Monozygotic (MZ) twins are partially concordant for most complex diseases, including autoimmune disorders. Whereas phenotypic concordance can be used to study heritability, discordance suggests the role of non-genetic factors. In autoimmune diseases, environmentally driven epigenetic changes are thought to contribute to their etiology. Here we report the first high-throughput and candidate sequence analyses of DNA methylation to investigate discordance for autoimmune disease in twins. We used a cohort of MZ twins discordant for three diseases whose clinical signs often overlap: systemic lupus erythematosus (SLE), rheumatoid arthritis, and dermatomyositis. Only MZ twins discordant for SLE featured widespread changes in the DNA methylation status of a significant number of genes. Gene ontology analysis revealed enrichment in categories associated with immune function. Individual analysis confirmed the existence of DNA methylation and expression changes in genes relevant to SLE pathogenesis. These changes occurred in parallel with a global decrease in the 5-methylcytosine content that was concomitantly accompanied with changes in DNA methylation and expression levels of ribosomal RNA genes, although no changes in repetitive sequences were found. Our findings not only identify potentially relevant DNA methylation markers for the clinical characterization of SLE patients but also support the notion that epigenetic changes may be critical in the clinical manifestations of autoimmune disease.[Supplemental material is available online at http://www.genome.org. The sequence data from this study have been submitted to the NCBI Gene Expression Omnibus (http://www.ncbi.nlm.nih.gov/geo) under accession no. GSE19033.]Human monozygotic (MZ) twins exhibit variable degrees of concordance for complex diseases, such as cancer, cardiovascular diseases, or autoimmune disorders. Whereas concordance rates close to 100% in identical twins apply to coinheritance of mutant genes that are dominant and highly penetrant, most diseases or traits show a concordance in identical twins in the broad range of 5%-75% (Nance 1978). Most of the twin-based studies have focused on the concordance between siblings that has led to the identification of traitspecific genes (Hrubec and Robinette 1984), while less attention has been paid to the degree of discordance, which suggests the participation of factors other than pure genetic changes. Recently, interest has shifted toward exploring the molecular mechanisms involved in determining phenotypic differences. The increasing recognition of the influence of epigenetics in phenotypic outcomes continues to open up new lines of research involving twin studies. DNA methylation and histone modifications, the major sources of epigenetic information, regulate gene expression levels and provide an alternative mechanism for modulating gene function to those arising from genetic changes (Esteller 2008). Interestingly, epigenetic changes are

Objective. In polymyositis and dermatomyositis (DM), identified autoantibodies occur in <50% of adult patients and in a smaller proportion of children. This study was undertaken as part of a larger effort to define novel autoantibodies that assist in the clinical evaluation of myositis.Methods. Sera from children and adults satisfying criteria for idiopathic inflammatory myopathies and from patients with other connective tissue diseases (CTDs), patients with noninflammatory myopathies, and healthy individuals were tested for autoantibodies by immunoprecipitation (IP). A previously unrecognized autoantibody that immunoprecipitated a 155-kd protein along with a weaker 140-kd protein was seen. When the presence of this anti-p155 autoantibody in test sera was suggested based on IP results, it was confirmed by immunoblotting of immunoprecipitates.Results. Sera from 51 of 244 myositis patients (21%), including 30 with juvenile DM (29%), 5 with juvenile CTD-associated myositis (33%), 8 with adult DM (21%), 6 with cancer-associated DM (75%), and 2 with adult CTD-associated myositis (15%), were found to have anti-p155 autoantibody. One of 49 patients with lupus, and none of 89 others without myositis, had anti-p155. Caucasian patients with anti-p155 had a unique HLA risk factor, DQA1*0301 (odds ratio 5.4, corrected P ‫؍‬ 0.004). In adults with anti-p155, of several clinical features assessed only the frequency of V-sign rash was increased, but patients with this antibody were clinically distinct from those with autoantibodies to aminoacyl-transfer RNA synthetases.Conclusion. A newly recognized autoantibody, antip155, is associated with DM and cancer-associated DM, and is one of the most common autoantibodies in this condition, occurring as frequently in children as in adults. The clinical features and immunogenetics associated with anti-p155 differ from those associated with antisynthetases.

Structural variations are among the most frequent interindividual genetic differences in the human genome. The frequency and distribution of de novo somatic structural variants in normal cells is, however, poorly explored. Using age-stratified cohorts of 318 monozygotic (MZ) twins and 296 single-born subjects, we describe age-related accumulation of copy-number variation in the nuclear genomes in vivo and frequency changes for both megabase- and kilobase-range variants. Megabase-range aberrations were found in 3.4% (9 of 264) of subjects ≥60 years old; these subjects included 78 MZ twin pairs and 108 single-born individuals. No such findings were observed in 81 MZ pairs or 180 single-born subjects who were ≤55 years old. Recurrent region- and gene-specific mutations, mostly deletions, were observed. Longitudinal analyses of 43 subjects whose data were collected 7-19 years apart suggest considerable variation in the rate of accumulation of clones carrying structural changes. Furthermore, the longitudinal analysis of individuals with structural aberrations suggests that there is a natural self-removal of aberrant cell clones from peripheral blood. In three healthy subjects, we detected somatic aberrations characteristic of patients with myelodysplastic syndrome. The recurrent rearrangements uncovered here are candidates for common age-related defects in human blood cells. We anticipate that extension of these results will allow determination of the genetic age of different somatic-cell lineages and estimation of possible individual differences between genetic and chronological age. Our work might also help to explain the cause of an age-related reduction in the number of cell clones in the blood; such a reduction is one of the hallmarks of immunosenescence.

The idiopathic inflammatory myopathies (IIM) are a heterogeneous group of rare autoimmune diseases characterized by muscle weakness and extramuscular manifestations such as skin rashes and interstitial lung disease. We genotyped 2,566 IIM cases of Caucasian descent using the Immunochip; a custom array covering 186 established autoimmune susceptibility loci. The cohort was predominantly comprised of dermatomyositis (DM, n=879), juvenile dermatomyositis (JDM, n=481), polymyositis (PM, n=931) and inclusion body myositis (IBM, n=252) patients collected from 14 countries through the Myositis Genetics Consortium. The human leukocyte antigen (HLA) and PTPN22 regions reached genome-wide significance (p<5×10−8). Nine regions were associated at a significance level of p<2.25×10−5, including UBE2L3, CD28 and TRAF6, with evidence of independent effects within STAT4. Analysis of clinical subgroups revealed distinct differences between PM, and DM and JDM. PTPN22 was associated at genome-wide significance with PM, but not DM and JDM, suggesting this effect is driven by PM. Additional suggestive associations including IL18R1 and RGS1 in PM and GSDMB in DM were identified. HLA imputation confirmed that alleles HLA-DRB1*03:01 and HLA-B*08:01 of the 8.1 ancestral haplotype (8.1AH) are most strongly associated with IIM, and provides evidence that amino acids within the HLA, such as HLA-DQB1 position 57 in DM, may explain part of the risk in this locus. Associations with alleles outside the 8.1AH reveal differences between PM, DM, and JDM. This work represents the largest IIM genetic study to date, reveals new insights into the genetic architecture of these rare diseases and suggests different predominating pathophysiology in different clinical subgroups.

We describe the clinical features of 28 patients with juvenile dermatomyositis (JDM) and 1 patient with adult-onset dermatomyositis (DM), all of whom developed lipodystrophy (LD) that could be categorized into 1 of 3 phenotypes, generalized, partial, or focal, based on the pattern of fat loss distribution. LD onset was often delayed, beginning a median of 4.6 years after diagnosis of DM. Calcinosis, muscle atrophy, joint contractures, and facial rash were DM disease features found to be associated with LD. Panniculitis was associated with focal lipoatrophy while the anti-p155 autoantibody, a newly described myositis-associated autoantibody, was more associated with generalized LD. Specific LD features such as acanthosis nigricans, hirsutism, fat redistribution, and steatosis/nonalcoholic steatohepatitis were frequent in patients with LD, in a gradient of frequency and severity among the 3 sub-phenotypes. Metabolic studies frequently revealed insulin resistance and hypertriglyceridemia in patients with generalized and partial LD. Regional fat loss from the thighs, with relative sparing of fat loss from the medial thighs, was more frequent in generalized than in partial LD and absent from DM patients without LD. Cytokine polymorphisms, the C3 nephritic factor, insulin receptor antibodies, and lamin mutations did not appear to play a pathogenic role in the development of LD in our patients. LD is an under-recognized sequela of JDM, and certain DM patients with a severe, prolonged clinical course and a high frequency of calcinosis appear to be at greater risk for the development of this complication. High-risk JDM patients should be screened for Address reprint requests to: Lisa G. Rider, MD, Environmental Autoimmunity Group, National Institute of Environmental Health Sciences, National Institutes of Health, CRC 4-2352, MSC 1301, 10, Center Drive, Bethesda, MD 20892-1301. Fax: 301-451-5588; email: E-mail: riderl@mail.nih.gov. * These authors contributed equally to this work. † Contributors to this study are listed in the appendix. NIH Public AccessAuthor Manuscript Medicine (Baltimore) NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript metabolic abnormalities, which are common in generalized and partial LD and result in much of the LD-associated morbidity. Further study is warranted to investigate the pathogenesis of acquired LD in patients with DM.