Systemic sclerosis. Novel molecular and epidemiological features of disease

Sammanfattning: Systemic sclerosis (SSc) is a systemic rheumatic disease with significant mortality and morbidity. Different estimations of disease prevalence and incidence have been presented from various parts of the world. While lung involvement is a common cause of SSc-related death, a majority of SSc patients suffer from symptoms originating in the gastrointestinal (GI) tract. By combining data from a population based register with individual case ascertainment, we investigated the epidemiology of SSc in a defined region in southern Sweden comprising one million adult inhabitants. The investigation was performed by using classification criteria presented in 1980 and in 2013 respectively. SSc prevalence was estimated to 305 per million and the annual incidence 19 per million and year by application of the 2013 classification criteria. We show that the novel criteria identify SSc subjects who were overlooked by the previous criteria. Usage of either criteria set resulted in prevalence estimates that are higher than previous reports from northern Europe, but similar to reports from southern Europe. Cartilage oligomeric matrix protein (COMP) is a promising biomarker of skin fibrosis in SSc. We have investigated the potential for S-COMP to serve as a biomarker for SSc associated lung fibrosis and as a predictor of SSc survival. S-COMP showed only minimal associations with the development or presence of pulmonary fibrosis. SSc patients with pathological S-COMP in early SSc were at an increased risk of death. To further explore the mechanisms behind COMP and fibrosis, we investigated skin fibrosis in mice deficient in COMP. These mice were not resistant to skin fibrosis. GI disease is a common visceral manifestation of SSc. The inflammatory protein complex S100A8/A9, also known as calprotectin, has been associated with several rheumatic diseases. Faecal calprotectin (FC) is a validated biomarker in inflammatory bowel disease. We have explored the biomarker potential of FC in SSc. FC correlated with SSc manifestations in the GI tract. FCs showed little variation upon repeated testing. FC was higher in SSc compared to other rheumatic diseases. The development of inflammation and fibrosis was investigated in reference to S100A8/A9 in an experimental mouse model. S100A8 and S100A9 were found to localise to inflamed and fibrotic skin tissue. Using the same model, we could not identify any significant reduction of inflammation or fibrosis in S100A9 deficient mice. I suggest that FC, a feasible biomarker already available in routine clinical care, could be a valid biomarker of GI disease in SSc. Further studies are warranted to elucidate the mechanisms behind pathological FC testing in SSc.