Analysis of the pseudoautosomal X-linked gene SYBL1in bipolar affective disorder: description of a new candidate allele for psychiatric disorders

Molecular cytogenetic characterization of a de novo derivative chromosome X with an unbalanced t(X;9) translocation in a fetus and literature review

Partial trisomy 9p is one of the most frequent autosome anomalies in newborn infants featured by craniofacial dysmorphism, intellectual disability and psychomotor growth. Female patients carrying monosomy Xq usually show mild symptoms due to skewed X-chromosome inactivation (XCI). Unbalanced translocation between chromosome X and chromosome 9 is rare in prenatal diagnosis. The skewed inactivation of abnormal X would spread into the extra segment of chromosome 9 presented in the der(X) leading to mild phenotypes. We reported on a fetus with high risk of trisomy 9p(13.32 Mb 9p23-p24.3 duplication)suggested by noninvasive prenatal testing (NIPT), the fetus was normal by ultrasonography. G-banding with trypsin-giemsa (GTG), copy number variations sequencing (CNV-seq) and fluorescence in situ hybridization (FISH) were carried out to delineate the nature of rearrangement. Final karyotype of the fetus was identified as 46,X,der(X)t(X;9)(q27;p23)dn. An unbalanced X-autosome translocation with a deletion of Xqter-q27.2 and a duplication of 9pter-p23 led to mild phenotypes with no obvious alteration by prenatal ultrasonography, or obvious pathological alterations after pregnancy termination.

SNAREs and developmental disorders

Members of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) family mediate membrane fusion processes associated with vesicular trafficking and autophagy. SNAREs mediate core membrane fusion processes essential for all cells, but some SNAREs serve cell/tissue type-specific exocytic/endocytic functions, and are therefore critical for various aspects of embryonic development. Mutations or variants of their encoding genes could give rise to developmental disorders, such as those affecting the nervous system and immune system in humans. Mutations to components in the canonical synaptic vesicle fusion SNARE complex (VAMP2, STX1A/B, and SNAP25) and a key regulator of SNARE complex formation MUNC18-1, produce variant phenotypes of autism, intellectual disability, movement disorders, and epilepsy. STX11 and MUNC18-2 mutations underlie 2 subtypes of familial hemophagocytic lymphohistiocytosis. STX3 mutations contribute to variant microvillus inclusion disease. Chromosomal microdeletions involving STX16 play a role in pseudohypoparathyroidism type IB associated with abnormal imprinting of the GNAS complex locus. In this short review, I discuss these and other SNARE gene mutations and variants that are known to be associated with a variety developmental disorders, with a focus on their underlying cellular and molecular pathological basis deciphered through disease modeling. Possible pathogenic potentials of other SNAREs whose variants could be disease predisposing are also speculated upon.

Inherited duplication of the pseudoautosomal region Xq28 in a subject with Gilles de la Tourette syndrome and intellectual disability: a case report

Background

Tourette syndrome (TS) is a complex neurodevelopmental disorder (NDD) characterized by multiple chronic involuntary motor and vocal tics with onset during childhood or adolescence. Most TS patients present with additional comorbidities, typically attention deficit hyperactivity disorder (ADHD), obsessive- compulsive disorder (OCD), autism spectrum disorder (ASD) and intellectual disability (ID). Both TS and ID are genetically complex disorders that likely occur as a result of the effects of multiple genes interacting with other environmental factors. In addition to single gene mutations and chromosomal disorders, copy number variations (CNVs) are implicated across many NDDs and ID and contribute to their shared genetic etiology. Screening of CNVs using microarray-based Comparative Genomic Hybridization (aCGH) is now routinely performed in all subjects with NDD and ID.

Case presentation

We report a case of a 12-year-old girl diagnosed with Gilles de la Tourette Syndrome associated to behavior disorders and intellectual disability in particular with regard to language. Array-CGH analysis showed a CNV of a subtelomeric region Xq28 (gain of 260 kb) inherited from the healthy father. The duplication contains two genes, VAMP7 and SPRY3 of the PAR2 pseudoautosomal region. FISH analysis revealed that the duplicated segment is located on the short arm of a chromosome 13, resulting in a trisomy of the region. In the proband the expression levels of the genes evaluated in the peripheral blood sample are comparable both those of the mother and to those of female control subjects.

Conclusions

Although the trisomy of the 260 kb region from Xq28 identified in proband is also shared by the healthy father, it is tantalizing to speculate that, together with genetic risk factors inherited from the mother, it may play a role in the development of a form of Tourette syndrome with intellectual disability. This hypothesis is also supported by the fact that both genes present in the duplicated region (VAMP7 and SPRY3) are expressed in the CNS and are implicated in neurotransmission and neurite growth and branching. In addition, similar CNVs have been identified in individuals whose phenotype is associated with autism spectrum disorders or intellectual disability.

Sex chromosome abnormalities and psychiatric diseases

Excesses of sex chromosome abnormalities in patients with psychiatric diseases have recently been observed. It remains unclear whether sex chromosome abnormalities are related to sex differences in some psychiatric diseases. While studies showed evidence of susceptibility loci over many sex chromosomal regions related to various mental diseases, others demonstrated that the sex chromosome aneuploidies may be the key to exploring the pathogenesis of psychiatric disease. In this review, we will outline the current evidence on the interaction of sex chromosome abnormalities with schizophrenia, autism, ADHD and mood disorders.

Genetic Studies on the Tripartite Glutamate Synapse in the Pathophysiology and Therapeutics of Mood Disorders

Both bipolar disorder (BD) and major depressive disorder (MDD) have high morbidity and share a genetic background. Treatment options for these mood disorders are currently suboptimal for many patients; however, specific genetic variables may be involved in both pathophysiology and response to treatment. Agents such as the glutamatergic modulator ketamine are effective in treatment-resistant mood disorders, underscoring the potential importance of the glutamatergic system as a target for improved therapeutics. Here we review genetic studies linking the glutamatergic system to the pathophysiology and therapeutics of mood disorders. We screened 763 original genetic studies of BD or MDD that investigated genes encoding targets of the pathway/mediators related to the so-called tripartite glutamate synapse, including pre- and post-synaptic neurons and glial cells; 60 papers were included in this review. The findings suggest the involvement of glutamate-related genes in risk for mood disorders, treatment response, and phenotypic characteristics, although there was no consistent evidence for a specific gene. Target genes of high interest included GRIA3 and GRIK2 (which likely play a role in emergent suicidal ideation after antidepressant treatment), GRIK4 (which may influence treatment response), and GRM7 (which potentially affects risk for mood disorders). There was stronger evidence that glutamate-related genes influence risk for BD compared with MDD. Taken together, the studies show a preliminary relationship between glutamate-related genes and risk for mood disorders, suicide, and treatment response, particularly with regard to targets on metabotropic and ionotropic receptors.

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.

Membrane Trafficking in Neuronal Development: Ins and Outs of Neural Connectivity

During development, neurons progress through rapid yet stereotypical shape changes to achieve proper neuronal connectivity. This morphological progression requires carefully orchestrated plasma membrane expansion, insertion of membrane components including receptors for extracellular cues into the plasma membrane and removal and trafficking of membrane materials and proteins to specific locations. This review outlines the cellular machinery of membrane trafficking that play an integral role in neuronal cell shape change and function from initial neurite formation to pathway navigation and synaptogenesis.

Rare genomic rearrangement in a boy with Williams-Beuren syndrome associated to XYY syndrome and intriguing behavior

Williams-Beuren syndrome (WBS) is caused by a hemizygous contiguous gene microdeletion of 1.55-1.84 Mb at 7q11.23 region. Approximately, 28 genes have been shown to contribute to classical phenotype of SWB with presence of dysmorphic facial features, supravalvular aortic stenosis (SVAS), intellectual disability, and overfriendliness. With the use of Microarray-based comparative genomic hybridization and other molecular cytogenetic techniques, is possible define with more accuracy partial or atypical deletion and refine the genotype-phenotype correlation. Here, we report on a rare genomic structural rearrangement in a boy with atypical deletion in 7q11.23 and XYY syndrome with characteristic clinical signs, but not sufficient for the diagnosis of WBS. Cytogenetic analysis of G-banding showed a karyotype 47,XYY. Analysis of DNA with the technique of MLPA (Multiplex Ligation-dependent Probe Amplification) using kits a combination of kits (P064, P036, P070, and P029) identified an atypical deletion on 7q11.23. In addition, high resolution SNP Oligonucleotide Microarray Analysis (SNP-array) confirmed the alterations found by MLPA and revealed others pathogenic CNVs, in the chromosomes 7 and X. The present report demonstrates an association not yet described in literature, between Williams-Beuren syndrome and 47,XYY. The identification of atypical deletion in 7q11.23 concomitant to additional pathogenic CNVs in others genomic regions allows a better comprehension of clinical consequences of atypical genomic rearrangements.

VAMP7 modulates ciliary biogenesis in kidney cells

Epithelial cells elaborate specialized domains that have distinct protein and lipid compositions, including the apical and basolateral surfaces and primary cilia. Maintaining the identity of these domains is required for proper cell function, and requires the efficient and selective SNARE-mediated fusion of vesicles containing newly synthesized and recycling proteins with the proper target membrane. Multiple pathways exist to deliver newly synthesized proteins to the apical surface of kidney cells, and the post-Golgi SNAREs, or VAMPs, involved in these distinct pathways have not been identified. VAMP7 has been implicated in apical protein delivery in other cell types, and we hypothesized that this SNARE would have differential effects on the trafficking of apical proteins known to take distinct routes to the apical surface in kidney cells. VAMP7 expressed in polarized Madin Darby canine kidney cells colocalized primarily with LAMP2-positive compartments, and siRNA-mediated knockdown modulated lysosome size, consistent with the known function of VAMP7 in lysosomal delivery. Surprisingly, VAMP7 knockdown had no effect on apical delivery of numerous cargoes tested, but did decrease the length and frequency of primary cilia. Additionally, VAMP7 knockdown disrupted cystogenesis in cells grown in a three-dimensional basement membrane matrix. The effects of VAMP7 depletion on ciliogenesis and cystogenesis are not directly linked to the disruption of lysosomal function, as cilia lengths and cyst morphology were unaffected in an MDCK lysosomal storage disorder model. Together, our data suggest that VAMP7 plays an essential role in ciliogenesis and lumen formation. To our knowledge, this is the first study implicating an R-SNARE in ciliogenesis and cystogenesis.

The XY gene hypothesis of psychosis: origins and current status

Sex differences in psychosis and their interaction with laterality (systematic departures from 50:50 left-right symmetry across the antero-posterior neural axis) are reviewed in the context of the X-Y gene hypothesis. Aspects of laterality (handedness/cerebral asymmetry/the torque) predict (1) verbal and non-verbal ability in childhood and across adult life and (2) anatomical, physiological, and linguistic variation relating to psychosis. Neuropsychological and MRI evidence from individuals with sex chromosome aneuploidies indicates that laterality is associated with an X-Y homologous gene pair. Within each mammalian species the complement of such X-Y gene pairs reflects their potential to account for taxon-specific sexual dimorphisms. As a consequence of the mechanism of meiotic suppression of unpaired chromosomes such X-Y gene pairs generate epigenetic variation around a species defining motif that is carried to the zygote with potential to initiate embryonic gene expression in XX or XY format. The Protocadherin11XY (PCDH11XY) gene pair in Xq21.3/Yp11.2 in probable coordination with a gene or genes within PAR2 (the second pseudo-autosomal region) is the prime candidate in relation to cerebral asymmetry and psychosis in Homo sapiens. The lately-described pattern of sequence variation associated with psychosis on the autosomes may reflect a component of the human genome's adjustment to selective pressures generated by the sexually dimorphic mate recognition system.

Sex-specific association of a common variant of the XG gene with autism spectrum disorders

Autism spectrum disorders (ASD) are much more common in males than in females. Studies using both linkage and candidate gene association approaches have identified genetic variants specific to families in which all affected cases were male, suggesting that sex may interact with or otherwise influence the expression of specific genes in association with ASD. In this study, we specifically evaluated the sex-specific genetic effects of ASD with a family-based genome-wide association study approach using the data from the Autism Genetic Resource Exchange repository. We evaluated the male-specific genetic effects of ASD in 374 multiplex families of European ancestry in which all affected were male (male-only; MO) and identified a novel genome-wide significant association in the pseudoautosomal boundary on chromosome Xp22.33/Yp11.31 in the MO families of predominantly paternal origin (rs2535443, p = 3.8 × 10(-8) ). Five markers that reside within a 550 kb intergenic region on chromosome 13q33.3, between the MYO16 and IRS2 genes, also showed suggestive association with ASD in the MO families (p = 3.3 × 10(-5) to 5.3 × 10(-7) ). In contrast, none of these markers appeared to be associated with ASD in the families containing any affected females. Our results suggest that the pseudoautosomal boundary on Xp22.33/Yp11.31 may harbor male-specific genetic variants for ASD.

Absence of TI-VAMP/Vamp7 leads to increased anxiety in mice

Vesicular (v)- and target (t)-SNARE proteins assemble in SNARE complex to mediate membrane fusion. Tetanus neurotoxin-insensitive vesicular-associated membrane protein (TI-VAMP/VAMP7), a vesicular SNARE expressed in several cell types including neurons, was previously shown to play a major role in exocytosis involved in neurite growth in cultured neurons. Here we generated a complete constitutive knock-out by deleting the exon 3 of Vamp7. Loss of TI-VAMP expression did not lead to any striking developmental or neurological defect. Knock-out mice displayed decreased brain weight and increased third ventricle volume. Axon growth appeared normal in cultured knock-out neurons. Behavioral characterization unraveled that TI-VAMP knock-out was associated with increased anxiety. Our results thus suggest compensatory mechanisms allowing the TI-VAMP knock-out mice to fulfill major developmental processes. The phenotypic traits unraveled here further indicate an unexpected role of TI-VAMP-mediated vesicular traffic in anxiety and suggest a role for TI-VAMP in higher brain functions.

The Human Pseudoautosomal Region (PAR): Origin, Function and Future

The pseudoautosomal regions (PAR1 and PAR2) of the human X and Y chromosomes pair and recombine during meiosis. Thus genes in this region are not inherited in a strictly sex-linked fashion. PAR1 is located at the terminal region of the short arms and PAR2 at the tips of the long arms of these chromosomes. To date, 24 genes have been assigned to the PAR1 region. Half of these have a known function. In contrast, so far only 4 genes have been discovered in the PAR2 region. Deletion of the PAR1 region results in failure of pairing and male sterility. The gene SHOX (short stature homeobox-containing) resides in PAR1. SHOX haploinsufficiency contributes to certain features in Turner syndrome as well as the characteristics of Leri-Weill dyschondrosteosis. Only two of the human PAR1 genes have mouse homologues. These do not, however, reside in the mouse PAR1 region but are autosomal. The PAR regions seem to be relics of differential additions, losses, rearrangements and degradation of the X and Y chromosome in different mammalian lineages. Marsupials have three homologues of human PAR1 genes in their autosomes, although, in contrast to mouse, do not have a PAR region at all. The disappearance of PAR from other species seems likely and this region will only be rescued by the addition of genes to both X and Y, as has occurred already in lemmings. The present review summarizes the current understanding of the evolution of PAR and provides up-to-date information about individual genes residing in this region.

Aberrations in pseudoautosomal regions (PARs) found in infertile men with Y-chromosome microdeletions

CONTEXT

The pseudoautosomal regions (PARs) of the Y-chromosome undergo meiotic recombination with the X-chromosome. PAR mutations are associated with infertility and mental and stature disorders.

OBJECTIVE

The aim of the study was to determine whether men with Y-chromosome microdeletions have structural defects in PARs.

DESIGN AND PARTICIPANTS

Eighty-seven infertile men with Y-chromosome microdeletions and 35 controls were evaluated for chromosomal rearrangements using commercial or custom (X- and Y-chromosome) array comparative genomic hybridization or by quantitative PCR of selected PAR genes. Multisoftware-defined chromosomal gains or losses were validated by quantitative PCR and FISH.

RESULTS

Array comparative genomic hybridization confirmed the AZF deletions identified by multiplex PCR. All men with Y-chromosome microdeletions and an abnormal karyotype displayed PAR abnormalities, as did 10% of men with Y-chromosome microdeletions and a normal karyotype. None of the control subjects or infertile men without Y-chromosome microdeletions had PAR duplications or deletions. SHOX aberrations occurred in 14 men (nine gains and five losses); four were short in stature (<10th percentile), and one was tall (>95th percentile). In contrast, the height of 23 men with Y-chromosome microdeletions and normal PARs was average at 176.8 cm (50th percentile).

CONCLUSIONS

Y-chromosome microdeletions can include PAR defects causing genomic disorders such as SHOX, which may be transmitted to offspring. Previously unrecognized PAR gains and losses in men with Y-chromosome microdeletions may have consequences for offspring.

Subtelomeric microduplications in three sisters with moderate mental retardation

Copy number changes of subtelomeric regions are a common cause of mental retardation, occurring in approximately 5% of mentally retarded patients. New molecular techniques allow the identification of subtelomeric microduplications. We report a Tunisian family of three sisters with moderate mental retardation, facial dysmorphism, cardiopathy, and bilateral clinodactyly of the third and fourth toes, explored by MLPA, showing the same associated microduplications, 15q and Xq, without a concurrent deletion.

SNAREs in neurons – beyond synaptic vesicle exocytosis (Review)

The paradigm for soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) function in mammalian cells has been built on advancements in our understanding of structural and biochemical aspects of synaptic vesicle exocytosis, involving specifically synaptobrevin, syntaxin 1 and SNAP25. Interestingly, a good number of SNAREs which are not directly involved in neurotransmitter exocytosis, are either brain-enriched or have distinct neuron-specific functions. Syntaxins 12/13 regulates glutamate receptor recycling via its interaction with neuron-enriched endosomal protein of 21 kDa (NEEP21). TI-VAMP/VAMP7 is essential for neuronal morphogenesis and mediates the vesicular transport processes underlying neurite outgrowth. Ykt6 is highly enriched in the cerebral cortex and hippocampus and is targeted to a novel compartment in neurons. Syntaxin 16 has a moderate expression level in many tissues, but is rather enriched in the brain. Here, we review and discuss the neuron-specific physiology and possible pathology of these and other (such as SNAP-29 and Vti1a-beta) members of the SNARE family.

The genetics of bipolar disorder: genome 'hot regions,' genes, new potential candidates and future directions

Bipolar disorder (BP) is a complex disorder caused by a number of liability genes interacting with the environment. In recent years, a large number of linkage and association studies have been conducted producing an extremely large number of findings often not replicated or partially replicated. Further, results from linkage and association studies are not always easily comparable. Unfortunately, at present a comprehensive coverage of available evidence is still lacking. In the present paper, we summarized results obtained from both linkage and association studies in BP. Further, we indicated new potential interesting genes, located in genome 'hot regions' for BP and being expressed in the brain. We reviewed published studies on the subject till December 2007. We precisely localized regions where positive linkage has been found, by the NCBI Map viewer (http://www.ncbi.nlm.nih.gov/mapview/); further, we identified genes located in interesting areas and expressed in the brain, by the Entrez gene, Unigene databases (http://www.ncbi.nlm.nih.gov/entrez/) and Human Protein Reference Database (http://www.hprd.org); these genes could be of interest in future investigations. The review of association studies gave interesting results, as a number of genes seem to be definitively involved in BP, such as SLC6A4, TPH2, DRD4, SLC6A3, DAOA, DTNBP1, NRG1, DISC1 and BDNF. A number of promising genes, which received independent confirmations, and genes that have to be further investigated in BP, have been also systematically listed. In conclusion, the combination of linkage and association approaches provided a number of liability genes. Nevertheless, other approaches are required to disentangle conflicting findings, such as gene interaction analyses, interaction with psychosocial and environmental factors and, finally, endophenotype investigations.

Methylation of two Homo sapiens-specific X-Y homologous genes in Klinefelter's syndrome (XXY)

An increased incidence of psychiatric and structural brain abnormalities in individuals with Klinefelter syndrome (KS, 47 XXY) could be due to the presence of extra copies of X-Y homologous genes that escape X inactivation. Of particular interest are the two brain-expressed genes Protocadherin11XY (PCDH11XY) and the Synaptobrevin-like gene (SYBL1) which have been duplicated from the X chromosome to the Y chromosome to give X-Y homologous gene pairs that are specific to modern humans. We examined the DNA of KS individuals reported recently by DeLisi et al. 2005 and determined the parental origin of the X alleles, the degree of skewed X inactivation and investigated the CpG island methylation status of PCDH11XY and SYBL1 by bisulphite sequencing and quantification of methylated HpaII sites. We used a novel method for quantification of unmethylated CpGs with the restriction enzyme McrBC which cuts methylated but not unmethylated CpGs. The results showed that KS individuals have two methylated and one unmethylated SYBL1 allele whereas PCDH11XY is unmethylated and escapes X inactivation on the extra X chromosome. Overexpression of PCDH11XY in KS is probable and variable escape from inactivation of this Homo sapiens-specific gene could account for some abnormalities in KS. The origin of the parental alleles or their preferential X inactivation was not associated with psychotic symptoms.

Bipolar affective disorder in a male with a deletion of Y chromosome -- a case report

We report on a 25-year-old male with bipolar disorder, dysmorphic features and a deletion of the long arm of Y chromosome. A potential association between sex chromosome abnormalities and a susceptibility to major psychiatric disorders has been documented. However there have been very few reports on the coincidence of Y chromosome aberrations with bipolar disorder. Cytogenetic studies have contributed to the identification of several disease genes. Karyotyping of patients with bipolar disorder in order to identify candidate regions for linkage studies has been recommended.

Sex-specific association between bipolar affective disorder in women and GPR50, an X-linked orphan G protein-coupled receptor

GPR50 is an orphan G protein-coupled receptor (GPCR) located on Xq28, a region previously implicated in multiple genetic studies of bipolar affective disorder (BPAD). Allele frequencies of three polymorphisms in GPR50 were compared in case-control studies between subjects with BPAD (264), major depressive disorder (MDD) (226), or schizophrenia (SCZ) (263) and ethnically matched controls (562). Significant associations were found between an insertion/deletion polymorphism in exon 2 and both BPAD (P=0.0070), and MDD (P=0.011) with increased risk associated with the deletion variant (GPR50(Delta502-505)). When the analysis was restricted to female subjects, the associations with BPAD and MDD increased in significance (P=0.00023 and P=0.0064, respectively). Two other single-nucleotide polymorphisms (SNPs) tested within this gene showed associations between: the female MDD group and an SNP in exon 2 (P=0.0096); and female SCZ and an intronic SNP (P=0.0014). No association was detected in males with either MDD, BPAD or SCZ. These results suggest that GPR50(Delta502-505), or a variant in tight linkage disequilibrium with this polymorphism, is a sex-specific risk factor for susceptibility to bipolar disorder, and that other variants in the gene may be sex-specific risk factors in the development of schizophrenia.

Quantitation of X-Y homologous genes in patients with schizophrenia by multiplex polymerase chain reaction

OBJECTIVES

The genetic basis of schizophrenia is obscure. In an XX male patient with schizophrenia we previously showed that one X;Y translocation breakpoint was in pseudoautosomal region 1 (PAR1) with the effect that the proximal segment of PAR1 from the PAR1 boundary to acetylserotonin N-methyl transferase (ASMT) distally was triplicated in this patient. This study determined whether dosage imbalances of X-Y homologous regions in general are associated with schizophrenia.

METHODS

A multiplex semi-quantitative polymerase chain reaction assay was developed to quantify MIC2 gene as a representative of PAR1 and compare it with the SYBL1 gene which maps in pseudoautosomal region 2 (PAR2) and protocadherin XY (PCDHXY), located at Xq21.3. Each of these three loci was co-amplified with the autosomal gene MSX2 using Cy5-labelled primers and the products separated by electrophoresis in polyacrylamide gels. Results were expressed as ratios of peak area of the target gene to MSX2 which served as an internal dosage control.

RESULTS

Using genomes with sex chromosome aneuploidies, the method was found sensitive enough to detect a two-fold difference in gene copy number. We confirmed the MIC2 triplication in the XX male patient but found no significant difference in gene dosage of MIC2, PCDHXY and SYBL1 in a panel of 17 patients with schizophrenia compared to controls.

CONCLUSIONS

No evidence was obtained for gene dosage imbalances in MIC2, PCDHXY and SYBL1 in patients with schizophrenia.

Bipolar disorder susceptibility region on Xq24-q27.1 in Finnish families

Bipolar disorder (BPD) is a common disorder characterized by episodes of mania, hypomania and depression. The genetic background of BPD remains undefined, although several putative loci predisposing to BPD have been identified. We have earlier reported significant evidence of linkage for BPD to chromosome Xq24-q27.1 in an extended pedigree from the late settlement region of the genetically isolated population of Finland. Further, we established a distinct chromosomal haplotype covering a 19 cM region on Xq24-q27.1 co-segregating with the disorder. Here, we have further analyzed this X-chromosomal region using a denser marker map and monitored X-chromosomal haplotypes in a study sample of 41 Finnish bipolar families. Only a fraction of the families provided any evidence of linkage to this region, suggesting that a relatively rare gene predisposing to BPD is enriched in this linked pedigree. The genome-wide scan for BPD predisposing loci in this large pedigree indicated that this particular X-chromosomal region provides the best evidence of linkage genome-wide, suggesting an X-chromosomal gene with a major role for the genetic predisposition of BPD in this family.

Excess of allele1 for alpha3 subunit GABA receptor gene (GABRA3) in bipolar patients: a multicentric association study

The available data from preclinical and pharmacological studies on the role of gamma amino butyric acid (GABA) support the hypothesis that a dysfunction in brain GABAergic system activity contributes to the vulnerability to bipolar affective disorders (BPAD). Moreover, the localization of the alpha3 subunit GABA receptor GABRA3 gene on the Xq28, a region of interest in certain forms of bipolar illness, suggests that GABRA3 may be a candidate gene in BPAD. In the present study, we tested the genetic contribution of the GABRA3 dinucleotide polymorphism in a European multicentric case-control sample, matched for sex and ethnogeographical origin. Allele and genotype (in females) frequencies were compared in 185 BPAD patients and 370 controls. A significant increase of genotype 1-1 was observed in BPAD females compared to controls (P=0.0004). Furthermore, when considering recessivity of allele 1 (females with genotype 1-1 and males carrying allele 1), results were even more significant (P= 0.00002). Our findings suggest that the GABRA3 polymorphism may confer susceptibility to or may be in linkage disequilibrium with another gene involved in the genetic etiology of BPAD.

Association between a polymorphism in the pseudoautosomal X-linked gene SYBL1 and bipolar affective disorder

In the past decade, several chromosomal regions have been analyzed for linkage with bipolar affective disorder (BPAD). There have been conflicting results regarding the involvement of X-chromosomal regions in harboring susceptibility genes for BPAD. Recently, a new candidate gene (SYBL1) for BPAD has been described on Xq28. SYBL1, which maps to the Xq pseudoautosomal region (PAR), encodes a member of the synaptobrevin family of proteins involved in synaptic vesicle docking, exocytosis, and membrane transport. A subsequent case-control association study, including 110 US-American patients with BPAD and 119 unrelated controls, investigated a potential etiological role of a novel polymorphism (G-->C transversion) in a regulatory region of the SYBL1 gene. In this analysis, the C allele showed a statistical trend to be more frequent in males with BPAD than in respective controls (P=0.06). This finding prompted us to verify whether a similar effect was also present in a larger German sample of 164 unrelated patients with BPAD (148 patients with BP I disorder, 16 patients with BP II disorder) and 267 controls. We observed a significantly increased frequency of genotypes homozygous for the C allele in females with BPAD in comparison with controls (P=0.017). Thus, our data strengthen the role of the SYBL1 gene as a candidate gene for BPAD.

Genetic basis of anxiety-like behaviour: a critical review

The way genetic and/or environmental factors influence psychiatric disorders is an enduring question in the field of human psychiatric diseases. Anxiety-related disorders provide a relevant example of how such an interaction is involved in the aetiology of a psychiatric disease. In this paper we review the literature on that subject, reporting data derived from human and rodent studies. We present in a critical way the animal models used in the studies aimed at investigating the genetic basis of anxiety, including inbred mice, selected lines, multiple marker strains, or knockout mice and review data reporting environmental components influencing anxiety-related behaviours. We conclude that anxiety is a complex behaviour, underlined not only by genetic or environmental factors but also by multiple interactions between these two factors.

Mutation analysis of SYNJ1: a possible candidate gene for chromosome 21q22-linked bipolar disorder

Genes involved in the regulation of synaptic vesicle function are potential candidates for the development of psychiatric disorders. In addition to experimental and theoretical considerations, a number of genes involved in synaptic vesicle function map to regions of the genome that have been linked to bipolar disorder (BPD) and schizophrenia (SZ). One is synaptojanin 1 (SYNJ1) which maps to 21q22.2, a chromosomal region that has been linked to BPD in a subset of families in several studies. Synaptojanin 1 is an inositol 5-phosphatase that has an important role in synaptic vesicle endocytosis. Mutation screening of 32 exons, intron--exon junctions, and 839 bases of 5'-flanking DNA resulted in the identification of 11 mutations of which four were very common and seven were very rare. Of the 11 mutations identified, several may have functional significance including two coding variants, two that may affect the binding of a transcription factor, and two that involve known splicing regulatory domains. Five bipolar patients out of 149 analyzed were found who have one of the four rare variants that were most likely to have functional significance compared with 0/148 controls. The allele frequencies for three of the four common variants were very similar in bipolar patients and controls. A slight difference in allele frequency was found for an interesting mutation we detected in intron 12 in which two non-adjacent thymidine residues are deleted in a poly-AT tract located near the exon 12 splice donor site (chi(2) = 2.45, P = 0.12, 2-tailed). Although we failed to unequivocally identify a specific SYNJ1 allele that could be responsible for putative chromosome 21q22-linked BPD, several interesting variants were found to be increased in bipolar subjects and should be further investigated.

Polymorphism in SNAP29 gene promoter region associated with schizophrenia

Linkage studies indicate that chromosome 22q contains a locus, or loci, for schizophrenia (SZ) and bipolar disorder (BPD). Furthermore, the congenital disorder velo cardio facial syndrome (VCFS), which is usually caused by a 22q11 microdeletion, is associated with an increased prevalence of psychiatric disease, including SZ and BPD. One plausible candidate gene that maps to 22q11, in a region deleted in the most common form of VCFS, is SNAP29, a member of the SNAP-25 family of SNARE proteins. To search for possible functional mutations in SNAP29 that could be analyzed as candidates for 22q11-linked psychiatric problems, exons, intron-exon junctions and the promoter region were screened. No coding variants were found, although a silent mutation at codon 6 and three single nucleotide polymorphisms (SNPs) were identified in the 5' untranslated and promoter regions. One SNP, an A-->G transition 923 [corrected] nucleotides upstream of the transcription start site, showed a moderately significant difference in the distribution of alleles and genotypes in patients with SZ compared with controls (allele frequency: chi(2) = 5.57, 1 df, P = 0.018; genotype: chi(2) = 9.49, 2 df, P = 0.009; odds ratio = 1.59, 95% Cl = 1.08--2.34). No significant difference was found in patients with BPD. Although the functional significance of this mutation is not known, the tetranucleotide core sequence of the ets and IK2 families of transcription factors is altered as a result of the SNP. These data suggest that a mutation in the SNAP29 gene promoter region, or a mutation in linkage disequilibrium with the promoter SNP, may be involved in the pathogenesis of chromosome 22-linked SZ.