N. Jacobsen

Mutations in ATP2A2, encoding a Ca2+ pump, cause Darier disease

Darier disease (DD) is an autosomal-dominant skin disorder characterized by loss of adhesion between epidermal cells (acantholysis) and abnormal keratinization. Recently we constructed a 2.4-Mb, P1-derived artificial chromosome contig spanning the DD candidate region on chromosome 12q23-24.1. After screening several genes that mapped to this region, we identified mutations in the ATP2A2 gene, which encodes the sarco/endoplasmic reticulum Ca2+ -ATPase type 2 isoform (SERCA2) and is highly expressed in keratinocytes. Thirteen mutations were identified, including frameshift deletions, in-frame deletions or insertions, splice-site mutations and non-conservative missense mutations in functional domains. Our results demonstrate that mutations in ATP2A2 cause DD and disclose a role for this pump in a Ca2+-signalling pathway regulating cell-to-cell adhesion and differentiation of the epidermis.

Exclusion of the Darier's disease gene, ATP2A2 , as a common susceptibility gene for bipolar disorder

Bipolar affective disorder is a genetically complex psychiatric disorder with a population prevalence of approximately 1%. We have previously reported cosegregation of bipolar affective disorder and Dariers disease, a dominant skin disorder with a neuropsychiatric component. The gene for Dariers disease was mapped to chromosome 12q23–q24.1 and linkage studies by us and others have subsequently implicated this region as harbouring a susceptibility gene for bipolar affective disorder. In this study we have investigated the Dariers disease gene ATP2A2, the calcium pumping ATPase SERCA2, as a potential susceptibility gene for bipolar disorder under the hypothesis that variations in SERCA2 have pleiotropic effects in brain. Support for this hypothesis comes from clinical evidence of neuropsychiatric abnormalities in Dariers disease, genetic data produced in our study showing non-random clustering of missense mutations in ATP2A2 in neuropsychiatric Darier patients, and functional data demonstrating the role of SERCA2 in intracellular calcium regulation. In a panel of 15 unrelated bipolar patients from multiply affected families showing increased allele sharing at markers in the 12q23–q24.1 region, we performed mutational screening of the ATP2A2 coding sequence, promoter regions, and 3′ untranslated region and identified six sequence variations. These were analysed in a large sample of bipolar patients (n = 324) and control subjects (n = 327). Analysis of allele and genotype distributions for all six variations, and of haplotype frequencies showed no evidence for the involvement of ATP2A2 in producing susceptibility to bipolar disorder.

Screening the human protocadherin 8 (PCDH8) gene in schizophrenia

Abnormalities in synaptic connectivity and plasticity have been implicated in the pathophysiology of schizophrenia. Molecules involved in the development and maintenance of neural circuitry include the recently cloned protocadherins. Human protocadherin 8 (PCDH8) is homologous to ‘arcadlin’, a molecule shown to play a role in hippocampal synaptic function in the rat. The gene encoding PCDH8 maps to a region on chromosome 13 where linkage to schizophrenia has been reported. In this study, the entire expressed sequence of the PCDH8 gene and over 800 bp of the 5′ flanking region were screened for polymorphisms in 30 DSM‐IV schizophrenia individuals using Denaturing High Performance Liquid Chromatography (DHPLC). A total of nine single nucleotide polymorphisms were identified, including three in the first exon that are predicted to change the amino acid sequence. One polymorphism, causing the Trp7Arg change in the putative signal peptide, showed a trend towards excess of the arginine encoding allele in a case‐control sample consisting of 520 DSM‐IV schizophrenia patients and 535 matched controls from the UK (χ2 = 3.72, P[1df] = 0.054). However, this polymorphism did not show preferential transmission to schizophrenic individuals in a separate sample of 203 proband–parent trios from Bulgaria. A second, rare single nucleotide variation, predicting the non‐conservative amino acid change Glu39Ala, was found in one schizophrenic individual and their affected sibling but not in a further 352 affected individuals, nor 357 controls. These results suggest that any contribution of PCDH8 polymorphisms to schizophrenia susceptibility is likely to be weak, although the existence of rare variations of stronger effect cannot be excluded.

Mutational analysis of phospholipase A2A : a positional candidate susceptibility gene for bipolar disorder

Evidence for the involvement of genetic factors in the pathogenesis of bipolar affective disorder is now well established.1 However, the mode of inheritance is non-mendelian and this makes the identification of susceptibility loci difficult. A short-cut to localisation of a disease gene for an oligogenic/multifactorial disorder such as bipolar disorder may come from observation of cosegregation with a monogenic trait. We have described a family (pedigree 324) in which there was cosegregation of major affective disorder and Dariers disease, a dominantly inherited skin disorder, and hypothesised that this reflects genetic linkage between genes involved in these disorders.2 Genetic mapping studies have placed the locus for Dariers disease on chromosome 12q23–q24.3–7 We conducted subsequent linkage studies (1995) upon 45 bipolar families (without Dariers disease). These results showed some evidence in favour of linkage with chromosome 12q markers with maximum evidence at a trinucleotide repeat marker within intron 1 of the phospholipase A2A (PLA2A) gene.8 Evidence for linkage was more significant when analysing the 22 families comprising the Cardiff centre sample, which were expected to be most genetically similar to pedigree 324.

Association study of bipolar disorder at the phospholipase A2 gene (PLA2A) in the Darier's disease (DAR) region of chromosome 12q23-q24.1.

We have previously described a pedigree in which affective disorder and Dariers disease cosegregate and, in an independent sample of 45 bipolar pedigrees, reported evidence in support of linkage between a putative susceptibility locus for bipolar disorder and markers in the Dariers disease region of chromosome 12q23-q24.1. The maximum evidence for linkage was given by a polymorphism at the gene encoding secretory phospholipase A2 (PLA2A), a candidate gene for affective disorder. Dawson et al. (Psychiatric Genetics, 5, 177–180) recently reported allelic association with the same polymorphism at PLA2A in a sample of 54 bipolar probands and 56 controls. We have been unable to replicate the association in 127 Caucasian British DSMIII-R bipolar probands and 223 Caucasian British controls. However, on the basis of several lines of evidence discussed in the paper, we believe that this genomic region in general, and the PLA2A gene in particular, are worthy of further study as candidates in the search for susceptibility genes for the functional psychoses.

CHAPTER 5.4 Finding liability genes for schizophrenia

Publisher Summary This chapter focuses on finding liability genes for schizophrenia. Concordance rates for schizophrenia are consistently higher in monozygotic (MZ) than in dizygotic (DZ) twins, with proband-wise MZ concordance rates averaging 46% versus DZ rates of about 14%. Research into the molecular genetics of schizophrenia is entering a new phase of optimism. Currently, the main challenge for the field is how to convert tentative and suggestive findings of linkage into confident assignments to well-circumscribed regions of the genome. This is almost involving the analysis of large samples of affected sibling-pairs and of large unrelated patient samples for linkage disequilibrium. A second challenge is the optimization of techniques that allows large samples to be analyzed in a realistic time frame. Finally, methods are also required that allows the high-throughput mutational analysis of many genes within candidate regions.