate of 0.7?0.8%. Elevated plasma total homocysteine has been suggested as a risk factor for SCZ, and various biological effects of hyperhomocysteinemia have been proposed to be relevant to the pathophysiology of SCZ. As increased attention is paid to aberrant DNA methylation in SCZ, homocysteine is attracting additional interest as a potential key substance. Homocysteine is formed in the methionine cycle, which is involved in one-carbon methyl group-transfer metabolism, and it acts as a methyl donor when it is converted to S-adenosyl-methionine. To date, no studies have examined the relationship between homocysteine and genome-wide DNA methylation in SCZ. We examined the relationship between plasma total homocysteine and DNA methylation patterns in the peripheral leukocytes of patients with SCZ (n = 42) using a quantitative high-resolution DNA methylation array (485,764 CpG sites). Significant homocysteine-related changes in DNA methylation were observed at 1,338 CpG sites that were located across whole gene regions, including promoters, gene bodies and 3?-untranslated regions. Of the 1,338 sites, 758 sites (56.6%) were located in the CpG islands (CGIs) and in the regions flanking CGIs (CGI: 15.8%; CGI shore: 28.2%; CGI shelf: 12.6%), and positive correlations between plasma total homocysteine and DNA methylation were observed predominantly at CpG sites in the CGIs. Our results suggest that homocysteine might play a role in the pathogenesis of SCZ via a molecular mechanism that involves alterations to DNA methylation.

Mutations in GNAL cause primary torsion dystonia

Dystonia is a movement disorder characterized by repetitive twisting muscle contractions and postures^1,2. Its molecular pathophysiology is poorly understood, in part due to limited knowledge of the genetic basis of the disorder. Only three genes for primary torsion dystonia (PTD), TOR1A (DYT1)³, THAP1 (DYT6)⁴, and CIZ1⁵ have been identified. Using exome sequencing in two PTD families we identified a novel causative gene, GNAL, with a nonsense p.S293X mutation resulting in premature stop codon in one family and a missense p.V137M mutation in the other. Screening of GNAL in 39 PTD families, revealed six additional novel mutations in this gene. Impaired function of several of the mutations was shown by bioluminescence resonance energy transfer (BRET) assays.

Paternal age effect on age of onset in bipolar I disorder is mediated by sex and family history

This study investigated for the first time in the psychiatric literature the effect of parental age on age-of-onset (AO) in bipolar I disorder (BPI) in relation to proband sex and family history (FH) for major psychoses in a sample of 564 BPI probands. All probands, 72.68% of their first-degree and 12.13% of their second-degree relatives were directly interviewed. The FH-method was used for all unavailable relatives. The diagnoses were made according to DSM-IV(TR) . The impact of parental age on proband early/late AO was evaluated through logistic regression with the cut-off for early AO determined through commingling analysis. We found evidence for a significant influence of increasing paternal age, and especially age ≥ 35 years, on AO of BPI disorder in the total sample (OR = 0.54, CI: 0.35-0.80), in the female subsample (OR = 0.44, CI: 0.25-0.78), in the sporadic subsample (OR = 0.64, CI: 0.38-0.95), and in the subsample with FH of recurrent unipolar major depression (Mdd-RUP) (OR = 0.55, CI: 0.34-0.87). No significant effect of paternal age on disease AO was found in patients with FH of bipolar (BP), schizoaffective disorders (SA), or schizophrenia (SCZ), nor in males. Mean age was significantly higher in fathers of sporadic cases and of cases with FH of Mdd-RUP than in fathers of cases with FH of BP/SA/SCZ (P = 0.011). Maternal age had no significant effect either in the total sample or in subsamples defined by proband sex or FH. In conclusion, in our sample increasing paternal age lowered the onset of BPI selectively, the effect being related to the female sex and FH-type.

XLGαolf regulates expression of p27Kip1 in a CSN5 and CDK2 dependent manner

XLGα(olf) is an extra large transcriptional variant of the heterotrimeric G protein, Gα(olf), which we previously reported to be localized in the Golgi apparatus and interacted with Rab3A and Rab8A through its N-terminal region. However, many physiological functions of XLGα(olf) remain to be elucidated. In this study, performance of yeast two-hybrid screening with XLGα(olf) allowed isolation of COP9 signalosome subunit 5 (CSN5), known to regulate the p27(Kip1) protein level through a proteasome dependent pathway. Co-immunoprecipitation experiments followed by Western blotting also showed association of CSN5 with XLGα(olf) linked to down-regulation of p27(Kip1). Gene silencing of endogenous CSN5 by siRNA attenuated the XLGα(olf)-mediated down-regulation, which was also demonstrated to require CDK2. Both knock down of CDK2 and the treatment with a CDK2 inhibitor reversed the reduction of p27(Kip1) due to XLGα(olf). Our findings provide important clues to understanding physiological functions of XLGα(olf).

Identification of a specific assembly of the g protein golf as a critical and regulated module of dopamine and adenosine-activated cAMP pathways in the striatum

In the principal neurons of striatum (medium spiny neurons, MSNs), cAMP pathway is primarily activated through the stimulation of dopamine D1 and adenosine A_2A receptors, these receptors being mainly expressed in striatonigral and striatopallidal MSNs, respectively. Since cAMP signaling pathway could be altered in various physiological and pathological circumstances, including drug addiction and Parkinson’s disease, it is of crucial importance to identify the molecular components involved in the activation of this pathway. In MSNs, cAMP pathway activation is not dependent on the classical Gs GTP-binding protein but requires a specific G protein subunit heterotrimer containing Gαolf/β2/γ7 in particular association with adenylyl cyclase type 5. This assembly forms an authentic functional signaling unit since loss of one of its members leads to defects of cAMP pathway activation in response to D1 or A_2A receptor stimulation, inducing dramatic impairments of behavioral responses dependent on these receptors. Interestingly, D1 receptor (D1R)-dependent cAMP signaling is modulated by the neuronal levels of Gαolf, indicating that Gαolf represents the rate-limiting step in this signaling cascade and could constitute a critical element for regulation of D1R responses. In both Parkinsonian patients and several animal models of Parkinson’s disease, the lesion of dopamine neurons produces a prolonged elevation of Gαolf levels. This observation gives an explanation for the cAMP pathway hypersensitivity to D1R stimulation, occurring despite an unaltered D1R density. In conclusion, alterations in the highly specialized assembly of Gαolf/β2/γ7 subunits can happen in pathological conditions, such as Parkinson’s disease, and it could have important functional consequences in relation to changes in D1R signaling in the striatum.

Evidence for somatic gene conversion and deletion in bipolar disorder, Crohn's disease, coronary artery disease, hypertension, rheumatoid arthritis, type-1 diabetes, and type-2 diabetes

BACKGROUND

During gene conversion, genetic information is transferred unidirectionally between highly homologous but non-allelic regions of DNA. While germ-line gene conversion has been implicated in the pathogenesis of some diseases, somatic gene conversion has remained technically difficult to investigate on a large scale.

METHODS

A novel analysis technique is proposed for detecting the signature of somatic gene conversion from SNP microarray data. The Wellcome Trust Case Control Consortium has gathered SNP microarray data for two control populations and cohorts for bipolar disorder (BD), cardiovascular disease (CAD), Crohn's disease (CD), hypertension (HT), rheumatoid arthritis (RA), type-1 diabetes (T1D) and type-2 diabetes (T2D). Using the new analysis technique, the seven disease cohorts are analyzed to identify cohort-specific SNPs at which conversion is predicted. The quality of the predictions is assessed by identifying known disease associations for genes in the homologous duplicons, and comparing the frequency of such associations with background rates.

RESULTS

Of 28 disease/locus pairs meeting stringent conditions, 22 show various degrees of disease association, compared with only 8 of 70 in a mock study designed to measure the background association rate (P < 10-9). Additional candidate genes are identified using less stringent filtering conditions. In some cases, somatic deletions appear likely. RA has a distinctive pattern of events relative to other diseases. Similarities in patterns are apparent between BD and HT.

CONCLUSIONS

The associations derived represent the first evidence that somatic gene conversion could be a significant causative factor in each of the seven diseases. The specific genes provide potential insights about disease mechanisms, and are strong candidates for further study.

Association analysis between polymorphisms in the myo-inositol monophosphatase 2 (IMPA2) gene and bipolar disorder

Linkage studies in bipolar disorder (BPD) suggest that a susceptibility locus exists on chromosome 18p11. The myo-inositol monophosphatase 2 gene (IMPA2) maps to this genomic region. Myo-inositol monophosphatase dephosphorylates inositol monophosphate, regenerating free inositol. Lithium, a common treatment for BPD, has been shown to inhibit IMPA2 activity and decrease levels of inositol. It is hypothesized that lithium conveys its therapeutic effect for BPD patients partially through inositol regulation. Hence, dysfunction of inositol caused by IMPA2 irregularity may contribute to the pathophysiology of BPD. In this study, we hypothesize that genetic variations in the IMPA2 gene contributes to increased susceptibility to BPD. We tested this hypothesis by genotyping 9 SNPs (rs1787984; rs585247; rs3974759; rs650727; rs589247; rs669838; rs636173; rs3786285; rs613993) in BPD patients (n=556) and controls (n=735). Genotype and allele frequencies were compared between groups using Chi square contingency analysis. Linkage disequilibrium (LD) between markers was calculated and estimated haplotype frequencies were compared between groups. Single marker analysis revealed several associations between IMPA2 variations and BPD, which were subsequently rendered non-significant after correction for multiple testing. Although our study did not show strong support for an association between the tested IMPA2 polymorphisms and susceptibility to BPD, additional larger studies are necessary to comprehensively investigate a role of the IMPA2 gene in the pathophysiology of BPD.

Association between polymorphisms in the metallophosphoesterase (MPPE1) gene and bipolar disorder

Genetic linkage studies in bipolar disorder (BPD) suggest that a susceptibility locus exists on chromosome 18p11. The metallophosphoesterase (MPPE1) gene maps to this region. Dysregulation of protein phosphorylation and subsequent abnormal cellular signaling has been postulated to be involved in neuropsychiatric disorders thus making MPPE1 a plausible biological candidate gene for BPD. In this study, we hypothesized that genetic variation in the MPPE1 gene contributes to BPD. We tested this hypothesis by genotyping four SNPs (rs871044; rs3974590; rs593713; rs602201) in BPD patients (n = 570) and healthy controls (n = 725). Genotypes and allele frequencies were compared between groups using Chi square contingency analysis. Linkage disequilibrium (LD) between markers was calculated and estimated haplotype frequencies were compared between groups. Single marker analysis revealed an association of rs3974590 with BPD (P = 0.009; permutation corrected P = 0.046). Haplotype analysis did not show any significant association with disease after permutation correction. Our results provide evidence of an association between a polymorphism in the MPPE1 gene and BPD. Additional studies are necessary to confirm and elucidate the role of MPPE1 as a susceptibility gene for BPD on chromosome 18p.

Characterization of a de novo balanced translocation t(9;18)(p23;q12.2) in a patient with oculoauriculovertebral spectrum

We report a patient presenting with oculoauriculovertebral spectrum and a de novo balanced reciprocal translocation t(9;18)(p23;q12.2). Physical mapping of the translocation breakpoints by fluorescent in situ hybridization showed that the breakpoints are located in two regions encompassing gene deserts. An additional paternally inherited duplication in 18p11.23p11.31 was identified by array-CGH. We discuss the possible involvement of these chromosomal abnormalities in OAVS.

Case-control association study of 65 candidate genes revealed a possible association of a SNP of HTR5A to be a factor susceptible to bipolar disease in Bulgarian population

BACKGROUND

Bipolar affective disorder (BAD) is a psychiatric illness characterized by episodes of mania and depression. Although the etiology is not clear, epidemiological studies suggest it is a result of an interaction of genetic and environmental factors. Despite of enormous efforts and abundant studies conducted, none has yet been identified definitively a gene susceptible to bipolar disorder.

METHODS

Ninety-four Bulgarian patients diagnosed with bipolar disorder and 184 Bulgarian healthy individuals, were used for genotyping of 191 single nucleotide polymorphisms (SNPs) by TaqMan and/or Invader assays. Seventeen SNPs that revealed P value less than 0.05 in the first screening were genotyped using an additional independent set of samples, consisting of 78 BAD cases and 372 controls.

RESULTS

After applying the Bonferonni correction on genotyping results of 172 cases and 556 controls, only one SNP, rs1800883, in the HTR5A gene revealed a significant level of P value (P=0.000097; odds ratio=1.80 (95%CI, 1.27-2.54); corrected P=0.017).

CONCLUSIONS

Our findings suggest that HTR5A gene could play an important role in the pathogenesis of bipolar disorder in our population. However these findings should be viewed with caution and replication studies in other populations are necessary in support of these findings.

Schizophrenia and birthplace of paternal and maternal grandfather in the Jerusalem perinatal cohort prospective study

Some forms of epigenetic abnormalities transmitted to offspring are manifested in differences in disease incidence that depend on parent-of-origin. To explore whether such phenomena might operate in schizophrenia spectrum disorders, we estimated the relative incidence of these conditions in relation to parent-of-origin by considering the two grandfathers' countries of birth. In a prospective cohort of 88,829 offspring, born in Jerusalem in 1964-76 we identified 637 cases through Israel's psychiatric registry. Relative risks (RR) were estimated for paternal and maternal grandfathers' countries of birth using proportional hazards methods, controlling for parents' ages, low social class and duration of marriage. After adjusting for multiple observations, we found no significant differences between descendants of maternal or paternal grandfathers born in Iraq, Iran, Turkey, Syria, Yemen, Morocco, Algeria, Tunisia, Libya/Egypt, Poland, USSR, Czechoslovakia, Germany or the USA. Those with paternal grandfathers from Romania (RR=1.9, 95% CI=1.3-2.8) or Hungary (1.6, 1.0-2.6) showed an increased incidence; however, those with maternal grandfathers from these countries experienced reduced incidence (RR=0.5, 0.3-0.8 and 0.4, 0.2-0.8). In post-hoc analyses we found that results were similar whether the comparison groups were restricted to descendants of other Europeans or included those from Western Asia and North Africa; and effects of paternal grandfathers from Romania/Hungary were more pronounced in females, while effects of maternal grandfathers from these countries were similar in males and females. These post-hoc "hypothesis-generating" findings lead one to question whether some families with ancestors in Romania or Hungary might carry a variant or mutation at a parentally imprinted locus that is altering susceptibility to schizophrenia. Such a locus, if it exists, might involve the X chromosome.

Subcellular localization of a novel G protein XLGalpha(olf)

XLGalpha(olf) was identified as a transcriptional variant of the heterotrimeric G protein, Galpha(olf). Previous work showed that XLGalpha(olf) couples with adenosine A2a receptor and dopamine D1 receptor in vitro. However, physiological functions of XLGalpha(olf) remain to be elucidated. In this study, we performed indirect immunofluorescence confocal analyses to examine the subcellular localization of XLGalpha(olf). With overexpression, surprisingly, many large endosomes resulted. We also observed that XLGalpha(olf) localizes at the Golgi apparatus. The N-terminal region of XLGalpha(olf) appears necessary for both endosome formation and the Golgi localization. The results indicate that XLGalpha(olf) and Galpha(olf) play distinctly separate roles. Moreover, XLGalpha(olf) colocalized with Rab3A and Rab8A, as well as partially with Rab11A, but not with other endocytotic endosomes. We could confirm the interaction between XLGalpha(olf) and Rab3A/Rab8A by co-immunoprecipitation experiments. Our study provides important clues toward understanding physiological functions of XLGalpha(olf).

Uniparentalism in sporadic colorectal cancer is independent of imprint status, and coordinate for chromosomes 14 and 18

Our previous allelotyping studies of 59 sporadic colorectal cancers revealed that loss of heterozygosity is most frequent for regions of chromosomes 14 and 18. Yet subsequent BAC microarray comparative genomic hybridization studies of the same tumor DNAs showed no corresponding pattern of copy number alteration for chromosome 14. To clarify this apparent discrepancy, we utilized hybridization to SNP microarrays; this revealed frequent uniparentalism for chromosome 14 and for chromosome 18. Based on the BAC array results combined with fluorescent in situ hybridization data, it was evident that uniparental disomy was occurring in many colorectal cancers as well as in additional chromosomes, and often coordinately involved chromosomes 14 and 18. Further studies examined the possibility that uniparentalism was directed towards the selection for imprinted genes, but no association with imprinting was observed.

Highly individual methylation patterns of alternative glucocorticoid receptor promoters suggest individualized epigenetic regulatory mechanisms

The transcription start sites (TSS) and promoters of many genes are located in upstream CpG islands. Methylation within such islands is known for both imprinted and oncogenes, although poorly studied for other genes, especially those with complex CpG islands containing multiple first exons and promoters. The glucocorticoid receptor (GR) CpG island contains seven alternative first exons and their promoters. Here we show for the five GR promoters activated in PBMCs that methylation patterns are highly variable between individuals. The majority of positions were methylated at levels >25% in at least one donor affecting each promoter and TSS. We also examined the evolutionarily conserved transcription factor binding sites (TFBS) using an improved in silico phylogenetic footprinting technique. The majority of these contain methylatable CpG sites, suggesting that methylation may orchestrates alternative first exon usage, silencing and controlling tissue-specific expression. The heterogeneity observed may reflect epigenetic mechanisms of GR fine tuning, programmed by early life environment and events. With 78% of evolutionarily conserved alternative first exons falling into such complex CpG islands, their internal structure and epigenetic modifications are bound to be biologically important, and may be a common transcriptional control mechanism used throughout many phyla.

Genomic imprinting in the development and evolution of psychotic spectrum conditions

I review and evaluate genetic and genomic evidence salient to the hypothesis that the development and evolution of psychotic spectrum conditions have been mediated in part by alterations of imprinted genes expressed in the brain. Evidence from the genetics and genomics of schizophrenia, bipolar disorder, major depression, Prader-Willi syndrome, Klinefelter syndrome, and other neurogenetic conditions support the hypothesis that the etiologies of psychotic spectrum conditions commonly involve genetic and epigenetic imbalances in the effects of imprinted genes, with a bias towards increased relative effects from imprinted genes with maternal expression or other genes favouring maternal interests. By contrast, autistic spectrum conditions, including Kanner autism, Asperger syndrome, Rett syndrome, Turner syndrome, Angelman syndrome, and Beckwith-Wiedemann syndrome, commonly engender increased relative effects from paternally expressed imprinted genes, or reduced effects from genes favouring maternal interests. Imprinted-gene effects on the etiologies of autistic and psychotic spectrum conditions parallel the diametric effects of imprinted genes in placental and foetal development, in that psychotic spectrum conditions tend to be associated with undergrowth and relatively-slow brain development, whereas some autistic spectrum conditions involve brain and body overgrowth, especially in foetal development and early childhood. An important role for imprinted genes in the etiologies of psychotic and autistic spectrum conditions is consistent with neurodevelopmental models of these disorders, and with predictions from the conflict theory of genomic imprinting.

Scaffolding proteins in highly purified rat olfactory cilia membranes

Odour-mediated signal transduction is a complex process that occurs in the cilia of olfactory sensory neurons. To gain insight in to the molecular organization of the odour transduction machinery, we developed a procedure to purify olfactory cilia membranes by differential centrifugation of rat olfactory epithelium extracts. We tested whether known scaffolding proteins that might participate in the assembly of the complex chemotransduction apparatus are present in the purified membrane fraction. Utilizing immunoblotting and immunohistochemistry, we show that the multidomain scaffolding proteins ProSAP/Shanks and calcium/calmodulin-dependent serine protein kinase CASK are present in the olfactory cilia. Ion channels involved in chemotransduction could be reconstituted into planar lipid bilayers for electrophysiological recordings. Our procedure should allow the identification of further chemotransduction-related proteins.

Association analysis of the pituitary adenylate cyclase-activating polypeptide (PACAP/ADCYAP1) gene in bipolar disorder

BACKGROUND

Linkage studies in bipolar disorder (BPD) suggest that a susceptibility locus exists on chromosome 18p11. The pituitary adenylate cyclase-activating polypeptide/adenylate cyclase-activating polypeptide 1 (pituitary) (PACAP/ADCYAP1) gene maps to this region. PACAP is a neuropeptide involved in neurotransmission in both the peripheral nervous system and central nervous system and is required for catecholamine secretion. Animal models of PACAP mutations show remarkable behavioral defects, including hyperactivity and increased exploratory behavior.

OBJECTIVE

In this study we tested the hypothesis that genetic variations in the human PACAP gene contribute to BPD.

METHODS

Genotyping of seven single nucleotide polymorphisms (rs1893154; rs2846811; rs8192595; rs2856966; rs928978; rs2231187; rs1610037) was performed in BPD patients (n=570) and healthy controls (n=710). Genotypes and allele frequencies were compared between groups using chi contingency analysis. Linkage disequilibrium between markers was calculated and estimated haplotype frequencies were compared between groups.

MAIN RESULTS

There were no significant differences between groups on the allele, genotype or haplotype level for any of the tested single nucleotide polymorphisms.

CONCLUSION

Our results provide no evidence of an association of the PACAP gene with BPD in this group of patients and controls. Additional studies are necessary to elucidate the BPD susceptibility locus on chromosome 18p.

Suggestive linkage of a chromosomal locus on 18p11 to cyclothymic temperament in bipolar disorder families

Attempts to identify bipolar disorder (BP) genes have only enjoyed limited success. One potential cause for this problem is that the traditional categorical BP phenotypes currently used in genetic linkage studies are not the most informative, efficient, or biologically relevant. An alternative to these strict categorical BP phenotypes is quantitative BP phenotypes. By isolating one aspect of a complex trait such as BP into a simple, intermediate, quantitative trait, genes that contribute to the larger complex trait can be more readily identified. Along these lines, we utilized a temperament-based measure (cyclothymic temperament) as a quantitative, intermediate BP phenotype in linkage analyses and hypothesized that this measure might more efficiently detect loci for BP or temperamental traits that predispose to BP. A total of 158 individuals with temperament data from 28 BP families were used in the linkage analyses. All pedigrees had a proband diagnosed with BPI or BPII and at least two other family members with a mood disorder diagnosis. An 8 cM genome scan was performed and analyzed using MERLIN nonparametric multipoint regression linkage for a cyclothymic temperament trait. The highest overall LOD score was on chromosome 18 (LOD = 2.71, P = 0.0002). Other linkage peaks which may indicate potential regions of interest were found on chromosomes 3 and 7. The temperament-based cyclothymic trait yielded a higher peak LOD score and a lower P-value than analyses using traditional, categorical phenotypes in a separate analysis including these same families.

The myelin-pathogenesis puzzle in schizophrenia: a literature review

Schizophrenia is a serious and disabling mental disorder with symptoms such as auditory hallucinations, disordered thinking and delusions, avolition, anhedonia, blunted affect and apathy. In this review article we seek to present the current scientific findings from linkage studies and susceptible genes and the pathophysiology of white matter in schizophrenia. The article has been reviewed in two parts. The first part deals with the linkage studies and susceptible genes in schizophrenia in order to have a clear-cut picture of the involvement of chromosomes and their genes in schizophrenia. The genetic linkage results seem to be replicated in some cases but in others are not. From these results, we cannot draw a fine map to a single locus or gene, leading to the conclusion that schizophrenia is not caused by a single factor/gene. In the second part of the article we present the oligodendrocyte-related genes that are associated with schizophrenia, as we hypothesize a potential role of oligodendrocyte-related genes in the pathology of the disorder.

Monosomy 18p

Monosomy 18p refers to a chromosomal disorder resulting from the deletion of all or part of the short arm of chromosome 18. The incidence is estimated to be about 1:50,000 live-born infants. In the commonest form of the disorder, the dysmorphic syndrome is very moderate and non-specific. The main clinical features are short stature, round face with short philtrum, palpebral ptosis and large ears with detached pinnae. Intellectual deficiency is mild to moderate. A small subset of patients, about 10–15 percent of cases, present with severe brain/facial malformations evocative of holoprosencephaly spectrum disorders. In two-thirds of the cases, the 18p- syndrome is due to a mere terminal deletion occurring de novo, in one-third the following are possible: a de novo translocation with loss of 18p, malsegregation of a parental translocation or inversion, or a ring chr18. Parental transmission of the 18p- syndrome has been reported. Cytogenetic analysis is necessary to make a definite diagnosis. Recurrence risk for siblings is low in de novo deletions and translocations, but is significant if a parental rearrangement is present. Deletion 18p can be detected prenatally by amniocentesis or chorionic villus sampling and cytogenetic testing. Differential diagnosis may include a wide number of syndromes with short stature and mild intellectual deficiency. In young children, deletion 18p syndrome may be vaguely evocative of either Turner syndrome or trisomy 21. No specific treatment exists but speech therapy and early educational programs may help to improve the performances of the children. Except for the patients with severe brain malformations, the life expectancy does not seem significantly reduced.

Investigation of the G protein subunit Galphaolf gene (GNAL) in attention deficit/hyperactivity disorder

The dopamine system plays an important role in the regulation of attention and motor behavior, subsequently, several dopamine-related genes have been associated with Attention Deficit/Hyperactivity Disorder (ADHD). Among them are the dopamine receptors D1 and D5 that mediate adenylyl cyclase activation through coupling with G(s)-like proteins. We thus hypothesized that the G(s)-like subunit Galpha(olf), expressed in D1-rich areas of the brain, contributes to the genetic susceptibility of ADHD. To evaluate the involvement of the Galpha(olf) gene, GNAL, in ADHD, we examined the inheritance pattern of 12 GNAL polymorphisms in 258 nuclear families ascertained through a proband with ADHD (311 affected children) using the transmission/disequilibrium test (TDT). Categorical analysis of individual marker alleles demonstrated biased transmission of one polymorphism in GNAL intron 3 (rs2161961; P=0.011). We also observed significant relationships between rs2161961 and dimensional symptoms of inattention and hyperactivity/impulsivity (P=0.003 and P=0.008). In addition, because of recent evidence of imprinting at the GNAL locus, secondary analyses were split into maternal and paternal transmissions to assess a contribution of parental effects. We found evidence of strong maternal effect, with preferential transmission of maternal alleles for rs2161961A (P=0.005) and rs8098539A (P=0.035). These preliminary findings suggest a possible contribution of GNAL in the susceptibility to ADHD, with possible involvement of parent-of-origin effects.

Epigenetics in mood disorders

Depression develops as an interaction between stress and an individual's vulnerability to stress. The effect of early life stress and a gene-environment interaction may play a role in the development of stress vulnerability as a risk factor for depression. The epigenetic regulation of the promoter of the glucocorticoid receptor gene has been suggested as a molecular basis of such stress vulnerability. It has also been suggested that antidepressive treatment, such as antidepressant medication and electroconvulsive therapy, may be mediated by histone modification on the promoter of the brain-derived neurotrophic factor gene. Clinical genetic studies in bipolar disorder suggest the role of genomic imprinting, although no direct molecular evidence of this has been reported. The role of DNA methylation in mood regulation is indicated by the antimanic effect of valproate, a histone deacetylase inhibitor, and the antidepressive effect of S-adenosyl methionine, a methyl donor in DNA methylation. Studies of postmortem brains of patients have implicated altered DNA meA methylation of the promoter region of membrane-bound catechol-O-methyltransferase in bipolar disorder. An altered DNA methylation status of PPIEL (peptidylprolyl isomerase E-like) was found in a pair of monozygotic twins discordant for bipolar disorder. Hypomethylation of PPIEL was also found in patients with bipolar II disorder in a case control analysis. These fragmentary findings suggest the possible role of epigenetics in mood disorders. Further studies of epigenetics in mood disorders are warranted.

A promoter haplotype of the inositol monophosphatase 2 gene (IMPA2) at 18p11.2 confers a possible risk for bipolar disorder by enhancing transcription

Lithium is an effective mood stabilizer for bipolar disorder patients and its therapeutic effect may involve inhibition of inositol monophosphatase activity. In humans, the enzyme is encoded by two genes, IMPA1 and IMPA2. IMPA2 maps to 18p11.2, a genomic interval for which evidence of linkage to bipolar disorder has been supported by several reports. We performed a genetic association study in Japanese cohorts (496 patients with bipolar disorder and 543 control subjects). Interestingly, we observed association of IMPA2 promoter single nucleotide polymorphisms (SNPs) (-461C and -207T) with bipolar disorder, the identical SNPs reported previously in a different population. In vitro promoter assay and genetic haplotype analysis showed that the combination of (-461C)-(-207T)-(-185A) drove enhanced transcription and the haplotypes containing (-461C)-(-207T)-(-185A) contributed to risk for bipolar disorder. Expression study on post-mortem brains revealed increased transcription from the IMPA2 allele that harbored (-461C)-(-207T)-(-185A) in the frontal cortex of bipolar disorder patients. The examination of allele-specific expressions in post-mortem brains did not support genomic imprinting of IMPA2, which was suggested nearby genomic locus. Contrasting to a prior report, therapeutic concentrations of lithium could not suppress the transcription of IMPA2 mRNA, and the mood-stabilizing effect of lithium is, if IMPA2 was one of the targets of lithium, deemed to be generated via inhibition of enzymatic reaction rather than transcriptional suppression. In conclusion, the present study suggests that a promoter haplotype of IMPA2 possibly contributes to risk for bipolar disorder by elevating IMPA2 levels in the brain, albeit the genetic effect varies among populations.

Dense SNP association study for bipolar I disorder on chromosome 18p11 suggests two loci with excess paternal transmission

Parent-of-origin effects have been implicated as mediators of genetic susceptibility for a number of complex disease phenotypes, including bipolar disorder. Specifically, evidence for linkage on chromosome 18 is modified when allelic parent-of-origin is accommodated in the analysis. Our goal was to characterize the susceptibility locus for bipolar I disorder on chromosome 18p11 and investigate this parent-of-origin hypothesis in an association context. This was achieved by genotyping single nucleotide polymorphisms (SNPs) at a high density (1 SNP/5 kb) along 13.6 megabases of the linkage region. To increase our ability to detect a susceptibility locus, we restricted the phenotype definition to include only bipolar I probands. We also restricted our study population to Ashkenazi Jewish individuals; this population has characteristics of a genetic isolate and may therefore facilitate detection of variants for complex disease. Three hundred and forty-four pedigrees (363 parent/child trios) where probands were affected with bipolar 1 disorder were genotyped. Transmission disequilibrium test analysis revealed no statistically significant association to SNPs or haplotypes within this region in this sample. However, when parent-of-origin of transmitted SNPs was taken into account, suggestive association was revealed for two separate loci.

Functional coupling of the Galpha(olf) variant XLGalpha(olf) with the human adenosine A2A receptor

A recently identified novel Galphaolf variant, XLGalphaolf, is shown to functionally couple to the human adenosine A2A receptor (A2AR). In Sf9 cells expressing A2AR, beta1, and gamma2, co-expression of XLGalphaolf increased NECA-induced [35S]GTPgammaS binding from approximately 130% to 300% of basal levels. Pharmacological characteristics of A2AR ligands on these cells were evaluated by using [3H]ZM241385- and [35S]GTPgammaS- binding assays. The rank order of the equilibrium binding constants (Kd or Ki) of adenosine receptor ligands were [3H]ZM241385 approximately CGS15943 < MRS1220 < < CV1808 approximately NECA < CGS21680 approximately adenosine < IBMECA < HEMADO approximately CPA approximately CCPA. The rank order of EC50 values for agonists were CV1808 approximately NECA < adenosine approximately CGS26180 < IBMECA < HEMADO approximately CPA approximately CCPA. This pharmacology is consistent with the literature for A2AR and suggests that Sf9 cells co-expressing A2AR, beta1, gamma2, and XLGalphaolf could serve as a heterologous expression system for A2AR drug screening.

The involvement of G proteins and regulators of receptor-G protein coupling in the pathophysiology, diagnosis and treatment of mood disorders

Biochemical research in mood disorders has focused, along the cascade of events involved in signal transduction, from studies at the level of the monoamine neurotransmitter to the level of the neurotransmitter receptors, and lately to information transduction mechanisms beyond receptors, involving the coupling of receptors with signal transducers. We review findings concerning (a) the involvement of G proteins, in the pathophysiology, diagnosis and treatment of mood disorders; (b) the importance of regulation of receptor-G protein coupling, G protein-coupled receptor kinases (GRKs), beta-arrestins, to the pathophysiology of mood disorders and the mechanism of action of antidepressants. We relate to the special complexity of mental disorders with regards to etiology and pathophysiological diagnosis as well as to the strength and limitations of the 'pharmacological bridge' approach governing studies to unravel the etiology of mental disorders. There are presently no established and reliable, sensitive and specific objective biological diagnostic markers in psychiatry that can serve as 'gold standards'. The future achievement of an objective biochemical differential diagnostic system for major mental disorders that will also enable an objective biological treatment monitoring is expected to be revolutionary for psychiatry with a magnitude similar to the impact of the discovery of psychopharmacological treatments for mental disorders more than 50 years ago.