Screening for 22q11 deletions in a schizophrenia population

Identification of 22q11.2 deletion in a patient with schizophrenia and clinically diagnosed Rubinstein-Taybi syndrome

Background

Rubinstein-Taybi syndrome (RTS) is a rare autosomal-dominant disease. Almost all cases are sporadic and attributed to de novo variant. Psychotic symptoms in RTS are rare and have been reported in only a few published cases. On the other hand, 22q11.2 deletion syndrome is the most common chromosomal microdeletion in humans. The 22q11.2 deletion is well recognized as a risk factor for schizophrenia. Here, we present a schizophrenic psychosis case clinically diagnosed as RTS but resolved as carrying 22q11.2 deletion by genomic analysis.

Case presentation

A 38-year-old Japanese male was admitted to our hospital due to psychotic symptoms. He had been diagnosed with RTS based on physical characteristics at the age of 9 months. On admission, we performed whole exome sequencing. He had no pathogenic variant in CREBBP or EP300. We detected 2.5 Mb deletion on 22q11.2 and one rare loss-of-function variant in a loss-of-function-constrained gene (MTSS1) and three rare missense variants in missense-constrained genes (CELSR3, HERC1, and TLN1). Psychotic symptoms were ameliorated by the treatment of risperidone.

Conclusion

The psychiatric manifestation and genomic analysis may be a clue to detecting 22q11.2 deletion syndrome in undiagnosed patients. The reason for similarity in physical characteristics in 22q11.2 deletion syndrome and RTS remains unresolved. The 22q11.2 deletion and HERC1 contribute to the patient's phenotype.

Childhood-Onset Schizophrenia and Early-onset Schizophrenia Spectrum Disorders: An Update

The clinical severity, impact on development, and poor prognosis of childhood-onset schizophrenia may represent a more homogeneous group. Positive symptoms in children are necessary for the diagnosis, and hallucinations are more often multimodal. In healthy children and children with a variety of other psychiatric illnesses, hallucinations are not uncommon and diagnosis should not be based on these alone. Childhood-onset schizophrenia is an extraordinarily rare illness that is poorly understood but seems continuous with the adult-onset disorder. Once a diagnosis is confirmed, aggressive medication treatment combined with family education and individual counseling may prevent further deterioration.

SlgA, encoded by the homolog of the human schizophrenia-associated gene PRODH, acts in clock neurons to regulate Drosophila aggression

Mutations in the proline dehydrogenase gene PRODH are linked to behavioral alterations in schizophrenia and as part of DiGeorge and velo-cardio-facial syndromes, but the role of PRODH in their etiology remains unclear. Here, we establish a Drosophila model to study the role of PRODH in behavioral disorders. We determine the distribution of the Drosophila PRODH homolog slgA in the brain and show that knockdown and overexpression of human PRODH and slgA in the lateral neurons ventral (LNv) lead to altered aggressive behavior. SlgA acts in an isoform-specific manner and is regulated by casein kinase II (CkII). Our data suggest that these effects are, at least partially, due to effects on mitochondrial function. We thus show that precise regulation of proline metabolism is essential to drive normal behavior and we identify Drosophila aggression as a model behavior relevant for the study of the mechanisms that are impaired in neuropsychiatric disorders.

Editors' choice: A Drosophila model to study the role of PRODH, a schizophrenia-associated gene, in behavioral disorders.

Association of copy number polymorphisms at the promoter and translated region of COMT with Japanese patients with schizophrenia

Chromosome 22q11.2 deletion syndrome and genetic variations including single-nucleotide polymorphism (SNP) and copy number variation (CNV) in catechol-O-methyltransferase (COMT) situated at 22q11.2 remains controversial. Here, the genetic relationship between COMT and Japanese patients with schizophrenia was investigated by examining whether the SNPs correlated with schizophrenia based on a common disease-common variant hypothesis. Additionally, 22q11.2DS were screened based on a common disease-rare variant hypothesis; low-frequency CNVs situated at two COMT promoters and exons were investigated based on the low-frequency variants with an intermediate effect; and positive findings from the first stage were reconfirmed using a second-stage replication study including a larger sample size. Eight SNPs and 10 CNVs were investigated using Taqman SNP and CNV quantitative real-time polymerase chain reaction method. For the first-stage analysis, 513 unrelated Japanese patients with schizophrenia and 705 healthy controls were examined. For the second-stage replication study, positive findings from the first stage were further investigated using a larger sample size, namely 1,854 patients with schizophrenia and 2,137 controls. The first-stage analysis showed significant associations among schizophrenia, intronic SNP rs165774, CNV6 situated at promoter 1, CNV8 at exon 6, and CNV9 at exon 7. The second-stage study showed that intronic SNP rs165774 (χ(2)  = 8.327, P = 0.0039), CNV6 (χ(2)  = 19.66, P = 0.00005), and CNV8 (χ(2)  = 16.57, P = 0.00025) were significantly associated with schizophrenia. Large and rare CNVs as well as low-frequency CNVs and relatively small CNVs, namely <30 kb in COMT, may be genetic risk factors for schizophrenia.

[22q11.2DS Syndrome as a Genetic Subtype of Schizophrenia]

INTRODUCTION

The 22q11.2 deletion syndrome (22q11.2DS) is associated with the microdeletion of this chromosomal region, and represents the second most common genetic syndrome after Down's syndrome. In patients with schizophrenia, 22q11.2DS has a prevalence of 2%, and in selected groups can be increased to between 32-53%.

OBJECTIVE

To describe the generalities of 22q11.2DS syndrome as a genetic subtype of schizophrenia, its clinical characteristics, molecular genetic aspects, and frequency in different populations.

METHODS

A review was performed from 1967 to 2013 in scientific databases, compiling articles about 22q11.2DS syndrome and its association with schizophrenia.

RESULTS

The 22q11.2 DS syndrome has a variable phenotype associated with other genetic syndromes, birth defects in many tissues and organs, and a high rate of psychiatric disorders, particularly schizophrenia. Likewise, it has been identified in clinical populations with schizophrenia selected by the presence of common syndromic characteristics. FISH, qPCR and MLPA techniques, and recently, aCGH and NGS technologies, are being used to diagnose this microdeletion.

CONCLUSIONS

It is important in clinical practice to remember that people suffering the 22q11.2DS have a high genetic risk for developing schizophrenia, and it is considered that the simultaneous presence of this disease and 22q11.2DS represents a genetic subtype of schizophrenia. There are clear phenotypic criteria, molecular and cytogenetic methods to diagnose this group of patients, and to optimize a multidisciplinary approach in their monitoring.

Copy number variation at 22q11.2: from rare variants to common mechanisms of developmental neuropsychiatric disorders

Recently discovered genome-wide rare copy number variants (CNVs) have unprecedented levels of statistical association with many developmental neuropsychiatric disorders, including schizophrenia, autism spectrum disorders, intellectual disability and attention deficit hyperactivity disorder. However, as CNVs often include multiple genes, causal genes responsible for CNV-associated diagnoses and traits are still poorly understood. Mouse models of CNVs are in use to delve into the precise mechanisms through which CNVs contribute to disorders and associated traits. Based on human and mouse model studies on rare CNVs within human chromosome 22q11.2, we propose that alterations of a distinct set of multiple, noncontiguous genes encoded in this chromosomal region, in concert with modulatory impacts of genetic background and environmental factors, variably shift the probabilities of phenotypes along a predetermined developmental trajectory. This model can be further extended to the study of other CNVs and may serve as a guide to help characterize the impact of genes in developmental neuropsychiatric disorders.

Childhood onset schizophrenia and early onset schizophrenia spectrum disorders

The clinical severity, impact on development, and poor prognosis of childhood onset schizophrenia may represent a more homogeneous group. Positive symptoms in children are necessary for the diagnosis and hallucinations are more often multimodal. In healthy children and children with a variety of other psychiatric illnesses, hallucinations are not uncommon and diagnosis should not be based on these alone. Childhood onset schizophrenia is an extraordinarily rare illness that is poorly understood but seems continuous with the adult onset disorder. Once a diagnosis is affirmed, aggressive medication treatment combined with family education and individual counseling may defer further deterioration.

Diagnosis and evaluation of hallucinations and other psychotic symptoms in children and adolescents

Recognizing positive psychotic symptoms and their diagnostic context in youth is challenging. A large minority say they "hear things others do not hear," though they seldom present with complaints of hallucinations or delusions. Few have schizophrenia spectrum disorder, but many have other psychiatric disorders. Frequently, they have psychotic symptoms for an extended period before diagnosis. Clinicians should understand psychotic symptoms and their differential diagnoses. This article reviews the epidemiology, associated diagnoses, and prognosis of hallucinations and delusions in youth. Strategies for optimizing the clinical diagnostic interview, appropriate laboratory tests, indications for psychological testing, and rating scales are reviewed.

How to diagnose the 22q11.2 deletion syndrome in patients with schizophrenia: a case report

The 22q11.2 deletion syndrome is caused by a microdeletion of chromosome 22. One third of all patients with 22q11.2 deletion develop schizophrenia-like symptoms. In general, the prevalence of 22q11.2 deletion in patients with schizophrenia is 1%-2%. The 22q11.2 deletion is one of the major known genetic risk factors for schizophrenia. However, clinical differences in the phenotypes between patients with schizophrenia who are 22q11.2 deletion carriers and those who are not are still unknown. Therefore, it may be difficult to diagnose 22q11.2 deletion in patients with schizophrenia on the basis of clinical symptoms. To date, only two Japanese patients with the deletion have been identified through microdeletion studies of patients with schizophrenia in the Japanese population. Herein, we report the case study of a 48-year-old Japanese woman with 22q11.2 deletion who had a 30-year history of schizophrenia. Based on craniofacial anomalies, unpredictable agitation, hypocalcemia, and brain imaging finding, we suspected the 22q11.2 deletion in clinical populations and diagnosed the deletion using fluorescence in situ hybridization analysis. To find common phenotypes in Japanese patients with the deletion who have schizophrenia-like symptoms, we compared phenotypes among three Japanese cases. The common phenotypes were an absence of congenital cardiovascular anomalies and the presence of current findings of low intellectual ability, agitation, and hypocalcemia. We propose that hypocalcemia and agitation in patients with schizophrenia may derive from the 22q11.2 deletion, particularly when these phenotypes are coupled with schizophrenia-like symptoms.

Defining new guidelines for screening the 22q11.2 deletion based on a clinical and dysmorphologic evaluation of 194 individuals and review of the literature

The 22q11.2 deletion is the most frequent interstitial deletion in humans and presents a wide phenotypic spectrum, with over 180 clinical manifestations described. Distinct studies have detected frequencies of the deletion ranging from 0 % to 75 %, depending on the studied population and selection criteria adopted. Due to the lack of consensus in this matter, several studies have been conducted aiming to define which patients would be eligible for screening; however, the issue is still up for debate. In order to contribute to the delineation of possible clinical and dysmorphologic guidelines to optimize decision making in the clinical setting, 194 individuals with variable features of the 22q11.2 deletion syndromes (22q11.2DS) were evaluated. Group I, clinical suspicion of 22q11.2DS with palatal anomalies; Group II, clinical suspicion without palatal anomalies; Group III, cardiac malformations associated with the 22q11.2DS; and Group IV, juvenile-onset schizophrenia. Multiplex ligation-dependent probe amplification was used for screening the 22q11.2 deletion, which was detected in 45 patients (23.2 %), distributed as such: Group I, 35/101 (34.7 %); Group II, 4/18 (22.2 %); Group III, 6/52 (11.5 %); and Group IV, 0/23 (0 %). Clinical data were analyzed by frequency distribution and statistically. Based on the present results and on the review of the literature, we propose a set of guidelines for screening patients with distinct manifestations of the 22q11.2DS in order to maximize resources. In addition, we report the dysmorphic features which we found to be statistically correlated with the presence of the 22q11.2DS.

Schizophrenia with the 22q11.2 deletion and additional genetic defects: case history

The 22q11.2 deletion is the most prominent known genetic risk factor for schizophrenia, but its penetrance is at most approximately 50% suggesting that additional risk factors are required for disease progression. We examined a woman with schizophrenia with this deletion for such risk factors. She had high plasma pentosidine levels ('carbonyl stress') and a frameshift mutation in the responsible gene, GLO1. She also had a constant exotropia, so we examined the PHOX2B gene associated with both schizophrenia and strabismus, and detected a 5-alanine deletion. We propose that the combination of these genetic defects may have exceeded the threshold for the manifestation of schizophrenia.

Top-down or bottom-up: Contrasting perspectives on psychiatric diagnoses

Clinical psychiatry is confronted with the expanding knowledge of medical genetics. Most of the research into the genetic underpinnings of major mental disorders as described in the categorical taxonomies, however, did reveal linkage with a variety of chromosomes. This heterogeneity of results is most probably due to the assumption that the nosological categories as used in these studies are disease entities with clear boundaries. If the reverse way of looking, the so-called bottom-up approach, is applied, it becomes clear that genetic abnormalities are in most cases not associated with a single psychiatric disorder but with a certain probability to develop a variety of aspecific psychiatric symptoms. The adequacy of the categorical taxonomy, the so-called top-down approach, seems to be inversely related to the amount of empirical etiological data. This is illustrated by four rather prevalent genetic syndromes, fragile X syndrome, Prader-Willi syndrome, 22q11 deletion syndrome, and Noonan syndrome, as well as by some cases with rare chromosomal abnormalities. From these examples, it becomes clear that psychotic symptoms as well as mood, anxiety, and autistic features can be found in a great variety of different genetic syndromes. A psychiatric phenotype exists, but comprises, apart from the chance to present several psychiatric symptoms, all elements from developmental, neurocognitive, and physical characteristics.

Heterozygosity at catechol-O-methyltransferase Val158Met and schizophrenia: new data and meta-analysis

Catechol-O-methyltransferase (COMT) has been largely studied in relation to schizophrenia susceptibility. Most studies focused on the functional single nucleotide polymorphism (SNP) rs4680 that causes a substitution of Val by Met at codon 158 of the COMT protein. Recent meta-analyses do not support an association between allelic variants at rs4680 and schizophrenia. However, the putative role of overdominance has not been tested in meta-analyses, despite its biological plausibility. In this work, we tested the overdominant model in two Spanish samples (from Valencia and Santiago de Compostela), representing a total of 762 schizophrenic patients and 1042 controls, and performed a meta-analysis of the available studies under this model. A total of 51 studies comprising 13,894 schizophrenic patients and 16,087 controls were included in the meta-analysis, that revealed a small but significant protective effect for heterozygosity at rs4680 (pooled OR=0.947, P=0.023). Post-hoc analysis on southwestern European samples suggested a stronger effect in these populations (pooled OR=0.813, P=0.0009). Thus, the COMT functional polymorphism rs4680 contributes to schizophrenia genetic susceptibility under an overdominant model, indicating that both too high and too low levels of dopamine (DA) signalling may be risk factors. This effect can be modulated by genetic background.

No Association Between Functional Polymorphisms in COMT and MTHFR and Schizophrenia Risk in Korean Population

OBJECTIVES

Common genetic SNPs in two genes, encoding catechol-O-methyltransferase (COMT) and methylenetetrahydrofolate reductase (MTHFR), which are interconnected with COMT gene regulation, have been reported to contribute to schizophrenia risk. In this study, we evaluated the association between functional polymorphisms in COMT and MTHFR and schizophrenia risk with a case-control study in a Korean population.

METHODS

We performed a case-control study by genotyping analysis using 360 cases and 348 controls in Korean subjects to determine the association between functional polymorphisms in COMT and MTHFR and schizophrenia risk.

RESULTS

Four functional SNPs in COMT (Val158Met and rs165599) and MTHFR (C677T and A1298C) were genotyped by primer extension assay. None of the genotype distributions for the four SNPs was significantly different between cases and controls. Stratified analysis did not show any significant gender difference for any polymorphism. In addition, we found no evidence of a gene-gene interaction in the analysis of combined genotypes.

CONCLUSION

Our results suggest no significant association between the selected functional polymorphisms of COMT or MTHFR in Korean schizophrenia subjects. However, further studies are required to confirm our findings in a larger number of subjects.

Clinically detectable copy number variations in a Canadian catchment population of schizophrenia

Copy number variation (CNV) is a highly topical area of research in schizophrenia, but the clinical relevance is uncertain and the translation to clinical practice is under-studied. There is a paucity of research involving truly community-based samples of schizophrenia and widely available laboratory techniques. Our objective was to determine the prevalence of clinically detectable CNVs in a community sample of schizophrenia, while mimicking typical clinical practice conditions. We used a brief clinical screening protocol for developmental features in adults with schizophrenia for identifying individuals with 22q11.2 deletions and karyotypically detectable chromosomal anomalies in 204 consecutive patients with schizophrenia from a single Canadian catchment area. Twenty-seven (13.2%) subjects met clinical criteria for a possible syndrome, and 26 of these individuals received clinical genetic testing. Five of these, representing 2.5% of the total sample (95% CI: 0.3%-4.6%), including two of ten patients with mental retardation, had clinically detectable anomalies: two 22q11.2 deletions (1.0%), one 47, XYY, and two other novel CNVs--an 8p23.3-p23.1 deletion and a de novo 19p13.3-p13.2 duplication. The results support the utility of screening and genetic testing to identify genetic syndromes in adults with schizophrenia in clinical practice. Identifying large, rare CNVs (particularly 22q11.2 deletions) can lead to significant changes in management, follow-up, and genetic counselling that are helpful to the patient, family, and clinicians.

Prevalence of incompletely penetrant Huntington's disease alleles among individuals with major depressive disorder

OBJECTIVE

Presymptomatic individuals with the Huntingtin (HTT) CAG expansion mutation that causes Huntington's disease may have higher levels of depressive symptoms than healthy comparison populations. However, the prevalence of HTT CAG repeat expansions among individuals diagnosed with major depressive disorder has not been established.

METHOD

This was a case-control genetic association study of HTT CAG allele size in two discovery cohorts of individuals with major depressive disorder and comparison subjects without major depression as well as a replication cohort of individuals with major depression and comparison subjects without major depression.

RESULTS

CAG repeat lengths of 36 or greater were observed in six of 3,054 chromosomes from individuals with major depression, compared with none of 4,155 chromosomes from comparison subjects. In a third cohort, one expanded allele was observed among 1,202 chromosomes in the major depression group, compared with none of 2,678 chromosomes in comparison subjects. No clear pattern of clinical features was shared among individuals with the expanded repeats.

CONCLUSIONS

In clinical populations of individuals diagnosed with major depression, approximately 3 in 1,000 carried expanded HTT CAG alleles.

Psychotic features as the first manifestation of 22q11.2 deletion syndrome

The 22q11.2 deletion is a genetic disorder which is characterized by abnormalities in cardiac functioning, facial structure, neurobehavioral development, T cell functioning, and velopharyngeal insufficiencies. In the presented case study, 22q11.2 deletion was found in a patient who has psychotic symptoms only. A 25-year-old woman with a history of hypoparathyroidism and hypothyroidism presented with auditory hallucinations and persecutory delusions. After three months of treatment with antipsychotic medications, the patient was readmitted with generalized tonic-clonic seizures. The following week, the patient went into sepsis. A fluorescent in situ hybridization (FISH) analysis revealed the presence of a 22q11.2 microdeletion. This case study suggests that psychotic symptoms can develop prior to the typical symptoms of a 22q11.2 deletion. As such, psychiatrists should test for genetic abnormalities in patients with schizophrenia when these patients present with seizures and immunodeficiencies.

Meta-analysis of association between genetic variants in COMT and schizophrenia: an update

A common functional polymorphism, Val108/158Met (rs4680), and haplotypes rs737865-rs4680-rs165599 in the Catechol-O-methyltransferase gene (COMT) have been extensively examined for association to schizophrenia; however, results of replication studies have been inconsistent. The aim of this study was to comprehensively evaluate the genetic risk of COMT for schizophrenia. First, we performed a mutation scan to detect the existence of potent functional variants in the 5'-flanking and exon regions. Second, we conducted a gene-based case-control study between tagging single nucleotide polymorphisms (SNPs) in COMT [19 SNPs including six possible functional SNPs (rs2075507, rs737865, rs4680, rs165599, rs165849)] and schizophrenia in large Japanese samples (schizophrenics 1118, controls 1100). Lastly, we carried out a meta-analysis of 5 functional SNPs and haplotypes (rs737865-rs4680-rs165599). No novel functional variant was detected in the mutation scan. There is no association between these tagging SNPs in COMT and Japanese schizophrenia. In this updated meta-analysis, no evidence was found for an association between Val108/158Met polymorphisms, rs6267, rs165599, and haplotypes (rs7378655-rs4680-rs165599) and schizophrenia, although rs2075507 and rs737865 showed trends for significance in allele-wise analyses (P=0.039 in a multiplicative model, P=0.025 in a recessive model for rs2075507, P=0.018 in a dominant model for rs737865, uncorrected). This significance did not remain, however, after correcting the P-values using a false discovery rate controlling procedure. Our results suggest that the COMT is unlikely to contribute to susceptibility to schizophrenia.

Velo-Cardio-Facial Syndrome

Velocardiofacial syndrome (VCFS) also known as DiGeorge, conotruncal anomaly face and Cayler syndromes is caused by a microdeletion in the long arm of chromosome 22. We review the history of the syndrome from the first clinical reports almost half a century ago to the current intriguing molecular findings associating genes from the microdeletion region and the physical and neuropsychiatric phenotype of the syndrome. Velocardiofacial syndrome has a wide spectrum of more than 200 physical manifestations including palate and cardiac anomalies. Yet, the most challenging manifestations of VCFS are the learning disabilities and neuropsychiatric disorders. As VCFS is relatively common and as up to one third of the subjects with VCFS develop schizophrenia like psychotic disorder the syndrome is the most commonly known genetic risk factor to schizophrenia. Identifying the genetic, cognitive and psychiatric risk factors for VCFS-schizophrenia is under the focus of intensive research.

Clinical perspectives on the genetics of schizophrenia: a bottom-up orientation

Phenomenology has been the reference point that investigators have used in their efforts to understand schizophrenia. Although symptoms and signs are crucial for the diagnosis of schizophrenia, there is an ongoing debate since Kraepelin attempted to group symptoms to understand the etiology of schizophrenia. Several operational criteria have been developed to establish the diagnosis of schizophrenia, making it obvious that there are no precise symptomatological boundaries. There is little clear indication which of the systems is valid for genetic and other biological research. Despite the enormous effort to find a linkage between schizophrenia and one or more loci, the results are far from conclusive. Another approach is the search for candidate genes of which DICS1 and 22q11 deletion syndrome are examples. In all studies into the genetic underpinnings of schizophrenia, however, the clinical vantage point is neglected in that a broad clinical phenotype with respect to, e.g., developmental issues, symptoms and comorbidity is narrowed down to one categorical diagnosis. This is illustrated by the lack of exclusion criteria in genetic studies and by the occurrence of schizophrenia-like psychoses in a broad array of genetic syndromes. In case of 22q11 deletion syndrome, the psychotic symptoms emerge in the context of brain anomalies, a plethora of somatic abnormalities and specific neurocognitive deficits. Prader-Willi syndrome is a hypothalamic disorder in which psychotic symptoms may occur that resemble schizophrenia. It is concluded that not only schizophrenia is a highly variable disease but that the genetic samples are even much more heterogeneous.

Genes, brain development and psychiatric phenotypes in velo-cardio-facial syndrome

Velo-cardio-facial syndrome (VCFS) has been in the focus of intensive research over the last 15 years. The syndrome represents a homogeneous model for studying the effect of a decreased dosage of genes on the development of brain structure and function and, consequently, on the emergence of schizophrenia-like psychotic disorder. In this review, we describe the psychiatric phenotype of children, adolescents, and young adults with VCFS. We redefine the concept of "behavioral phenotype" and suggest that psychosis fulfills the criteria of a behavioral phenotype of the syndrome. Identifying the risk factors for the emergence of psychosis in VCFS is a major goal of several large-scale longitudinal studies that are currently underway. We review the knowledge gained so far about risk factors for psychosis in VCFS, including early neuropsychiatric symptoms, development of brain structure and function, and the effect of a reduced dosage of genes from the 22q11 deletion region. Although the brain structure in subjects with VCFS is not drastically different from typically developing controls, newer imaging modalities that measure white matter tracts, cortical thickness, and cortical gyrification are likely to identify more subtle and specific neuroanatomical substrates of the syndrome. Among the 24 genes within the deletion region, the role of catechol-O-methyltransferase (COMT) on the VCFS phenotype has been investigated in depth. The findings suggest that because of haploinsufficiency of the COMT gene individuals with VCFS are exposed to a high level of prefrontal dopamine, and this interferes with their prefrontal cognitive functioning and may contribute to their high rate of psychosis and other psychiatric disorders. The other genes and environmental factors that shape the unique neuropsychiatric phenotype of VCFS are yet to be discovered.

Case reports: an opportunity for early intervention: velo-cardio-facial syndrome and psychosis

AIMS AND METHOD

Velo-cardio-facial syndrome is the most common micro deletion syndrome in man, with the typically deleted region in the 22q11area, an area that contains many genes with possible links to mental illnesses. The syndrome phenotype includes multiple physical abnormalities, learning disorders and a greatly increased risk of developing a psychotic disorder. A series of three cases is presented to describe some of the psychiatric manifestations of the velo-cardio-facial syndrome.

RESULTS

The three young people presented here all had an illness of long duration that was difficult to treat, with significant side effects of treatment and varying degrees of recovery.

CONCLUSIONS

As more children with genetic syndromes are identified early and monitored by genetic clinics and other paediatric services, there is an opportunity for psychiatric services to provide early intervention for a group of patients who are likely to have a poor response to treatment if they present with an advanced psychosis. Studying the deletions in the 22q11 area also has great potential for investigating possible causes of a genetic vulnerability to psychotic illness.

Schizophrenia and 22q11.2 deletion syndrome

22q11.2 deletion syndrome (22qDS) is a genetic syndrome associated with a chromosome 22q11.2 deletion and variable phenotypic expression that commonly includes schizophrenia. Approximately 1% of patients with schizophrenia have 22qDS. The schizophrenia in 22qDS appears broadly similar to that found in the general population with respect to core signs and symptoms, treatment response, neurocognitive profile, and MRI brain anomalies. However, individuals with a 22qDS form of schizophrenia typically have distinguishable physical features, have a lower IQ, and may differ in auxiliary clinical features. IQ, length of 22q11.2 deletions, and COMT functional allele do not appear to be major risk factors for schizophrenia in 22qDS. Ascertainment biases and small sample sizes are limitations of most studies. Larger studies over the lifespan and continuing education about this underrecognized condition are needed. 22qDS-schizophrenia is an important genetic subtype and a valuable model of neurodevelopmental mechanisms involved in the pathogenesis of schizophrenia.

Failure to detect the 22q11.2 duplication syndrome rearrangement among patients with schizophrenia

Chromosome aberrations have long been studied in an effort to identify susceptibility genes for schizophrenia. Chromosome 22q11.2 microdeletion is associated with DiGeorge and Velocardiofacial syndromes (DG/VCF) and provides the most convincing evidence of an association between molecular cytogenetic abnormality and schizophrenia. In addition, this region is one of the best replicated linkage findings for schizophrenia. Recently, the reciprocal microduplication on 22q11.2 has been reported as a new syndrome. Preliminary data indicates that individuals with these duplications also suffer from neuropsychiatric disorders. In this study we have investigated the appropriateness of testing schizophrenia patients for the 22q11.2 microduplication. We used multiplex ligation-dependent probe amplification (MLPA) to measure copy number changes on the 22q11.2 region in a sample of 190 patients with schizophrenia. Our results corroborate the prevalence of the 22q11.2 microdeletion in patients with schizophrenia and clinical features of DG/VCFS and do not suggest an association between 22q11.2 microduplication and schizophrenia.

Prevalence of 22q11.2 deletions in 311 Dutch patients with schizophrenia

The objectives of this study were 1) to examine whether the prevalence of 22q11.2 deletion syndrome (22q11DS) in schizophrenia patients with the Deficit syndrome is higher than the reported approximately 2% for the population of schizophrenia patients as a whole, and 2) to estimate the overall prevalence of 22q11DS among schizophrenia patients by combining all available studies. Our sample, enriched for patients with the Deficit syndrome, had 88% power to detect an estimated prevalence of 5% of 22q11.2 deletions. No 22q11.2 deletions were detected in 311 schizophrenia patients, 146 of whom met criteria for the Deficit syndrome. Our literature research revealed that in eight studies sixteen deletions were identified in 2133 patients with schizophrenia. This corresponds to a prevalence of 0.75% (95%CI: 0.5%-1.2%).

IN CONCLUSION

The prevalence of 22q11.2DS in schizophrenia patients with the Deficit syndrome is not higher than in the population of schizophrenia patients as a whole. The prevalence of 22q11.2DS in schizophrenia patients is lower than the frequently reported prevalence of 2% or more.

An association study between the genetic polymorphisms within TBX1 and schizophrenia in the Chinese population

The strong association between common psychiatric disorders and the 22q11.2 microdeletion suggests that haploinsufficiency of one or more genes in the region confers susceptibility to these disorders. Recent mouse studies have shown that the T-box 1 (TBX1) gene in the 22q11.2 region can cause prepulse inhibition (PPI) impairment in the heterozygous state. A study has also shown that phenotypic features of 22q11 deletion syndrome (22q11DS) were segregated with an inactivating mutation of TBX1 in one family, suggesting that the TBX1 gene plays a role in the pathogenesis of some psychiatric disorders. We performed an association study between three single nucleotide polymorphisms (SNPs) in the TBX1 gene and schizophrenia. However, we found no significant difference in the genotype or allele distributions between the 328 schizophrenics and 288 controls for any of the polymorphisms, nor was there any haplotype association. Our data suggest that the genetic polymorphisms within TBX1 do not confer an increased susceptibility to schizophrenia in the Chinese population.

Velocardiofacial syndrome

Velocardiofacial syndrome (VCFS) is the most common known microdeletion in humans. It is also the most common known genetic risk factor for schizophrenia. The aim of this article is to describe the clinical characteristics of the syndrome, with emphasis on the myriad psychiatric disorders and abnormal behaviors from a developmental perspective. In addition, the possible pathways that lead to the psychotic symptoms and cognitive deficits are discussed. Guidelines are suggested to alert clinicians to the possibility of the presence of VCFS, and the cumulative clinical experience and limited research on psychiatric treatments for VCFS are presented. There is an urgent need to conduct treatment trials in this high-risk population.

Association analysis of COMT polymorphisms and schizophrenia in a Chinese Han population: a case-control study

Schizophrenia is a common disease with complex mode of inheritance; great efforts have been made to identify the susceptible genes. Catechol-O-methyltransferase (COMT) gene has long been considered as a candidate gene mainly because of two reasons: First, it encodes a key dopamine catabolic enzyme. Second, it maps to the velocardiofacial syndrome (VCFS) region of chromosome 22q11, which is associated with schizophrenia predisposition. Numerous case-control and family-based studies have been conducted, majority of them focused on a functional Val/Met polymorphism (rs4680). Unfortunately, these studies have produced conflicting results. In a previous report, Shifman et al. found a three-marker haplotype (rs737865-rs4680-rs165599) that showed significant association with schizophrenia. In this study, we try to replicate their findings in Chinese Han population and failed to find any associations.

No associations exist between five functional polymorphisms in the catechol-O-methyltransferase gene and schizophrenia in a Japanese population

Catechol-O-methyltransferase (COMT) is one of the enzymes that degrade catecholamine neurotransmitters including dopamine. The COMT gene is located on 22q11.2, a common susceptibility locus for schizophrenia. Therefore, COMT is a strong functional and positional candidate gene for schizophrenia. A common functional polymorphism (rs4680, Val158Met) has been extensively tested for an association with schizophrenia, but with conflicting results. Recent studies indicate that if COMT is implicated in susceptibility to schizophrenia, this cannot be wholly accounted for by the Val158Met polymorphism. To assess this view, the authors conducted a case-control association study (399 patients with schizophrenia and 440 control subjects) for five functional polymorphisms (rs2075507, rs737865, rs6267, rs4680 and rs165599) in Japanese subjects. There were no significant associations found between the polymorphisms or haplotypes of COMT and schizophrenia. The present study shows that these five functional COMT polymorphisms do not play a major role in conferring susceptibility to schizophrenia in Japanese.

Susceptibility genes for schizophrenia: Characterisation of mutant mouse models at the level of phenotypic behaviour

A wealth of evidence indicates that schizophrenia is heritable. However, the genetic mechanisms involved are poorly understood. Furthermore, it may be that genes conferring susceptibility interact with one another and with non-genetic factors to modulate risk status and/or the expression of symptoms. Genome-wide scanning and the mapping of several regions linked with risk for schizophrenia have led to the identification of several putative susceptibility genes including neuregulin-1 (NRG1), dysbindin (DTNBP1), regulator of G-protein signalling 4 (RGS4), catechol-o-methyltransferase (COMT), proline dehydrogenase (PRODH) and disrupted-in-schizophrenia 1 (DISC1). Genetic animal models involving targeted mutation via gene knockout or transgenesis have the potential to inform on the role of a given susceptibility gene on the development and behaviour of the whole organism and on whether disruption of gene function is associated with schizophrenia-related structural and functional deficits. This review focuses on data regarding the behavioural phenotype of mice mutant for schizophrenia susceptibility genes identified by positional candidate analysis and the study of chromosomal abnormalities. We also consider methodological issues that are likely to influence phenotypic effects, as well as the limitations associated with existing molecular techniques.

Analyses of the associations between the genes of 22q11 deletion syndrome and schizophrenia

Schizophrenia is a severe, debilitating mental disorder characterized by profound disturbances of cognition, emotion and social functioning. The lifetime morbid risk is surprisingly uniform at slightly less than 1% across different populations and different cultures. The evidence of genetic risk factors is our strongest clue to the cause of schizophrenia. Linkage and association analyses have identified genes associated with the development of schizophrenia. However, most of the alleles or haplotypes identified thus far have only a weak association or are reported to be population specific. A deletion of 22q11.2 that causes the most common microdeletion syndrome (22q11DS) with an estimated prevalence of 1:2,500-1:4,000 live births may represent one of the greatest known genetic risk factors for schizophrenia. Schizophrenia is a late manifestation in approximately 30% of patients with 22q11.2 deletion, comparable to the risk to offspring of two parents with schizophrenia. Clinical and neuroimaging assessments indicate that 22q11DS-schizophrenia is a neurodevelopmental model of schizophrenia. Recent studies have provided evidence that haploinsufficiency of TBX1 is likely to be responsible for many of the physical features associated with the deletion. Most of the genes in the 22q11 deletion region are conserved together on mouse chromosome 16, enabling the generation of mouse models. Similarities in the cardiovascular and other phenotypes between 22q11DS patients and mouse models can provide important insights into roles of genes in neurobehavioral phenotypes. Because more than one gene in the 22q11DS region is likely to contribute to the marked risk for schizophrenia, further extensive studies are necessary. Analyses of 22q11DS will help clarify the molecular pathogenesis of schizophrenia.

Cardiac Registry screening for DiGeorge Critical Region deletion using loss of heterozygosity analysis

DiGeorge (DGS), velocardiofacial, and conotruncal anomaly face syndromes comprise a phenotypic spectrum that is associated with a submicroscopic 22q11.2 deletion in the majority of cases. These syndromes variably express complex congenital heart disease, cellular immune deficits, hypocalcemia, craniofacial anomalies, and learning disabilities. This retrospective study correlates the presence of a deletion in this region with autopsy and clinical findings in a cohort of patients selected from the Cardiac Registry at Boston Children's Hospital. DNA was extracted from formalin-fixed paraffin-embedded cardiac tissue sampled from 189 patients with conotruncal anomalies. Polymerase chain reaction (PCR) was performed using 4 fluorescently labeled oligonucleotide primer pairs for unique short tandem repeat polymorphisms in the DGS critical region. The PCR products were analyzed for loss of heterozygosity (LOH), and a deletion was assumed when at least 3 consecutive loci demonstrated homozygosity. Of the 189 cases, 16 (8%) met our criteria for LOH and were assumed to have a deletion. These patients included 6 (35%) of 17 patients diagnosed clinically with DGS prior to death. Of the 10 non-DGS patients with LOH, 4 had aortic atresia and 3 had tetralogy of Fallot, both frequently seen in DGS. Polymerase chain reaction is a useful screening alternative to fluorescence in situ hydridization for detecting 22q11.2 deletions in archived tissue samples. This study identified a probable deletion in a subset of cases from a cardiac registry with cardiac defects associated with the DGS phenotype.

A complete genetic association scan of the 22q11 deletion region and functional evidence reveal an association between DGCR2 and schizophrenia

Several lines of evidence have established the presence of an association between a 3-Mb deletion in chromosome 22q11 and schizophrenia. In this paper we present a complete high-density SNP scan of this segment using DNA pools, and demonstrate significant association between two distinct regions and schizophrenia in an Ashkenazi Jewish population. One of these regions contains the previously identified COMT gene. The pattern of association and linkage disequilibrium (LD) in the second region suggest that DGCR2, which encodes a putative adhesion receptor protein, is the susceptibility gene. We confirmed the association between DGCR2 and schizophrenia through individual genotyping of 1,400 subjects. In a gene expression analysis the risk allele of a coding SNP associated with schizophrenia was found to be associated with a reduced expression of DGCR2. Interestingly, the expression of DGCR2 was also found to be elevated in the dorsolateral prefrontal cortex of schizophrenic patients relative to matched controls. This increase is likely to be explained by exposure to antipsychotic drugs. To test that hypothesis, we looked at rats exposed to antipsychotic medication and found significantly elevated levels of DGCR2 transcripts. The genetic and functional evidences here reported suggest a possible role of the DGCR2 gene in the pathology of schizophrenia and also in the therapeutic effects of antipsychotic drugs.

Identification of DNA copy-number aberrations by array-comparative genomic hybridization in patients with schizophrenia

Chromosomal abnormalities are implicated as important markers for the pathogenesis in patients with schizophrenia. In this study, with using bacterial artificial chromosome (BAC) array-based comparative genomic hybridization (CGH), we analyzed DNA copy-number changes among 30 patients with schizophrenia. The most frequent changes were partial gain of Xq23 (52%) and loss of 3q13.12 (32%). Other frequent gains were found in: 1p, 6q, 10p, 11p, 11q, 14p, and 15q regions, and frequent losses were found in: 2p, 9q, 10q, 14q, 20q, and 22q regions. The set of abnormal regions was confirmed by real-time PCR (9q12, 9q34.2, 11p15.4, 14q32.33, 15q15.1, 22q11.21, and Xq23). All real-time PCR results were consistent with the array-CGH results. Therefore, it is suggested that array-CGH and real-time PCR analysis could be used as powerful tools in screening for schizophrenia-related genes. Our results might be useful for further exploration of candidate genomic regions in the pathogenesis of schizophrenia.

A biologic model to study the genetics of psychotic, mood, and anxiety disorders: the velocardiofacial syndrome

Recent advances in molecular genetics have led to new insights on the velocardiofacial syndrome (VCFS). Most patients have a large deletion on one copy of chromosome 22 (encompassing up to 30 genes), which can be confirmed with genetic testing. A wide spectrum of psychiatric symptoms has been reported in patients with VCFS, including schizophrenia and bipolar disorder. Preliminary studies of candidate genes from the deletion region suggest that allelic differences may increase susceptibility to psychiatric disorders, but these studies await replication. Mouse models with genetically engineered deletions have the potential to isolate the genes associated with VCFS neuropsychiatric symptoms. VCFS is likely to represent the deficiency of several genes with complex interactions. Further psychiatric research is warranted to delineate more comprehensively the neuro-psychiatric phenotype associated with VCFS. Accurate psychiatric diagnosis will better inform and advance ongoing genetic research.

Velocardiofacial syndrome: is there a neuropsychiatric phenotype?

A neuropsychiatric phenotype specific to the velocardiofacial syndrome (VCFS) has not yet been identified. Neuropsychological research suggests that children with VCFS have problems in the domains of cognition, attention, and social interaction. Preliminary psychiatric studies of children and adolescents with VCFS suggest that they may be at higher risk than their nonaffected peers to develop mood disorders (including bipolar disorder), anxiety disorders, and attention deficit disorders. An unresolved question remains whether adults are at higher risk to develop psychotic mood disorders or schizophrenia in early adulthood. A research paradigm developed by Robins and Guze for the validation of psychiatric disorders may be helpful. Systematic studies in the areas of phenomenology, neurobiology, heredity, and the natural course of VCFS may clarify its psychiatric manifestations. Better understanding of the neuropsychiatric phenotype associated with VCFS will better inform ongoing genetic research. The study of VCFS holds the potential to give important insight into the pathogenesis of psychiatric disorders.

No association found between 158 Val/Met polymorphism of the COMT gene and schizophrenia with minor physical anomalies

The catechol-O-methyl transferase (COMT) gene has been a promising candidate in genetic research on schizophrenia because of its function in dopamine metabolism and its location on chromosome 22q11.2, which may be implicated in both schizophrenia and velocardiofacial syndrome (VCFS). To explore the possible genetic contribution of COMT to the development of schizophrenia, we focused on the subgroup of patients with schizophrenia characterized by minor physical anomalies as a phenotype and the 158 Val/Met polymorphism as a genotype. Since some physical anomalies are found in both schizophrenia and VCFS, schizophrenia patients with minor physical anomalies could represent the putative subgroup of schizophrenia linked to a disruption in neurodevelopment. Genotyping for the 158 Val/Met (472 G>A) polymorphism in the COMT gene was done for 239 patients with schizophrenia and 248 normal controls. Our analysis did not yield any significant between-group differences in terms of either allele or genotype frequency. We also could not find any association between the COMT gene and the schizophrenia subgroup with minor physical anomalies, although there was a significant difference in Waldrop total scores between the patients with schizophrenia and the normal controls. Analyses of subgroups based on other clinical variables also did not reveal significant differences. Overall, this study does not support the hypothesis that the 158 Val/Met polymorphism in the COMT gene is associated with schizophrenia in Koreans.

Differential detection of deletion 22q11.2 syndrome by specialty and indication

This study identified cytogenetic abnormalities in a population screened for deletion 22q11.2 syndrome (D22S) by fluorescence in situ hybridization (FISH) and G-banding and correlated these abnormalities to referring specialty and submitted indications. Requests for the D22S FISH assay were retrospectively reviewed over a 29-month period in our institution. Positive test results for D22S FISH and other abnormalities found by other FISH assays and G-banding were correlated to submitting specialist and indication. Thirteen medical services ordered D22S FISH testing on 297 patients over 29 months. The detection rate for all cytogenetic aberrations was 9.4% (28 of 297) including 5.4% (16 of 297) for D22S detection by FISH and 2.7% (8 of 297) for detection of additional cytogenetic anomalies by G-banding cytogenetics. Sixty-six of 297 patients negative by D22S FISH and G-banding were screened using other FISH assays and 3 of 47 (6.4%) patients screened using subtelomeric probes were positive for deletion and 1 of 3 (33%) patients screened for Prader-Willi syndrome was positive for deletion. Pediatric geneticists requested 53.9% (160 of 297) of the tests, yielding 60.7% (17 of 28) of positive test results. Tetralogy of Fallot and developmental delay were the indications associated with the most positive test results. In our institution, pediatric geneticists identify the largest spectrum of indications with D22S and appear most aware of the association of developmental delay with D22S. Performing conventional cytogenetics and other FISH assays, in addition to FISH for D22S, is important because there is considerable overlap between D22S and the phenotype of several other syndromes.

Lack of association of the COMT (Val158/108 Met) gene and schizophrenia: a meta-analysis of case-control studies

There is strong evidence for a genetic contribution to schizophrenia, but the contribution of individual candidate genes remains uncertain. We attempted to replicate a recent meta-analysis that reported an association of the catechol O-methyltransferase (COMT) Val allele with schizophrenia, and suggested that this effect may be moderated by ancestry. We included reports published subsequent to the original meta-analysis, and included a formal test of the moderating effect of ancestry in order to test whether the association operates differently in populations of European ancestry compared to populations of Asian ancestry. A corrected P-value for the 5% significance threshold was employed where appropriate, using Bonferroni's method, and studies that demonstrated departure from Hardy-Weinberg equilibrium among controls were excluded. When all studies were included in a meta-regression, there was evidence for a significant association of COMT Val allele frequency with schizophrenia case status and a significant main effect of ancestry. The interaction of COMT Val allele frequency and ancestry was also significant. However, when only studies that reported allele frequencies that did not depart significantly from Hardy-Weinberg equilibrium among controls were included, these effects were no longer significant. The results of our meta-analysis do not support an association between the COMT Val allele and schizophrenia case status, and do not support recent claims that this association may be moderated by ancestry.

Annotation: velo-cardio-facial syndrome

BACKGROUND

Velo-cardio-facial syndrome (VCFS), the most frequent known interstitial deletion identified in man, is associated with chromosomal microdeletions in the q11 band of chromosome 22. Individuals with VCFS are reported to have a characteristic behavioural phenotype with high rates of behavioural, psychiatric, neuropsychological and linguistic disorders.

METHODS

A selective literature review was undertaken.

RESULTS

Children and adults with VCFS have high rates of behavioural, psychiatric and communication disorders. While VCFS children have high rates of ADHD, anxiety and affective disorders, adults have high rates of psychotic disorders, particularly schizophrenia. In addition, the presence of a chromosome 22q11 deletion is associated with specific neuropsychological and neuroanatomical abnormalities.

CONCLUSIONS

People with VCFS have a characteristic behavioural phenotype with high rates of behavioural, psychiatric, neuropsychological and communication disorders. Early diagnosis and treatment within a multidisciplinary framework is of paramount importance for VCFS individuals as this will have a major effect in determining the long-term outcome in affected individuals. Longitudinal studies of VCFS children are currently under way to identify precursor symptoms and areas of dysfunction which precede the later development of major psychiatric disorder. Identification of such prodromal features in VCFS may have enormous implications for the clinical management of major psychiatric disorder in VCFS and in the wider population.

Hyperprolinemia is a risk factor for schizoaffective disorder

DNA sequence variations within the 22q11 DiGeorge chromosomal region are likely to confer susceptibility to psychotic disorders. In a previous report, we identified several heterozygous alterations, including a complete deletion, of the proline dehydrogenase (PRODH) gene, which were associated with moderate hyperprolinemia in a subset of DSM III schizophrenic patients. Our objective was (i) to determine whether hyperprolinemia is associated with increased susceptibility for any of three psychiatric conditions (schizophrenia, schizoaffective disorder and bipolar disorder) and (ii) to establish a correlation between hyperprolinemia and PRODH genotypes. We have conducted a case-control study including 114 control subjects, 188 patients with schizophrenia, 63 with schizoaffective disorder and 69 with bipolar disorder. We report that, taking into account a confounding effect due to valproate treatment, hyperprolinemia is a risk factor for DSM IIIR schizoaffective disorder (P=0.02, Odds ratio=4.6, 95% confidence interval 1.3-16.3). We did not detect 22q11 interstitial deletions associated with the DiGeorge syndrome among the 320 patients of our sample and we found no association between common PRODH polymorphisms and any of the psychotic disorders. In contrast, we found that five rare PRODH alterations (including a complete PRODH deletion and four missense substitutions) were associated with hyperprolinemia. In several cases, two variations were present simultaneously, either in cis or trans in the same subject. A total of 11 from 30 hyperprolinemic subjects bore at least one genetic variation associated with hyperprolinemia. This study demonstrates that moderate hyperprolinemia is an intermediate phenotype associated with certain forms of psychosis.

Catechol-O-methyl transferase Val158Met gene polymorphism in schizophrenia: working memory, frontal lobe MRI morphology and frontal cerebral blood flow

The catechol-O-methyl transferase (COMT) gene is considered a leading schizophrenia candidate gene. Although its role in increasing schizophrenia susceptibility has been conflicting, recent studies suggest the valine allele may contribute to poor cognitive function in schizophrenia. V(158)M COMT genotype was obtained on 159 schizophrenia patients and 84 healthy controls. The effects of COMT genotype on four measures of working memory/executive functions (Wisconsin Card Sorting, digit span backward, Trail Making and N-back tests) and on MRI frontal brain volumes were examined. Genotype distributions were not significantly different between patients and controls. There were no significant genotype or genotype-by-group effects on any working memory/executive function measures. No genotype or genotype-by-diagnosis interaction effects were found with MRI frontal lobe volumes. Randomization analyses using [(15)O]H(2)O positron emission tomography (PET) cerebral blood flow data found Val/Val patients had higher frontal lobe activation than Met/Met patients while performing the one-back task. Overall, these findings do not support a major role for COMT in increasing susceptibility for schizophrenia or in mediating frontal lobe function. Age-related changes and phenotypic heterogeneity of schizophrenia may influence the complex relationships between COMT genotype and cognition.

A survey of the 22q11 microdeletion in a large cohort of schizophrenia patients

The occurrence of a microdeletion at 22q11 has long been considered to constitute a risk factor for schizophrenia. Higher rates of 22q11 deletions have been reported in cohorts of patients with schizophrenia. In order to estimate the prevalence of the 22q11 deletion in schizophrenia patients more accurately, a screening for 22q11 deletions was conducted on a cohort of 634 schizophrenia patients, the largest sample size screened to date. Seven microsatellites and three SNPs were used to assess the deletion genotype. In cases where all markers were found to be homozygous (hemizygous), the individual was assumed to carry the deletion. The method used here is simple and efficient in comparison with hybridization technologies. Moreover, the rate of false positives is very low (P-value in the range of 10(-4) to 10(-3)). Approximately 1% of the patient cohort was found to carry 22q11 deletions.

The molecular genetics of the 22q11-associated schizophrenia

Schizophrenia has a strong genetic component but the mode of inheritance of the disease is complex and in all likelihood involves interaction among multiple genes and also possibly environmental or stochastic factors. A number of studies have shown that the 22q11 deletion syndrome (22q11DS) is a true genetic subtype of schizophrenia and as such may play an extremely important role in deciphering the genetic basis of schizophrenia. Microdeletions of the 22q11 locus are associated with a staggering increased risk to develop schizophrenia. The same locus has also been implicated by some linkage studies. Systematic examination of individual genes from the 1.5 Mb critical region has identified so far the PRODH and ZDHHC8 as strong candidate schizophrenia susceptibility genes from this locus. Discovery of these genes implicates neuromodulatory aminoacids and protein palmitoylation as important for disease development. Other genes, including the gene encoding for COMT, have been implicated by candidate gene approaches. It therefore appears that the 22q11-associated schizophrenia may have the characteristics of a contiguous gene syndrome, where deficiency in more than one gene contributes to the strikingly increased disease risk. Mouse models for individual candidate genes will provide the investigators with the opportunity to start understanding the function of these genes and how they may impact on schizophrenia. Mouse models that carry long-range deletions will likely capture the interactions among the culprit genes and help explain the genetic contribution of this locus to the high risk for schizophrenia. In-depth human and animal model studies of 22q11DS promise to answer critical questions relating to the devastating illness of schizophrenia, whose causes remain largely unknown.

Catechol-O-methyltransferase gene Val/Met functional polymorphism and risk of schizophrenia: a large-scale association study plus meta-analysis

BACKGROUND

A common functional polymorphism (Val/Met) in the catechol-O-methyltransferase gene (COMT) that markedly affects enzyme activity has been shown to affect executive cognition and the physiology of the prefrontal cortex in humans. It is hypothesized that the high activity Val allele slightly increases risk for schizophrenia through its effect on dopamine-mediated prefrontal information processing.

METHODS

We compared the allele/genotype frequencies of the Val/Met polymorphism in a large independent patient-control sample (862 patient and 928 healthy control subjects) from Han Chinese population, and an update meta-analysis was performed to assess the collective evidence across individual studies.

RESULTS

No statistically significant differences were found in allele or genotype frequencies between patient and normal control subjects, although a nonsignificant overrepresentation of the Val allele in schizophrenia patients (odds ratio [OR] = 1.09, 95% confidence interval [CI] = .94-1.26) was suggested. Comparatively, the meta-analysis of all published population-based association studies showed statistically significant evidence for heterogeneity among the group of studies. Stratification of the studies by ethnicity of the samples yielded no significant evidence for an association with the Val allele in Asian population (OR = .96, 95% CI = .85-1.09), nor in European population (OR = 1.06, 95% CI = .95-1.19).

CONCLUSIONS

Our data provide minimal evidence that the Val allele is a susceptibility factor for schizophrenia in either European or Asian populations.

Assessment of the frequency of the 22q11 deletion in Afrikaner schizophrenic patients

A hemizygous deletion of the q11 band on chromosome 22 occurs in 1 of every 5,950 live births (0.017%). The deletion is mediated by low copy repeats (LCRs) flanking this locus. Presence of the deletion is associated with variable phenotypic expression, which can include distinctive facial dysmorphologies, congenital heart disease and learning disabilities. An unusually high percentage of individuals with this deletion (25-30%) have been described to develop schizophrenia or schizoaffective disorder. In previous studies, the prevalence of the 22q11 deletion in patients with schizophrenia was found to be approximately 2% in Caucasian adults and 6% in childhood-onset cases. Both these frequencies represent a dramatic increase from the prevalence of the deletion in the general population. In this study, we investigate the occurrence of the 22q11 deletion in an independent sample of schizophrenic patients of Afrikaner origin. We first ascertained a sample of 85 patients who meet full diagnostic criteria for schizophrenia for presence of two or more of the clinical features associated with presence of the 22q11 deletion. A group of six patients (7%) met these criteria. This group was subjected to fluorescent in situ hybridization (FISH) and presence of the 22q11 deletion was confirmed for two subjects. Our study therefore confirms the previously reported rate of 2% frequency of the 22q11 deletion in adult schizophrenic patients and provides a two-stage screening protocol to identify these patients.