Document resource
Objectives There is a link between the number of X chromosomes and SLE risk.The disease is more common in women (XX) than in men (XY), and the risk increases in patients with triple X (XXX) and Klinefelter (XXY) syndromes and decreases in Turner syndrome (X0). The mechanisms behind this observation remain unclear.In females, one X chromosome is randomly silenced by XIST, a long noncoding RNA.We hypothesize that abnormal X chromosome inactivation (XCI) or increased escape from X inactivation, leading to biallelic gene expression, may contribute to SLE and to its higher prevalence in women.Methods We studied children and adults with SLE (n=37), who fulfilled the 2019 ACR/EULAR SLE criteria, 54% with lupus nephritis (20/37), and healthy controls (n=29).Monocytes, B lymphocytes, CD4+ and CD8+ T lymphocytes were isolated by cell sorting.XIST was quantified by RT-qPCR.To evaluate the preferential inactivation of one of the two X chromosomes, we used the HUMARA assay and pyrosequencing with the SNIPs XIST rs16 and XIST rs18.Results 1) XIST was overexpressed in SLE patients compared to healthy controls in all cells studied. This difference was statistically significant for B lymphocytes (p=0.008) and CD4+ T lymphocytes (p=0.044).2) XIST expression was four times higher in monocytes of patients with lupus nephritis than in patients without renal involvement. Moreover, XIST expression was significantly increased in monocytes of patients with active lupus nephritis compared with patients with inactive lupus nephritis (p=0.020).3) HUMARA assay, non-random XCI (>=70%) was more common in SLE patients than in healthy controls. In CD4+ T lymphocytes, 43% of SLE patients and 15% of controls showed preferential inactivation of one of the X chromosomes. In B lymphocytes, 32% of SLE patients and 8% of controls had a preferential inactivation. Skewing ratios >80% were only detected in SLE patients.Pyrosequencing method in B lymphocytes, the controls were all randomly inactivated, and preferential inactivation was found in 27% of SLE patients with the SNIP XIST rs16 and 11% with the SNIP XIST rs18.Conclusions These results highlight the potential involvement of XCI in the pathogenesis of SLE and lupus nephritis.