Serum RANKL, osteoprotegerin (OPG) and RANKL/OPG ratio in children with systemic lupus erythematosus

Background:Systemic lupus erythematosus (SLE) patients have lower bone mineral density (BMD) compared with healthy individuals because of general, genetic, disease and medication-related factors. The disturbance of the receptor activator of nuclear factor-kappa B ligand (RANKL)/osteoprotegerin (OPG) ratio has been reported to be associated with low BMD in many disorders in adults and children alike. Objectives:The objectives of this study were (i) to assess serum OPG, RANKL and RANKL/OPG ratio levels in SLE children and controls, (ii) to determine whether the cumulative glucocorticoid (CGCS) dose had any effect on the concentration of serum RANKL, OPG and RANKL/OPG ratio, and (iii) to determine the relation of these parameters to BMD. Methods:We evaluated 50 SLE children and 50 age- and sex-matched healthy controls. RANKL and OPG were assessed in serum and compared between patients and controls. For SLE patients, a univariate followed by multivariable analysis were carried out to detect the possible predictors of the changes in RANKL, OPG and RANKL/OPG ratio levels. Lumbar BMD for all patients was assessed by dual-energy X-ray absorptiometry (DXA) scan and then correlated to different probable correlated factors. Results:RANKL, OPG and RANKL/OPG ratio were significantly higher in SLE patients (p <= 0.001). Univariate analysis showed significant correlations of RANKL with CGCS (p <= 0.001) and with DXA scan z-score (p = 0.007): OPG was significantly correlated to Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) score (p = 0.001) and anti-double-stranded DNA (p = 0.001), whereas RANKL/OPG was significantly correlated to duration of illness and DXA z-score (p = 0.002). The multivariable analysis showed that DXA z-score was an independent predictor of RANKL and RANKL/OPG ratio (p = 0.019 and 0.008, respectively), whereas SLEDAI score was an independent predictor of OPG levels. BMD was negatively correlated to disease duration (p = 0.008) and CGCS dose (p = 0.015), but no significant correlation has been found between BMD and cumulative SLEDAI score (p = 0.29). Conclusions:Serum RANKL/OPG ratio is elevated in Egyptian children with SLE and is considered a risk factor for reduced bone mass in these children. Other risk factors for low BMD include high CGCS dose and disease duration, supporting that osteoporosis in SLE is multifactorial.