AB0006 ESTABLISHED RISK LOCI FOR SYSTEMIC LUPUS ERYTHEMATOSUS AT NCF2, STAT4, TNPO3, IRF5 AND ITGAM ASSOCIATE WITH DISTINCT CLINICAL MANIFESTATIONS: A DANISH GENOME-WIDE ASSOCIATION STUDY

Background

Systemic lupus erythematosus (SLE) has been associated with more than 100 genetic loci. This parallels positively to the clinical diversity that is reflected by the classification of SLE.

Objectives

We aimed to investigate associations between disease manifestations of SLE and risk gene variants relevant to Danish subjects of European ancestry.

Methods

We included 427 SLE patients of European ancestry similar to previous reports.[1] We also included 89,699 controls from the Danish Blood Donor Study Genomic Cohort. SLE risk loci in this population were identified by genome-wide association methodology and hereafter correlated to cumulative occurrence of SLE classification items.

Results

Fourteen variants mapped to the following genes: NCF2, STAT4, TNPO3/TPI1P2, IRF5, and ITGAM, were significantly associated (p<5E-8) with SLE.

The five lead variants were associated (p<0.05) with the following manifestations; NCF2: proteinuria and anti-phospholipid antibodies, STAT4: arthritis, serositis, neurologic disorder, lymphopenia, and anti-Smith antibodies, IRF5: seizures and proteinuria, TNPO3: proteinuria, and ITGAM: photosensitivity (Table 2).

Conclusion

Our findings support the future use of select, relevant genetic markers in predicting various SLE phenotypes.

References

[1]Leffers HCB, Troldborg A, Voss A, et al. Smoking associates with distinct clinical phenotypes in patients with systemic lupus erythematosus: a nationwide Danish cross-sectional study. Lupus Sci Med 2021;8(1).

Table 1.

Associations between five SLE risk loci and specific disease manifestations in 427 Danish patients with SLE*.

NCF2STAT4IRF5TNPO3ITGAMrs17849502_Trs7574865_Trs4728142_Ars13239597_Ars11860650_TN (%)Malar rash233 (55%)1.28 (0.84-1.96)0.83 (0.62-1.11)1.01 (0.74-1.38)1.44 (0.97-2.12)1.14 (0.80-1.61)Discoid rash46 (11%)1.49 (0.81-2.73)0.90 (0.56-1.45)1.01 (0.62-1.66)1.16 (0.63-2.12)0.76 (0.42-1.41)Photosensitivity219 (51%)0.96 (0.63-1.46)1.09 (0.81-1.47)0.98 (0.71-1.34)0.84 (0.57-1.25)0.67 (0.47-0.97)Oral ulcers132 (31%)0.96 (0.61-1.50)0.90 (0.65-1.23)0.83 (0.60-1.16)1.30 (0.87-1.96)1.43 (0.99-2.05)Non-erosive Arthritis342 (80%)0.84 (0.52-1.37)1.49 (1.02-2.18)0.93 (0.63-1.36)1.04 (0.64-1.68)1.16 (0.74-1.80)Serositis-Pleuritis124 (29%)0.63 (0.38-1.05)1.38 (1.01-1.89)1.22 (0.87-1.72)0.85 (0.56-1.29)0.84 (0.57-1.24)-Pericarditis72 (17%)0.75 (0.41-1.40)1.35 (0.93-1.96)1.05 (0.70-1.58)1.15 (0.70-1.89)1.09 (0.70-1.72)Persistent proteinuria158 (37%)1.63 (1.07-2.49)1.08 (0.80-1.46)0.68 (0.49-0.94)1.74 (1.16-2.61)1.09 (0.76-1.57)Neurologic disorder-Seizures23 (5%)1.58 (0.75-3.35)1.49 (0.80-2.76)2.10 (1.04-4.25)0.61 (0.26-1.44)0.93 (0.42-2.06)-Psychosis8 (2%)0.76 (0.097-5.87)2.77 (0.94-8.15)0.35 (0.10-1.23)0 (0)2.96 (0.85-10.3)Haematologic disorder-Haemolytic anaemia38 (9%)0.78 (0.34-1.76)1.37 (0.85-2.22)0.75 (0.44-1.29)1.11 (0.57-2.19)1.24 (0.70-2.20)-Leukopenia130 (30%)1.04 (0.67-1.61)1.19 (0.87-1.63)1.00 (0.72-1.39)0.90 (0.60-1.37)0.94 (0.64-1.37)-Lymphopenia228 (53%)0.95 (0.63-1.44)1.35 (1.01-1.81)0.95 (0.70-1.29)1.16 (0.79-1.70)1.09 (0.77-1.54)-Thrombocytopenia102 (24%)1.42 (0.91-2.22)0.84 (0.60-1.18)0.83 (0.58-1.18)1.35 (0.86-2.11)0.91 (0.60-1.37)Immunologic disorder-anti-DNA ab.330 (77%)0.69 (0.44-1.09)1.02 (0.72-1.44)0.94 (0.65-1.35)0.97 (0.62-1.53)1.08 (0.71-1.65)-anti-Smith ab.44 (10%)1.44 (0.79-2.64)1.58 (1.00-2.49)1.23 (0.73-2.07)1.47 (0.80-2.69)1.07 (0.61-1.84)-anti-phospholipid ab.183 (43%)1.63 (1.07-2.49)1.05 (0.79-1.41)0.84 (0.61-1.14)1.14 (0.77-1.68)1.14 (0.80-1.62)

* Logistic regression models for each manifestation included all five lead variants (multivariate) and were adjusted for age and sex

Disclosure of Interests

Henrik Leffers: None declared, David Westergaard: None declared, Saedis Saevarsdottir: None declared, Ingileif Jonsdottir: None declared, Ole Birger Pedersen: None declared, Anne Troldborg: None declared, Anne Voss: None declared, Salome Kristensen: None declared, Jesper Lindhardsen: None declared, Prabhat Kumar: None declared, Asta Linauskas: None declared, Lars Juul: None declared, Niels Steen Krogh: None declared, Bent Deleuran: None declared, Lene Dreyer Speakers bureau: Speakers bureau: Eli Lilly, Galderma and Janssen, Grant/research support from: from BMS outside the present work, Michael Schwinn: None declared, Lise wegner Thørner: None declared, Lotte Hindhede: None declared, Christian Erikstrup: None declared, Henrik Ullum: None declared, Søren Brunak Shareholder of: SB has ownerships in Intomics A/S, Hoba Therapeutics Aps, Novo Nordisk A/S, Lundbeck A/S, Kari Stefansson: None declared, Karina Banasik: None declared, Søren Jacobsen: None declared

Brain age prediction using deep learning uncovers associated sequence variants

Machine learning algorithms can be trained to estimate age from brain structural MRI. The difference between an individual’s predicted and chronological age, predicted age difference (PAD), is a phenotype of relevance to aging and brain disease. Here, we present a new deep learning approach to predict brain age from a T1-weighted MRI. The method was trained on a dataset of healthy Icelanders and tested on two datasets, IXI and UK Biobank, utilizing transfer learning to improve accuracy on new sites. A genome-wide association study (GWAS) of PAD in the UK Biobank data (discovery set: \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$N=12378$$\end{document}N=12378, replication set: \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$N=4456$$\end{document}N=4456) yielded two sequence variants, rs1452628-T (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\beta =-0.08$$\end{document}β=−0.08, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$P=1.15\times{10}^{-9}$$\end{document}P=1.15×10−9) and rs2435204-G (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\beta =0.102$$\end{document}β=0.102, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$P=9.73\times 1{0}^{-12}$$\end{document}P=9.73×10−12). The former is near KCNK2 and correlates with reduced sulcal width, whereas the latter correlates with reduced white matter surface area and tags a well-known inversion at 17q21.31 (H2).

Machine learning algorithms can be trained to estimate age from brain structural MRI. Here, the authors introduce a new deep-learning-based age prediction approach, and then carry out a GWAS of the difference between predicted and chronological age, revealing two associated variants.

Genome-wide association study across European and African American ancestries identifies a SNP in DNMT3B contributing to nicotine dependence

Cigarette smoking is a leading cause of preventable mortality worldwide. Nicotine dependence, which reduces the likelihood of quitting smoking, is a heritable trait with firmly established associations with sequence variants in nicotine acetylcholine receptor genes and at other loci. To search for additional loci, we conducted a genome-wide association study (GWAS) meta-analysis of nicotine dependence, totaling 38,602 smokers (28,677 Europeans/European Americans and 9925 African Americans) across 15 studies. In this largest-ever GWAS meta-analysis for nicotine dependence and the largest-ever cross-ancestry GWAS meta-analysis for any smoking phenotype, we reconfirmed the well-known CHRNA5-CHRNA3-CHRNB4 genes and further yielded a novel association in the DNA methyltransferase gene DNMT3B. The intronic DNMT3B rs910083-C allele (frequency=44-77%) was associated with increased risk of nicotine dependence at P=3.7 × 10-8 (odds ratio (OR)=1.06 and 95% confidence interval (CI)=1.04-1.07 for severe vs mild dependence). The association was independently confirmed in the UK Biobank (N=48,931) using heavy vs never smoking as a proxy phenotype (P=3.6 × 10-4, OR=1.05, and 95% CI=1.02-1.08). Rs910083-C is also associated with increased risk of squamous cell lung carcinoma in the International Lung Cancer Consortium (N=60,586, meta-analysis P=0.0095, OR=1.05, and 95% CI=1.01-1.09). Moreover, rs910083-C was implicated as a cis-methylation quantitative trait locus (QTL) variant associated with higher DNMT3B methylation in fetal brain (N=166, P=2.3 × 10-26) and a cis-expression QTL variant associated with higher DNMT3B expression in adult cerebellum from the Genotype-Tissue Expression project (N=103, P=3.0 × 10-6) and the independent Brain eQTL Almanac (N=134, P=0.028). This novel DNMT3B cis-acting QTL variant highlights the importance of genetically influenced regulation in brain on the risks of nicotine dependence, heavy smoking and consequent lung cancer.

Rare and Common Variants Conferring Risk of Tooth Agenesis

We present association results from a large genome-wide association study of tooth agenesis (TA) as well as selective TA, including 1,944 subjects with congenitally missing teeth, excluding third molars, and 338,554 controls, all of European ancestry. We also tested the association of previously identified risk variants, for timing of tooth eruption and orofacial clefts, with TA. We report associations between TA and 9 novel risk variants. Five of these variants associate with selective TA, including a variant conferring risk of orofacial clefts. These results contribute to a deeper understanding of the genetic architecture of tooth development and disease. The few variants previously associated with TA were uncovered through candidate gene studies guided by mouse knockouts. Knowing the etiology and clinical features of TA is important for planning oral rehabilitation that often involves an interdisciplinary approach.

15q11.2 CNV affects cognitive, structural and functional correlates of dyslexia and dyscalculia

Several copy number variants have been associated with neuropsychiatric disorders and these variants have been shown to also influence cognitive abilities in carriers unaffected by psychiatric disorders. Previously, we associated the 15q11.2(BP1-BP2) deletion with specific learning disabilities and a larger corpus callosum. Here we investigate, in a much larger sample, the effect of the 15q11.2(BP1-BP2) deletion on cognitive, structural and functional correlates of dyslexia and dyscalculia. We report that the deletion confers greatest risk of the combined phenotype of dyslexia and dyscalculia. We also show that the deletion associates with a smaller left fusiform gyrus. Moreover, tailored functional magnetic resonance imaging experiments using phonological lexical decision and multiplication verification tasks demonstrate altered activation in the left fusiform and the left angular gyri in carriers. Thus, by using convergent evidence from neuropsychological testing, and structural and functional neuroimaging, we show that the 15q11.2(BP1-BP2) deletion affects cognitive, structural and functional correlates of both dyslexia and dyscalculia.

A rare missense mutation in CHRNA4 associates with smoking behavior and its consequences

Using Icelandic whole-genome sequence data and an imputation approach we searched for rare sequence variants in CHRNA4 and tested them for association with nicotine dependence. We show that carriers of a rare missense variant (allele frequency=0.24%) within CHRNA4, encoding an R336C substitution, have greater risk of nicotine addiction than non-carriers as assessed by the Fagerstrom Test for Nicotine Dependence (P=1.2 × 10(-4)). The variant also confers risk of several serious smoking-related diseases previously shown to be associated with the D398N substitution in CHRNA5. We observed odds ratios (ORs) of 1.7-2.3 for lung cancer (LC; P=4.0 × 10(-4)), chronic obstructive pulmonary disease (COPD; P=9.3 × 10(-4)), peripheral artery disease (PAD; P=0.090) and abdominal aortic aneurysms (AAAs; P=0.12), and the variant associates strongly with the early-onset forms of LC (OR=4.49, P=2.2 × 10(-4)), COPD (OR=3.22, P=2.9 × 10(-4)), PAD (OR=3.47, P=9.2 × 10(-3)) and AAA (OR=6.44, P=6.3 × 10(-3)). Joint analysis of the four smoking-related diseases reveals significant association (P=6.8 × 10(-5)), particularly for early-onset cases (P=2.1 × 10(-7)). Our results are in agreement with functional studies showing that the human α4β2 isoform of the channel containing R336C has less sensitivity for its agonists than the wild-type form following nicotine incubation.

Genome-wide meta-analysis reveals common splice site acceptor variant in CHRNA4 associated with nicotine dependence

We conducted a 1000 Genomes-imputed genome-wide association study (GWAS) meta-analysis for nicotine dependence, defined by the Fagerström Test for Nicotine Dependence in 17 074 ever smokers from five European-ancestry samples. We followed up novel variants in 7469 ever smokers from five independent European-ancestry samples. We identified genome-wide significant association in the alpha-4 nicotinic receptor subunit (CHRNA4) gene on chromosome 20q13: lowest P=8.0 × 10(-9) across all the samples for rs2273500-C (frequency=0.15; odds ratio=1.12 and 95% confidence interval=1.08-1.17 for severe vs mild dependence). rs2273500-C, a splice site acceptor variant resulting in an alternate CHRNA4 transcript predicted to be targeted for nonsense-mediated decay, was associated with decreased CHRNA4 expression in physiologically normal human brains (lowest P=7.3 × 10(-4)). Importantly, rs2273500-C was associated with increased lung cancer risk (N=28 998, odds ratio=1.06 and 95% confidence interval=1.00-1.12), likely through its effect on smoking, as rs2273500-C was no longer associated with lung cancer after adjustment for smoking. Using criteria for smoking behavior that encompass more than the single 'cigarettes per day' item, we identified a common CHRNA4 variant with important regulatory properties that contributes to nicotine dependence and smoking-related consequences.

A common biological basis of obesity and nicotine addiction

Smoking influences body weight such that smokers weigh less than non-smokers and smoking cessation often leads to weight increase. The relationship between body weight and smoking is partly explained by the effect of nicotine on appetite and metabolism. However, the brain reward system is involved in the control of the intake of both food and tobacco. We evaluated the effect of single-nucleotide polymorphisms (SNPs) affecting body mass index (BMI) on smoking behavior, and tested the 32 SNPs identified in a meta-analysis for association with two smoking phenotypes, smoking initiation (SI) and the number of cigarettes smoked per day (CPD) in an Icelandic sample (N=34,216 smokers). Combined according to their effect on BMI, the SNPs correlate with both SI (r=0.019, P=0.00054) and CPD (r=0.032, P=8.0 × 10(-7)). These findings replicate in a second large data set (N=127,274, thereof 76,242 smokers) for both SI (P=1.2 × 10(-5)) and CPD (P=9.3 × 10(-5)). Notably, the variant most strongly associated with BMI (rs1558902-A in FTO) did not associate with smoking behavior. The association with smoking behavior is not due to the effect of the SNPs on BMI. Our results strongly point to a common biological basis of the regulation of our appetite for tobacco and food, and thus the vulnerability to nicotine addiction and obesity.

Genome-wide association analysis of coffee drinking suggests association with CYP1A1/CYP1A2 and NRCAM

Coffee consumption is a model for addictive behavior. We performed a meta-analysis of genome-wide association studies (GWASs) on coffee intake from 8 Caucasian cohorts (N=18 176) and sought replication of our top findings in a further 7929 individuals. We also performed a gene expression analysis treating different cell lines with caffeine. Genome-wide significant association was observed for two single-nucleotide polymorphisms (SNPs) in the 15q24 region. The two SNPs rs2470893 and rs2472297 (P-values=1.6 × 10(-11) and 2.7 × 10(-11)), which were also in strong linkage disequilibrium (r(2)=0.7) with each other, lie in the 23-kb long commonly shared 5' flanking region between CYP1A1 and CYP1A2 genes. CYP1A1 was found to be downregulated in lymphoblastoid cell lines treated with caffeine. CYP1A1 is known to metabolize polycyclic aromatic hydrocarbons, which are important constituents of coffee, whereas CYP1A2 is involved in the primary metabolism of caffeine. Significant evidence of association was also detected at rs382140 (P-value=3.9 × 10(-09)) near NRCAM-a gene implicated in vulnerability to addiction, and at another independent hit rs6495122 (P-value=7.1 × 10(-09))-an SNP associated with blood pressure-in the 15q24 region near the gene ULK3, in the meta-analysis of discovery and replication cohorts. Our results from GWASs and expression analysis also strongly implicate CAB39L in coffee drinking. Pathway analysis of differentially expressed genes revealed significantly enriched ubiquitin proteasome (P-value=2.2 × 10(-05)) and Parkinson's disease pathways (P-value=3.6 × 10(-05)).

De novo CNV analysis implicates specific abnormalities of postsynaptic signalling complexes in the pathogenesis of schizophrenia

A small number of rare, recurrent genomic copy number variants (CNVs) are known to substantially increase susceptibility to schizophrenia. As a consequence of the low fecundity in people with schizophrenia and other neurodevelopmental phenotypes to which these CNVs contribute, CNVs with large effects on risk are likely to be rapidly removed from the population by natural selection. Accordingly, such CNVs must frequently occur as recurrent de novo mutations. In a sample of 662 schizophrenia proband-parent trios, we found that rare de novo CNV mutations were significantly more frequent in cases (5.1% all cases, 5.5% family history negative) compared with 2.2% among 2623 controls, confirming the involvement of de novo CNVs in the pathogenesis of schizophrenia. Eight de novo CNVs occurred at four known schizophrenia loci (3q29, 15q11.2, 15q13.3 and 16p11.2). De novo CNVs of known pathogenic significance in other genomic disorders were also observed, including deletion at the TAR (thrombocytopenia absent radius) region on 1q21.1 and duplication at the WBS (Williams-Beuren syndrome) region at 7q11.23. Multiple de novos spanned genes encoding members of the DLG (discs large) family of membrane-associated guanylate kinases (MAGUKs) that are components of the postsynaptic density (PSD). Two de novos also affected EHMT1, a histone methyl transferase known to directly regulate DLG family members. Using a systems biology approach and merging novel CNV and proteomics data sets, systematic analysis of synaptic protein complexes showed that, compared with control CNVs, case de novos were significantly enriched for the PSD proteome (P=1.72 × 10⁻⁶. This was largely explained by enrichment for members of the N-methyl-D-aspartate receptor (NMDAR) (P=4.24 × 10⁻⁶) and neuronal activity-regulated cytoskeleton-associated protein (ARC) (P=3.78 × 10⁻⁸) postsynaptic signalling complexes. In an analysis of 18 492 subjects (7907 cases and 10 585 controls), case CNVs were enriched for members of the NMDAR complex (P=0.0015) but not ARC (P=0.14). Our data indicate that defects in NMDAR postsynaptic signalling and, possibly, ARC complexes, which are known to be important in synaptic plasticity and cognition, play a significant role in the pathogenesis of schizophrenia.

Copy number variations of chromosome 16p13.1 region associated with schizophrenia

Deletions and reciprocal duplications of the chromosome 16p13.1 region have recently been reported in several cases of autism and mental retardation (MR). As genomic copy number variants found in these two disorders may also associate with schizophrenia, we examined 4345 schizophrenia patients and 35,079 controls from 8 European populations for duplications and deletions at the 16p13.1 locus, using microarray data. We found a threefold excess of duplications and deletions in schizophrenia cases compared with controls, with duplications present in 0.30% of cases versus 0.09% of controls (P=0.007) and deletions in 0.12 % of cases and 0.04% of controls (P>0.05). The region can be divided into three intervals defined by flanking low copy repeats. Duplications spanning intervals I and II showed the most significant (P = 0.00010) association with schizophrenia. The age of onset in duplication and deletion carriers among cases ranged from 12 to 35 years, and the majority were males with a family history of psychiatric disorders. In a single Icelandic family, a duplication spanning intervals I and II was present in two cases of schizophrenia, and individual cases of alcoholism, attention deficit hyperactivity disorder and dyslexia. Candidate genes in the region include NTAN1 and NDE1. We conclude that duplications and perhaps also deletions of chromosome 16p13.1, previously reported to be associated with autism and MR, also confer risk of schizophrenia.

Insights into the genetic architecture of osteoarthritis from stage 1 of the arcOGEN study

Objectives

The genetic aetiology of osteoarthritis has not yet been elucidated. To enable a well-powered genome-wide association study (GWAS) for osteoarthritis, the authors have formed the arcOGEN Consortium, a UK-wide collaborative effort aiming to scan genome-wide over 7500 osteoarthritis cases in a two-stage genome-wide association scan. Here the authors report the findings of the stage 1 interim analysis.

Methods

The authors have performed a genome-wide association scan for knee and hip osteoarthritis in 3177 cases and 4894 population-based controls from the UK. Replication of promising signals was carried out in silico in five further scans (44 449 individuals), and de novo in 14 534 independent samples, all of European descent.

Results

None of the association signals the authors identified reach genome-wide levels of statistical significance, therefore stressing the need for corroboration in sample sets of a larger size. Application of analytical approaches to examine the allelic architecture of disease to the stage 1 genome-wide association scan data suggests that osteoarthritis is a highly polygenic disease with multiple risk variants conferring small effects.

Conclusions

Identifying loci conferring susceptibility to osteoarthritis will require large-scale sample sizes and well-defined phenotypes to minimise heterogeneity.

Screen for CACNA1A and ATP1A2 mutations in sporadic hemiplegic migraine patients

The aim of this study was to investigate the involvement of the CACNA1A and ATP1A2 gene in a population-based sample of sporadic hemiplegic migraine (SHM). Patients with SHM (n = 105) were identified in a nationwide search in the Danish population. We sequenced all exons and promoter regions of the CACNA1A and ATP1A2 genes in 100 patients with SHM to search for possible SHM mutations. Novel DNA variants were discovered in eight SHM patients, four in exons of the CACNA1A gene and four in exons of the ATP1A2 gene. Six of the variants were considered non-pathogenic. The causal role of the two remaining DNA variants is unknown until functional studies have been made or independent genetic evidence is discovered. Only very few DNA variants were identified in 100 SHM patients, and regardless of whether the identified variants are causal the CACNA1A and ATP1A2 genes are not major genes in SHM.

CDKN2A mutations and melanoma risk in the Icelandic population

BACKGROUND

Germline CDKN2A mutations have been observed in 20-40% of high risk, melanoma prone families; however, little is known about their prevalence in population based series of melanoma cases and controls.

METHODS

We resequenced the CDKN2A gene, including the p14ARF variant and promoter regions, in approximately 703 registry ascertained melanoma cases and 691 population based controls from Iceland, a country in which the incidence of melanoma has increased rapidly.

RESULTS

We identified a novel germline variant, G89D, that was strongly associated with increased melanoma risk and appeared to be an Icelandic founder mutation. The G89D variant was present in about 2% of Icelandic invasive cutaneous malignant melanoma cases. Relatives of affected G89D carriers were at significantly increased risk of melanoma, head and neck cancers, and pancreatic carcinoma compared to relatives of other melanoma patients. Nineteen other germline variants were identified, but none conferred an unequivocal risk of melanoma.

CONCLUSIONS

This population based study of Icelandic melanoma cases and controls showed a frequency of disease related CDKN2A mutant alleles ranging from 0.7% to 1.0%, thus expanding our knowledge about the frequency of CDKN2A mutations in different populations. In contrast to North America and Australia where a broad spectrum of mutations was observed at a similar frequency, in Iceland, functional CDKN2A mutations consist of only one or two different variants. Additional genetic and/or environmental factors are likely critical for explaining the high incidence rates for melanoma in Iceland. This study adds to the geographic regions for which population based estimates of CDKN2A mutation frequencies are available.

The genetic spectrum of a population-based sample of familial hemiplegic migraine

Familial hemiplegic migraine (FHM) is a rare subtype of migraine with aura and transient hemiplegia. FHM mutations are known in three genes, the CACNA1A (FHM1) gene, the ATP1A2 (FHM2) and the SCN1A (FHM3) gene and seem to have an autosomal-dominant mode of inheritance. The aim of this study was to search for FHM mutations in FHM families identified through a screen of the Danish population of 5.2 million people. FHM patients were diagnosed according to the International Classification of Headache Disorders and all FHM patients had a physical and neurological examination by a physician. A total of 147 FHM patients from 44 different families were identified; 43 FHM families participated in this study. Linkage analysis of these families shows clear linkage to the FHM locus (FHM1) on chromosome 19, supportive linkage to the FHM2 locus whereas no linkage was found to the FHM3 locus. Furthermore, we sequenced all exons and promoter regions of the CACNA1A and ATP1A2 genes and screened for the Q1489K mutation in the SCN1A gene. CACNA1A gene mutations were identified in three of the FHM families, two known FHM mutations, R583Q and T666M and one novel C1369Y mutation. Three FHM families were identified with novel mutations in the ATP1A2 gene; a family with a V138A mutation, a family with a R202Q mutation and a family with a R763C mutation. None of the Danish FHM families have the Q1489K mutation in the SCN1A gene. Our study shows that only 14% (6/42) of FHM families in the general Danish population have exonic FHM mutations in the CACNA1A or ATP1A2 gene. The families we identified with FHM mutations in the CACNA1A and ATP1A2 genes were extended, multiple affected families whereas the remaining FHM families were smaller. The existence of many small families in the Danish FHM cohort may reflect less bias in FHM family ascertainment and/or more locus heterogeneity than described previously.

Contribution of ADAM33 polymorphisms to the population risk of asthma

BACKGROUND

ADAM 33 is the first gene identified as a candidate for asthma by positional cloning techniques, with association studies reaching impressive statistical significance. It has a postulated role in myogenesis, airway modelling, and signalling via protein shedding. Concerns over the methodology of the initial study have led to several attempts at replication, with inconsistent results.

METHOD

To clarify the role of ADAM33 in determining the risk of asthma in the general population, new transmission disequilibrium and case-control studies were undertaken followed by a meta-analysis of all existing data.

RESULTS

Studies in Icelandic and UK populations revealed no association when taken in isolation. The meta-analysis, however, showed that the F+1 and ST+7 variants were significantly associated with asthma in both types of study.

CONCLUSIONS

The additional risk imparted by this variation would account for 50,000 excess asthma cases in the UK alone. This study also demonstrates the size of study required to investigate such hypotheses adequately.

Association between the gene encoding 5-lipoxygenase-activating protein and stroke replicated in a Scottish population

Cardiovascular diseases, including myocardial infarction (MI) and stroke, most often occur on the background of atherosclerosis, a condition attributed to the interactions between multiple genetic and environmental risk factors. We recently reported a linkage and association study of MI and stroke that yielded a genetic variant, HapA, in the gene encoding 5-lipoxygenase-activating protein (ALOX5AP), that associates with both diseases in Iceland. We also described another ALOX5AP variant, HapB, that associates with MI in England. To further assess the contribution of the ALOX5AP variants to cardiovascular diseases in a population outside Iceland, we genotyped seven single-nucleotide polymorphisms that define both HapA and HapB from 450 patients with ischemic stroke and 710 controls from Aberdeenshire, Scotland. The Icelandic at-risk haplotype, HapA, had significantly greater frequency in Scottish patients than in controls. The carrier frequency in patients and controls was 33.4% and 26.4%, respectively, which resulted in a relative risk of 1.36, under the assumption of a multiplicative model (P=.007). We did not detect association between HapB and ischemic stroke in the Scottish cohort. However, we observed that HapB was overrepresented in male patients. This replication of haplotype association with stroke in a population outside Iceland further supports a role for ALOX5AP in cardiovascular diseases.

Identification of a novel neuregulin 1 at-risk haplotype in Han schizophrenia Chinese patients, but no association with the Icelandic/Scottish risk haplotype

To determine if neuregulin 1 (NRG1) is associated with schizophrenia in Asian populations, we investigated a Han Chinese population using both a family trio design and a case-control design. A total of 25 microsatellite markers and single nucleotide polymorphisms (SNPs) were genotyped spanning the 1.1 Mb NRG1 gene including markers of a seven-marker haplotype at the 5' end of the gene found to be in excess in Icelandic and Scottish schizophrenia patients. The alleles of the individual markers forming the seven marker at-risk haplotype are not likely to be causative as they are not in excess in patients in the Chinese population studied here. However using unrelated patients, we find a novel haplotype (HAP(China 1)), immediately upstream of the Icelandic haplotype, in excess in patients (11.9% in patients vs 4.2% in controls; P=0.0000065, risk ratio (rr) 3.1), which was not significant when parental controls were used. Another haplotype (HAP(China 2)) overlapping the Icelandic risk haplotype was found in excess in the Chinese (8.5% of patients vs 4.0% of unrelated controls; P=0.003, rr 2.2) and was also significant using parental controls only (P=0.0047, rr 2.1). A four-marker haplotype at the 3' end of the NRG1 gene, HAP(China 3), was found at a frequency of 23.8% in patients and 13.7% in nontransmitted parental haplotypes (P=0.000042, rr=2.0) but was not significant in the case-control comparison. We conclude that different haplotypes within the boundaries of the NRG1 gene may be associated with schizophrenia in the Han Chinese.

Genome-wide TDT analysis in a localized population with a high prevalence of multiple sclerosis indicates the importance of a region on chromosome 14q

Epidemiological studies show that susceptibility to multiple sclerosis (MS) has a strong genetic component, but apart from the HLA gene complex, additional genetic factors have proven difficult to map in the general population. Thus, localized populations, where MS patients are assumed to be more closely related, may offer a better opportunity to identify shared chromosomal regions. We have performed a genome-wide scan with 834 microsatellite markers in a data set consisting of 54 MS patients and 114 healthy family members. A group of families from a small village were possible to track back to common ancestors living in the 17th century. We used single marker- and haplotype-based transmission disequilibrium test (TDT) analysis and nonparametric linkage analysis to analyze genotyping data. Regions on chromosomes 2q23-31, 6p24-21, 6q25-27, 14q24-32, 16p13-12 and 17q12-24 were found to be in transmission disequilibrium with MS. Strong transmission disequilibrium was detected in 14q24-32, where several dimarker haplotypes were in transmission disequilibrium in affected individuals. Several regions showed modest evidence for linkage, but linkage and TDT were both clearly positive only for 17q12-24. All patients and controls were also typed for HLA class II genes; however, no evidence for a gene-gene interaction was observed.

Psoriasis patients who are homozygous for the HLA-Cw*0602 allele have a 2.5-fold increased risk of developing psoriasis compared with Cw6 heterozygotes

BACKGROUND

Psoriasis is strongly associated with certain human leucocyte-associated antigens, especially HLA-Cw*0602. Patients who are HLA-Cw*0602 positive have been reported to have more active disease and a younger age at disease onset than HLA-Cw6-negative patients.

OBJECTIVES

To ascertain whether there are differences in the clinical features and relative risk between HLA-Cw*0602 homozygous and heterozygous psoriasis patients.

METHODS

One thousand and six patients with chronic plaque psoriasis were evaluated clinically and HLA-C typed. In addition, 512 unrelated controls were typed for HLA-C.

RESULTS

Of the patients 646 (64.2%) were HLA-Cw*0602 positive, and 68 (6.8%) were homozygous for this allele. Heterozygosity was associated with a relative risk of developing psoriasis of 8.9 compared with 23.1 for the Cw6 homozygous patients. The homozygous patients also had an earlier disease onset (mean 15.0 vs. 17.8 years, P = 0.04). However, the Cw6 homozygotes did not differ from the heterozygotes with respect to disease severity, guttate onset, distribution of plaques, nail changes or any other clinical parameter recorded.

CONCLUSIONS

Homozygosity for the gene in the major histocompatibility complex region has a major additive impact on the risk of developing psoriasis and predisposes to an earlier disease onset, but does not have any marked influence on the phenotype or the severity of the disease.

Genetic factors contribute to the risk of developing endometriosis

BACKGROUND

Endometriosis is known to cluster within nuclear families. The extent of familial clustering can be evaluated in Iceland with its large population-based genealogical database.

METHODS AND RESULTS

Applying several measures of familiality we demonstrated that 750 women with endometriosis were significantly more interrelated than matched control groups. The risk ratio for sisters was 5.20 (P < 0.001) and for cousins 1.56 (P = 0.003). The average kinship coefficient for the patients was significantly higher than that calculated for 1000 sets of 750 matched controls (P < 0.001) and this remained significant when contribution from first-degree relatives was excluded (P < 0.05). The minimum number of ancestors required to account for the group of patients was compared with the minimum number of ancestors required to account for the control groups at different time points in the past. The minimum number of founders for the group of patients was significantly smaller than for the control groups. Affected cousin pairs were as likely to be paternally connected as maternally connected.

CONCLUSIONS

This is the first population-based study using an extensive genealogy database to examine the genetic contribution to endometriosis. A genetic factor is present, with a raised risk in close and more distant relatives, and a definite kinship factor with maternal and paternal inheritance contributing.

Allelic frequencies and patterns of single-nucleotide polymorphisms in candidate genes for asthma and atopy in Iceland

Numerous asthma and atopy loci have been reported in studies demonstrating associations of the asthma-related phenotypes atopy, elevated IgE levels, and bronchial hyperresponsiveness with alleles of microsatellite markers and single-nucleotide polymorphisms (SNPs) within specific cytokine/chemokine and IgE-regulating genes. Although the studies reporting these observations are compelling, most of them lack statistical power. We assessed the nature, pattern, and frequency of SNPs in 24 candidate genes in Iceland and looked for associations with asthma and atopy. We identified 42 SNPs with an average minor allele frequency of 20.3% (asthma) and 20.7% (control). Twenty SNPs (48%) were within coding sequences and 90% of those led to a predicted change in protein sequence. No differences were detected in the allelic frequencies of SNPs in any of these candidate genes between control subjects and the patients with atopic asthma. Moreover, linkage analysis that included 269 patients with atopic asthma uncovered no evidence of linkage to markers associated with these genes. We conclude that this study has failed to produce evidence in support of the notion that variations within these 24 candidate atopy and asthma genes significantly influence the expression of the atopic asthmatic phenotype or contribute to the susceptibility of atopic asthma.

Association between IL-1beta/TNF-alpha-induced glucocorticoid-sensitive changes in multiple gene expression and altered responsiveness in airway smooth muscle

The pleiotropic cytokines interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha have been implicated in the pathophysiology of asthma. To elucidate the role of these cytokines in the pro-asthmatic state, the effects of IL-1beta and TNF-alpha on airway smooth muscle (ASM) responsiveness and ASM expression of multiple genes, assessed by high-density oligonucleotide array analysis, were examined in the absence and presence of the glucocorticoid dexamethasone (DEX). Administration of IL-1beta/TNF-alpha increased ASM contractility to acetylcholine and impaired ASM relaxation to isoproterenol. These pro-asthmatic- like changes in ASM responsiveness were associated with IL-1beta/ TNF-alpha-induced mRNA expression of a host of proinflammatory genes that regulate transcription, cytokines and chemokines, cellular adhesion molecules, and various signal transduction molecules that regulate ASM responsiveness. In the presence of DEX, the changes induced in ASM responsiveness were abrogated, and most of the IL-1beta/TNF-alpha-mediated changes in proinflammatory gene expression were repressed, although mRNA expression of a small number of genes was enhanced by DEX. Collectively, the observations support the concept that, together with its role as a regulator of airway tone, in response to IL-1beta/TNF-alpha, the ASM expresses a host of glucocorticoid-sensitive genes that contribute to the altered structure and function of the airways in the pro-asthmatic state. We speculate that glucocorticoid-sensitive, cytokine-induced pathways involved in ASM cell signaling represent important targets for new therapeutic interventions.

Endometriosis is not associated with or linked to the GALT gene

OBJECTIVE

To investigate a possible association between the carrier frequency of the N314D mutation in the galactose-1-phosphate uridyl transferase (GALT) gene and endometriosis and linkage to the short arm of chromosome 9, where the GALT gene resides.

DESIGN

Association and linkage study.

SETTING

Population material collected for case and family studies in endometriosis.

PATIENT(S)

Women diagnosed with endometriosis by laparotomy or laparoscopy.

INTERVENTION(S)

Association with the GALT gene investigated by genotyping 85 affected women and 213 unrelated control women and a scan for linkage to chromosome 9 in 205 women from 64 families with endometriosis.

MAIN OUTCOME MEASURE(S)

Multipoint parametric lod scores and frequency of alleles.

RESULT(S)

There was no significant difference in allele frequency for the N314D polymorphism in patients compared with control subjects. No evidence for linkage was found to chromosome 9p, where the GALT gene resides.

CONCLUSION(S)

The experiments reported herein provide no evidence supporting involvement of the GALT locus in the development of endometriosis.

The role of linkage studies for common diseases

Linkage analysis when applied to common diseases has had limited success in mapping the genes contributing to them. We present a genealogic approach applied to the relatively isolated population of Iceland. We use an affecteds-only, allele-sharing method--which does not specify any particular inheritance model--implemented in the new statistical program, Allegro, which calculates lod scores based on multipoint calculations. We describe how this approach has helped us to map a gene contributing to the common late-onset form of Parkinson's disease to statistical significance.

The genealogic approach to human genetics of disease

The goal of modern human genetics is to correlate genes with disease or, more specifically, relate genetic variation to phenotypic variation. Although this correlation is usually straightforward in the Mendelian disorders, it has proved to be much more difficult to find in the common diseases because they appear to be more complex, likely involving an interplay among multiple genes and between genes and the environment. Although the strategy of linkage mapping of families was very successful when it was applied to the rare monogenic diseases, few common diseases have been mapped to statistical significance. Many investigators are now abandoning linkage analysis altogether and are moving to a candidate gene case-control strategy. In this article, we describe a genealogic approach to mapping human disease genes and provide three examples of how we have used it to map common diseases to statistical significance. We focus on a simple population with little historic migration and use a computerized genealogy database to increase the number of patients who can be compared with other affected relatives through high-density microsatellite genotyping. The genealogy helps determine which phenotypic classification is inherited and therefore possible to map. It may represent a more efficient strategy than candidate gene case-control studies for determination of what alleles or haplotypes are shared by patients in a population. We suggest that the genetics community not give up on linkage analysis, nor should it assume that the common diseases are too complex to map.

Familial aggregation of Parkinson's disease in Iceland

BACKGROUND

The role of genetics in early-onset Parkinson's disease has been established, but whether there is a genetic contribution to the more common, late-onset form remains uncertain.

METHODS

We reviewed the medical records and confirmed the diagnosis of Parkinson's disease in 772 living and deceased patients in whom the disease had been diagnosed during the previous 50 years in Iceland. With the use of an extensive computerized data base containing genealogic information on 610,920 people in Iceland during the past 11 centuries, several analyses were conducted to determine whether the patients were more related to each other than random members of the population (control subjects).

RESULTS

Patients with Parkinson's disease, including a subgroup of 560 patients with late-onset disease (onset at >50 years of age), were significantly more related to each other than were subjects in matched groups of controls, and this relatedness extended beyond the nuclear family. The risk ratio for Parkinson's disease was 6.7 (95 percent confidence interval, 4.3 to 9.6) for siblings, 3.2 (95 percent confidence interval, 1.2 to 7.8) for offspring, and 2.7 (95 percent confidence interval, 1.6 to 3.9) for nephews and nieces of patients with late-onset Parkinson's disease.

CONCLUSIONS

Late-onset Parkinson's disease has a genetic component as well as an environmental component.

Long PCR detection of the C4A null allele in B8-C4AQ0-C4B1-DR3

The genes coding for the two components of complement 4 (C4), C4A and C4B, are located within the major histocompatibility complex (MHC) on the short arm of chromosome 6. Several studies have shown that deficiency of C4A is associated with systemic lupus erythematosus (SLE), rheumatoid arthritis and scleroderma. A large deletion covering most of the C4A gene and the 21-hydroxylase-A (21-OHA) pseudogene found on the extended haplotype B8-C4AQ0-C4B1-DR3 is estimated to account for approximately two-thirds of C4A deficiency in Caucasian SLE patients. Detection of this C4A null allele has been technically difficult due to the high degree of homology between C4A and C4B, with protein analysis and restriction fragment length polymorphism (RFLP) analysis using Southern blotting being the only approaches available. In this study, a long PCR strategy was used to rapidly genotype for the C4A deletion through specific primer design. The methodology makes use of the unique sequence of the G11 gene upstream of C4A and the sequence of a 6.4 kb retrotransposon, the human endogenous retrovirus HERV-K(C4), which is present in intron 9 of C4A but absent in the case of the deletion.

The mutation rate in the human mtDNA control region

The mutation rate of the mitochondrial control region has been widely used to calibrate human population history. However, estimates of the mutation rate in this region have spanned two orders of magnitude. To readdress this rate, we sequenced the mtDNA control region in 272 individuals, who were related by a total of 705 mtDNA transmission events, from 26 large Icelandic pedigrees. Three base substitutions were observed, and the mutation rate across the two hypervariable regions was estimated to be 3/705 =.0043 per generation (95% confidence interval [CI].00088-.013), or.32/site/1 million years (95% CI.065-.97). This study is substantially larger than others published, which have directly assessed mtDNA mutation rates on the basis of pedigrees, and the estimated mutation rate is intermediate among those derived from pedigree-based studies. Our estimated rate remains higher than those based on phylogenetic comparisons. We discuss possible reasons for-and consequences of-this discrepancy. The present study also provides information on rates of insertion/deletion mutations, rates of heteroplasmy, and the reliability of maternal links in the Icelandic genealogy database.

Population genomics: laying the groundwork for genetic disease modeling and targeting

The family has proven the most appropriate unit with which to study Mendelian diseases. There are, however, certain limitations on the use of the family as a fundamental unit in the study of common diseases, most of which are complex genetic diseases. The groups that are most likely to yield the genetics of complex diseases are isolated populations with strong founder effects. Therefore, access to such populations is proving to be a precious resource in the work on the genetics of common diseases. The Icelandic population is an excellent population for the study of the genetics of common diseases; it is genetically homogeneous, with founder effects for many traits, and the genealogy of the entire nation is well documented back to the founding days. Furthermore, the nature of the Icelandic national health care system facilitates the assignment of phenotypes in the search for disease genes. Decode Genetics has begun to study of the genetics of 20 of the most common diseases in the Western parts of the world. The company has placed the groundwork for the construction of an encrypted database with information on the health care of the entire nation, genealogy of the entire nation, genotyping information with high density of markers on a large part of the nation (including typing for known disease genes), and resource use in the Icelandic health care system. The plan is to build the database with approval of participating individuals as well as Icelandic government and health care officials. The database will be used to model health care as viewed in the context of genetic predisposition to the development of disease. The database will also be used in the search for drug targets in complex diseases and in the solution of pharmacogenomic problems. Basing the company in Iceland directly benefits the population in terms of employment and return on investment as well as providing the health care system with an information resource which may be used in preventive medicine and in the optimization of health care in Iceland.

Expression of the oligodendrocyte-myelin glycoprotein by neurons in the mouse central nervous system

The oligodendrocyte-myelin glycoprotein (OMgp) is a 110-kDa glycosylphosphatidylinositol-linked protein that was initially identified as a myelin-specific protein but whose precise function remains unknown. In this study, immunohistochemistry, western blots, in situ hybridization, and northern blots were used to determine the distribution of OMgp in the mouse brain. OMgp is present in a concentration detectable on western blots in the brains of newborn mice, and its concentration gradually increases until day 24 of life. OMgp mRNA is also present in amounts detectable on northern blots in the brains of newborn mice, and its concentration gradually increases until day 21 of life, after which the concentration diminishes a little. Most of the OMgp in the mouse brain appears to be expressed in diverse groups of neurons, but it is particularly prominent in large projection neurons such as the pyramidal cells of the hippocampus, the Purkinje cells of the cerebellum, motoneurons in the brainstem, and anterior horn cells of the spinal cord. However, OMgp is not confined to these cells and is expressed in cells in the white matter as well. The OMgp gene is placed within an intron of the neurofibromatosis type I gene and on the opposite strand. This organization raises the possibility that there may be a relationship between the functions of the products of the two genes. In support of this possibility, we show that within the mouse CNS OMgp and neurofibromin are expressed in the same cell types.

Beta-trace gene expression is regulated by a core promoter and a distal thyroid hormone response element

We isolated and characterized the human beta-Trace protein (betaTP) gene promoter. betaTP, also known as prostaglandin D2 synthase, is a lipocalin secreted from the choroid plexus and meninges into cerebrospinal fluid. Basal transcription of the betaTP gene is directed from a core promoter found within the first 325 bases of the 5'-flanking sequence. The betaTP gene promoter is responsive to thyroid hormone (3,3',5-triiodothyronine, T3) and efficiently repressed by unliganded human thyroid hormone receptor beta (TRbeta). Functional analysis of the betaTP promoter in TE671 cells revealed that responsiveness to T3 occurs in sequences 2.5 kilobase pairs 5' of the start site. Within the hormone-responsive region we identified a thyroid hormone response element (TRE) located from -2576 to -2562 base pairs relative to the transcription start site. The betaTP TRE is composed of two directly repeated consensus half-sites separated by a 3-base pair space (DR3). The betaTP TRE forms specific complexes with TRbeta. We have shown that a gene active in the choroid plexus and meninges is responsive to T3. T3 may play a role in the regulated transport of substances into the cerebrospinal fluid and ultimately the brain.

Molecular evolution of tau protein: implications for Alzheimer's disease

The brains of patients with Alzheimer's disease contain deposits of hyperphosphorylated tau proteins that have polymerized into insoluble fibrils. These deposits, in neurofibrillary tangles and dystrophic neurites, correlate with loss of cells and synapses, and consequently with dementia. Neurofibrillary pathology occurs in humans, as well as certain ungulates, including goats, sheep, and cows, but not in nonhuman primates. We hypothesize that the differences among species in the propensity to develop neurofibrillary pathology may be attributable to variations in the amino acid sequence of tau proteins. To investigate this hypothesis, we sequenced tau-encoding mRNA transcripts from the brains of rhesus monkey and domesticated goat and compared them with the known sequences of tau mRNAs from humans. The major difference we observed was that some tau mRNAs from rhesus monkey neocortex contain exon 8, whereas this exon has not been found in cortical tau from human or goat. Cows express very low levels of exon 8, and they tend to develop sparse neurofibrillary pathology with aging. We also found a transcribed tau-related pseudogene in rhesus monkey, which may be present in humans. We propose that differences in the expression of tau and tau-related protein sequences may underlie the predilection of human but not monkey brains to develop neurofibrillary degeneration.

Interferon-gamma-induced oligodendrocyte cell death: implications for the pathogenesis of multiple sclerosis

BACKGROUND

The histopathology of multiple sclerosis (MS) is characterized by a loss of myelin and oligodendrocytes, relative preservation of axons, and a modest inflammatory response. The reasons for this selective oligodendrocyte death and demyelination are unknown.

MATERIALS AND METHODS

In light of the T lymphocyte and macrophage infiltrates in MS lesions and the numerous cytokines these cells secrete, the direct influence of cytokines on survival of cultured oligodendrocytes and sensory neurons was investigated. Expression of cytokines in vivo was determined by immunolabeling cryostat sections of snap-frozen tissue containing chronic active lesions from four different patients. The samples were also analyzed for the presence of apoptotic nuclei by in situ labeling of 3'-OH ends of degraded nuclear DNA.

RESULTS

The results showed: (i) interferon-gamma (IFN gamma) to be a potent inducer of apoptosis among oligodendrocytes in vitro and that this effect can be reversed by leukemia inhibitory factor (LIF); (ii) IFN gamma has a minimal effect on the survival of cultured neurons; (iii) IFN gamma at the margins of active MS plaques but not in unaffected white matter; (iv) evidence for apoptosis of oligodendrocytes at the advancing margins of chronic active MS plaques.

CONCLUSIONS

Injury to a substantial number of oligodendrocytes in MS is the results of programmed cell death rather than necrotic cell death mechanisms. We postulate that IFN gamma plays a role in the pathogenesis of MS by activating apoptosis in oligodendrocytes.

Nitric oxide synthase and guanylate cyclase levels in canine basilar artery after subarachnoid hemorrhage

Endothelium-dependent vasodilation may be impaired during cerebral vasospasm following subarachnoid hemorrhage. Under normal circumstances nitric oxide (NO) released by endothelial cells induces relaxation of smooth muscle by activating the soluble form of guanylate cyclase within muscle cells. In this study the levels of both endothelial NO synthase, the enzyme that produces NO, and soluble guanylate cyclase were determined in canine basilar arteries in a double-hemorrhage model using Western blot immunoassays. Thirty dogs were assigned to three groups: Group D0, control; Group D2, dogs sacrificed 2 days after cisternal injection of blood; and Group D7, dogs given double cisternal injections of blood and sacrificed 7 days after the first injection. Constriction of the basilar artery was confirmed by arterial angiography. Portions of the affected arteries or the corresponding region in control animals were solubilized for sodium dodecylsulfate-polyacrylamide gel electrophoresis and Western blotting. A specific monoclonal antibody against endothelial NO synthase was used. The extract from basilar arteries showed two bands on the blots: 135 kD, characteristic of endothelial NO synthase, and 120 kD, which may be a degradation product of the enzyme. The densitometer values of the bands were presented as percentages of D0 control values. Although the total signal in the D7 group was less than that of the D0 control group (D2, 97% +/- 22%; D7, 78% +/- 40%), it was not statistically significant. The proportion of the 135-kD form decreased between Groups D0 and D7, but the difference was not significant. A single major band corresponding to the alpha-subunit of soluble guanylate cyclase was seen at 70 kD in the basilar artery extracts. The signals of D2 and D7 samples were 69% +/- 40% and 25% +/- 18%, respectively. There was a significant difference between D7 and D0 (p < 0.001). The reduced expression of soluble guanylate cyclase may be related to the impairment of endothelium-dependent vasodilation in vasospasm.

Focal brain injury and upregulation of a developmentally regulated extracellular matrix protein

Tenascin is an extracellular matrix glycoprotein expressed during both normal development and neoplastic growth in both neural and nonneural tissues. During development of the central nervous system (CNS), tenascin is synthesized by glial cells, in particular by immature astrocytes, and is concentrated in transient boundaries around emerging groups of functionally distinct neurons. In the mature CNS, only low levels of the glycoprotein can be detected. The present study demonstrates that following trauma to the adult human cerebral cortex, discrete populations of reactive astrocytes upregulate their expression of tenascin and dramatically increase their transcription of the tenascin gene. The enhanced expression of tenascin may be involved in CNS wound healing, and may also affect neurite growth within and around a brain lesion.

A role for the acetylcholine receptor-inducing protein ARIA in oligodendrocyte development

ARIA acetylcholine receptor-inducing activity protein, is a member of a family of ligands that includes the Neu differentiation factor, heregulin, and glial growth factor. These ligands all act through one or more receptor tyrosine kinases of approximately 185 kDa. In some conditions these ligands promote proliferation, whereas in others they induce differentiation. ARIA was originally isolated from chick brain on the basis of its ability to induce synthesis of nicotinic acetylcholine receptors in skeletal muscle. In this paper we show that ARIA is expressed in the subventricular zone of the rat brain and that it enhances the development of oligodendrocytes from bipotential (O2A) glial progenitor cells. We have also found that ARIA induces tyrosine phosphorylation of a 185-kDa protein in O2A progenitor cells. ARIA does not increase bromodeoxyuridine incorporation by oligodendrocytes but is mitogenic when added to Schwann cells in vitro. Thus, ARIA accelerates the formation of oligodendrocytes in vitro and is expressed where it could exercise the same influence in vivo.