Skeletal muscles of untreated children with juvenile dermatomyositis

Background :To evaluate the impact of the duration of chronic inflammation on gene expression in skeletal muscle biopsies (MBx) from untreated children with juvenile dermatomyositis (JDM) and identify genes and biological processes associated with the disease progression, expression profiling data from 16 girls with active symptoms of JDM greater or equal to 2 months were compared with 3 girls with active symptoms less than 2 months. Results: Seventy-nine genes were differentially expressed between the groups with long or short duration of untreated disease. Genes involved in immune responses and vasculature remodeling were expressed at a higher level in muscle biopsies from children with greater or equal to 2 months of symptoms, while genes involved in stress responses and protein turnover were expressed at a lower level. Among the 79 genes, expression of 9 genes showed a significant linear regression relationship with the duration of untreated disease. Five differentially expressed genes--HLA-DQA1, smooth muscle myosin heavy chain, clustering, plexin D1 and tenomodulin--were verified by quantitative RT-PCR. The chronic inflammation of longer disease duration was also associated with increased DC-LAMP+ and BDCA2+ mature dendritic cells, identified by immunohistochemistry. Conclusions: We conclude that chronic inflammation alters the gene expression patterns in muscle of untreated children with JDM. Symptoms lasting greater or equal to 2 months were associated with dendritic cell maturation and anti-angiogenic vascular remodelling, directly contributing to disease pathophysiology. Keywords: Disease progression; time course After obtaining informed consent, 23 girls with definite JDM were enrolled in this study prior to obtaining the MRI directed diagnostic muscle biopsy. All 23 JDM samples and 4 healthy age- and sex-matched controls were expression profiled and for first gene filtering. Only profiling data from untreated patients (19 profiles) were then analyzed statistically. disease duration : less than 2 months: YJD-JDM-2UA-s2,YJD-JDM-1UA-s2,YJD-JDM-16UA-s2 disease duration : more than 2 months:YJD-JDM-30UA-s2,YJD-JDM-19UA-s2,YJD-JDM-5UA-s2,YJD-JDM-21UA-s2,YJD-JDM-18UA-s2,YJD-JDM-3UA-s2,YJD-JDM-23UA-s2,YJD-JDM-9UA-S2,YJD-JDM-12UA-s2,YJD-JDM-14UA-s2,YJD-JDM-25UA-s2,YJD-JDM-8UA-s2,YJD-JDM-15UA-s2,YJD-JDM-13UA-s2,YJD-JDM-10UA-S2,YJD-JDM-6UA-s2.