Identification of rare copy number variants in high burden schizophrenia families

Diagnostic Value of Microarray Method in Autism Spectrum Disorder, Intellectual Disability, and Multiple Congenital Anomalies and Some Candidate Genes for Autism: Experience of Two Centers

Objective:

This study aimed to demonstrate the diagnostic value of microarray testing in autism spectrum disorder, intellectual disability, and multiple congenital anomalies of unknown etiology, as well as to report some potential candidate genes for autism.

Methods:

Microarray analysis records between January 2016 and December 2017 from two Genetic Diagnostic Centers in Turkey, Kanuni Sultan Suleyman and Adana Numune Training and Research Hospital, were compiled. Detected copy number variations (CNVs) were classified as benign, likely benign, variants of uncertain significance (VUS), likely pathogenic, and pathogenic according to American College of Medical Genetics and Genomics guidelines. The clinical findings of the some patients and the literature data were compared.

Results:

In 109 (24.5%) of 445 patients, a total of 163 CNVs with reporting criterion feature were detected. Sixty-nine (42%) and 8 (5%) of these were evaluated as pathogenic and likely pathogenic, respectively. Fifteen (9%) CNVs were also evaluated as VUS. Pathogenic or likely pathogenic CNVs were detected in 61 (13.6%) of 445 patients.

Conclusions:

We found that the probability of elucidating the etiology of microarray method in autism spectrum disorder, intellectual disability, and multiple congenital anomalies is 13.6% with a percentage similar to the literature. We suggest that the MYT1L, PXDN, TPO, and AUTS2 genes are all strong candidate genes for autism spectrum disorders. We detailed the clinical findings of the cases and reported that some CNV regions in the genome may be associated with autism.

Strawberry notch homolog 2 regulates the response to interleukin-6 in the central nervous system

BACKGROUND

The cytokine interleukin-6 (IL-6) modulates a variety of inflammatory processes and, context depending, can mediate either pro- or anti-inflammatory effects. Excessive IL-6 signalling in the brain is associated with chronic inflammation resulting in neurodegeneration. Strawberry notch homolog 2 (Sbno2) is an IL-6-regulated gene whose function is largely unknown. Here we aimed to address this issue by investigating the impact of Sbno2 disruption in mice with IL-6-mediated neuroinflammation.

METHODS

Mice with germline disruption of Sbno2 (Sbno2-/-) were generated and crossed with transgenic mice with chronic astrocyte production of IL-6 (GFAP-IL6). Phenotypic, molecular and transcriptomic analyses were performed on tissues and primary cell cultures to clarify the role of SBNO2 in IL-6-mediated neuroinflammation.

RESULTS

We found Sbno2-/- mice to be viable and overtly normal. By contrast GFAP-IL6 × Sbno2-/- mice had more severe disease compared with GFAP-IL6 mice. This was evidenced by exacerbated neuroinflammation and neurodegeneration and enhanced IL-6-responsive gene expression. Cell culture experiments on primary astrocytes from Sbno2-/- mice further showed elevated and sustained transcript levels of a number of IL-6 stimulated genes. Notably, despite enhanced disease in vivo and gene expression both in vivo and in vitro, IL-6-stimulated gp130 pathway activation was reduced when Sbno2 is disrupted.

CONCLUSION

Based on these results, we propose a role for SBNO2 as a novel negative feedback regulator of IL-6 that restrains the excessive inflammatory actions of this cytokine in the brain.

Myt1l haploinsufficiency leads to obesity and multifaceted behavioral alterations in mice

BACKGROUND

The zinc finger domain containing transcription factor Myt1l is tightly associated with neuronal identity and is the only transcription factor known that is both neuron-specific and expressed in all neuronal subtypes. We identified Myt1l as a powerful reprogramming factor that, in combination with the proneural bHLH factor Ascl1, could induce neuronal fate in fibroblasts. Molecularly, we found it to repress many non-neuronal gene programs, explaining its supportive role to induce and safeguard neuronal identity in combination with proneural bHLH transcriptional activators. Moreover, human genetics studies found MYT1L mutations to cause intellectual disability and autism spectrum disorder often coupled with obesity.

METHODS

Here, we generated and characterized Myt1l-deficient mice. A comprehensive, longitudinal behavioral phenotyping approach was applied.

RESULTS

Myt1l was necessary for survival beyond 24 h but not for overall histological brain organization. Myt1l heterozygous mice became increasingly overweight and exhibited multifaceted behavioral alterations. In mouse pups, Myt1l haploinsufficiency caused mild alterations in early socio-affective communication through ultrasonic vocalizations. In adulthood, Myt1l heterozygous mice displayed hyperactivity due to impaired habituation learning. Motor performance was reduced in Myt1l heterozygous mice despite intact motor learning, possibly due to muscular hypotonia. While anxiety-related behavior was reduced, acoustic startle reactivity was enhanced, in line with higher sensitivity to loud sound. Finally, Myt1l haploinsufficiency had a negative impact on contextual fear memory retrieval, while cued fear memory retrieval appeared to be intact.

LIMITATIONS

In future studies, additional phenotypes might be identified and a detailed characterization of direct reciprocal social interaction behavior might help to reveal effects of Myt1l haploinsufficiency on social behavior in juvenile and adult mice.

CONCLUSIONS

Behavioral alterations in Myt1l haploinsufficient mice recapitulate several clinical phenotypes observed in humans carrying heterozygous MYT1L mutations and thus serve as an informative model of the human MYT1L syndrome.

Long non-coding RNA-associated competing endogenous RNA axes in the olfactory epithelium in schizophrenia: a bioinformatics analysis

The etiology of schizophrenia (SCZ), as a serious mental illness, is unknown. The significance of genetics in SCZ pathophysiology is yet unknown, and newly identified mechanisms involved in the regulation of gene transcription may be helpful in determining how these changes affect SCZ development and progression. In the current work, we used a bioinformatics approach to describe the role of long non-coding RNA (lncRNA)-associated competing endogenous RNAs (ceRNAs) in the olfactory epithelium (OE) samples in order to better understand the molecular regulatory processes implicated in SCZ disorders in living individuals. The Gene Expression Omnibus database was used to obtain the OE microarray dataset (GSE73129) from SCZ sufferers and control subjects, which contained information about both lncRNAs and mRNAs. The limma package of R software was used to identify the differentially expressed lncRNAs (DElncRNAs) and mRNAs (DEmRNAs). RNA interaction pairs were discovered using the Human MicroRNA Disease Database, DIANA-LncBase, and miRTarBase databases. In this study, the Pearson correlation coefficient was utilized to find positive correlations between DEmRNAs and DElncRNAs in the ceRNA network. Eventually, lncRNA-associated ceRNA axes were developed based on co-expression relations and DElncRNA-miRNA-DEmRNA interactions. This work found six potential DElncRNA-miRNA-DEmRNA loops in SCZ pathogenesis, including, SNTG2-AS1/hsa-miR-7-5p/SLC7A5, FLG-AS1/hsa-miR-34a-5p/FOSL1, LINC00960/hsa-miR-34a-5p/FOSL1, AQP4-AS1/hsa-miR-335-5p/FMN2, SOX2-OT/hsa-miR-24-3p/NOS3, and CASC2/hsa-miR-24-3p/NOS3. According to the findings, ceRNAs in OE might be promising research targets for studying SCZ molecular mechanisms. This could be a great opportunity to examine different aspects of neurodevelopment that may have been hampered early in SCZ patients.

The conserved ASTN2/BRINP1 locus at 9q33.1-33.2 is associated with major psychiatric disorders in a large pedigree from Southern Spain

We investigated the genetic causes of major mental disorders (MMDs) including schizophrenia, bipolar disorder I, major depressive disorder and attention deficit hyperactive disorder, in a large family pedigree from Alpujarras, South of Spain, a region with high prevalence of psychotic disorders. We applied a systematic genomic approach based on karyotyping (n = 4), genotyping by genome-wide SNP array (n = 34) and whole-genome sequencing (n = 12). We performed genome-wide linkage analysis, family-based association analysis and polygenic risk score estimates. Significant linkage was obtained at chromosome 9 (9q33.1–33.2, LOD score = 4.11), a suggestive region that contains five candidate genes ASTN2, BRINP1, C5, TLR4 and TRIM32, previously associated with MMDs. Comprehensive analysis associated the MMD phenotype with genes of the immune system with dual brain functions. Moreover, the psychotic phenotype was enriched for genes involved in synapsis. These results should be considered once studying the genetics of psychiatric disorders in other families, especially the ones from the same region, since founder effects may be related to the high prevalence.

Inherited L1 Retrotransposon Insertions Associated With Risk for Schizophrenia and Bipolar Disorder

Studies of the genetic heritability of schizophrenia and bipolar disorder examining single nucleotide polymorphisms (SNPs) and copy number variations have failed to explain a large portion of the genetic liability, resulting in substantial missing heritability. Long interspersed element 1 (L1) retrotransposons are a type of inherited polymorphic variant that may be associated with risk for schizophrenia and bipolar disorder. We performed REBELseq, a genome wide assay for L1 sequences, on DNA from male and female persons with schizophrenia and controls (n = 63 each) to identify inherited L1 insertions and validated priority insertions. L1 insertions of interest were genotyped in DNA from a replication cohort of persons with schizophrenia, bipolar disorder, and controls (n = 2268 each) to examine differences in carrier frequencies. We identified an inherited L1 insertion in ARHGAP24 and a quadallelic SNP (rs74169643) inside an L1 insertion in SNTG2 that are associated with risk for developing schizophrenia and bipolar disorder (all odds ratios ~1.2). Pathway analysis identified 15 gene ontologies that were differentially affected by L1 burden, including multiple ontologies related to glutamatergic signaling and immune function, which have been previously associated with schizophrenia. These findings provide further evidence supporting the role of inherited repetitive genetic elements in the heritability of psychiatric disorders.

MYT1L: A systematic review of genetic variation encompassing schizophrenia and autism

Variations in MYT1L, a gene encoding a transcription factor expressed in the brain, have been associated with autism, intellectual disability, and schizophrenia. Here we provide an updated review of published reports of neuropsychiatric correlates of loss of function and duplication of MYT1L. Of 27 duplications all were partial; 33% were associated exclusively with schizophrenia, and the chromosomal locations of schizophrenia-associated duplications exhibited a distinct difference in pattern-of-location from those associated with autism and/or intellectual disability. Of 51 published heterozygous loss of function variants, all but one were associated with intellectual disability, autism, or both, and one resulted in no neuropsychiatric diagnosis. There were no reports of schizophrenia associated with loss of function variants of MYT1L (Fisher's exact p < .00001, for contrast with all reported duplications). Although the precise function of the various mutations remains unspecified, these data collectively establish the candidacy of MYT1L as a reciprocal mutation, in which schizophrenia may be engendered by partial duplications, typically involving the 3' end of the gene, while developmental disability-notably autism-is associated with both loss of function and partial duplication. Future research on the specific effects of contrasting mutations in MYT1L may provide insight into the causal origins of autism and schizophrenia.

Phenotypic spectrum of NRXN1 mono- and bi-allelic deficiency: A systematic review

Neurexins are presynaptic cell adhesion molecules critically involved in synaptogenesis and vesicular neurotransmitter release. They are encoded by three genes (NRXN1-3), each yielding a longer alpha (α) and a shorter beta (β) transcript. Deletions spanning the promoter and the initial exons of the NRXN1 gene, located in chromosome 2p16.3, are associated with a variety of neurodevelopmental, psychiatric, neurological and neuropsychological phenotypes. We have performed a systematic review to define (a) the clinical phenotypes most associated with mono-allelic exonic NRXN1 deletions, and (b) the phenotypic features of NRXN1 bi-allelic deficiency due to compound heterozygous deletions/mutations. Clinically, three major conclusions can be drawn: (a) incomplete penetrance and pleiotropy do not allow reliable predictions of clinical outcome following prenatal detection of mono-allelic exonic NRXN1 deletions. Newborn carriers should undergo periodic neuro-behavioral observations for the timely detection of warning signs and the prescription of early behavioral intervention; (b) the presence of additional independent genetic risk factors should always be sought, as they may influence prognosis; (c) children with exonic NRXN1 deletions displaying early-onset, severe psychomotor delay in the context of a Pitt-Hopkins-like syndrome 2 phenotype, should undergo DNA sequencing of the spared NRXN1 allele in search for mutations or very small insertions/deletions.

Gene-environment interplay in the etiology of psychosis

Schizophrenia and other types of psychosis incur suffering, high health care costs and loss of human potential, due to the combination of early onset and poor response to treatment. Our ability to prevent or cure psychosis depends on knowledge of causal mechanisms. Molecular genetic studies show that thousands of common and rare variants contribute to the genetic risk for psychosis. Epidemiological studies have identified many environmental factors associated with increased risk of psychosis. However, no single genetic or environmental factor is sufficient to cause psychosis on its own. The risk of developing psychosis increases with the accumulation of many genetic risk variants and exposures to multiple adverse environmental factors. Additionally, the impact of environmental exposures likely depends on genetic factors, through gene-environment interactions. Only a few specific gene-environment combinations that lead to increased risk of psychosis have been identified to date. An example of replicable gene-environment interaction is a common polymorphism in the AKT1 gene that makes its carriers sensitive to developing psychosis with regular cannabis use. A synthesis of results from twin studies, molecular genetics, and epidemiological research outlines the many genetic and environmental factors contributing to psychosis. The interplay between these factors needs to be considered to draw a complete picture of etiology. To reach a more complete explanation of psychosis that can inform preventive strategies, future research should focus on longitudinal assessments of multiple environmental exposures within large, genotyped cohorts beginning early in life.

Clinical significance of germline copy number variation in susceptibility of human diseases

Germline copy number variation (CNV) is considered to be an important form of human genetic polymorphisms. Previous studies have identified amounts of CNVs in human genome by advanced technologies, such as comparative genomic hybridization, single nucleotide genotyping, and high-throughput sequencing. CNV is speculated to be derived from multiple mechanisms, such as nonallelic homologous recombination (NAHR) and nonhomologous end-joining (NHEJ). CNVs cover a much larger genome scale than single nucleotide polymorphisms (SNPs), and may alter gene expression levels by means of gene dosage, gene fusion, gene disruption, and long-range regulation effects, thus affecting individual phenotypes and playing crucial roles in human pathogenesis. The number of studies linking CNVs with common complex diseases has increased dramatically in recent years. Here, we provide a comprehensive review of the current understanding of germline CNVs, and summarize the association of germline CNVs with the susceptibility to a wide variety of human diseases that were identified in recent years. We also propose potential issues that should be addressed in future studies.

Family studies to find rare high risk variants in migraine

INTRODUCTION

Migraine has long been known as a common complex disease caused by genetic and environmental factors. The pathophysiology and the specific genetic susceptibility are poorly understood. Common variants only explain a small part of the heritability of migraine. It is thought that rare genetic variants with bigger effect size may be involved in the disease. Since migraine has a tendency to cluster in families, a family approach might be the way to find these variants. This is also indicated by identification of migraine-associated loci in classical linkage-analyses in migraine families. A single migraine study using a candidate-gene approach was performed in 2010 identifying a rare mutation in the TRESK potassium channel segregating in a large family with migraine with aura, but this finding has later become questioned. The technologies of next-generation sequencing (NGS) now provides an affordable tool to investigate the genetic variation in the entire exome or genome. The family-based study design using NGS is described in this paper. We also review family studies using NGS that have been successful in finding rare variants in other common complex diseases in order to argue the promising application of a family approach to migraine.

METHOD

PubMed was searched to find studies that looked for rare genetic variants in common complex diseases through a family-based design using NGS, excluding studies looking for de-novo mutations, or using a candidate-gene approach and studies on cancer. All issues from Nature Genetics and PLOS genetics 2014, 2015 and 2016 (UTAI June) were screened for relevant papers. Reference lists from included and other relevant papers were also searched. For the description of the family-based study design using NGS an in-house protocol was used.

RESULTS

Thirty-two successful studies, which covered 16 different common complex diseases, were included in this paper. We also found a single migraine study. Twenty-three studies found one or a few family specific variants (less than five), while other studies found several possible variants. Not all of them were genome wide significant. Four studies performed follow-up analyses in unrelated cases and controls and calculated odds ratios that supported an association between detected variants and risk of disease. Studies of 11 diseases identified rare variants that segregated fully or to a large degree with the disease in the pedigrees.

CONCLUSION

It is possible to find rare high risk variants for common complex diseases through a family-based approach. One study using a family approach and NGS to find rare variants in migraine has already been published but with strong limitations. More studies are under way.

Copy number variants analysis in a cohort of isolated and syndromic developmental delay/intellectual disability reveals novel genomic disorders, position effects and candidate disease genes

BACKGROUND

Array-comparative genomic hybridization (array-CGH) is a widely used technique to detect copy number variants (CNVs) associated with developmental delay/intellectual disability (DD/ID).

AIMS

Identification of genomic disorders in DD/ID.

MATERIALS AND METHODS

We performed a comprehensive array-CGH investigation of 1,015 consecutive cases with DD/ID and combined literature mining, genetic evidence, evolutionary constraint scores, and functional information in order to assess the pathogenicity of the CNVs.

RESULTS

We identified non-benign CNVs in 29% of patients. Amongst the pathogenic variants (11%), detected with a yield consistent with the literature, we found rare genomic disorders and CNVs spanning known disease genes. We further identified and discussed 51 cases with likely pathogenic CNVs spanning novel candidate genes, including genes encoding synaptic components and/or proteins involved in corticogenesis. Additionally, we identified two deletions spanning potential Topological Associated Domain (TAD) boundaries probably affecting the regulatory landscape.

DISCUSSION AND CONCLUSION

We show how phenotypic and genetic analyses of array-CGH data allow unraveling complex cases, identifying rare disease genes, and revealing unexpected position effects.

A genome-wide CNV analysis of schizophrenia reveals a potential role for a multiple-hit model

Schizophrenia is a chronic and severe psychiatric disorder that is highly heritable. While both common and rare genetic variants contribute to disease risk, many questions still remain about disease etiology. We performed a genome-wide analysis of copy number variants (CNVs) in 166 schizophrenia subjects and 52 psychiatrically healthy controls. First, overall CNV characteristics were compared between cases and controls. The only statistically significant finding was that deletions comprised a greater proportion of CNVs in cases. High interest CNVs were then identified as conservative using the following filtering criteria: (i) known deleterious CNVs; (ii) CNVs > 1 Mb that were novel (not found in a database of control individuals); and (iii) CNVs < 1 Mb that were novel and that overlapped the coding region of a gene of interest. Cases did not harbor a higher proportion of conservative CNVs in comparison to controls. However, similar to previous reports, cases had a slightly higher proportion of individuals with clinically significant CNVs (known deleterious or conservative CNVs > 1 Mb) or with multiple conservative CNVs. Two case individuals with the highest burden of conservative CNVs also share a recurrent 15q11.2 BP1-2 deletion, indicating a role for a potential multiple-hit CNV model for schizophrenia. In total, we report three 15q11.2 BP1-2 deletion individuals with schizophrenia, adding to a growing body of evidence that this CNV is involved in disease etiology.

Refinement of the critical 2p25.3 deletion region: the role of MYT1L in intellectual disability and obesity

PURPOSE

Submicroscopic deletions of chromosome band 2p25.3 are associated with intellectual disability and/or central obesity. Although MYT1L is believed to be a critical gene responsible for intellectual disability, so far no unequivocal data have confirmed this hypothesis.

METHODS

In this study we evaluated a cohort of 22 patients (15 sporadic patients and two families) with a 2p25.3 aberration to further refine the clinical phenotype and to delineate the role of MYT1L in intellectual disability and obesity. In addition, myt1l spatiotemporal expression in zebrafish embryos was analyzed by quantitative polymerase chain reaction and whole-mount in situ hybridization.

RESULTS

Complete MYT1L deletion, intragenic deletion, or duplication was observed in all sporadic patients, in addition to two patients with a de novo point mutation in MYT1L. The familial cases comprise a 6-Mb deletion in a father and his three children and a 5' MYT1L overlapping duplication in a father and his two children. Expression analysis in zebrafish embryos shows specific myt1l expression in the developing brain.

CONCLUSION

Our data strongly strengthen the hypothesis that MYT1L is the causal gene for the observed syndromal intellectual disability. Moreover, because 17 patients present with obesity/overweight, haploinsufficiency of MYT1L might predispose to weight problems with childhood onset.Genet Med 17 6, 460-466.

Novel treatment strategies for schizophrenia from improved understanding of genetic risk

Recent years have seen significant advances in our understanding of the genetic basis of schizophrenia. In particular, genome-wide approaches have suggested the involvement of many common genetic variants of small effect, together with a few rare variants exerting relatively large effects. While unequivocal identification of the relevant genes has, for the most part, remained elusive, the genes revealed as potential candidates can in many cases be clustered into functionally related groups which are potentially open to therapeutic intervention. In this review, we summarise this information, focusing on the accumulating evidence that genetic dysfunction at glutamatergic synapses and post-synaptic signalling complexes contributes to the aetiology of the disease. In particular, there is converging support for involvement of post-synaptic JNK pathways in disease aetiology. An expansion of our neurobiological knowledge of the basis of schizophrenia is urgently needed, yet some promising novel pharmacological targets can already be discerned.

Genetic Associations with Plasma B12, B6, and Folate Levels in an Ischemic Stroke Population from the Vitamin Intervention for Stroke Prevention (VISP) Trial

Background: B vitamins play an important role in homocysteine metabolism, with vitamin deficiencies resulting in increased levels of homocysteine and increased risk for stroke. We performed a genome-wide association study (GWAS) in 2,100 stroke patients from the Vitamin Intervention for Stroke Prevention (VISP) trial, a clinical trial designed to determine whether the daily intake of high-dose folic acid, vitamins B₆, and B₁₂ reduce recurrent cerebral infarction.

Methods: Extensive quality control (QC) measures resulted in a total of 737,081 SNPs for analysis. Genome-wide association analyses for baseline quantitative measures of folate, Vitamins B₁₂, and B₆ were completed using linear regression approaches, implemented in PLINK.

Results: Six associations met or exceeded genome-wide significance (P ≤ 5 × 10⁻⁰⁸). For baseline Vitamin B₁₂, the strongest association was observed with a non-synonymous SNP (nsSNP) located in the CUBN gene (P = 1.76 × 10⁻¹³). Two additional CUBN intronic SNPs demonstrated strong associations with B₁₂ (P = 2.92 × 10⁻¹⁰ and 4.11 × 10⁻¹⁰), while a second nsSNP, located in the TCN1 gene, also reached genome-wide significance (P = 5.14 × 10⁻¹¹). For baseline measures of Vitamin B₆, we identified genome-wide significant associations for SNPs at the ALPL locus (rs1697421; P = 7.06 × 10⁻¹⁰ and rs1780316; P = 2.25 × 10⁻⁰⁸). In addition to the six genome-wide significant associations, nine SNPs (two for Vitamin B₆, six for Vitamin B₁₂, and one for folate measures) provided suggestive evidence for association (P ≤ 10⁻⁰⁷).

Conclusion: Our GWAS study has identified six genome-wide significant associations, nine suggestive associations, and successfully replicated 5 of 16 SNPs previously reported to be associated with measures of B vitamins. The six genome-wide significant associations are located in gene regions that have shown previous associations with measures of B vitamins; however, four of the nine suggestive associations represent novel finding and warrant further investigation in additional populations.

Aberrant DNA methylation of blood in schizophrenia by adjusting for estimated cellular proportions

DNA methylation, which is the transference of a methyl group to the 5'-carbon position of the cytosine in a CpG dinucleotide, is one of the major mechanisms of epigenetic modifications. A number of studies have demonstrated altered DNA methylation of peripheral blood cells in schizophrenia (SCZ) in previous studies. However, most of these studies have been limited to the analysis of the CpG sites in CpG islands in gene promoter regions, and cell-type proportions of peripheral leukocytes, which may be one of the potential confounding factors for DNA methylation, have not been adjusted in these studies. In this study, we performed a genome-wide DNA methylation profiling of the peripheral leukocytes from patients with SCZ and from non-psychiatric controls (N = 105; 63 SCZ and 42 control subjects) using a quantitative high-resolution DNA methylation microarray which covered across the whole gene region (485,764 CpG dinucleotides). In the DNA methylation data analysis, we first estimated the cell-type proportions of each sample with a published algorithm. Next, we performed a surrogate variable analysis to identify potential confounding factors in our microarray data. Finally, we conducted a multiple linear regression analysis in consideration of these factors, including estimated cell-type proportions, and identified aberrant DNA methylation in SCZ at 2,552 CpG loci at a 5% false discovery rate correction. Our results suggest that altered DNA methylation may be involved in the pathophysiology of SCZ, and cell heterogeneity adjustments may be necessary for DNA methylation analysis.

Orchestration of neurodevelopmental programs by RBFOX1: implications for autism spectrum disorder

Neurodevelopmental and neuropsychiatric disorders result from complex interactions between critical genetic factors and as-yet-unknown environmental components. To gain clinical insight, it is critical to develop a comprehensive understanding of these genetic components. RBFOX1, an RNA splicing factor, regulates expression of large genetic networks during early neuronal development, and haploinsufficiency causes severe neurodevelopmental phenotypes including autism spectrum disorder (ASD), intellectual disability, and epilepsy. Genomic testing in individuals and large patient cohorts has identified phenotypically similar cases possessing copy number variations in RBFOX1, implicating the gene as an important cause of neurodevelopmental disease. However, a significant proportion of the observed structural variation is inherited from phenotypically normal individuals, raising questions regarding overall pathogenicity of variation at the RBFOX1 locus. In this chapter, we discuss the molecular, cellular, and clinical evidence supporting the role of RBFOX1 in neurodevelopment and present a comprehensive model for the contribution of structural variation in RBFOX1 to ASD.

Copy number variation distribution in six monozygotic twin pairs discordant for schizophrenia

We have evaluated copy number variants (CNVs) in six monozygotic twin pairs discordant for schizophrenia. The data from Affymetrix® Human SNP 6.0 arrays™ were analyzed using Affymetrix® Genotyping Console™, Partek® Genomics Suite™, PennCNV, and Golden Helix SVS™. This yielded both program-specific and overlapping results. Only CNVs called by Affymetrix Genotyping Console, Partek Genomics Suite, and PennCNV were used in further analysis. This analysis included an assessment of calls in each of the six twin pairs towards identification of unique CNVs in affected and unaffected co-twins. Real time polymerase chain reaction (PCR) experiments confirmed one CNV loss at 7q11.21 that was found in the affected patient but not in the unaffected twin. The results identified CNVs and genes that were previously implicated in mental abnormalities in four of the six twin pairs. It included PYY (twin pairs 1 and 5), EPHA3 (twin pair 3), KIAA1211L (twin pair 4), and GPR139 (twin pair 5). They represent likely candidate genes and CNVs for the discordance of four of the six monozygotic twin pairs for this heterogeneous neurodevelopmental disorder. An explanation for these differences is ontogenetic de novo events that differentiate in the monozygotic twins during development.

Olanzapine induced DNA methylation changes support the dopamine hypothesis of psychosis

Background

The dopamine (DA) hypothesis of schizophrenia proposes the mental illness is caused by excessive transmission of dopamine in selected brain regions. Multiple lines of evidence, including blockage of dopamine receptors by antipsychotic drugs that are used to treat schizophrenia, support the hypothesis. However, the dopamine D2 receptor (DRD2) blockade cannot explain some important aspects of the therapeutic effect of antipsychotic drugs. In this study, we hypothesized that antipsychotic drugs could affect the transcription of genes in the DA pathway by altering their epigenetic profile.

Methods

To test this hypothesis, we examined the effect of olanzapine, a commonly used atypical antipsychotic drug, on the DNA methylation status of genes from DA neurotransmission in the brain and liver of rats. Genomic DNA isolated from hippocampus, cerebellum, and liver of olanzapine treated (n = 2) and control (n = 2) rats were analyzed using rat specific methylation arrays.

Results

Our results show that olanzapine causes methylation changes in genes encoding for DA receptors (dopamine D1 receptor, dopamine D2 receptor and dopamine D5 receptor), a DA transporter (solute carrier family 18 member 2), a DA synthesis (differential display clone 8), and a DA metabolism (catechol-O-methyltransferase). We assessed a total of 40 genes in the DA pathway and found 19 to be differentially methylated between olanzapine treated and control rats. Most (17/19) genes showed an increase in methylation, in their promoter regions with in silico analysis strongly indicating a functional potential to suppress transcription in the brain.

Conclusion

Our results suggest that chronic olanzapine may reduce DA activity by altering gene methylation. It may also explain the delayed therapeutic effect of antipsychotics, which occurs despite rapid dopamine blockade. Furthermore, given the common nature of epigenetic variation, this lends insight into the differential therapeutic response of psychotic patients who display adequate blockage of dopamine receptors.