Eleven trinucleotide repeat loci that map to chromosome 12 excluded from involvement in the pathogenesis of bipolar disorder

[Darier disease]

Darier disease (Darier-White disease, dyskeratosis follicularis) is a rare autosomal dominant genodermatosis with regional differences in prevalence. The responsible mutations have been identified on chromosome 12q23-24.1. The gene encodes a calcium-ATPase type 2 in the sarco-/endoplasmic reticulum (SERCA2), which belongs to the large family of P-type cation pumps. This pump couples ATP hydrolysis to the transport of cations across membranes and thus plays a significant role in intracellular calcium signaling. Neuropsychiatric disorders are often associated with Darier disease. However, these diseases are not due to mutations in the gene ATP2A2 but to a susceptibility locus in a 6.5 Mb region near this gene. Currently, the treatment is strictly limited to the relief of symptoms. In severe cases, oral retinoids (acitretin: initial 10-20 mg/Tag and isotretinoin: 0.5-1 mg/kg/day) lead to a response in 90% of cases. However, side effects often prevent long-term use of vitamin A derivatives.

[Possible genetic link between Darier's disease and depression. Review of the literature and case history]

Darier's disease is a rare, inherited autosomal dominant skin disorder caused by a mutation in the sarcoendoplasmatic reticulum calcium transporter (SERCA)-2-gene. In a number of pedigrees, Darier's disease closely relates with affective disorder. The most likely hypothesis for this is a susceptibility gene for affective disorder near the SERCA-2-gene. A 6.5-megabase region could be identified as a susceptibility locus. This region constitutes a susceptability locus also in affective disorder without Darier's disease. The underlying gene has not yet been identified.

Bipolar affective disorder: advances in genetics and mood-stabilising medication

The lifetime prevalence of bipolar affective disorder is between 1 % and 2%. This educational review paper focuses on two areas of interest and relevance to trainees preparing for the membership examination of the Royal College of Psychiatrists: (a) advances in the genetics of bipolar affective disorder; and (b) mood-stabilising medication in bipolar affective disorder.

Analysis of a variable number tandem repeat polymorphism in the huntingtin interacting protein-1 related gene for anticipation in bipolar affective disorder

The anticipation phenomenon, described as either an increase in disease severity, a decrease in age at onset, or both, in successive generations, has been suggested as a possibility of genetic transmission for bipolar affective disorder. We report here investigation of the stability of intergenerational transmission of a variable number tandem repeat (VNTR) polymorphism, found in the Huntingtin interacting protein-1 related gene (HIP12/HIP1R) that is mapped to the chromosome 12q24.31 region, in nine pedigrees showing decreased age at onset in successive generations. We did not observe any allelic instability but we report a deletion that includes this VNTR polymorphism. Allelic and genotypic association studies should be undertaken to verify the involvement of HIP12/HIP1R in bipolar disorder.

Anticipation and repeat expansion in bipolar disorder

Anticipation is the phenomenon whereby a disease becomes more severe and/or presents with earlier onset as it is transmitted down through generations of a family. The only known mechanism for true anticipation is a class of mutations containing repetitive sequences exemplified by the pathogenic trinucleotide repeat. Studies of bipolar disorder (BPD) are consistent with the presence of anticipation and, by inference, the possibility that trinucleotide repeats contribute to this disorder, although it is possible that these data are the result of methodological problems. On the assumption that anticipation in BPD may be real, several surveys of the genome of BPD probands for large trinucleotide repeats have been conducted, as have studies of many repeat-containing candidate genes. No pathogenic triplet repeat has yet been unambiguously implicated.

Triplet repeats and bipolar disorder

Anticipation, the phenomenon of a disease becoming more severe or having earlier onset as it is transmitted down the generations, was originally described in families with psychiatric illness but was thought due to ascertainment bias and became forgotten. Interest was rekindled when a number of neurodegenerative disorders that show this phenomenon, were found to be due to a novel form of mutation--unstable triplet repeats showing intergenerational expansion. Some recent studies of anticipation are consistent with its occurrence in bipolar disorder but are still associated with methodological problems making interpretation difficult. A number of case-control studies employing the repeat expansion detection (RED) technique have found longer repeats in bipolar probands but other studies have found no such association. Despite a large number of studies examining the role of various repeat containing candidate genes, a pathogenic triplet repeat has yet to be found for bipolar disorder. It is likely that the controversy surrounding anticipation and the existence of triplet repeats will only finally be resolved with the demonstration of such a mutation in the aetiology of bipolar disorder.

Trinucleotide repeat expansions: do they contribute to bipolar disorder?

It has long been known that bipolar disorder has a true but complex genetic background. Reports on genetic anticipation in bipolar disorder opened the way to a new approach for genetic studies. Indeed, anticipation, a decreasing age at onset, and/or increasing disease severity in successive generations, were recently explained by an expansion of trinucleotide repeats in monogenic diseases like Huntington's disease and Fragile X syndrome. The involvement of trinucleotide repeat expansions in bipolar disorder received even more support when studies reported association of large CAG/CTG repeats with bipolar disorder. Even though a large number of studies have been conducted, this association is still unexplained. Here, we review the studies investigating the trinucleotide repeat expansion hypothesis in bipolar disorder. Studies on anticipation, on association of anonymous large CAG/CTG repeats and on specific trinucleotide repeats are critically analysed and discussed, showing a field with precipitate conclusions or inconclusive results. The analysis suggests that there are indications, though disputable, supporting the trinucleotide repeat expansion hypothesis in bipolar disorder, but no conclusive evidence has been hitherto provided.

Molecular genetic and family studies in affective disorders: state of the art

The identification of genes responsible for mood disorders will contribute to significant advances in the awareness of diagnosis (diagnostic process and early recognition), pathophysiology, epidemiology and treatment issues. During the past two decades, the search for genes for mood disorders has mainly contributed to better understand and confirm the genetic complexities inherent to these disorders. The large amount of results available and the difficulty to digest them corroborate this observation. The major contribution of these findings should be integrated in the context of the world-wide efforts to identify the thousands of genes of the human genome. Some of these genes may be identified within the next decade. Several consistent hypotheses are currently being tested and will, hopefully, speed up the process of narrowing the important regions when the complete genome map will be available. The most promising chromosomal regions have been localized on chromosomes 4, 5, 11, 12, 18, 21 and X. A number of candidate genes have also been investigated, some of these are directly linked to neurobiological hypotheses of the aetiology of affective disorders. In parallel, specific hypotheses have been implicated, such as anticipation and dynamic mutations. Further research should concentrate on these hypotheses and confirm positive findings through interdisciplinary and multicenter projects.

No evidence of association from transmission disequilibrium analysis of the hKCa3 gene in bipolar disorder

OBJECTIVE

A recent case control study has suggested that modest enlargements of a highly polymorphic CAG repeat in exon 1 of the gene encoding potassium channel hKCa3 may be associated with bipolar disorder (BPD). We have examined this hypothesis by genotyping this locus in a family-based association study.

METHOD

One hundred and twenty-eight parent offspring trios of British Caucasian origin were examined where the proband was diagnosed with the American Psychiatric Association's Diagnostic and Statistical Manual (DSM)-IV BPD I (n = 123) or II (n = 5). An improved assay was used, with redesigned polymerase chain reaction (PCR) primers, permitting quicker and higher resolution genotyping. The resultant genotypes were analysed using the extended transmission/ disequilibrium test (ETDT).

RESULTS

The experimental data did not provide evidence for the preferential transmission of large alleles to bipolar cases (chi2 = 11.12, df = 10, p = 0.349).

CONCLUSIONS

Our data provide no support for the hypothesis that variation at the hKCa3 gene contributes to susceptibility to BPD.

A case of vesiculo-bullous Darier's disease associated with bipolar psychiatric disorder

We describe the case of a 71-year-old men suffering from Darier's disease since his youth and presenting with intensely itching, vesicular and pustular lesions, localized on his arms, legs and on the ulnar side of his right hand. The patient also had a 30 year-history of bipolar psychiatric disorders. The histopathological examination of lesional skin showed suprabasal acantholytic clefting, hyperparakeratosis, and dyskeratosis. Histopathological and immunopathological (direct and indirect immunofluorescence) results, were consistent with vesiculo-bullous Darier's disease. Corticosteroid therapy with methylprednisolone at low dosage (0.2 mg/kg/day) was started with a quick resolution of the vesicular lesions on his arms and legs.

Genetics of bipolar disorders

Advances towards the understanding of the etiological mechanisms involved in mood disorders provide interesting yet diverse hypotheses and promising models. In this context, molecular genetics has now been widely incorporated into genetic epidemiological research in psychiatry. Affective disorders and, in particular, bipolar affective disorder (BPAD) have been examined in many molecular genetic studies which have covered a large part of the genome, specific hypotheses such as mutations have also been studied. Most recent studies indicate that several chromosomal regions may be involved in the aetiology of BPAD. Other studies have reported the presence of anticipation in BPAD. This phenomenon describes the increase in clinical severity and decrease in age of onset observed in successive generations. This mode of transmission correlates with the presence of specific mutations (Trinucleotide Repeat Sequences) and may represent a genetic factor involved in the transmission of the disorder. In parallel to these new developments in molecular genetics, the classical genetic epidemiology, represented by twin, adoption and family studies, provided additional evidence in favour of the genetic hypothesis in mood disorders. Moreover, these methods have been improved through models to test the gene-environment interactions. While significant advances have been made in this major field of research, it appears that integrative models, taking into account the interactions between biological (genetic) factors and social (psychosocial environment) variables offer the most reliable way to approach the complex mechanisms involved in the etiology and outcome of mood disorders.

Gene targets related to phospholipid and fatty acid metabolism in schizophrenia and other psychiatric disorders: an update

Phospholipids make up about 60% of the brain's dry weight and play key roles in many brain signal tranduction mechanisms. A recent review(1)identified the increasing evidence that abnormal phospholipid and related fatty acid metabolism may contribute to illnesses such as schizophrenia, bipolar disorder, depression and attention deficit hyperactivity disorder. This current paper reviews the main pathways of phospholipid metabolism, emphasizing the role of phospholipases of the A2 in signal tranduction processes. It also updates the chromosomal locations of regions likely to be involved in these disorders, and relates these to the known locations of genes directly or indirectly involved in phospholipid and fatty acid metabolism.

Genetics of bipolar affective disorder

Bipolar affective disorder is a highly heritable condition, as demonstrated in twin, family, and adoption studies. Morbid risk in first degree relatives is four to six times higher than the population prevalence of about 1%. However, the mode of inheritance is complex, and linkage findings have been difficult to replicate. Despite these limitations, consistent linkage findings have emerged on several chromosomes, notably 18p, 18q, 21q, 12q, 4p, and Xq. Two additional areas, 10p and 13q, have shown linkage in regions that appear to overlap with significant linkage findings in schizophrenia. Separate linkage studies in schizophrenia also have targeted the replicated bipolar linkages on 18p and 22q. New methods are being developed for fine mapping and candidate identification. Recent candidate gene studies include some positive results for the serotonin transporter gene on 17q and the catechol-o-methyltransferase gene on 22q. No other candidate gene studies are yet showing replicated results. A convincing demonstration for a susceptibility gene will probably require a mixture of case- control studies, family-based association methods, and pathophysiologic studies.

Searching high and low: a review of the genetics of bipolar disorder

OBJECTIVES

To review the methodologies and findings in the genetics of bipolar disorder (BPD), and to suggest future directions for research.

METHODS

Reports of family, twin, adoption, linkage, association, cytogenetic, and animal model studies, and segregation analyses in English, were identified from multiple MEDLINE searches. Hand searches were carried out in bibliographies from review articles.

RESULTS

Family, twin, and adoption studies have provided strong evidence for a genetic etiology in BPD. Early reports of linkage of BPD to DNA markers at several chromosomal sites have not proven robust, perhaps because of the complex nature of BPD inheritance. However, linkage findings in the 1990s, on chromosomes 18, 21q, 12q, and 4p, have provided leads that are being pursued through both genetic and physical mapping. No gene has yet been definitively implicated in BPD.

CONCLUSIONS

Strategies for increasing the power to detect BPD genes include: (1) dividing the phenotype into genetically meaningful subtypes to decrease heterogeneity: and (2) ascertaining a very large family sample--a multicenter study now in progress will collect 700 bipolar I sibling pairs. BPD may result from several genes acting in concert so that new multilocus statistical methods could enhance the capacity to detect loci involved. Family-based association studies using a very large number of newly identified single nucleotide polymorphisms (SNPs) may allow for more efficient screening of the genome. As the Human Genome Project approaches its goal of isolating all genes by 2003, the data generated is likely to speed identification of candidate BPD genes.

Chromosomes 12 and 16 workshop

Recent linkage results independently derived from a large French Canadian pedigree and Danish kindreds coupled with supportive data from other studies provide compelling evidence for a bipolar disorder susceptibility locus on chromosome 12q23-q24. The idea is further strengthened by the finding that Darier's disease, which maps to this region, has been shown to cosegregate with affective disorder in a family. This linkage finding, however, was not supported in other independent genome scans. On chromosome 16, bipolar families from Denmark exhibited suggestive linkage with D16S510, on 16p13. Multipoint nonparametric analysis on the NIMH Genetics Initiative bipolar pedigrees yielded increased allele sharing that maximized approximately 18 cM proximal to the latter locus. In contrast, evidence of linkage was not detected in other panels of bipolar families that were presented. At 16p13, a maximum multipoint lod score of 4 for a latent class-derived phenotype that has aspects of alcohol dependence was found in a genome scan of 105 families from the Collaborative Study of the Genetics of Alcoholism, identifying a potential vulnerability locus.

Molecular genetic findings in mood disorders

Traditional methods used to asses genetic effects, such as twins, adoption and family studies, have demonstrated the role genetic vulnerability factors in the etiology of major psychiatric diseases such as affective disorders and schizophrenia. It remains however impossible, using these methods, to specify the genetic variables involved and the exact mode of transmission of these diseases. New genetic approaches in psychiatry include the use of DNA markers in sophisticated strategies to examine families and populations. Genetic linkage (in families) and allelic association (in unrelated subjects) are the most frequent techniques applied searching for genes in psychiatric diseases. Advances in these methods have permitted their application to complex diseases in which the mode of genetic transmission is unknown. Affective disorders and, in particular, bipolar affective disorder (BPAD) have been examined in many molecular genetic studies which have covered a large part of the genome, specific hypotheses such as mutations have also, been studied. Most recent studies indicate that several chromosomal regions may be involved in the aetiology of affective disorders. Large multi-centre and multi-disciplinary projects are currently underway in Europe and in the US and hopefully will improve our understanding of the genetic factors involved in affective disorders. In parallel to these new developments in molecular genetics, the classical genetic epidemiology, represented by twin, adoption and family studies, have been improved, providing validated models to test the gene-environment interactions.