P0237COMPARISONS OF CLINICAL FEATURES IN GITELMAN SYNDROME PATIENTS WITH DIFFERENT URINARY CALCIUM EXCRETIONS

Abstract Background and Aims Hypocalciuria is considered typical in Gitelman syndrome (GS). However, a few GS cases diagnosed by gene testing presented as normocalciuria have been reported in recent years. Our study is to observe the clinical features in GS patients with different urinary calcium excretions, and investigate the value of urinary calcium excretion in the clinical classification for GS. Method GS cases from the National Rare Diseases Registry System of China (NRSC) (2016-2018) with SLCl2A3 gene screened in Peking Union Medical College Hospital were collected. The features of urinary calcium excretion were analyzed, and the phenotypes of patients with hypocalciuria were compared to those with normocalciuria. Hydrochlorothiazide (HCT) test was performed and the maximal increasement of chloride excretion fraction (△FECl) was calculated to evaluate the extent of NCC dysfunction. Results A total of 83 genetically proven GS patients was included, with the mean age at diagnosis of 31.0±13.0 years, and the male/female ratio was 1.4:1. Among them, 53 (63.9%) patients had hypocalciuria. The ratio of urinary calcium/creatine was significantly lower in patients with hypocalciuria (0.08±0.06mmol/mmol) compared to those with normocalciuria (0.47±0.28mmol/mmol), with a P value of <0.001. Age, gender, estimated glomerular filtration rate, blood pressure, alkalosis, and serum and urinary electrolytes including potassium, magnesium, natrium, chloride, and phosphorus were all comparable between patients with hypocalciuria and normocalciuria. Based on a standardized symptom questionnaire, fatigue (52.8% vs. 76.7%, P=0.03) and polyuria (9.4% vs. 30.0%, P=0.02) were less frequently reported in hypocalciuria patients, while all the other clinical symptoms were comparable. Sixteen patients in each group underwent HCT test, and the △FECl value was comparable between patients with hypocalciuria and normocalciuria (median, 0.54% vs. 0.83%, P=0.88), both of which indicated a blunt response to HCT (<2.86% according to our previous study). Conclusion The results show that 63.9% of the GS patients in this study had hypocalciuria. There is no definite relationship between urinary calcium excretion, phenotype and the extent of NCC dysfunction.