Gabriela Ortega

A missense mutation in a novel gene encoding a putative cation channel is associated with catatonic schizophrenia in a large pedigree.

Schizophrenia is a common and etiologically heterogeneous disorder. Although inheritance of schizophrenic syndromes is complex with genetic and environmental factors contributing to the clinical phenotype, periodic catatonia, a familial subtype of catatonic schizophrenia, appears to be transmitted in an autosomal dominant manner. We report here that a Leu309Met mutation in WKL1, a positional candidate gene on chromosome 22q13.33 encoding a putative non-selective cation channel expressed exclusively in brain, co-segregates with periodic catatonia in an extended pedigree. Structural analyses revealed that this missense mutation results in conformational changes of the mutant protein. Our results not only underscore the importance of genetic mechanisms in the etiology of schizophrenic syndromes, but also provide a better understanding of the pathogenesis and incapacitating course of catatonic schizophrenia and related disorders.

Differential effects of prenatal stress in 5-Htt deficient mice: towards molecular mechanisms of gene × environment interactions.

Prenatal stress (PS) has been shown to influence the development of the fetal brain and to increase the risk for the development of psychiatric disorders in later life. Furthermore, the variation of human serotonin transporter (5-HTT, SLC6A4) gene was suggested to exert a modulating effect on the association between early life stress and the risk for depression. In the present study, we used a 5-Htt×PS paradigm to investigate whether the effects of PS are dependent on the 5-Htt genotype. For this purpose, the effects of PS on cognition, anxiety- and depression-related behavior were examined using a maternal restraint stress paradigm of PS in C57BL6 wild-type (WT) and heterozygous 5-Htt deficient (5-Htt +/−) mice. Additionally, in female offspring, a genome-wide hippocampal gene expression profiling was performed using the Affymetrix GeneChip® Mouse Genome 430 2.0 Array. 5-Htt +/− offspring showed enhanced memory performance and signs of reduced anxiety as compared to WT offspring. In contrast, exposure of 5-Htt +/− mice to PS was associated with increased depressive-like behavior, an effect that tended to be more pronounced in female offspring. Further, 5-Htt genotype, PS and their interaction differentially affected the expression of numerous genes and related pathways within the female hippocampus. Specifically, MAPK and neurotrophin signaling were regulated by both the 5-Htt +/− genotype and PS exposure, whereas cytokine and Wnt signaling were affected in a 5-Htt genotype×PS manner, indicating a gene×environment interaction at the molecular level. In conclusion, our data suggest that although the 5-Htt +/− genotype shows clear adaptive capacity, 5-Htt +/− mice –particularly females– at the same time appear to be more vulnerable to developmental stress exposure when compared to WT offspring. Moreover, hippocampal gene expression profiles suggest that distinct molecular mechanisms mediate the behavioral effects of the 5-Htt genotype, PS exposure, and their interaction.

Follow-up of loci from the International Genomics of Alzheimer's Disease Project identifies TRIP4 as a novel susceptibility gene

To follow-up loci discovered by the International Genomics of Alzheimer’s Disease Project, we attempted independent replication of 19 single nucleotide polymorphisms (SNPs) in a large Spanish sample (Fundació ACE data set; 1808 patients and 2564 controls). Our results corroborate association with four SNPs located in the genes INPP5D, MEF2C, ZCWPW1 and FERMT2, respectively. Of these, ZCWPW1 was the only SNP to withstand correction for multiple testing (P=0.000655). Furthermore, we identify TRIP4 (rs74615166) as a novel genome-wide significant locus for Alzheimer’s disease risk (odds ratio=1.31; confidence interval 95% (1.19–1.44); P=9.74 × 10−9).

Prenatal stress-induced programming of genome-wide promoter DNA methylation in 5-HTT-deficient mice

The serotonin transporter gene (5-HTT/SLC6A4)-linked polymorphic region has been suggested to have a modulatory role in mediating effects of early-life stress exposure on psychopathology rendering carriers of the low-expression short (s)-variant more vulnerable to environmental adversity in later life. The underlying molecular mechanisms of this gene-by-environment interaction are not well understood, but epigenetic regulation including differential DNA methylation has been postulated to have a critical role. Recently, we used a maternal restraint stress paradigm of prenatal stress (PS) in 5-HTT-deficient mice and showed that the effects on behavior and gene expression were particularly marked in the hippocampus of female 5-Htt+/− offspring. Here, we examined to which extent these effects are mediated by differential methylation of DNA. For this purpose, we performed a genome-wide hippocampal DNA methylation screening using methylated-DNA immunoprecipitation (MeDIP) on Affymetrix GeneChip Mouse Promoter 1.0 R arrays. Using hippocampal DNA from the same mice as assessed before enabled us to correlate gene-specific DNA methylation, mRNA expression and behavior. We found that 5-Htt genotype, PS and their interaction differentially affected the DNA methylation signature of numerous genes, a subset of which showed overlap with the expression profiles of the corresponding transcripts. For example, a differentially methylated region in the gene encoding myelin basic protein (Mbp) was associated with its expression in a 5-Htt-, PS- and 5-Htt × PS-dependent manner. Subsequent fine-mapping of this Mbp locus linked the methylation status of two specific CpG sites to Mbp expression and anxiety-related behavior. In conclusion, hippocampal DNA methylation patterns and expression profiles of female prenatally stressed 5-Htt+/− mice suggest that distinct molecular mechanisms, some of which are promoter methylation-dependent, contribute to the behavioral effects of the 5-Htt genotype, PS exposure and their interaction.

Exclusion of the neuronal nicotinic acetylcholine receptor α7 subunit gene as a candidate for catatonic schizophrenia in a large family supporting the chromosome 15q13–22 locus

The gene encoding the neuronal nicotinic acetylcholine receptor α7 subunit (CHRNA7) is located on chromosome 15q13.2. This region was suggested to be involved in the etiopathogenesis of: (a) schizophrenia combined with a neurophysiological deficit; (b) lithium-responsive bipolar disorder; and (c) familial catatonic schizophrenia (periodic catatonia). Therefore, members of a large family with periodic catatonia strongly supporting the chromosome 15q13–22 region were genotyped with polymorphic markers localized around the CHRNA7 locus. A recombination event distally of marker D15S144 leading to the exclusion of the CHRNA7 locus from this candidate region was detected in one branch of the pedigree. This result provides strong evidence that a gene located telomeric to CHRNA7 is causative for the pathogenesis of catatonic schizophrenia in this family.

Genome-wide significant risk factors for Alzheimer’s disease: role in progression to dementia due to Alzheimer's disease among subjects with mild cognitive impairment

Few data are available concerning the role of risk markers for Alzheimer’s disease (AD) in progression to AD dementia among subjects with mild cognitive impairment (MCI). We therefore investigated the role of well-known AD-associated single-nucleotide polymorphism (SNP) in the progression from MCI to AD dementia. Four independent MCI data sets were included in the analysis: (a) the German study on Aging, Cognition and Dementia in primary care patients (n=853); (b) the German Dementia Competence Network (n=812); (c) the Fundació ACE from Barcelona, Spain (n=1245); and (d) the MCI data set of the Amsterdam Dementia Cohort (n=306). The effects of single markers and combined polygenic scores were measured using Cox proportional hazards models and meta-analyses. The clusterin (CLU) locus was an independent genetic risk factor for MCI to AD progression (CLU rs9331888: hazard ratio (HR)=1.187 (1.054–1.32); P=0.0035). A polygenic score (PGS1) comprising nine established genome-wide AD risk loci predicted a small effect on the risk of MCI to AD progression in APOE-ɛ4 (apolipoprotein E-ɛ4) carriers (HR=1.746 (1.029–2.965); P=0.038). The novel AD loci reported by the International Genomics of Alzheimers Project were not implicated in MCI to AD dementia progression. SNP-based polygenic risk scores comprising currently available AD genetic markers did not predict MCI to AD progression. We conclude that SNPs in CLU are potential markers for MCI to AD progression.

Evolutionary conserved microsatellites in the promoter region of the 5-hydroxytryptamine receptor 2C gene (HTR2C) are not associated with bipolar disorder in females.

Summary. Two polymorphic dinucleotide repeats separated by a short spacer are localized in the promoter region of the serotonin receptor 2C gene (HTR2C). One of the repeats was found to be evolutionary conserved between humans and rhesus monkeys. Although promoter-associated microsatellites have previously been shown to regulate expression of different genes, we did not find any significant influence of distinct HTR2C promoter microsatellite alleles on transcriptional efficiency as measured by luciferase activity and receptor availiability as assayed by [3H]-mesulergine binding. Furthermore, no association of specific alleles with bipolar disorder was found. These results indicate that the HTR2C promoter polymorphism does not contribute significantly to the etiopathogenesis of bipolar disorder in females.

Mutational analysis of the connexin 36 gene (CX36) and exclusion of the coding sequence as a candidate region for catatonic schizophrenia in a large pedigree

The murine connexin 36 gene (Cx36) encodes a gap-junction channel protein which is preferentially expressed in brain and retina. The human orthologue CX36 is located on chromosome 15q14, a region recently shown to contain a susceptibility gene for hereditary catatonic schizophrenia. Therefore, CX36 was considered as a positional candidate for mutational analysis. Three polymorphic sites within CX36 were found by sequencing the two exons, the intron-exon boundaries and the putative promoter region of the gene derived from patients and control subjects. No variant exclusively cosegregates with the disease in a large pedigree that mainly supports the chromosome 15q14 locus, providing evidence that CX36 is not causative for the pathogenesis of catatonic schizophrenia in this family.

The genomic organization of the murine Mlc1 (Wkl1, KIAA0027) gene.

Summary. The human MLC1 (WKL1, KIAA0027) gene encodes a putative transmembrane protein expressed exclusively in brain. Recessive mutations within this gene cause megalencephalic leukoencephalopathy with subcortical cysts (MLC, MIM 604004, 605908). Furthermore, a missense mutation in this gene is suggestively linked with hereditary catatonic schizophrenia in a large pedigree. The murine gene Mlc1 is composed of 12 exons spanning ∼20 kb, and all exon-intron boundaries conform to the GT/AG consensus. The single copy transcript after splicing is ∼2.8 kb in length, it contains 496 bp of 5′ untranslated region (5′-UTR) and 1143 bp of 3′-UTR, and encodes a protein of 382 amino acids. Potential binding sites for transcription factors including CCAAT-boxes are present in the 5′-flanking region. Fluorescent in situ hybridization localizes the gene to mouse chromosome 15E-F, a region syntenic to human chromosome 22q13. The characterization of the genomic structure of the murine gene will facilitate studies of gene function and physiological properties of the encoded protein in transgenic mouse models.

Mutational analysis of the neuronal cadherin gene CELSR1 and exclusion as a candidate for catatonic schizophrenia in a large family.

The cadherin gene CELSR1 is specifically expressed in the brain and located on chromosome 22q13.33, a region that has recently been shown to be involved in the etiopathogenesis of familial catatonic schizophrenia. The gene is a strong positional candidate and was considered for mutational analysis. A total of 17 allelic variants of CELSR1 was found by sequencing all 35 exons, intron–exon junctions, and the putative promoter region by screening two patients from a large family mainly supporting this locus, and three control subjects in a first step. No variant exclusively co-segregates with the disease in the large pedigree, providing evidence that CELSR1 is not causative for the pathogenesis of catatonic schizophrenia in this family.