Astrocyte-Derived Exosomes in an iPSC Model of Bipolar Disorder

Bipolar I Disorder (BP) is a serious, recurrent mood disorder that is characterized by alternating episodes of mania and depression. To begin to identify novel approaches and pathways involved in BP, we have obtained skin samples from BP patients and undiagnosed control (C) individuals, reprogrammed them to form induced pluripotent stem cells (iPSC), and then differentiated the stem cells into astrocytes. RNAs from BP and C astrocytes were extracted and RNAseq analysis carried out. 501 differentially expressed genes were identified, including genes for cytoskeletal elements, extracellular matrix, signaling pathways, neurodegeneration, and notably transcripts that identify exosomes. When we compared highly expressed genes using hierarchial cluster analysis, "Exosome" was the first and most highly significant cluster identified, p < 5 × 10^-13, Benjamini correction. Exosomes are membrane-bound vesicles that package and remove toxic proteins from cells and also enable cell to cell communication. They carry genetic material, including DNA, mRNA and microRNAs, proteins, and lipids to target cells throughout the body. Exosomes are released by cortical neurons and astrocytes in culture and are present in BP vs C postmortem brain tissue. Little is known about what transcripts and proteins are targeted to neurons, how they regulate biological functions of the acceptor cell, or how that may be altered in mood disorders. Since astrocyte-derived exosomes have been suggested to promote neuronal plasticity, as well as to remove toxic proteins in the brain, alterations in their function or content may be involved in neurodevelopmental, neuropathological, and neuropsychiatric conditions. To examine exosome cargos and interactions with neural precursor cells, astrocytes were differentiated from four bipolar disorder (BP) and four control (C) iPSC lines. Culture supernatants from these astrocytes were collected, and exosomes isolated by ultra-centrifugation. Western blot analysis demonstrated the presence of the exosome markers CD9, CD81, and Hsp70. Nanosight technology was used to characterize exosomes from each astrocyte cell line, suggesting that exosomes were slightly more concentrated in culture supernatants derived from BP compared with C astrocytes but there was no difference in the mean sizes of the exosomes. Analysis of their function in neuronal differentiation is being carried out by labeling exosomes derived from bipolar patient and control astrocytes and adding them to control neural progenitor cells. Given the current interest in clearing toxic proteins from brains of patients with neurodegenerative disorders, exosomes may present similar opportunities in BP.

A comparative study of engagement in mobile and wearable health monitoring for bipolar disorder

OBJECTIVES

Self-monitoring is recommended for individuals with bipolar disorder, with numerous technological solutions available. This study aimed to identify basic components of these solutions that increase engagement with self-monitoring.

METHODS

Participants with bipolar disorder (n = 47) monitored their symptoms with a Fitbit and a smartphone app and were randomly assigned to either review or not review recorded symptoms weekly. We tested whether individuals would better adhere to and prefer monitoring with passive monitoring with an activity tracker compared to active monitoring with a smartphone app and whether individuals would better adhere to self-monitoring if their recorded symptoms were reviewed with an interviewer.

RESULTS

Monitoring with a smartphone app achieved similar adherence and preference to Fitbit (P > .85). Linear mixed effects modeling found adherence decreased significantly more over the study for the Fitbit (12% more, P < .001) even though more participants reported they would use the Fitbit over a year compared to the app (72.3% vs 46.8%). Reviewing symptoms weekly did not improve adherence, but most participants reported they would prefer to review symptoms with a clinician (74.5%) and on monthly basis (57.5%) compared to alternatives. Participants endorsed sleep as the most important symptom to monitor, forgetfulness as the largest barrier to self-monitoring, and raising self-awareness as the best reason for self-monitoring.

CONCLUSIONS

We recommend a combined strategy of wearable and mobile monitoring that includes reminders, targets raising self-awareness, and tracks sleep. A clinician may want to review symptoms on a monthly basis.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03358238.

Transcripts involved in calcium signaling and telencephalic neuronal fate are altered in induced pluripotent stem cells from bipolar disorder patients

Bipolar disorder (BP) is a chronic psychiatric condition characterized by dynamic, pathological mood fluctuations from mania to depression. To date, a major challenge in studying human neuropsychiatric conditions such as BP has been limited access to viable central nervous system tissue to examine disease progression. Patient-derived induced pluripotent stem cells (iPSCs) now offer an opportunity to analyze the full compliment of neural tissues and the prospect of identifying novel disease mechanisms. We have examined changes in gene expression as iPSC derived from well-characterized patients differentiate into neurons; there was little difference in the transcriptome of iPSC, but BP neurons were significantly different than controls in their transcriptional profile. Expression of transcripts for membrane bound receptors and ion channels was significantly increased in BP-derived neurons compared with controls, and we found that lithium pretreatment of BP neurons significantly altered their calcium transient and wave amplitude. The expression of transcription factors involved in the specification of telencephalic neuronal identity was also altered. Control neurons expressed transcripts that confer dorsal telencephalic fate, whereas BP neurons expressed genes involved in the differentiation of ventral (medial ganglionic eminence) regions. Cells were responsive to dorsal/ventral patterning cues, as addition of the Hedgehog (ventral) pathway activator purmorphamine or a dorsalizing agent (lithium) stimulated expression of NKX2-1 (ventral identity) or EMX2 (dorsal) in both groups. Cell-based models should have a significant impact on our understanding of the genesis and therefore treatment of BP; the iPSC cell lines themselves provide an important resource for comparison with other neurodevelopmental disorders.

Enrichment of cis-regulatory gene expression SNPs and methylation quantitative trait loci among bipolar disorder susceptibility variants

We conducted a systematic study of top susceptibility variants from a genome-wide association (GWA) study of bipolar disorder to gain insight into the functional consequences of genetic variation influencing disease risk. We report here the results of experiments to explore the effects of these susceptibility variants on DNA methylation and mRNA expression in human cerebellum samples. Among the top susceptibility variants, we identified an enrichment of cis regulatory loci on mRNA expression (eQTLs), and a significant excess of quantitative trait loci for DNA CpG methylation, hereafter referred to as methylation quantitative trait loci (mQTLs). Bipolar disorder susceptibility variants that cis regulate both cerebellar expression and methylation of the same gene are a very small proportion of bipolar disorder susceptibility variants. This finding suggests that mQTLs and eQTLs provide orthogonal ways of functionally annotating genetic variation within the context of studies of pathophysiology in brain. No lymphocyte mQTL enrichment was found, suggesting that mQTL enrichment was specific to the cerebellum, in contrast to eQTLs. Separately, we found that using mQTL information to restrict the number of single-nucleotide polymorphisms studied enhances our ability to detect a significant association. With this restriction a priori informed by the observed functional enrichment, we identified a significant association (rs12618769, P(bonferroni)<0.05) from two other GWA studies (TGen+GAIN; 2191 cases and 1434 controls) of bipolar disorder, which we replicated in an independent GWA study (WTCCC). Collectively, our findings highlight the importance of integrating functional annotation of genetic variants for gene expression and DNA methylation to advance the biological understanding of bipolar disorder.

Genome-wide linkage scan of 98 bipolar pedigrees and analysis of clinical covariates

Despite compelling evidence that genetic factors contribute to bipolar disorder (BP), attempts to identify susceptibility genes have met with limited success. This may be due to the genetic heterogeneity of the disorder. We sought to identify susceptibility loci for BP in a genome-wide linkage scan with and without clinical covariates that might reflect the underlying heterogeneity of the disorder. We genotyped 428 subjects in 98 BP families at the Center for Inherited Disease Research with 402 microsatellite markers. We first carried out a non-parametric linkage analysis with MERLIN, and then reanalyzed the data with LODPAL to incorporate clinical covariates for age at onset (AAO), psychosis and comorbid anxiety. We sought to further examine the top findings in the covariate analysis in an independent sample of 64 previously collected BP families. In the non-parametric linkage analysis, three loci were nominally significant under a narrow diagnostic model and seven other loci were nominally significant under a broader model. The top findings were on chromosomes 2q24 and 3q28. The covariate analyses yielded additional evidence for linkage on 3q28 with AAO in the primary and independent samples. Although none of the linked loci were genome-wide significant, their congruence with prior results and, for the covariate analyses, their identification in two separate samples increases the likelihood that they are true positives and deserve further investigation. These findings further demonstrate the value of considering clinical features that may reflect the underlying heterogeneity of disease in order to facilitate gene mapping.

Linkage of bipolar affective disorder on chromosome 8q24: follow-up and parametric analysis

Our group first reported a linkage finding for bipolar (BP) disorder on chromosome 8q24 in a study of 50 multiplex pedigrees, with an HLOD score reaching 2.39. Recently, Cichon et al reported an LOD score of 3.62 in the same region using two-point parametric analysis. Subsequently, we published the results of a genome scan for linkage to BP disorder using a sample extended to 65 pedigrees in which chromosome 8q24 provided the best finding, an NPL score of 3.13, approaching the accepted score for suggestive linkage. We have now fine mapped this region of chromosome 8 in our 65 pedigrees by the addition of 19 microsatellite markers reaching a marker density of 0.8 cM and an information content of 0.84. After the addition of the new data, the original NPL score slightly increased to 3.25. Two-point parametric analysis using the model employed by Cichon et al obtained an LOD score of 3.32 for marker D8S256 at theta=0.14 exceeding the proposed threshold for genomewide significance. After adjusting the parameters in accordance with the 'common disease-common variant' hypothesis, multipoint parametric analysis resulted in an HLOD of 2.49 (alpha=0.78) between D8S529 and D8S256, and defined a 1-LOD interval corresponding to a 2.3 Mb region. No allelic association with the disease was observed for our set of microsatellite markers. Biologically, plausible candidate genes in this region include thyroglobulin, KCNQ3 coding for a voltage-gated potassium channel and the gene for brain adenyl-cyclase (ADCY8).

Findings in an independent sample support an association between bipolar affective disorder and the G72/G30 locus on chromosome 13q33

Markers near the nested genes G72 and G30 on chromosome 13q33 have been implicated in the etiology of schizophrenia and, recently, bipolar affective disorder (BPAD). Hattori et al (2003) reported that single-nucleotide polymorphisms (SNPs) near the G72/G30 locus were associated with BPAD in a sample of 22 pedigrees, and that SNP haplotypes were associated in a second, larger sample of triads. The present study attempts to replicate this finding in an independent case-control sample. Six SNPs near the G72/G30 locus, including the most strongly associated markers in the previous study, were tested in 139 cases and 113 ethnically matched controls. Significant association was detected between BPAD and two adjacent SNPs (smallest P=0.007; global P=0.024). Haplotype analysis produced additional support for association (smallest P=0.004; global P=0.004). Analysis of 31 unlinked microsatellite markers detected no population stratification in the cases or controls studied. Although the associated alleles and haplotypes differ from those previously reported, these new results provide further evidence, in an independent sample, for an association between BPAD and genetic variation in the vicinity of the genes G72 and G30.

Novel CAG/CTG repeat expansion mutations do not contribute to the genetic risk for most cases of bipolar disorder or schizophrenia

The possible presence of anticipation in bipolar affective disorder and schizophrenia has led to the hypothesis that repeat expansion mutations could contribute to the genetic etiology of these diseases. Using the repeat expansion detection (RED) assay, we have systematically examined genomic DNA from 100 unrelated probands with schizophrenia and 68 unrelated probands with bipolar affective disorder for the presence of CAG/CTG repeat expansions. Our results show that 28% of the probands with schizophrenia and 30% of probands with bipolar disorder have a CAG/CTG repeat in the expanded range, but that each expansion could be explained by one of three nonpathogenic repeat expansions known to exist in the general population. We conclude that novel CAG/CTG repeat expansions are not a common genetic risk factor for bipolar disorder or schizophrenia.

Trapping and sequence analysis of 1138 putative exons from human chromosome 18

In a search for novel genes on chromosome 18 (HC18), on which several regions have been linked to bipolar disorder, we applied exon trapping to HC18-specific cosmids. Among the 1138 exons trapped, 1052 of them have been mapped to HC18, and the remaining 86 have not been localized. No exons were localized to genomic regions other than HC18. BLAST database search revealed that 190 exons were identical to 98 Unigenes on HC18; 98 identical to additional 82 clusters of ESTs not present in the HC18 Unigene set; 39 homologous to genes from human and other species (e<10(-3)); and the remaining 811 exons had no significant homology to transcripts in public databases. The mapped exons were compared to the 867 annotated genes on HC18 in the Celera databases; 216 exons were identical to 104 Celera 'genes' and the remaining 836 exons were not found in the Celera databases. On average, there were two exons for a matched transcript (known genes and ESTs). Therefore, the 850 novel exons may represent hundreds of novel genes on chromosome 18.

Genome-wide scan of bipolar disorder in 65 pedigrees: supportive evidence for linkage at 8q24, 18q22, 4q32, 2p12, and 13q12

The purpose of this study was to assess 65 pedigrees ascertained through a Bipolar I (BPI) proband for evidence of linkage, using nonparametric methods in a genome-wide scan and for possible parent of origin effect using several analytical methods. We identified 15 loci with nominally significant evidence for increased allele sharing among affected relative pairs. Eight of these regions, at 8q24, 18q22, 4q32, 13q12, 4q35, 10q26, 2p12, and 12q24, directly overlap with previously reported evidence of linkage to bipolar disorder. Five regions at 20p13, 2p22, 14q23, 9p13, and 1q41 are within several Mb of previously reported regions. We report our findings in rank order and the top five markers had an NPL>2.5. The peak finding in these regions were D8S256 at 8q24, NPL 3.13; D18S878 at 18q22, NPL 2.90; D4S1629 at 4q32, NPL 2.80; D2S99 at 2p12, NPL 2.54; and D13S1493 at 13q12, NPL 2.53. No locus produced statistically significant evidence for linkage at the genome-wide level. The parent of origin effect was studied and consistent with our previous findings, evidence for a locus on 18q22 was predominantly from families wherein the father or paternal lineage was affected. There was evidence consistent with paternal imprinting at the loci on 13q12 and 1q41.

Family-based association study of 76 candidate genes in bipolar disorder: BDNF is a potential risk locus. Brain-derived neutrophic factor

Identification of the genetic bases for bipolar disorder remains a challenge for the understanding of this disease. Association between 76 candidate genes and bipolar disorder was tested by genotyping 90 single-nucleotide polymorphisms (SNPs) in these genes in 136 parent-proband trios. In this preliminary analysis, SNPs in two genes, brain-derived neurotrophic factor (BDNF) and the alpha subunit of the voltage-dependent calcium channel were associated with bipolar disorder at the P<0.05 level. In view of the large number of hypotheses tested, the two nominally positive associations were then tested in independent populations of bipolar patients and only BDNF remains a potential risk gene. In the replication samples, excess transmission of the valine allele of amino acid 66 of BDNF was observed in the direction of the original result in an additional sample of 334 parent-proband trios (T/U=108/87, P=0.066). Resequencing of 29 kb surrounding the BDNF gene identified 44 additional SNPs. Genotyping eight common SNPs identified three additional markers transmitted to bipolar probands at the P < 0.05 level. Strong LD was observed across this region and all adjacent pairwise haplotypes showed excess transmission to the bipolar proband. Analysis of these haplotypes using TRANSMIT revealed a global P value of 0.03. A single haplotype was identified that is shared by both the original dataset and the replication sample that is uniquely marked by both the rare A allele of the original SNP and a novel allele 11.5 kb 3'. Therefore, this study of 76 candidate genes has identified BDNF as a potential risk allele that will require additional study to confirm.

A molecular genetic approach to amyotrophic lateral sclerosis

Disorders of the motor neurons may affect both the upper and lower neurons, primarily the lower motor neurons as in the spinal muscular atrophies are primarily the upper motor neurons as in the familial spastic paraplegias. Amyotrophic lateral sclerosis is a degenerative disorder of the motor neuron that results in paralysis and wasting of voluntary muscles. Large motor neurons in the cerebral cortex, brain stem and spinal cord degenerate or are lost. Hyaline inclusions may be seen in the cytoplasm of surviving motor neurons. Acute axonal degeneration of peripheral motor fibers occurs at all levels, including the distal axon. Subclinical involvement of the spinecerebellar tracts, posterior column and Clarke's column as well as loss of large neurons in the dorsal root ganglia and neurons of oculomotor nuclei has been reported. The average duration of life onset of symptoms of amyotrophic lateral sclerosis is three years and ninety per cent of patients died within 5 years. The basic mechanism of disease in amyotrophic lateral sclerosis remains unknown. There is no known treatment that will prevent, reverse or otherwise alter the course of the disease. Autosomal dominant and autosomal recessive forms of amyotrophic lateral sclerosis are genetic models of amyotrophic lateral sclerosis which may provide insight into the disease mechanism of sporadic amyotrophic lateral sclerosis, five to ten percent of adult cases of amyotrophic lateral sclerosis with early onset of symptoms and a more benign course. It is conceivable that both genetic and sporadic forms of amyotrophic lateral sclerosis result from failure of the same or similar neuronal mechanism triggered by defective genes and by an environment agent in sporadic amyotrophic lateral sclerosis.

Genetic analysis of the (CTG)n NOTCH4 polymorphism in 65 multiplex bipolar pedigrees

A strong genetic association between the NOTCH4 locus on chromosome 6 and schizophrenia was recently reported. Based on the data suggesting overlapping susceptibility for schizophrenia and bipolar disorder, we genotyped the polymorphic (CTG)n encoding polyleucine repeat in exon 1 of NOTCH4 in 65 pedigrees ascertained for a genetic linkage study of bipolar disorder. In addition, we analyzed a subset of our pedigrees with psychotic features at this locus. We failed to find any association between the (CTG)n NOTCH4 polymorphism and either the bipolar or the psychotic bipolar phenotype in our 65 pedigrees.

NEDD4L on human chromosome 18q21 has multiple forms of transcripts and is a homologue of the mouse Nedd4-2 gene

The validation of full-length cDNA represents a crucial step in gene identification and subsequent functional analysis. In searching for candidate genes for bipolar disorder on chromosome 18q21, a novel gene homologous to NEDD4 (Neural precursor cells expressed developmentally down-regulated) was identified using exon trapping and cDNA cloning. This novel gene is termed NEDD4L (Human Gene Nomenclature Committee symbol). Typical NEDD4 orthologues that contain a C2 (Ca(2+)/lipid-binding) and a HECT (Homologous to the E6-AP Carboxyl Terminus) ubiquitin-protein ligase domain, and multiple WW domains have been shown to regulate the epithelial sodium channel (ENaC). In mice, Nedd4 has two distinct isoforms termed Nedd4-1 that belongs to the typical NEDD4 class, and Nedd4-2 that is homologous to Nedd4-1 but lacks the C2 domain. NEDD4L contains the WW and HECT domains seen in the NEDD4 gene family, but lacks the C2 domain in the N-terminus. BLAST database search showed that the deduced polypeptide of NEDD4L has 97 and 62% sequence identity to mouse Nedd4-2 and human NEDD4, respectively. Multiple forms of transcripts of NEDD4L have been isolated, which differ in transcription start and termination sites together with the presence or absence of an alternative spliced exon. Northern blot analysis showed a 3.4 kb mRNA species was specifically expressed in heart and skeletal muscle, while a 3.2 kb band and/or an additional 3.6 kb band is seen in other tissues tested. Striking homology of NEDD4L to mouse Nedd4-2 suggests it is the human homologue of mouse Nedd4-2. Its position in a region of linkage for autosomal dominant orthostatic hypotensive disorder and its potential role in regulating ENaC make NEDD4L a candidate gene for this disorder.

Linkage of bipolar disorder to chromosome 18q and the validity of bipolar II disorder

BACKGROUND

An analysis of the relationship between clinical features and allele sharing could clarify the issue of genetic linkage between bipolar affective disorder (BPAD) and chromosome 18q, contributing to the definition of genetically valid clinical subtypes.

METHODS

Relatives ascertained through a proband who had bipolar I disorder (BPI) were interviewed by a psychiatrist, assigned an all-sources diagnosis, and genotyped with 32 markers on 18q21-23. Exploratory findings from the first 28 families (n = 247) were tested prospectively in an additional 30 families (n = 259), and the effect of confirmed findings on the linkage evidence was assessed.

RESULTS

In exploratory analyses, paternal allele sharing on 18q21 was significantly (P =.03) associated with a diagnostic subtype, and was greatest in pairs where both siblings had bipolar II disorder (BPII). Prospective analysis confirmed the finding that BPII-BPII sibling pairs showed significantly (P =.016) greater paternal allele sharing. Paternal allele sharing across 18q21-23 was also significantly greater in families with at least one BPII-BPII sibling pair. In these families, multipoint affected sibling-pair linkage analysis produced a peak paternal lod score of 4.67 (1-lod confidence interval, 12 centimorgans [cM]) vs 1.53 (1-lod confidence interval, 44 cM) in all families.

CONCLUSIONS

Affected sibling pairs with BPII discriminated between families who showed evidence of linkage to 18q, and families who did not. Families with a BPII sibling pair produced an increased lod score and improved linkage resolution. These findings, limited by the small number of BPII-BPII sibling pairs, strengthen the evidence of genetic linkage between BPAD and chromosome 18q, and provide preliminary support for BPII as a genetically valid subtype of BPAD.

The familial aggregation of psychotic symptoms in bipolar disorder pedigrees

OBJECTIVE

Symptomatic overlap between affective disorders and schizophrenia has long been noted. More recently, family and linkage studies have provided some evidence for overlapping genetic susceptibility between bipolar disorder and schizophrenia. If shared genes are responsible for the psychotic manifestations of both disorders, these genes may result in clustering of psychotic symptoms in some bipolar disorder pedigrees. The authors tested this hypothesis in families ascertained for a genetic study of bipolar disorder.

METHOD

Rates of psychotic symptoms-defined as hallucinations or delusions-during affective episodes were compared in families of 47 psychotic and 18 nonpsychotic probands with bipolar I disorder. The analysis included 202 first-degree relatives with major affective disorder.

RESULTS

Significantly more families of psychotic probands than families of nonpsychotic probands (64% versus 28%) contained at least one relative who had affective disorder with psychotic symptoms. Significantly more affectively ill relatives of psychotic probands than of nonpsychotic probands (34% versus 11%) had psychotic symptoms. An analysis of clustering of psychotic subjects across all families revealed significant familial aggregation. Clustering of psychosis was also apparent when only bipolar I disorder was considered the affected phenotype.

CONCLUSIONS

Psychotic bipolar disorder may delineate a subtype of value for genetic and biological investigations. Families with this subtype should be used to search for linkage in chromosomal regions 10p12-13, 13q32, 18p11.2, and 22q11-13, where susceptibility genes common to bipolar disorder and schizophrenia may reside. Putative schizophrenia-associated biological markers, such as abnormal evoked response, oculomotor, and neuroimaging measures, could similarly be explored in such families.

Evidence for genetic linkage of Alzheimer's disease to chromosome 10q

Recent studies suggest that insulin-degrading enzyme (IDE) in neurons and microglia degrades Abeta, the principal component of beta-amyloid and one of the neuropathological hallmarks of Alzheimer's disease (AD). We performed parametric and nonparametric linkage analyses of seven genetic markers on chromosome 10q, six of which map near the IDE gene, in 435 multiplex AD families. These analyses revealed significant evidence of linkage for adjacent markers (D10S1671, D10S583, D10S1710, and D10S566), which was most pronounced in late-onset families. Furthermore, we found evidence for allele-specific association between the putative disease locus and marker D10S583, which has recently been located within 195 kilobases of the IDE gene.

Association of a haplotype for tumor necrosis factor in siblings with late-onset Alzheimer disease: the NIMH Alzheimer Disease Genetics Initiative

Tumor necrosis factor (TNF), a proinflammatory cytokine, may be involved in the pathogenesis of Alzheimer disease (AD) based on observations that senile plaques have been found to upregulate proinflammatory cytokines. Additionally, nonsteroidal anti-inflammatory drugs have been found to delay and prevent the onset of AD. A collaborative genome-wide scan for AD genes in 266 late-onset families implicated a 20 centimorgan region at chromosome 6p21.3 that includes the TNF gene. Three TNF polymorphisms, a -308 TNF promoter polymorphism, whose TNF2 allele is associated with autoimmune inflammatory diseases and strong transcriptional activity, the -238 TNF promoter polymorphism, and the microsatellite TNFa, whose 2 allele is associated with a high TNF secretion, were typed in 145 families consisting of 562 affected and unaffected siblings. These polymorphisms formed a haplotype, 2-1-2, respectively, that was significantly associated with AD (P = 0.005) using the sibling disequilibrium test. Singly, the TNFa2 allele was also significantly associated (P = 0.04) with AD in these 145 families. This TNF association with AD lends further support for an inflammatory process in the pathogenesis of AD. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:823-830, 2000.

Attempted suicide and alcoholism in bipolar disorder: clinical and familial relationships

OBJECTIVE

This study examined the clinical and familial relationships between comorbid alcoholism and attempted suicide in affectively ill relatives of probands with bipolar I disorder.

METHOD

In 71 families ascertained for a genetic linkage study, 337 subjects with major affective disorder were assessed by using the Schedule for Affective Disorders and Schizophrenia-Lifetime Version.

RESULTS

Subjects with bipolar disorder and alcoholism had a 38.4% lifetime rate of attempted suicide, whereas those without alcoholism had a 21.7% rate. Attempted suicide among subjects with bipolar disorder and alcoholism clustered in a subset of seven families. Families with alcoholic and suicidal probands had a 40.7% rate of attempted suicide in first-degree relatives with bipolar disorder, whereas other families had a 19.0% rate.

CONCLUSIONS

Comorbid alcoholism was associated with a higher rate of attempted suicide among family members with bipolar disorder. Attempted suicide and alcoholism clustered in a subset of families. These relationships may have a genetic origin and may be mediated by intoxication, mixed states, and/or temperamental instability.

Gene identification using exon amplification on human chromosome 18q21: implications for bipolar disorder

We previously reported linkage between bipolar disorder and a region on human chromosome (HC) 18q21. To identify genes in this region, exon trapping was performed on cosmids isolated from an HC18-specific cosmid library (LL18NC02) using 47 sequence tagged site (STS) markers from 18q21 as hybridization probes. A total of 285 unique sequences (exons) were obtained from 850 sequenced clones. Homology searching of the databases using NCBI's BLAST algorithms revealed that 31 exons have identity to known genes and/or ESTs, seven are identical to regions of finished genomic sequences in the 18q21 region, 20 have significant similarity (>30% sequence identity) to genes from human and/or other species, 19 were repetitive sequences, and 208 sequences (72%) are novel. Seventy per cent of the trapped sequences were predicted to be derived from genes using library screening and RT-PCR analyses. This represents an initial stage in characterizing genes in a susceptibility region for further study in bipolar disorder or other diseases that map to this region.

Allelic distribution of CTG18.1 in Caucasian populations: association studies in bipolar disorder, schizophrenia, and ataxia

CTG18.1 is a highly polymorphic and unstable CTG repeat within an intron of the SEF2-1 gene. We tested the CTG18.1 repeat length in affective disorder, schizophrenia, and nonspecific ataxia; these diseases all have shown clinical evidence for anticipation. There was no difference in the allele frequencies comparing the controls and disease groups. The most common allele contains 11 CAGs (35%) followed by alleles with 14-17 CAGs (35%). There was no difference in the distribution of the alleles in the cases vs controls for ataxia (P = 0.11), affective disorders (P = 0.21), or schizophrenia (P = 0.26). The frequency of unstable CTG18.1 alleles was approximately 3% in a population of N. European descent and is not related to the phenotypes tested.

Anticipation in schizophrenia: a review and reconsideration

There have been several reports on anticipation and schizophrenia, and the purpose of the present article is to review the literature and present data from an ongoing family study of schizophrenia. The published data find on average a 10-year difference in the age of onset between the parental and offspring generation in family sets that have been ascertained for a genetic linkage study. The biases inherent in such studies include the biases of ascertainment that were described by Penrose [1948]. Several investigators have searched for evidence of enlarged triplet repeats, and some find evidence consistent with expanded triplet repeats, whereas others do not. In any event the phenomenon of anticipation in schizophrenia appears to be consistently found and an explanation is needed. Data are presented from pairwise analyses using intergenerational pairs from 61 pedigrees with schizophrenia showing evidence of anticipation as well as the fertility bias. Anticipation was found in aunt:niece/nephew pairs (14.5 years) but not in uncle:niece/nephew pairs (0.5 years). The sex difference in age of onset was accentuated in uncles versus aunts (8.5 years), present in parents (4.5 years), but absent in the proband generation. Therefore, there appears to be an interaction within families between age of onset and sex that deserves further investigation. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:686-693, 1999.

Trinucleotide repeat expansion and neuropsychiatric disease

Trinucleotide, or triplet, repeats consist of 3 nucleotides consecutively repeated (e.g., CCG CCG CCG CCG CCG) within a region of DNA, a not uncommon motif in the genome of humans and other species. In 1991, a new type of genetic mutation was discovered, known as a dynamic or expansion mutation, in which the number of triplets in a repeat increases and the length becomes unstable. During the past decade, nearly 20 diseases-including Huntington disease, 2 forms of the fragile X syndrome, and myotonic dystrophy-caused by trinucleotide repeat expansions have been identified. The unstable nature of the expanded repeat leads to remarkable patterns of inheritance in these diseases, distinctly at odds with traditional notions of mendelian genetics. We review the clinical and genetic features of these disorders, with a particular emphasis on their psychiatric manifestations. We also critically examine the hypothesis that expansion mutations may have an etiologic role in psychiatric diseases such as bipolar disorder, schizophrenia, and autism.

The assent of a nation: genethics and Iceland

The Icelandic parliament passed legislation authorizing the establishment of a national health sector database which will be sponsored financially by private enterprises through DeCode Genetics Inc. Health related data will be gathered from patients, without their informed consent, from all points of contact with Icelandic public and private health care providers. A centralized data curator will 'non-personalize' the identity of the subjects in a one-way coding system which the government and DeCode Genetics argue overrides the need for informed consent. This legislation is in conflict with the European Data Protection Act, which requires informed consent for the collection of personal data. The law raises many ethical questions regarding the central tenets of informed consent, the power of government, the rights of the human subject, and finally, the responsibility of the clinician balancing commitments of the patient and research.

Alpha-2 macroglobulin is genetically associated with Alzheimer disease

Alpha-2-macroglobulin (alpha-2M; encoded by the gene A2M) is a serum pan-protease inhibitor that has been implicated in Alzheimer disease (AD) based on its ability to mediate the clearance and degradation of A beta, the major component of beta-amyloid deposits. Analysis of a deletion in the A2M gene at the 5' splice site of 'exon II' of the bait region (exon 18) revealed that inheritance of the deletion (A2M-2) confers increased risk for AD (Mantel-Haenzel odds ratio=3.56, P=0.001). The sibship disequilibrium test (SDT) also revealed a significant association between A2M and AD (P=0.00009). These values were comparable to those obtained for the APOE-epsilon4 allele in the same sample, but in contrast to APOE-epsilon4, A2M-2 did not affect age of onset. The observed association of A2M with AD did not appear to account for the previously published linkage of AD to chromosome 12, which we were unable to confirm in this sample. A2M, LRP1 (encoding the alpha-2M receptor) and the genes for two other LRP ligands, APOE and APP (encoding the amyloid beta-protein precursor), have now all been genetically linked to AD, suggesting that these proteins may participate in a common neuropathogenic pathway leading to AD.

No evidence of expansion of CAG or GAA repeats in schizophrenia families and monozygotic twins

Many diseases caused by trinucleotide expansion exhibit increased severity and decreased age of onset (genetic anticipation) in successive generations. Apparent evidence of genetic anticipation in schizophrenia has led to a search for trinucleotide repeat expansions. We have used several techniques, including Southern blot hybridization, repeat expansion detection (RED) and locus-specific PCR to search for expanded CAG/CTG repeats in 12 families from the United Kingdom and 11 from Iceland that are multiplex for schizophrenia and demonstrate anticipation. The unstable DNA theory could also explain discordance of phenotype for schizophrenia in pairs of monozygotic twins, where the affected twin has a greater number of repeats than the unaffected twin. We used these techniques to look for evidence of different CAG/CTG repeat size in 27 pairs of monozygotic twins who are either concordant or discordant for schizophrenia. We have found no evidence of an increase in CAG/CTG repeat size for affected members in the families, or for the affected twins in the MZ twin sample. Southern hybridization and RED analysis were also performed for the twin and family samples to look for evidence of expansion of GAA/TTC repeats. However, no evidence of expansion was found in either sample. Whilst these results suggest that these repeats are not involved in the etiology of schizophrenia, the techniques used for detecting repeat expansions have limits to their sensitivity. The involvement of other trinucleotide repeats or other expandable repeat sequences cannot be ruled out.

Bipolar disorder and panic disorder in families: an analysis of chromosome 18 data

OBJECTIVE

The authors performed an analysis of their published chromosome 18 linkage data on 28 families in which there was bipolar disorder to test the potential of comorbid panic disorder to define a genetic subtype of bipolar disorder.

METHOD

Families ascertained through probands with bipolar I disorder were stratified into three groups based on a history of panic disorder, panic attacks, or no panic attacks in the probands. Multipoint nonparametric linkage analysis was performed on data from bipolar I and II family members in each group.

RESULTS

Linkage scores for five consecutive 18q marker loci were highest in the families of the probands with panic disorder and lowest for the families of the probands without panic attacks.

CONCLUSIONS

This study supports the authors' previously reported clinical hypothesis of a genetic subtype of bipolar disorder identified by comorbid panic disorder. The hypothesis merits prospective testing.

Integrating clinical and laboratory data in genetic studies of complex phenotypes: a network-based data management system

The identification of genes underlying a complex phenotype can be a massive undertaking, and may require a much larger sample size than thought previously. The integration of such large volumes of clinical and laboratory data has become a major challenge. In this paper we describe a network-based data management system designed to address this challenge. Our system offers several advantages. Since the system uses commercial software, it obviates the acquisition, installation, and debugging of privately-available software, and is fully compatible with Windows and other commercial software. The system uses relational database architecture, which offers exceptional flexibility, facilitates complex data queries, and expedites extensive data quality control. The system is particularly designed to integrate clinical and laboratory data efficiently, producing summary reports, pedigrees, and exported files containing both phenotype and genotype data in a virtually unlimited range of formats. We describe a comprehensive system that manages clinical, DNA, cell line, and genotype data, but since the system is modular, researchers can set up only those elements which they need immediately, expanding later as needed.

Linkage of bipolar affective disorder to chromosome 18 markers in a new pedigree series

Several groups have reported evidence suggesting linkage of bipolar affective disorder (BPAD) to chromosome 18. We have reported data from 28 pedigrees that showed linkage to marker loci on 18p and to loci 40 cM distant on 18q. Most of the linkage evidence derived from families with affected phenotypes in only the paternal lineage and from marker alleles transmitted on the paternal chromosome. We now report results from a series of 30 new pedigrees (259 individuals) genotyped for 13 polymorphic markers spanning chromosome 18. Subjects were interviewed by a psychiatrist and were diagnosed by highly reliable methods. Genotypes were generated with automated technology and were scored blind to phenotype. Affected sib pairs showed excess allele sharing at the 18q markers D18S541 and D18S38. A parent-of-origin effect was observed, but it was not consistently paternal. No robust evidence of linkage was detected for markers elsewhere on chromosome 18. Multipoint nonparametric linkage analysis in the new sample combined with the original sample of families supports linkage on chromosome 18q, but the susceptibility gene is not well localized.

A novel, heritable, expanding CTG repeat in an intron of the SEF2-1 gene on chromosome 18q21.1

There are currently 13 diseases known to be caused by unstable triplet repeat mutations; however, there are some instances (as with FRAXF and FRA16) when these mutations appear to be asymptomatic. In a search for polymorphic CTG repeats as candidate genes for bipolar disorder, we screened a genomic human chromosome 18-specific library and identified a 1.6 kb clone (7,6A) with a CTG24 repeat that maps to 18q21.1. The CTG repeat locus, termed CTG18.1, is located within an intron of human SEF2-1, a gene encoding a basic hellx-loop-hellx DNA binding protein involved in transcriptional regulation. The CTGn repeat is highly polymorphic and very enlarged alleles, consistent with expansions of up to CTG2100, were identified. PCR and Southern blot analysis in pedigrees ascertained for a Johns Hopkins University bipolar disorder linkage study and in CEPH reference pedigrees revealed a tripartite distribution of CTG18.1 alleles with stable alleles (CTG10-CTG37), moderately enlarged and unstable alleles (CTG53-CTG250), and very enlarged, unstable alleles (CTG800-CTG2100). Moderately enlarged alleles were not associated with an abnormal phenotype and have a combined enlarged allele frequency of 3% in the CEPH and bipolar populations. Very enlarged alleles, detectable only by Southern blot analysis of genomic digests, have thus far been found in only three individuals from our bipolar pedigrees, and to date, have not been found in any of the CEPH reference pedigrees. These enlarged alleles may arise, at least in part, via somatic mutation.

Panic disorder with familial bipolar disorder

If bipolar disorder is genetically heterogeneous, it may be possible to discern clinically heterogeneous familial subtypes based on differential risk for psychiatric comorbidity, for example panic disorder. We evaluated 528 members of 57 families ascertained for a genetic linkage study of bipolar disorder. Families were assorted according to the panic disorder diagnosis of the bipolar proband; the rates of panic and other disorders in relatives were compared. Eighty-eight percent of the 41 subjects with panic disorder had bipolar disorder. Panic disorder was diagnosed in 18% of family members with bipolar disorder. Ten of 57 bipolar probands had panic disorder. Their bipolar first-degree relatives had a significantly higher prevalence of panic disorder, bipolar II, cyclothymia, and dysthymia, but had lower prevalence of substance abuse than the relatives of the bipolar probands without panic disorder. These findings suggest the testable hypothesis that comorbid panic disorder is a marker of genetic heterogeneity in bipolar disorder.

cDNAs with long CAG trinucleotide repeats from human brain

Twelve diseases, most with neuropsychiatric features, arise from trinucleotide repeat expansion mutations. Expansion mutations may also cause a number of other disorders, including several additional forms of spinocerebellar ataxia, bipolar affective disorder, schizophrenia, and autism. To obtain candiate genes for these disorders, cDNA libraries from adult and fetal human brain were screened at high stringency for clones containing CAG repeats. Nineteen cDNAs were isolated and mapped to chromosomes 1, 2, 4, 6, 7, 8, 9, 12, 16, 19, 20, and X. The clones contain between 4 and 17 consecutive CAG, CTG, TCG, or GCA triplets. Clone H44 encodes 40 consecutive glutamines, more than any other entry in the nonredundant GenBank protein database and well within the range that causes neuronal degeneration in several of the glutamine expansion diseases. Eight cDNAs encode 15 or more consecutive glutamine residues, suggesting that the gene products may function as transcription factors, with a potential role in the regulation of neurodevelopment or neuroplasticity. In particular, the conceptual translation of clone CTG3a contains 18 consecutive glutamines and is 45% identical to the C-terminal 306 residues of the mouse numb gene product. These genes are therefore candidates for diseases featuring anticipation, neurodegeneration, or abnormalities of neurodevelopment.

Initial genome screen for bipolar disorder in the NIMH genetics initiative pedigrees: chromosomes 2, 11, 13, 14, and X

We report on an initial genome screen of 540 individuals from 97 families collected as part of the NIMH Genetics Initiative Bipolar Group. Among the individuals studied, 232 were diagnosed with bipolar (BP) I, 72 with BPII, 88 with major depressive disorder-recurrent type (UPR), and 32 with schizoaffective disorder, bipolar type (SA/BP). A total of 53 markers on chromosomes 2, 11, 13, 14, and X (average spacing: 11.5 cM) were studied at Johns Hopkins University. Tests for linkage were performed using nonparametric affected sib-pair and whole pedigree methods with three definitions of affected status. Three regions of interest were identified (13q14-32, Xp22, and Xq26-28). On chromosomes 2, 11, and 14, a disease locus with relative risk lambda(i) = 1.5 could be excluded in <10% of the genetic distance studied, while a locus conferring lambda(i) = 3 or greater could be excluded across at least 96%. The autosomal region that could not be excluded even with lambda(i) = 5 was near 13q14-32. In this region, two-point affected sib-pair analyses revealed a pair of consecutive loci with excess sharing (P < 0.05) and a multipoint affected sib-pair LOD score of 1.12. On the X chromosome, nonparametric multipoint affected sib-pair analyses revealed peak total LOD scores of 0.94 on Xp22 and 1.34 on Xq26-28. A locus linked to the markers in Xp22 would have lambda(i) = 3.6 in affected brother-brother pairs, while a locus linked to the markers in Xq26-28 would have lambda(i) > 1.9 in affected sister-sister pairs. The results on 13q14-32, Xp22, and Xq26-28 suggest areas of interest for further studies.

Linkage disequilibrium analysis of G-olf alpha (GNAL) in bipolar affective disorder

This study examines G-olf alpha as a possible candidate gene for susceptibility to bipolar affective disorder (BPAD) using the Transmission Disequilibrium Test (TDT). G-olf alpha, which encodes a subunit of a G-protein involved in intracellular signaling, maps within a region of chromosome 18 that has been implicated by two different linkage studies as a potential site of BPAD susceptibility loci. The expression pattern of G-olf alpha in the brain, its coupling to dopamine receptors, and the effects of lithium salts on G-proteins all support G-olf alpha as a candidate gene for BPAD. Our study population consisted of 106 probands and sibs with bipolar I disorder, with a median age-at-onset of 21.5 years ascertained from the United States. There was no evidence of linkage disequilibrium between BPAD and any of the observed G-olf alpha alleles in our sample. Division of families based on sex of the transmitting parent did not significantly change the results. This sample had good power (78%) to detect linkage disequilibrium with alleles conferring a relative risk equal to that estimated for the putative 18p locus (2.58). Our results do not support a major role for G-olf alpha as a susceptibility locus for BPAD in a substantial portion of our sample. Other genes lying near G-olf alpha within the linked region on chromosome 18 cannot be excluded by our data. This study illustrates the use of the TDT in evaluating candidate genes within linked chromosome regions.

cDNA cloning of a human homologue of the Caenorhabditis elegans cell fate-determining gene mab-21: expression, chromosomal localization and analysis of a highly polymorphic (CAG)n trinucleotide repeat

The two most consistent features of the diseases caused by trinucleotide repeat expansion-neuropsychiatric symptoms and the phenomenon of genetic anticipation-may be present in forms of dementia, hereditary ataxia, Parkinsonism, bipolar affective disorder, schizophrenia and autism. To identify candidate genes for these disorders, we have screened human brain cDNA libraries for the presence of gene fragments containing polymorphic trinucleotide repeats. Here we report the cDNA cloning of CAGR1, originally detected in a retinal cDNA library. The 2743 bp cDNA contains a 1077 bp open reading frame encoding 359 amino acids. This amino acid sequence is homologous (56% amino acid identify and 81% amino acid conservation) to the Caenorhabditis elegans cell fate-determining protein mab-21. CAGR1 is expressed in several human tissues, most prominently in the cerebellum, as a message of approximately 3.0 kb. The gene was mapped to 13q13, just telomeric to D13S220. A 5'-untranslated CAG trinucleotide repeat is highly polymorphic, with repeat length ranging from six to 31 triplets and a heterozygosity of 87-88% in 684 chromosomes from several human populations. One allele from an individual with an atypical movement disorder and bipolar affective disorder type II contains 46 triplets, 15 triplets longer than any other allele detected. Though insufficient data are available to link the long repeat to this clinical phenotype, an expansion mutation of the CAGR1 repeat can be considered a candidate for the etiology of disorders with anticipation or developmental abnormalities, and particularly any such disorders linked to chromosome 13.

Psychosis and genes with trinucleotide repeat polymorphism

Abnormal expansion of genes with trinucleotide repeat (TNR) polymorphism has been found in a number of neuropsychiatric disorders. These disorders and the major psychoses, schizophrenia and bipolar affective disorder, appear to share an interesting phenomenon: genetic anticipation. Because TNR expansion correlates with anticipation, these unstable DNA sites are considered important candidate loci for the major psychoses. We investigated genes with TNR polymorphisms, including B1, B33, B37, and the N-cadherin gene, in unrelated Caucasian North American and Italian schizophrenics (n = 53 to 74), and matched controls. Also, unrelated Caucasian North American patients with bipolar I affective disorder were screened for the B33 and N-cadherin genes (n = 49 and 63, respectively). No unusually long alleles that would suggest abnormal expansion of the TNR were observed for any of these genes. Also, no statistically significant results were found in tests for genetic association between any of these genes and schizophrenia. For B37, a trend toward a difference in allele counts between schizophrenics and controls was observed. However, no clear evidence for a role of these TNR-containing genes in schizophrenia or bipolar affective disorders was found.

Evidence for linkage of bipolar disorder to chromosome 18 with a parent-of-origin effect

A susceptibility gene on chromosome 18 and a parent-of-origin effect have been suggested for bipolar affective disorder (BPAD). We have studied 28 nuclear families selected for apparent unilineal transmission of the BPAD phenotype, by using 31 polymorphic markers spanning chromosome 18. Evidence for linkage was tested with affected-sib-pair and LOD score methods under two definitions of the affected phenotype. The affected-sibpair analyses indicated excess allele sharing for markers on 18p within the region reported previously. The greatest sharing was at D18S37: 64% in bipolar and recurrent unipolar (RUP) sib pairs (P = .0006). In addition, excess sharing of the paternally, but not maternally, transmitted alleles was observed at three markers on 18q: at D18S41, 51 bipolar and RUP sib pairs were concordant for paternally transmitted alleles, and 21 pairs were discordant (P = 0004). The evidence for linkage to loci on both 18p and 18q was strongest in the 11 paternal pedigrees, i.e., those in which the father or one of the father's sibs is affected. In these pedigrees, the greatest allele sharing (81%; P = .00002) and the highest LOD score (3.51; phi = 0.0) were observed at D18S41. Our results provide further support for linkage of BPAD to chromosome 18 and the first molecular evidence for a parent-of-origin effect operating in this disorder. The number of loci involved, and their precise location, require further study..

Polymorphic (AAT) in trinucleotide repeats derived from a human brain cDNA library

Seven cDNA fragments containing polymorphic (AAT)n trinucleotide repeats were isolated from a human brain cDNA library and mapped by linkage to specific loci. These repeats may serve as gene markers or as candidates for diseases caused by expansion mutation.

Structure of the human CRFB4 gene: comparison with its IFNAR neighbor

The cytokine receptor family consists of a growing number of structurally and evolutionarily related transmembrane receptors. CRFB4 and IFNAR are two of the most similar members of this family. They are encoded by two neighboring genes on both human chromosome 21 and murine chromosome 16. The sequence of the human CRFB4 gene was determined from the first exon to the last intron. The nature of the repetitive sequences present in the introns was analyzed and compared with those present in the human IFNAR gene. This analysis leads to considerations of the antiquity of the duplication that gave rise to both genes from a common ancestor. A pseudogene for USF has been identified in the IFNAR gene and a new definition for the repetitive sequence MER37 is proposed. The polymorphism associated with two CA repeats present in the CRFB4 gene is described.

Characterization of cDNA clones containing CCA trinucleotide repeats derived from human brain

Expansion mutation is the cause of eight neuropsychiatric disorders. Thus far each disease is the result of expansion of a C-G rich trinucleotide repeat that is polymorphic for length in the general population. We now report the identification of seven novel cDNA clones with CCA or equivalent trinucleotide repeats obtained by screening a human frontal cortex cDNA library. The repeat lengths of two clones, CCA11 (linked to D20S101, expressed in human brain as a 3.2 kb message) and CCA38 (linked to D5S404), are highly polymorphic in a normal human population. CCA54, mapped to chromosome 19, appears to correspond to a portion of the human gene encoding the alpha 1 subunit of a P-type calcium channel. Expansion mutations at these loci should be considered as possible candidates in evaluating the genetic etiologies of diseases linked to chromosomes 5, 19, and 20.

Identification of flanking markers for the familial amyotrophic lateral sclerosis gene ALS1 on chromosome 21

Amyotrophic lateral sclerosis (ALS) is a progressive, adult-onset, neurodegenerative disorder characterized by the death of large motor neurons from the cerebral cortex, brainstem, and spinal cord. The etiology of ALS remains unknown; however, approximately 10% of the cases are familial in nature. In the majority of these families, the mode of transmission is autosomal dominant. Recently, linkage of an autosomal dominant familial ALS (FALS) gene to the locus ALS1 on chromosome 21q was established. In addition, evidence was provided for genetic heterogeneity, with approximately 55% of families most likely linked to chromosome 21. The development of a number of highly informative simple sequence repeat polymorphisms in the region of linkage-21q21 through 21q22.1-has permitted us to confirm both the assignment of ALS1 to 21q and the genetic heterogeneity of FALS. In addition, we have been able to refine the mapping of ALS1, based on recombination events in two of the linked families. Flanking markers for the FALS gene are D21S213 on the centromeric side and D21S219 on the telomeric side. The candidate region is approximately 4 Mb and contains the genes copper/zinc superoxide dismutase (CuZnSOD); the fourth member of the class II cytokine receptor family (CRF2-4); and the interferon-alpha receptor (IFNAR).

Anticipation in bipolar affective disorder

Anticipation refers to the increase in disease severity or decrease in age at onset in succeeding generations. This phenomenon, formerly ascribed to observation biases, correlates with the expansion of trinucleotide repeat sequences (TNRs) in some disorders. If present in bipolar affective disorder (BPAD), anticipation could provide clues to its genetic etiology. We compared age at onset and disease severity between two generations of 34 unilineal families ascertained for a genetic linkage study of BPAD. Life-table analyses showed a significant decrease in survival to first mania or depression from the first to the second generation (P < .001). Intergenerational pairwise comparisons showed both a significantly earlier age at onset (P < .001) and a significantly increased disease severity (P < .001) in the second generation. This difference was significant under each of four data-sampling schemes which excluded probands in the second generation. The second generation experienced onset 8.9-13.5 years earlier and illness 1.8-3.4 times more severe than did the first generation. In additional analyses, drug abuse, deaths of affected individuals prior to interview, decreased fertility, censoring of age at onset, and the cohort effect did not affect our results. We conclude that genetic anticipation occurs in this sample of unilineal BPAD families. These findings may implicate genes with expanding TNRs in the genetic etiology of BPAD.

Genes with triplet repeats: candidate mediators of neuropsychiatric disorders

Recently a new form of human mutation-expansion of trinucleotide repeats-has been found to cause the diseases of fragile X syndrome, spinal and bulbar muscular atrophy, myotonic dystrophy and, most recently, Huntington's disease. We review the emerging data on the genetics and neurobiology of these disorders. Three are characterized by unusual patterns of inheritance, in particular, genetic 'anticipation', in which the severity of the disorder increases and the age of onset decreases in successive generations of a pedigree. Several idiopathic neuropsychiatric disorders have features of inheritance consistent with anticipation. In bipolar affective disorder, there is evidence for both earlier age of onset and more severe illness in the second generation of a subset of unilineal pedigrees. There is also the suggestion of anticipation in some forms of schizophrenia, spinocerebellar atrophy and autism. Triplet repeats are present in additional known genes, both in coding regions and untranslated regions. Furthermore, many novel genes with triplet repeats are expressed in the human brain, and these are candidates to cause some forms of these neuropsychiatric disorders.

Novel triplet repeat containing genes in human brain: cloning, expression, and length polymorphisms

Human genes containing triplet repeats may markedly expand in length and cause neuropsychiatric disease, explaining the phenomenon of anticipation (increasing severity or earlier age of onset in successive generations in a pedigree). To identify novel genes with triplet repeats, we screened a human brain cDNA library with oligonucleotide probes containing CTG or CCG triplet repeats. Fourteen of 40 clones encoded novel human genes, and 8 of these inserts have been sequenced on both strands. All contain repeats, and 5 of the 8 have 9 or more consecutive perfect repeats. All are expressed in brain. Chromosomal assignments reveal a distribution of these genes on multiple autosomes and the X-chromosome. Further, the repeat length in two of the genes is highly polymorphic, making them valuable index linkage markers. We predict that many triplet repeat-containing genes exist; screening with the CTG probe suggests approximately 50-100 genes containing this type of repeat are expressed in the human brain. Since additional disorders, such as Huntington's disease, bipolar affective disorder, and possibly others, show features of anticipation, we suggest that these novel human genes with triplet repeats are candidates for causing neuropsychiatric diseases.