Genetic mapping using haplotype, association and linkage methods suggests a locus for severe bipolar disorder (BPI) at 18q22-q23

Disease classification and transmission effects on linkage analyses in the NIMH1 bipolar disorder pedigrees

In this analysis of bipolar affective disorder, 22 families from the NIMH1 data set were further grouped into three transmission patterns: male to male, male to female, and maternal. The data were analyzed under three classifications of affection status: Bipolar I (BPI) only, BPI and Bipolar II (BPII), and BPI, BPII, and recurrent unipolar. LINKAGE was run on each of the subsets, and SIBPAL was run on the full and grouped data sets. A lod score of 1.09 was found for marker D18S62 in the maternal subset, when classifying affecteds as BPI, BPII, or recurrent unipolar. Affected sib-pair analysis showed evidence for linkage with markers D18S62, D18S37, D18S53, D18S40, D18S45, and D18S56 in the male to male transmission groups and the full data set. Linkage was not consistently found in the maternal and father/daughter groups. These results indicate that subsetting by parental transmission may result in less heterogeneity and have significant effects on linkage findings. Studies using a broader definition of affection status may provide considerably more information for linkage.

Parental transmission and D18S37 allele sharing in bipolar affective disorder

We combined the five chromosome 18 bipolar affective disorder data sets provided by GAW10, totaling 185 families with 3,394 individuals, and performed analysis of differential parental transmission and chromosome 18 marker allele sharing in families with transmission through fathers vs those through mothers. Results indicated a significant excess of maternal transmission of bipolar disorder. All pedigrees were then broken into nuclear families and affected sib-pair linkage analyses performed on the marker, D18S37. There was significant linkage in the data overall, as well as in each subgroup of paternal, maternal and unknown parental transmission nuclear families. There were no significant differences in identical-by-descent (IBD) scores among the three transmission subgroups. These findings support an excess of maternal transmission, and linkage between bipolar disorder and marker D18S37. However, our results do not support the previous suggestion that there are differences in chromosome 18 marker allele sharing depending on the transmitting parent.

Analysis of the pseudoautosomal X-linked gene SYBL1in bipolar affective disorder: description of a new candidate allele for psychiatric disorders

The absence of father-to-son transmission has been observed in a subset of families with bipolar disorder (BPD), suggestive of a susceptibility gene on the sex-linked portion of the X chromosome. This is supported by some genetic linkage studies that have provided evidence for a susceptibility locus near Xq28. We have analyzed one candidate gene on Xq28, SYBL1, which maps to the Xq pseudoautosomal region (PAR). SYBL1 encodes a member of the synaptobrevin family of proteins that is involved in synaptic vesicle docking and membrane transport. Genes in the PAR generally escape X-chromosome inactivation and have an active homolog on the Y chromosome, which would result in an increase in same-sex concordance in paternal transmitted traits. However, SYBL1 is neither expressed on the Y chromosome nor the inactive X chromosome and would therefore be expected to show typical sex-linked transmission. We have screened SYBL1 for mutations that could be tested as candidate alleles in the development of BPD. Following single-strand conformation polymorphism (SSCP) analysis and DNA sequencing, four single nucleotide polymorphisms were detected: a silent mutation at codon 108, two intron mutations without any obvious biological significance, and a G-->C transversion in the polypyrimidine tract at the 3' splice acceptor site preceding exon 8. This polymorphism, which creates a perfect 16/16 stretch of pyrimidines, was analyzed in 110 patients with BPD not selected for sex-linked transmission and 119 control subjects. The results show a statistical trend toward an increase in the frequency of the C allele in males with BPD but not females. Males: chi(2) = 3.46, 1 df, p =.06; Females: chi(2) =.20, 1 df, p =.66.

Genetics of psychiatric disease

Genetic epidemiologic studies reveal that relatives of bipolar (BIP) probands are at increased risk for recurrent unipolar (RUP), BIP, and schizoaffective (SA) disorders, while relatives of schizophrenia (SZ) probands are at increased risk for SZ, SA, and RUP disorders. The overlap in familial risk may reflect shared genetic susceptibility. Recent genetic linkage studies have defined confirmed susceptibility loci for BIP disorder for multiple regions of the human genome, including 4p16, 12q24, 18p11.2, 18q22, 21q21, 22q11-13, and Xq26. Studies of SZ kindreds have yielded robust evidence for susceptibility at 18p11.2 and 22q11-13, both of which are implicated in susceptibility to BIP disorder. Similarly, confirmed SZ vulnerability loci have been mapped for 6p24, 8p and 13q32. Strong statistical evidence for a 13q32 BIP susceptibility locus has been reported. Thus, both family and molecular studies of these disorders suggest shared genetic susceptibility. These two group of disorders may not be so distinct as current nosology suggests.

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.

Susceptibility loci for bipolar disorder: overlap with inherited vulnerability to schizophrenia

Genetic epidemiological studies reveal that relatives of bipolar probands are at increased risk for recurrent unipolar, bipolar, and schizoaffective disorders, whereas relatives of probands with schizophrenia are at increased risk for schizophrenia, schizoaffective, and recurrent unipolar disorders. The overlap in familial risk may reflect shared genetic susceptibility. Recent genetic linkage studies have defined confirmed bipolar susceptibility loci for multiple regions of the human genome, including 4p16, 12q24, 18p11.2, 18q22, 21q21, 22q11-13, and Xq26. Studies of schizophrenia kindreds have yielded robust evidence for susceptibility at 18p11.2 and 22q11-13, both of which are implicated in susceptibility to bipolar disorder. Similarly, confirmed schizophrenia vulnerability loci have been mapped, too, for 6p24, 8p, and 13q32. Strong statistical evidence for a 13q32 bipolar susceptibility locus has been reported. Thus, both family and molecular studies of these disorders suggest shared genetic susceptibility. These two groups of disorders may not be as distinct as current nosology suggests.

From genome to drug--optimising the drug discovery process

Current drug discovery and development practices are technologically sophisticated and highly efficient. At the same time the failure rate of compounds in both preclinical and clinical development is high. These failures can be attributed to many factors. Two predominant causes of failure are lack of efficacy and toxicity. Often lack of efficacy is only determined late in the clinical trial process and can be difficult if not impossible to explain, as well as being expensive. Toxicity accounts for many failures during preclinical development, which are less costly, but it also occurs in the clinic. Often the underlying cause of clinical toxicity is never identified. Studies of the structure and activity of the human and other genomes has over the last decade lead to a revolution in biological and medical research. Disease associated genes can now be identified through the application of human genetics, whole genomes have been sequenced and tools have been developed that allow the complete characterization of an organism's gene expression profile in a single experiment. These tools are now being applied to pharmaceutical research and development with the aim to increase the efficiency of the process and the quality of the product.

Chromosomal abnormalities and schizophrenia

Schizophrenia is a common and serious psychiatric illness with strong evidence for genetic causation, but no specific loci yet identified. Chromosomal abnormalities associated with schizophrenia may help to understand the genetic complexity of the illness. This paper reviews the evidence for associations between chromosomal abnormalities and schizophrenia and related disorders. The results indicate that 22q11.2 microdeletions detected by fluorescence in-situ hybridization (FISH) are significantly associated with schizophrenia. Sex chromosome abnormalities seem to be increased in schizophrenia but insufficient data are available to indicate whether schizophrenia or related disorders are increased in patients with sex chromosome aneuploidies. Other reports of chromosomal abnormalities associated with schizophrenia have the potential to be important adjuncts to linkage studies in gene localization. Advances in molecular cytogenetic techniques (i.e., FISH) have produced significant increases in rates of identified abnormalities in schizophrenia, particularly in patients with very early age at onset, learning difficulties or mental retardation, or dysmorphic features. The results emphasize the importance of considering behavioral phenotypes, including adult onset psychiatric illnesses, in genetic syndromes and the need for clinicians to actively consider identifying chromosomal abnormalities and genetic syndromes in selected psychiatric patients.

Long homozygous chromosomal segments in reference families from the centre d'Etude du polymorphisme humain

Using genotypes from nearly 8,000 short tandem-repeat polymorphisms typed in eight of the reference families from the Centre d'Etude du Polymorphisme Humain (CEPH), we identified numerous long chromosomal segments of marker homozygosity in many CEPH individuals. These segments are likely to represent autozygosity, the result of the mating of related individuals. Confidence that the complete segment is homozygous is gained only with markers of high density. The longest segment in the eight families spanned 77 cM and included 118 homozygous markers. All individuals in family 884 showed at least one segment of homozygosity: the father and mother were homozygous in 8 and 10 segments with an average length of 13 and 16 cM, respectively, and covering a total of 105 and 160 cM, respectively. The progeny in family 884 were homozygous over 5-16 segments with average length 11 cM. The progeny in family 102 were homozygous over 4-12 segments with average length 19 cM. Of the 100 individuals in the other six families, 1 had especially long homozygous segments, and 19 had short but significant homozygous segments. Our results indicate that long homozygous segments are common in humans and that these segments could have a substantial impact on gene mapping and health.

Recent progress in the search for genes for bipolar disorder

Over many decades, much evidence has been accumulated to demonstrate the strong role of genetic factors in bipolar disorder. Recently, genetic studies of bipolar disorder have turned from proving the role of genetics to identifying the specific genes involved. This has been made possible by the development of powerful methods to identify disease genes by their locations on chromosomes, an approach termed positional cloning. Currently, about a dozen regions in the genome have been implicated as the location of susceptibility genes for bipolar disorder. Several of these have been replicated and will likely lead to the identification of novel disease mechanisms. An intriguing development is that a few of these are the same locations implicated in studies of schizophrenia, suggesting a greater genetic relationship between these disorders than had been previously thought. It is hoped that the identification of novel disease genes will lead to a better understanding of the pathophysiology of bipolar disorder and to the development of more effective treatments.

Genetic models for handedness, brain lateralization, schizophrenia, and manic-depression

There has been a long-standing debate to explain the complex correlation of development of human hand preference with brain lateralization, and occasionally, the correlation of both lateralizations with psychiatric disorders. A major unanswered question in this debate is whether nature (i.e., genetics) or nurture (environment/culture) controls the development of these attributes of human behavior. Simple genetic models have failed to satisfactorily explain the mode of inheritance of psychotic disorders as well as of the handedness trait. This paper advances several hypothetical and testable genetic models to explain the complex inheritance of these traits. In one model, brain lateralization is proposed to result from nonrandom segregation of the 'Watson' and 'Crick' strands of a particular chromosome, causing hemisphere lateralization, and that a gene, designated RGHT (for right), is further proposed to be responsible for the distribution of DNA chains to specific hemispheres. Accordingly, dominant, familially inherited schizophrenia and bipolar disorders are postulated to result from chromosomal rearrangements disrupting strand segregation, while sporadic cases are proposed to occur at increased frequencies in individuals with the recessive handedness genotype. Finally, discordance in monozygotic twins is suggested to occur due to developmental differences in brain lateralization in twins of the recessive genotype. Psychotic disorders are suggested to be due to developmental anomalies of cerebral asymmetry.

Genome-wide search for linkage of bipolar affective disorders in a very large pedigree derived from a homogeneous population in quebec points to a locus of major effect on chromosome 12q23-q24

We completed a genome-wide scan for susceptibility loci for bipolar affective disorders in families derived from a rather homogeneous population in the Province of Québec. The genetic homogeneity of this population stems from the migration of founding families into this relatively isolated area of Québec in the 1830s. A possible founder effect, combined with a prevalence of very large families, makes this population ideal for linkage studies. Genealogies for probands can be readily constructed from a population database of acts of baptism and marriage from the early 1830s up to the present time (the BALSAC register). We chose probands with a DSM III diagnosis of bipolar affective disorder and who may be grouped within large families having genealogical origins with the founding population of the Saguenay-Lac-St-Jean area. Living members (n approximately 120) of a very large pedigree were interviewed using the Structured Clinical Interview for DSM III (SCID I), SCID II, and with a family history questionnaire. A diagnostic panel evaluated multisource information (interview, medical records, family history) and pronounced best-estimate consensus diagnoses on all family members. Linkage, SimAPM, SimIBD, and sib-pair analyses have been performed with 332 microsatellite probes covering the entire genome at an average spacing of 11 cM. GENEHUNTER and haplotype analyses were performed on regions of interest. Analysis of a second large pedigree in the same regions of interest permitted confirmation of presumed linkages found in the region of chromosome 12q23-q24.

Transtorno bipolar

Os resultados de estudos de famílias sugerem que o transtorno bipolar tenha uma base genética. Essa hipótese foi reforçada em estudos de adoção e de gêmeos. A herança do transtorno bipolar é complexa, envolve vários genes, além de apresentar heterogeneidade e interação entre fatores genéticos e não-genéticos. Achados, que já foram replicados, já implicaram os cromossomos 4, 12, 18 e 21, entre outros, na busca por genes de suscetibilidade. Os resultados mais promissores foram obtidos através de estudos de ligação. Por outro lado, os estudos de associação geraram dados interessantes, mas ainda vagos. Os estudos de populações de pacientes homogêneos e a melhor definição do fenótipo deverão contribuir para avanços futuros. A identificação dos genes relacionados ao transtorno bipolar irá permitir o melhor entendimento e tratamento dessa doença.

Epidemiological comparison of schizophrenia and bipolar disorder

Schizophrenia and bipolar disorder share many epidemiological features in common, but there are also differences. Both disorders share some risk factors, suggesting etiological antecedents that date to the perinatal period; these include excess of winter-spring births, abnormal dermatoglyphics, and probably an excess of perinatal complications. By contrast, an excess of urban births and an excess of minor physical anomalies are present in schizophrenia, but apparently not in bipolar disorder. Bipolar disorder also may be found in geographic, presumably genetic, isolates and in higher prevalence in higher socio-economic groups, which also differentiates it from schizophrenia. It is hypothesized that a subset of individuals with bipolar disorder constitutes a distinct disease entity, but that the majority share some common etiological antecedents with schizophrenia and may represent a disease continuum.

Galanin and galanin receptors

The development of a strain of galanin knockout mice has provided confirmation of a neuroendocrine role for galanin, as well as supporting results of previous physiological investigations indicating a role for galanin in analgesia and neuropathic pain, and potentially in neuronal growth and regeneration processes. Whether elevation of galanin expression in neurodegenerative disorders such as Alzheimer's disease represents a survival response or exacerbates functional deficit in afflicted individuals remains to be determined. More detailed analysis of the phenotype of the galanin knockout mouse should provide insights into the physiological role of galanin in memory and learning processes, as well as in hypothalamic function and other aspects of neuroendocrine regulation. Biochemical and molecular cloning efforts have demonstrated that the multiplicity of actions of galanin is matched by complexity in the distribution and regulation of galanin and its receptors. A focus on characterisation of galanin receptors has resulted in the molecular cloning of three receptor subtypes to date. The distribution and functional properties of these receptors have not yet been fully elucidated, currently precluding assignment of discrete functions of galanin to any one receptor subtype. It is not currently possible to reconcile available pharmacological data using analogs of galanin and chimeric peptides in functional assay systems with the pharmacological properties of cloned receptor subtypes. This highlights the value of further knockout approaches targeting galanin receptor subtypes, but also raises the possibility of the existence of additional receptor subtypes that have yet to be cloned, or that receptor activity may be modulated by regulatory molecules that remain to be identified. The development of receptor subtype-specific compounds remains a high priority to advance work in this area. The ability to selectively modulate the many different actions of galanin, through a clearer understanding of receptor structure-function relationships and neuronal distribution, promises to provide important insights into the molecular and cellular basis of galanin action in normal physiology, and may provide lead compounds with therapeutic application in the prevention and treatment of a range of disorders.

Lithium responsive bipolar disorder, unilineality, and chromosome 18: A linkage study

Over the last three years several studies have investigated the hypothesis of linkage between bipolar disorder and markers on chromosome 18. Although independent groups have reported positive results, it is still not clear how these should be interpreted, as linkage spans a considerably large segment of the chromosome. In this study we have investigated linkage with chromosome 18 markers in 19 families of lithium-responsive bipolar patients, as a way to select a more homogeneous population. In addition, we have investigated whether there is evidence of a parent-of-origin effect as suggested by previous studies. Eleven markers spanning the whole chromosome were typed and linkage analysis was carried out using parametric and nonparametric methods. Analysis of the whole sample provided nonsignificant linkage results. However, when the sample included only unilineal families, and was further stratified according to parental origin, two chromosomal regions provided modestly positive lod scores. Maximum lod scores of 1.04 (P = 0.001) at D18S53 and 0.87 (P = 0.045) at D18S61 were observed for maternal and paternal pedigrees, respectively. Nonparametric analysis yielded similar results. In conclusion, our results are congruent with previous reports that suggest an advantage of unilineal pedigrees in linkage analysis of bipolar disorder and cannot rule out a parent-of-origin effect in this genomic region.

Analysis of GNAZ gene polymorphism in bipolar affective disorder

Evidence for a bipolar disorder (BPD) susceptibility locus on chromosome 22q11 has been provided in several studies. One candidate gene that maps to this region is the G-protein alpha subunit gene Galphaz (GNAZ). We have identified a common silent polymorphism in GNAZ exon 2 by single strand conformation polymorphism analysis. The frequency of this polymorphism was determined in a control population (n=84) and in patients with BPD (n=88). The data showed a statistical trend toward a difference in the distribution of alleles in patients with BPD compared with control subjects (chi square=3.2, 1 df, P=0.073, two-tailed). No significant difference was detected when the GNAZ polymorphism was analyzed in control subjects and schizophrenia patients (n=63, P=0.92). These data continue to provide some support for a BPD susceptibility gene on 22q11, possibly in linkage disequilibrium with the GNAZ 309 polymorphism.

Genetics of bipolar disorder

Bipolar disorder (also known as manic depressive illness) is a complex genetic disorder in which the core feature is pathological disturbance in mood (affect) ranging from extreme elation, or mania, to severe depression usually accompanied by disturbances in thinking and behaviour. The lifetime prevalence of 1% is similar in males and females and family, twin, and adoption studies provide robust evidence for a major genetic contribution to risk. There are methodological impediments to precise quantification, but the approximate lifetime risk of bipolar disorder in relatives of a bipolar proband are: monozygotic co-twin 40-70%; first degree relative 5-10%; unrelated person 0.5-1.5%. Occasional families may exist in which a single gene plays the major role in determining susceptibility, but the majority of bipolar disorder involves the interaction of multiple genes (epistasis) or more complex genetic mechanisms (such as dynamic mutation or imprinting). Molecular genetic positional and candidate gene approaches are being used for the genetic dissection of bipolar disorder. No gene has yet been identified but promising findings are emerging. Regions of interest identified in linkage studies include 4p16, 12q23-q24, 16p13, 21q22, and Xq24-q26. Chromosome 18 is also of interest but the findings are confusing with up to three possible regions implicated. To date most candidate gene studies have focused on neurotransmitter systems influenced by medication used in clinical management of the disorder but no robust positive findings have yet emerged. It is, however, almost certain that over the next few years bipolar susceptibility genes will be identified. This will have a major impact on our understanding of disease pathophysiology and will provide important opportunities to investigate the interaction between genetic and environmental factors involved in pathogenesis. This is likely to lead to major improvements in treatment and patient care but will also raise important ethical issues that will need to be addressed.

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.

Assessing the feasibility of linkage disequilibrium methods for mapping complex traits: an initial screen for bipolar disorder loci on chromosome 18

Linkage disequilibrium (LD) analysis has been promoted as a method of mapping disease genes, particularly in isolated populations, but has not yet been used for genome-screening studies of complex disorders. We present results of a study to investigate the feasibility of LD methods for genome screening using a sample of individuals affected with severe bipolar mood disorder (BP-I), from an isolated population of the Costa Rican central valley. Forty-eight patients with BP-I were genotyped for markers spaced at approximately 6-cM intervals across chromosome 18. Chromosome 18 was chosen because a previous genome-screening linkage study of two Costa Rican families had suggested a BP-I locus on this chromosome. Results of the current study suggest that LD methods will be useful for mapping BP-I in a larger sample. The results also support previously reported possible localizations (obtained from a separate collection of patients) of BP-I-susceptibility genes at two distinct sites on this chromosome. Current limitations of LD screening for identifying loci for complex traits are discussed, and recommendations are made for future research with these methods.

A high-density genome scan detects evidence for a bipolar-disorder susceptibility locus on 13q32 and other potential loci on 1q32 and 18p11.2

Bipolar disorder is a severe mental illness characterized by mood swings of elation and depression. Family, twin, and adoption studies suggest a complex genetic etiology that may involve multiple susceptibility genes and an environmental component. To identify chromosomal loci contributing to vulnerability, we have conducted a genome-wide scan on approximately 396 individuals from 22 multiplex pedigrees by using 607 microsatellite markers. Multipoint nonparametric analysis detected the strongest evidence for linkage at 13q32 with a maximal logarithm of odds (lod) score of 3.5 (P = 0. 000028) under a phenotype model that included bipolar I, bipolar II with major depression, schizoaffective disorder, and recurrent unipolar disorder. Suggestive linkage was found on 1q31-q32 (lod = 2. 67; P = 0.00022) and 18p11.2 (lod = 2.32; P = 0.00054). Recent reports have linked schizophrenia to 13q32 and 18p11.2. Our genome scan identified other interesting regions, 7q31 (lod = 2.08; P = 0. 00099) and 22q11-q13 (lod = 2.1; P = 0.00094), and also confirmed reported linkages on 4p16, 12q23-q24, and 21q22. By comprehensive screening of the entire genome, we detected unreported loci for bipolar disorder, found support for proposed linkages, and gained evidence for the overlap of susceptibility regions for bipolar disorder and schizophrenia.

Cloning, expression, and chromosomal mapping of a human ATPase II gene, member of the third subfamily of P-type ATPases and orthologous to the presumed bovine and murine aminophospholipid translocase

Recently, a P-type ATPase was cloned from bovine chromaffin granules (b-ATPase II) and a mouse teratocarcinoma cell line (m-ATPase II) and was shown to be homologous to the Saccharomyces cerevisiae DRS2 gene, the inactivation of which resulted in defective transport of phosphatidylserine. Here, we report the cloning from a human skeletal muscle cDNA library of a human ATPase II (h-ATPase II), orthologous to the presumed bovine and mouse aminophospholipid translocase (95.3 and 95.9% amino acid identity, respectively). Compared with the bovine and mouse counterparts, the cloned h-ATPase II polypeptide exhibits a similar membrane topology, but contains 15 additional amino acids (1163 vs 1148) located in the second intracytoplasmic loop, near the DKTGTLT-phosphorylation site. However, RT-PCR analysis performed with RNA from different human tissues and cell lines revealed that the coding sequence for these 15 residues is sometimes present and sometimes absent, most likely as a result of a tissue-specific alternative splicing event. The h-ATPase II gene, which was mapped to chromosome 4p14-p12, is expressed as a 9.5-kb RNA species in a large variety of tissues, but was not detected in liver, testis, and placenta, nor in the erythroleukemic cell line K562.

Basic concepts in the study of diseases with complex genetics

Most diseases run in families--this is also true of virtually all psychiatric disorders. Twin and adoption studies have shown that most psychiatric disorders have a genetic component, yet very few genetic factors are known, as is true for most disorders with a complex genetic origin. Here I review, for nongeneticists, some of the basic terminology and concepts used when studying complex genetic diseases, with examples from psychiatric genetics. This review is intended to help in the understanding and critical evaluation of reports on genetics of psychiatric illnesses in the literature.

Nonparametric simulation-based statistical analyses for bipolar affective disorder locus on chromosome 21q22.3

Straub et al. [1994: Nat Genet 8:291-296] reported a candidate bipolar affective disorder (BAD) locus on chromosome 21q22.3. As a replication study, we analyzed 12 Australian BAD pedigrees for the presence of excess allele sharing and cosegregation with the putative chromosome 21q22.3 BAD locus, using six microsatellite markers. The nonparametric simulation-based statistic SimAPM produced positive results for the marker PFKL (P < 0.001) and D21S198 (P = 0.007). PFKL also demonstrated linkage (P < 0.001) when analyzed using the more conservative statistic, SimIBD. Comparable results were obtained when using the original APM statistic (P = 0.02 for D21S198). However, other nonparametric analyses such as GENEHUNTER and model-free linkage (MFLINK) analysis did not yield significant results. Combined LOD scores for the 12 families were strongly negative for all six markers under six genetic models. Two-point and multipoint analyses of individual families revealed one family, family 17, with maximal LOD scores greater than 1.41 for the 10.5-cM region between PFKL and D21S198. This report provides additional support for the suggestive linkage of a susceptibility locus for BAD on chromosome 21q22.3.

A genome-wide search for chromosomal loci linked to mental health wellness in relatives at high risk for bipolar affective disorder among the Old Order Amish

Bipolar affective disorder (BPAD; manic-depressive illness) is characterized by episodes of mania and/or hypomania interspersed with periods of depression. Compelling evidence supports a significant genetic component in the susceptibility to develop BPAD. To date, however, linkage studies have attempted only to identify chromosomal loci that cause or increase the risk of developing BPAD. To determine whether there could be protective alleles that prevent or reduce the risk of developing BPAD, similar to what is observed in other genetic disorders, we used mental health wellness (absence of any psychiatric disorder) as the phenotype in our genome-wide linkage scan of several large multigeneration Old Order Amish pedigrees exhibiting an extremely high incidence of BPAD. We have found strong evidence for a locus on chromosome 4p at D4S2949 (maximum GENEHUNTER-PLUS nonparametric linkage score = 4.05, P = 5. 22 x 10(-4); SIBPAL Pempirical value <3 x 10(-5)) and suggestive evidence for a locus on chromosome 4q at D4S397 (maximum GENEHUNTER-PLUS nonparametric linkage score = 3.29, P = 2.57 x 10(-3); SIBPAL Pempirical value <1 x 10(-3)) that are linked to mental health wellness. These findings are consistent with the hypothesis that certain alleles could prevent or modify the clinical manifestations of BPAD and perhaps other related affective disorders.

Structural organization and chromosomal localization of three human galanin receptor genes

Human galanin receptor subtypes GALR1, GALR2, and GALR3 are encoded by separate genes that are located on human chromosomes 18q23, 17q25.3, and 22q13.1, respectively. The exon:intron organization of the gene encoding GALR2 (GALNR2) and GALR3 (GALNR3) is conserved, with exon 1 encoding the NH2-terminus to the end of transmembrane domain 3 and exon 2 encoding the remainder of the receptor, from the second intracellular loop to the COOH-terminus. This conservation of structural organization is indicative of a common evolutionary origin for GALNR2 and GALNR3. The exon:intron organization of the gene encoding GALR1 (GALNR1) is different from that of GALNR2 and GALNR3, with exon 1 encoding the NH2-terminus to the end of transmembrane domain 5, exon 2 encoding the third intracellular loop, and exon 3 encoding the remainder of the receptor, from transmembrane domain 6 to the COOH-terminus. The structural organization of GALNR1 suggests convergent evolution for this gene and represents a structural organization that is unique among genes encoding G-protein-coupled receptors.

Use of isolated inbred human populations for identification of disease genes

The genetic mapping of disease loci involves the use of patient phenotype and genotype data in the search for genetic markers that segregate, or are associated with, a trait or disorder. Genetically isolated populations offer many advantages for such studies. The high degree of inbreeding and/or founder effects in some small population isolates result in an increased incidence of recessive disorders. Monogenic disorders are less likely to show non-allelic heterogeneity in isolated populations than in more diverse populations. The use of isolated populations also reduces the complexity of polygenic disorders by reducing the number of loci probably involved in the disorder. Finally, a variety of strategies can be used with particular efficacy for the mapping of disease genes in isolated populations.

Molecular genetic investigations of autism

Genetic factors are likely to play a major role in the etiology of autism. The genetics of the disorder is however complex, probably involving the action of several genes. In an attempt to identify autism susceptibility loci we are currently undertaking a systematic screening of the whole human genome using multiplex families. We describe the resources and the methods needed to achieve such a task, including extensive collection of family data, semiautomated genotyping technology, and specialized statistical approaches for linkage analysis of complex traits.

Support for a chromosome 18p locus conferring susceptibility to functional psychoses in families with schizophrenia, by association and linkage analysis

The action of antipsychotic drugs on dopamine receptors suggests that dopaminergic signal transmission may play a role in the development of schizophrenia. We tested eight candidate genes (coding for dopamine receptors, the dopamine transporter, and G-proteins) in 59 families from Germany and Israel, for association. A P value of .00055 (.0044 when corrected for the no. of markers tested) was obtained for the intronic CA-repeat marker G-olfalpha on chromosome 18p. The value decreased to .000088 (.0007) when nine sibs with recurrent unipolar depressive disorder were included. Linkage analysis using SSLP markers densely spaced around G-olfalpha yielded a maximum two-point LOD score of 3.1 for a marker 0.5 cM distal to G-olfalpha. Multipoint analysis under the assumption of heterogeneity supported this linkage-whether the affected pheotype was defined narrowly or broadly-as did nonparametric linkage (NPL). In 12 families with exclusively maternal transmission of the disease, the NPL value also supported linkage to this marker. In order to test for association/linkage disequilibrium in the presence of linkage, the sample was restricted to independent offspring. When this sample was combined with 65 additional simplex families (each of them comprising one schizophrenic offspring and his or her parents), the 124-bp allele of G-olfalpha was transmitted 47 times and was not transmitted 21 times (P=.009). These results suggest the existence, on chromosome 18p, of a potential susceptibility locus for functional psychoses.

CAG repeat expansion in autosomal dominant familial spastic paraparesis: novel expansion in a subset of patients

Autosomal dominant familial spastic paraplegia (FSP) is a genetically heterogeneous neurodegenerative disorder displaying anticipation for which three loci have been mapped to the chromosomal positions 14q11.2-q24.3 (SPG3), 2p21-p24 (SPG4) and 15q11.1 (SPG6). The repeat expansion detection (RED) method has been used to demonstrate expanded CAG repeats in some FSP families that map to SPG4. We analyzed 20 FSP families, including four for which there is evidence for linkage to SPG4, and found that in most cases the repeat expansion detected by RED is due to non-pathogenic expansions of the chromosome 18q21.1 SEF2-1 or 17q21.3 ERDA1 locus. Polymorphic expansions at SEF2-1 and ERDA1 appear frequent and may confound RED studies in the search for genes causing disorders demonstrating anticipation. In six FSP families, however, CAG repeat expansion was detected in a subset of affected and at-risk individuals that did not result from expansion of the SEF2-1 and ERDA1 loci. Overall, 11 of 37 (30%) of the FSP patients with a CAG/CTG repeat expansion are unaccounted for by the SEF2-1 and ERDA1 loci, compared with two of 23 (9%) of the unaffected at-risk individuals and none of 19 controls. In the majority of cases these novel expansions were shorter than those previously reported.

Progress and pitfalls: bipolar molecular linkage studies

This paper reviews the history of molecular genetic linkage studies of bipolar disorder. The topic is introduced with a brief discussion of various genetic concepts, including linkage, lod scores and non-parametric statistics. It is emphasized that criteria for declaring linkage must include independent confirmation by a second group of investigators. Given that the inherited susceptibility for bipolar disorder is most likely explained by multiple genes of small effect, simulations indicate that universal confirmation of valid linkages cannot be expected. With this background, several valid linkages of BP disorder to genomic regions are reviewed. These valid linkages include 18p11, 18q22, 21q21, Xq26 and 4pter. The issue of anticipation and expanding triplet repeats is discussed. Finally, there is a brief section on recommendations for future genetic linkage studies of bipolar disorder.

Founder effect at PGL1 in hereditary head and neck paraganglioma families from the Netherlands

PGL1, a gene responsible for hereditary paragangliomas of the head and neck, recently was mapped to a 2-cM interval on chromosome 11q22-q23, by linkage and haplotype-sharing analysis of a large multibranch Dutch family. We determined the disease-linked haplotype, as defined by 13 markers encompassing a large interval on 11q21-q23, in 10 additional families ascertained from the same geographical locale. Alleles were identical for six contiguous markers, spanning a genetic distance of 6 cM and containing PGL1. Despite this strong indication of a common ancestor, no kinships between the families could be demonstrated through genealogical surveys going back to 1800 a.d. We conclude that a single ancestral mutation is responsible for most, if not all, hereditary paragangliomas, in this region of The Netherlands, and that strong founder effects may exist at the PGL1 locus.

Psychoneuroendocrinology of depression. Hypothalamic-pituitary-adrenal axis

Among the more consistent observations in patients with major depression is dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis presenting as elevation of basal cortisol, dexamethasone-mediated negative feedback resistance, increased cerebrospinal fluid levels of corticotropin-releasing factor (CRF), and a blunted adrenocorticotropic hormone (ACTH) response to challenge with exogenous CRF. These features appear to be state, rather than trait markers, and are normalized upon successful treatment. These pathophysiologic adaptations may arise from defects in central drive to the neuroendocrine hypothalamus, disruption of normal adrenocortical hormone receptor function or a modification of HPA axis function at any level. Functional assessment of the HPA axis is thought to provide a window into central nervous system operation that may be of diagnostic value in this and other affective disorders regardless of whether CRF and glucocorticoids are directly involved in the origin of major depression or merely exacerbate the consequences of other primary defects.

A susceptibility locus for bipolar affective disorder on chromosome 4q35

Bipolar affective disorder (BAD) affects approximately 1% of the population and shows strong heritability. To identify potential BAD susceptibility loci, we undertook a 15-cM genome screen, using 214 microsatellite markers on the 35 most informative individuals of a large, statistically powerful pedigree. Data were analyzed by parametric two-point linkage methods under several diagnostic models. LOD scores >1.00 were obtained for 21 markers, with four of these >2.00 for at least one model. The remaining 52 individuals in the family were genotyped with these four markers, and LOD scores remained positive for three markers. A more intensive screen was undertaken in these regions, with the most positive results being obtained for chromosome 4q35. Using a dominant model of inheritance with 90% maximum age-specific penetrance and including bipolar I, II, schizoaffective/mania, and unipolar individuals as affected, we obtained a maximum two-point LOD score of 2.20 (theta = .15) at D4S1652 and a maximum three-point LOD score of 3.19 between D4S408 and D4S2924. Nonparametric analyses further supported the presence of a locus on chromosome 4q35. A maximum score of 2.62 (P=.01) was obtained between D4S1652 and D4S171 by use of the GENEHUNTER program, and a maximum score of 3.57 (P=.0002) was obtained at D4S2924 using the affected pedigree member method. Analysis of a further 10 pedigrees suggests the presence of this locus in at least one additional family, indicating a possible predisposing locus and not a pedigree-specific mutation. Our results suggest the presence of a novel BAD susceptibility locus on chromosome 4q35.

No evidence for significant linkage between bipolar affective disorder and chromosome 18 pericentromeric markers in a large series of multiplex extended pedigrees

Bipolar affective disorder (BP) is a major neuropsychiatric disorder with high heritability and complex inheritance. Previously reported linkage between BP and DNA markers in the pericentromeric region of chromosome 18, with a parent-of-origin effect (linkage was present in pedigrees with paternal transmission and absent in pedigrees with exclusive maternal inheritance), has been a focus of interest in human genetics. We reexamined the evidence in one of the largest samples reported to date (1,013 genotyped individuals in 53 unilineal multiplex pedigrees), using 10 highly polymorphic markers and a range of parametric and nonparametric analyses. There was no evidence for significant linkage between BP and chromosome 18 pericentromeric markers in the sample as a whole, nor was there evidence for significant parent-of-origin effect (pedigrees with paternal transmission were not differentially linked to the implicated chromosomal region). Two-point LOD scores and single-locus sib-pair results gave some support for suggestive linkage, but this was not substantiated by multilocus analysis, and the results were further tempered by multiple test effects. We conclude that there is no compelling evidence for linkage between BP and chromosome 18 pericentromeric markers in this sample.

Multiple members of a third subfamily of P-type ATPases identified by genomic sequences and ESTs

The Saccharomyces cerevisiae genome contains five P-type ATPases divergent from both of the well-known subfamilies of these membrane ion transporters. This newly recognized third subfamily can be further divided into four classes of genes with nearly equal relatedness to each other. Genes of this new subfamily are also present and expressed in multicellular organisms such as Caenorhabditis elegans and mammals; some, but not all, can be assigned to the classes identified in yeast. Different classes of genes and different genes within a class are expressed differentially in tissues of the mouse. The recently cloned gene for the mammalian aminophospholipid translocase belongs to this new subfamily, suggesting that other subfamily members may transport other lipids or lipid-like molecules from one leaflet of the membrane bilayer to the other.

Manic depressive illness and tyrosine hydroxylase gene: linkage heterogeneity and association

Several studies have implicated the tyrosine hydroxylase (TH) locus within the 11p15 region in susceptibility to manic depressive illness (MDI). This possibility was further investigated by both parametric (lod score) and nonparametric (affected-pedigree-member and a case-control study) methods of analysis in 11 French MDI families and in a sample of 200 unrelated subjects. Both types of analyses corroborate the implication of this locus, and positive lod scores were obtained in two families, which most likely reflects genetic heterogeneity. Statistical analyses were also performed including available data from published reports. These analyses, which allowed for genetic heterogeneity, substantiated our findings. The combined maximum lod score for all the families studied was 3.68 at theta = 0.00 (number of families: 36) assuming heterogeneity (alpha = 15%, P = 0.01). Taken together these results converge to suggest that the risk factors for MDI lie in the 11p15 region with TH being the most likely candidate gene.

Mania and bipolar disorder: Current concepts on assessment, diagnosis and management

Mania is a common psychiatric syndrome characterized by pathological mood elevation, grandiose thinking and motor overactivity. Although current consensus upholds a true distinction between unipolar depression and bipolar disorders, the distinction between various bipolar sub-categories is still a matter for debate, as is the exact distinction between schizophrenia and mania. Most cases are functional in origin but many organic causes have been identified as well as iatrogenic causes from prescribed medication, particularly in susceptible individuals. The underlying aetiology is still poorly understood, although a number of biochemical abnormalities have recently been identified, and the evidence for a genetic role is strong. Its prevalence is universal, with some differences between gender and ethnicity reported, and it displays marked Axis I and II comorbidity. Treatment, both acute and long term, still relies on various traditional combinations of neuroleptics, benzodiazepines and mood stabilisers, particularly Lithium, which now appears to be less effective than previously thought and a shift towards using other mood stabilisers from the anticonvulsant class is now apparent. The exact role for psychological treatment remains unclear with more research required. Good medical management includes; adequate treatment, physical and laboratory investigations, dedicated follow-up and supervision by hospital psychiatrists and community-based care agencies.

The genetics of schizophrenia: past, present, and future concepts

Although a genetic susceptibility for schizophrenia has been long established and even noted by Kraepelin in 1907, the mechanisms for its inheritance remains unknown. No candidates have proven to be correct and while many weakly positive chromosomal linkages have been reported, none have yet been consistently replicated. The following review examines the present status of these findings. The conclusion is that the field must move on to finding a consistently replicable mutation segregating with schizophrenia in families, before any of the present linkage results can be resolved.