RNA-sequencing of the brain transcriptome implicates dysregulation of neuroplasticity, circadian rhythms and GTPase binding in bipolar disorder.

RNA-sequencing (RNA-seq) is a powerful technique to investigate the complexity of gene expression in the human brain. We used RNA-seq to survey the brain transcriptome in high-quality postmortem dorsolateral prefrontal cortex from 11 individuals diagnosed with bipolar disorder (BD) and from 11 age- and gender-matched controls. Deep sequencing was performed, with over 350 million reads per specimen. At a false discovery rate of <5%, we detected five differentially expressed (DE) genes and 12 DE transcripts, most of which have not been previously implicated in BD. Among these, Prominin 1/CD133 and ATP-binding cassette-sub-family G-member2 (ABCG2) have important roles in neuroplasticity. We also show for the first time differential expression of long noncoding RNAs (lncRNAs) in BD. DE transcripts include those of serine/arginine-rich splicing factor 5 (SRSF5) and regulatory factor X4 (RFX4), which along with lncRNAs have a role in mammalian circadian rhythms. The DE genes were significantly enriched for several Gene Ontology categories. Of these, genes involved with GTPase binding were also enriched for BD-associated SNPs from previous genome-wide association studies, suggesting that differential expression of these genes is not simply a consequence of BD or its treatment. Many of these findings were replicated by microarray in an independent sample of 60 cases and controls. These results highlight common pathways for inherited and non-inherited influences on disease risk that may constitute good targets for novel therapies.

Interaction networks of lithium and valproate molecular targets reveal a striking enrichment of apoptosis functional clusters and neurotrophin signaling.

The overall neurobiological mechanisms by which lithium and valproate stabilize mood in bipolar disorder patients have yet to be fully defined. The therapeutic efficacy and dissimilar chemical structures of these medications suggest that they perturb both shared and disparate cellular processes. To investigate key pathways and functional clusters involved in the global action of lithium and valproate, we generated interaction networks formed by well-supported drug targets. Striking functional similarities emerged. Intersecting nodes in lithium and valproate networks highlighted a strong enrichment of apoptosis clusters and neurotrophin signaling. Other enriched pathways included MAPK, ErbB, insulin, VEGF, Wnt and long-term potentiation indicating a widespread effect of both drugs on diverse signaling systems. MAPK1/3 and AKT1/2 were the most preponderant nodes across pathways suggesting a central role in mediating pathway interactions. The convergence of biological responses unveils a functional signature for lithium and valproate that could be key modulators of their therapeutic efficacy.

A systems approach to the biology of mood disorders through network analysis of candidate genes.

Meta analysis of association data of mood disorders has shown evidence for the role of particular genes in genetic risk. Integration of association data from meta analysis with differential expression data in brains of mood disorder patients could heighten the level of support for specific genes. To identify molecular mechanisms that may be disrupted in disease, a systems approach that involves analysis of biological networks created by these selected genes was employed.Interaction networks of hierarchical groupings of selected genes were generated using the Michigan Molecular Interactions (MiMI) software. Large networks were deconvoluted into subclusters of core complexes by using a community clustering program, GLay. Network nodes were functionally annotated in DAVID Bioinformatics Resource to identify enriched pathways and functional clusters. MAPK and beta adrenergic receptor signaling pathways were significantly enriched in the ANK3 and CACNA1C network. The PBRM1 network bolstered the enrichment of chromatin remodeling and transcription regulation functional clusters. Lowering the stringency for inclusion of other genes in network seeds increased network complexity and expanded the recruitment of enriched pathways to include signaling by neurotransmitter and hormone receptors, neurotrophin, ErbB and the cell cycle. We present a strategy to interrogate mechanisms in the cellular system that might be perturbed in disease. Network analysis of meta analysis- generated candidate genes that exhibited differential expression in mood disorder brains identified signaling pathways and functional clusters that may be involved in genetic risk for mood disorders.

Two variants in Ankyrin 3 (ANK3) are independent genetic risk factors for bipolar disorder.

Two recent reports have highlighted ANK3 as a susceptibility gene for bipolar disorder (BD). We first reported association between BD and the ANK3 marker rs9804190 in a genome-wide association study (GWAS) of two independent samples (Baum et al., 2008). Subsequently, a meta-analysis of GWAS data based on samples from the US and the UK reported association with a different ANK3 marker, rs10994336 (Ferreira et al., 2008). The markers lie about 340 kb apart in the gene. Here, we test both markers in additional samples and characterize the contribution of each marker to BD risk. Our previously reported findings at rs9804190, which had been based on DNA pooling, were confirmed by individual genotyping in the National Institute of Mental Health (NIMH) waves 1-4 (P=0.05; odds ratio (OR)=1.24) and German (P=0.0006; OR=1.34) samples. This association was replicated in an independent US sample known as NIMH wave 5 (466 cases, 212 controls; P=0.017; OR=1.38). A random-effects meta-analysis of all three samples was significant (P=3 x 10(-6); OR=1.32), with no heterogeneity. Individual genotyping of rs10994336 revealed a significant association in the German sample (P=0.0001; OR=1.70), and similar ORs in the NIMH 1-4 and NIMH 5 samples that were not significant at the P<0.05 level. Meta-analysis of all three samples supported an association with rs10994336 (P=1.7 x 10(-5); OR=1.54), again with no heterogeneity. There was little linkage disequilibrium between the two markers. Further analysis suggested that each marker contributed independently to BD, with no significant marker x marker interaction. Our findings strongly support ANK3 as a BD susceptibility gene and suggest true allelic heterogeneity.

Detection, simultaneous display and direct sequencing of multiple nuclear hormone receptor genes using bilaterally targeted RNA fingerprinting.

We have developed a PCR-based method to detect, display and directly sequence multiple members of the nuclear hormone receptor (NHR) gene family. Our approach employs the basic concepts of RNA fingerprinting (Welsh et al. (1992) Nucleic Acids Res. 20, 4965-4970; Stone, B. and Wharton, W. (1994) Nucleic Acids Res. 22, 2612-2618) and differential display PCR (Liang, P. and Pardee, A.B. (1992) Science 257, 967-971), with modifications. In contrast to the previous methods, two conserved regions within the gene family were targeted to derive primers for PCR amplification. One of the conserved sites was used to deduce primers for cDNA synthesis. We believe that this strategy led to increased specificity. The use of degenerate primers with low redundancy in both reverse transcription and PCR steps also contributed to enhanced signal-to-noise ratio. The ability to directly sequence the amplified fragments constitutes a vast improvement over the previous methods. This method permitted the successful identification and simultaneous display of six different NHR genes, which included the previously unreported rat homolog of COUP-TFI and a recently described orphan receptor. We believe that this approach provides a convenient and rapid screening method for detecting and characterizing members of a gene family.

X-chromosome markers and manic-depressive illness. Rejection of linkage to Xq28 in nine bipolar pedigrees.

Numerous reports have been published concerning linkage of X-chromosome markers of the q28 region (including protan and deutan color blindness [CB] and glucose-6-phosphate dehydrogenase deficiency) to manic-depressive illness. We studied nine bipolar pedigrees (in which there was no male-to-male transmission) in an attempt to detect linkage, using three tightly linked polymorphic DNA loci, DXS15, DXS52 and F8C (factor 8 gene), all of which are closely linked to the CB and glucose 6-phosphate dehydrogenase classic Xq28 markers. Linkage to this region of Xq28 could be excluded unequivocally in these nine families. When these data were combined with our earlier series of bipolar pedigrees, informative for either protan or deutan CB, a total of 14 bipolar pedigrees have been studied, with no evidence of linkage or heterogeneity. At a recombination fraction (theta) of 1%, this series had greater than 95% power to detect linkage if only 50% of the pedigrees studied were linked to the CB region. Our failure to confirm the previously reported linkage of manic-depressive illness to the CB region of the X chromosome indicates that this linkage is not as common as previously suggested.

A linkage study of bipolar illness.

BACKGROUND: Although genetic epidemiological studies of bipolar (BP) illness are consistent with a heritable component, inherited risk factors remain unknown. The goal of the present study is to describe the localization of BP susceptibility loci through linkage strategies, including a genome-wide search. METHODS: A linkage study of 22 BP families has been performed. These BP families include almost 400 persons, 173 of whom have been diagnosed as having BP I, schizoaffective, BP II with major depression, or recurrent unipolar illness. Using an autosomal dominant disease model with 85% or 50% age-dependent penetrance, and a recessive model with 85% penetrance, linkage analyses were performed assuming a narrow (BP and schizoaffective) or a broad (BP, schizoaffective, or unipolar) definition of the BP spectrum. Affected sibling pairs and affected pedigree member analyses were performed when positive lod scores were observed in multiple pedigrees. The present article describes linkage analysis of 310 DNA markers on chromosomes 1, 5p, 6, 8, 10q, 11q, and 12 to 18. RESULTS: None of the loci examined disclosed compelling evidence for linkage using lod score analyses. Model-independent analysis by multilocus affected pedigree member method in the pericentromeric chromosome 18 region disclosed statistically significant evidence (P < .0001) for a BP susceptibility gene in this region. Multilocus analysis by affected sibling pair method also disclosed evidence for linkage (P < .00008). CONCLUSIONS: Our results imply that a BP susceptibility gene exists near the centromere of chromosome 18. Confirmation of this finding (by independent investigators studying different pedigrees) has been published, suggesting that a valid BP disease linkage may have been discovered.

Refinement of regions with allelic loss on chromosome 18p11.2 and 18q12.2 in esophageal squamous cell carcinoma.

Esophageal cancer ranks among the 10 most common cancers worldwide and is almost invariably fatal. The detailed genetic repertoire involved in esophageal carcinogenesis has not been defined. We have shown previously that the esophageal squamous cell carcinoma genome exhibits a frequent loss of heterozygosity (LOH) in the pericentromeric region of chromosome 18. To construct a fine deletion map, we screened 76 new samples composed of microdissected esophageal squamous cell carcinoma and matched morphologically normal epithelial cells using closely spaced markers. Maximal LOH frequency (54%) was displayed by D18S542 on 18p11.2. The pattern of LOH in selected patients indicated that the short region of overlap extends 3 cM on either side of D18S542. On the long arm of chromosome 18, the highest frequency of allelic loss (42%) was detected by D18S978 on 18q12.2-q21.1. This analysis revealed a short region of overlap of approximately 0.8 cM. These findings further implicate unreported tumor suppressor genes encoded by 18p11.2 and 18q12.2 in esophageal squamous cell carcinogenesis and they indicate a refinement of their map location.

Expression of the smoothelin gene is mediated by alternative promoters.

OBJECTIVE: Two major isoforms of smoothelin have been reported, a 59-kDa smoothelin-A in visceral smooth muscle cells and a 110-kDa smoothelin-B in vascular smooth muscle cells. The present study was undertaken to investigate the expression of these smoothelin isoforms in different smooth muscle tissues and to determine how they are generated. METHODS: Western blotting with a new, well-defined, smoothelin antibody was used to confirm the existence of two major smoothelin isoforms. Northern blotting, RT-PCR, primer extension and 5'RACE were applied to analyse the expression of these isoforms in human and mouse. Promoter reporter assays were carried out to establish the existence of a dual promoter system governing the expression pattern of the gene. RESULTS: Antibody C6G confirmed the existence of two smoothelin proteins. Northern blotting showed that in vascular tissues a larger smoothelin transcript is generated than in visceral tissue. The cDNA of this larger smoothelin-B was cloned. Computer analysis of the open reading frame suggests an alpha-helical structure of 130 amino acids at the amino terminus of smoothelin-B. The smoothelin gene was cloned and sequenced. It comprises about 25 kb and contains 21 exons. The translational start of smoothelin-B is located in exon 2, whereas transcription and translation of the previously described smoothelin-A starts inside exon 10. Smoothelin-A and -B were demonstrated to be generated by two physically separated promoters. Splice variants within the calponin homology domain at the 3' end of the gene were found for both isoforms. CONCLUSIONS: Two major smoothelin isoforms are generated from a single gene by a dual promoter system in a tissue specific manner. Further variation in the smoothelin proteins is achieved by alternative splicing in the calponin homology domain.

Splice variants of rat TR4 orphan receptor: differential expression of novel sequences in the 5'-untranslated region and C-terminal domain.

The use of rapid amplification of 5'-cDNA ends-PCR yielded two novel sequences for the rat orphan receptor, TR4, representing heterogeneity on the 5'-untranslated region. Genomic structure analysis revealed that the 5'-untranslated region of the longer messenger RNA fragment, rTR4-1, contained three exons, alpha, beta, and gamma. The skipping of exon gamma gave rise to rTR4-2, indicating that rTR4-1 and rTR4-2 are products of alternative splicing. We isolated another novel rat TR4 splice variant, rTR4-NS, which was found to diverge from rTR4-2 at codon 504. rTR4-NS contained an unspliced intronic sequence with in-frame codons for eight amino acids followed by a termination codon. The three TR4 messenger RNA variants were differentially expressed. rTR4-NS appeared to be a rare transcript found in limited areas of the brain. In situ hybridization detect prominent TR4 signals in brain areas known to be involved in stress response. In cerebellar granule cells, the rise in TR4 expression correlated with the progression of neuronal maturation. N-Methyl-D-aspartate treatment triggered a marked increase in TR4 expression. These results suggest a possible role for TR4 in neuronal differentiation.

Familial glucocorticoid resistance caused by a splice site deletion in the human glucocorticoid receptor gene.

The clinical syndrome of generalized, compensated glucocorticoid resistance is characterized by increased cortisol secretion without clinical evidence of hyper- or hypocortisolism, and manifestations of androgen and/or mineralocorticoid excess. This condition results from partial failure of the glucocorticoid receptor (GR) to modulate transcription of its target genes. We studied the molecular mechanisms of this syndrome in a Dutch kindred, whose affected members had hypercortisolism and approximately half of normal GRs, and whose proband was a young woman with manifestations of hyperandrogenism. Using the polymerase chain reaction to amplify and sequence each of the nine exons of the GR gene alpha, along with their 5'- and 3'-flanking regions, we identified a 4-base deletion at the 3'-boundary of exon 6 in one GR allele (delta 4), which removed a donor splice site in all three affected members studied. In contrast, the sequence of exon 6 in the two unaffected siblings was normal. A single nucleotide substitution causing an amino acid substitution in the amino terminal domain of the GR (asparagine to serine, codon 363) was also discovered in exon 2 of the other allele (G1220) in the proband, in one of her affected brothers and in her unaffected sister. The functional importance of this mutation was tested in a cotransfection study using the recombinant expression vector pRShGR-Ser363 and the glucocorticoid responsive vector mouse mammary tumor virus-chloramphenicol transferase. This amino acid substitution did not alter the function of the glucocorticoid receptor. Using reverse transcription-polymerase chain reaction we could only identify messenger RNA transcripts of the G1220-allele but not of the delta 4-allele in the affected members of this family who were heterozygous for the G1220 mutation. This deletion in the glucocorticoid receptor gene was, thus, associated with the expression of only one allele and a decrease of GR protein by 50% in affected members of this glucocorticoid resistant family. The mutation identified in exon 2 did not segregate with the disease and appears to be of no functional significance. The presence of the null allele was apparently compensated for by increased cortisol production at the expense of concurrent hyperandrogenism.

Mutation screening of two candidate genes from 13q32 in families affected with Bipolar disorder: human peptide transporter (SLC15A1) and human glypican5 (GPC5).

BACKGROUND: Multiple candidate regions as sites for Schizophrenia and Bipolar susceptibility genes have been reported, suggesting heterogeneity of susceptibility genes or oligogenic inheritance. Linkage analysis has suggested chromosome 13q32 as one of the regions with evidence of linkage to Schizophrenia and, separately, to Bipolar disorder (BP). SLC15A1 and GPC5 are two of the candidate genes within an approximately 10-cM region of linkage on chromosome 13q32. In order to identify a possible role for these candidates as susceptibility genes, we performed mutation screening on the coding regions of these two genes in 7 families (n-20) affected with Bipolar disorder showing linkage to 13q32. RESULTS: Genomic organization revealed 23 exons in SLC15A1 and 8 exons in GPC5 gene respectively. Sequencing of the exons did not reveal mutations in the GPC5 gene in the 7 families affected with BP. Two polymorphic variants were discovered in the SLC15A1 gene. One was T to C substitution in the third position of codon encoding alanine at 1403 position of mRNA in exon 17, and the other was A to G substitution in the untranslated region at position 2242 of mRNA in exon 23. CONCLUSIONS: Mutation analysis of 2 candidate genes for Bipolar disorder on chromosome 13q32 did not identify any potentially causative mutations within the coding regions or splice junctions of the SLC15A1 or GPC5 genes in 7 families showing linkage to 13q32. Further studies of the regulatory regions are needed to completely exclude these genes as causative for Bipolar disorder.

Experimental gene interaction studies with SERT mutant mice as models for human polygenic and epistatic traits and disorders.

Current evidence indicates that virtually all neuropsychiatric disorders, like many other common medical disorders, are genetically complex, with combined influences from multiple interacting genes, as well as from the environment. However, additive or epistatic gene interactions have proved quite difficult to detect and evaluate in human studies. Mouse phenotypes, including behaviors and drug responses, can provide relevant models for human disorders. Studies of gene-gene interactions in mice could thus help efforts to understand the molecular genetic bases of complex human disorders. The serotonin transporter (SERT, 5-HTT, SLC6A4) provides a relevant model for studying such interactions for several reasons: human variants in SERT have been associated with several neuropsychiatric and other medical disorders and quantitative traits; SERT blockers are effective treatments for a number of neuropsychiatric disorders; there is a good initial understanding of the phenotypic features of heterozygous and homozygous SERT knockout mice; and there is an expanding understanding of the interactions between variations in SERT expression and variations in the expression of a number of other genes of interest for neuropsychiatry and neuropharmacology. This paper provides examples of experimentally-obtained interactions between quantitative variations in SERT gene expression and variations in the expression of five other mouse genes: DAT, NET, MAOA, 5-HT(1B) and BDNF. In humans, all six of these genes possess polymorphisms that have been independently investigated as candidates for neuropsychiatric and other disorders in a total of > 500 reports. In the experimental studies in mice reviewed here, gene-gene interactions resulted in either synergistic, antagonistic (including 'rescue' or 'complementation') or more complex, quantitative alterations. These were identified in comparisons of the behavioral, physiological and neurochemical phenotypes of wildtype mice vs. mice with single allele or single gene targeted disruptions and mice with partial or complete disruptions of multiple genes. Several of the descriptive phenotypes could be best understood on the basis of intermediate, quantitative alterations such as brain serotonin differences. We discuss the ways in which these interactions could provide models for studies of gene-gene interactions in complex human neuropsychiatric and other disorders to which SERT may contribute, including developmental disorders, obesity, polysubstance abuse and others.

Mutation analysis of oculopharyngeal muscular dystrophy in Hispanic American families.

BACKGROUND: Oculopharyngeal muscular dystrophy (OPMD) is a late-onset autosomal dominant muscular dystrophy characterized by progressive ptosis, swallowing difficulties, and proximal limb weakness. Recently, the genetic basis of this disease has been characterized by mutations in the PABP2 gene that involve short expansions of the trinucleotide repeat GCG. OBJECTIVES: To independently confirm the presence and study the meiotic stability of the GCG expansion mutations in a distinct ethnic population with OPMD. SETTINGS: Hospital and university research laboratories in Los Angeles, Calif. SUBJECTS AND METHODS: Three unrelated families of Hispanic American descent were identified in whom OPMD was transmitted in an autosomal dominant pattern. All of these families can trace affected ancestors to the southwestern United States or to the bordering states of Mexico. In these families, 14 persons with OPMD were identified and studied. RESULTS: Our results confirm that in these families, expansion mutations characterized by a gain of 3 GCG repeats in the wild-type allele result in an abnormal nucleotide length of 9 GCG repeats in the PABP2 gene. In these families, these mutations are associated with the OPMD phenotype. The identical repeat mutation ([GCG]9) is found in all affected members of these unrelated families and shows relative meiotic stability. CONCLUSIONS: These results support and extend our study of haplotype analysis and suggest that a founder effect may have occurred for OPMD in this Hispanic American population.

Reduced sensitivity to glucocorticoid feedback and reduced glucocorticoid receptor mRNA expression in the luteal phase of the menstrual cycle.

We examined the effects of the menstrual cycle on hypothalamic-pituitary adrenal axis regulation in healthy women with no history of psychiatric illness by measuring plasma cortisol responses to a low-dose (0.25 mg) of dexamethasone (N = 23) and by measuring glucocorticoid receptor (type II) mRNA expression in lymphocytes using Northern blotting (N = 19). Both measures were performed in the early follicular and mid-luteal phases of the menstrual cycle. Dexamethasone suppression of plasma cortisol was greater in the follicular phase of the menstrual cycle compared to the mid-luteal phase (p < .01). In addition, type II glucocorticoid receptor mRNA expression in lymphocytes was 78% higher in the follicular phase compared to the mid-luteal phase (p < .02). These results indicate that glucocorticoid feedback regulation of the hypothalamic-pituitary-adrenal axis is reduced in the mid-luteal phase of the menstrual cycle. Reduced feedback regulation of central stress response systems may play a role in generation of common premenstrual symptoms of irritability and dysphoria.

Closing in on genes for manic-depressive illness and schizophrenia.

Advances in the human genetic map, and in genetic analysis of linkage and association in complex inheritance traits, have led to genetic progress in the major psychoses. For chromosome 6 in schizophrenia, and chromosomes 18 and 21 in manic-depressive illness, there are reports of linkage in several independent data sets. These are small effect genes, best detected with affected-relative-pair linkage methods. Association with candidate genes is an alternative strategy to uncovering susceptibility genes for these illnesses, but convincing associations remain to be demonstrated. New clinical and laboratory investigation methods are being developed. Testing every gene in the human genome for association with illness has recently been proposed (Risch and Merikangas 1996). This would require further progress in characterizing the genome and in automated large-scale genotyping. The best type of pedigree sampling for common disease studies, whether for linkage or association, is not yet established. An endophenotype hybrid strategy can combine genetic linkage, association, and pathophysiologic studies. As clinical molecular investigation methods advance, identification of disease susceptibility mutations and delineation of their pathophysiological roles may be expected.

A systematic search for a bipolar predisposing locus on chromosome 5.

Chromosome 5 markers spanning the pter to the qter were used to examine linkage to bipolar illness in 14 pedigrees. Twenty-four loci were examined in 237 individuals, of whom 69 were either bipolars or schizoaffectives. Marker genotypes were determined for each individual and lod scores were calculated under a dominant disease model with a maximum penetrance of 85%, a disease gene frequency of 0.015, a variable age of onset, and a phenocopy rate of 0.001. Under the assumption that bipolar illness is genetically homogeneous, the total lod scores from all pedigrees with each marker were uniformly lower than -2.0, suggesting the absence of linkage to disease at any of these loci. Multipoint analysis allowed exclusion of intervals between markers. When lod scores were calculated allowing for heterogeneity, no subset of linked families was found. These results indicate that in our pedigree series almost the entire mapped region of chromosome 5 can be excluded for linkage to bipolar illness.

An ACTH-producing small cell lung cancer expresses aberrant glucocorticoid receptor transcripts from a normal gene.

ACTH production by non-pituitary tumors is generally not suppressible by exogenous glucocorticoid administration. We had postulated that defects in the glucocorticoid receptor (GR) signaling system might be responsible for this apparent glucocorticoid resistance and had previously demonstrated that DMS-79 cells, derived from an ectopic ACTH-producing tumor, express an abnormal GR mRNA. In this DMS-79 cell GR the sequence normally derived from exons 8 and 9 is replaced by sequence unmatched in the DNA databases. The protein encoded by this mRNA lacks the steroid-binding domain and does not function as a ligand-activated transcription factor. In the present work, we sought to identify the origin of the novel GR mRNA sequence. Southern blot analysis of DMS-79 genomic DNA showed no major structural alteration of the GR gene. Southern blotting of cosmid clones of the normal GR gene revealed that the novel DMS-79 GR mRNA sequence is derived from intron G, between exons 7 and 8. No splice site mutations were found in PCR-amplified DMS-79 DNA fragments surrounding the downstream splice junctions. Further sequencing indicated that the aberrant GR transcript appears to be generated by use of a consensus cleavage/polyadenylation signal found 3650 base pairs into the normal intron G. We conclude that abnormal GR pre-mRNA processing rather than a GR gene mutation confers glucocorticoid resistance on DMS-79 cells.

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.

Maternal inheritance and chromosome 18 allele sharing in unilineal bipolar illness pedigrees.

We have replicated the observation of McMahon et al. [1995] that there is excess maternal transmission of illness in a series of previously described unilineal Bipolar manic-depressive illness extended pedigrees [Berrettini et al., 1991]. ("Transmission" is defined for any ill person in a pedigree when father or mother has a personal or immediate family history of major affective disorder.) We divided our pedigrees into exclusively maternal transmission (Mat) and mixed maternal-paternal transmission (in different pedigree branches) (Pat). Using affected sib-pair-analysis, linkage to a series of markers on chromosome 18p-cen was observed in the Pat but not the Mat pedigrees, with significantly greater identity by descent (IBD) at these markers in the Pat pedigrees. As compared with the pedigree series as a whole, the proportion of alleles IBD in the linkage region is much increased in the Pat pedigrees. As shown by Kruglyak and Lander [1995], as the sharing proportion of alleles in affected relative pairs increases, the number of such pairs needed to resolve the linkage region to a 1 cM interval becomes smaller. Genetic subdivision of an illness by clinical or pedigree configuration criteria may thus play an important role in discovery of disease susceptibility mutations.