RESUMEN
OBJECTIVES: Tubular maximum phosphate reabsorption per glomerular filtration rate (TmP/GFR) is used to evaluate renal phosphate reabsorption and it is a useful tool for the differential diagnosis of hypophosphatemic syndromes. TmP/GFR is typically calculated from fasting plasma and second morning void urine samples, obtained 2â¯h after the first void (TmP/GFR 2â¯h). The purpose of this study was to evaluate if TmP/GFR calculated from 24â¯h urine collection (TmP/GFR 24â¯h) can be used as an alternative for TmP/GFR 2â¯h in patients with urine phosphate wasting. METHODS: We enrolled adult patients with X-linked hypophosphatemia (XLH) or tumor-induced osteomalacia (TIO). All patients underwent blood and urine sample collections, to calculate TmP/GFR 24â¯h and TmP/GFR 2â¯h. RESULTS: Twenty patients (17 XLH and 3 TIO), aged 24-78 years, were included. All patients had low TmP/GFR 2â¯h (0.35â¯mmol/L, IQR 0.24-0.47â¯mmol/L) and TmP/GFR 24â¯h (0.31â¯mmol/L, IQR 0.22-0.43â¯mmol/L). The concordance correlation coefficient between TmP/GFR 2â¯h and TmP/GFR 24â¯h was 0.86 (95â¯% CI: 0.69-0.93), with a systematic bias of 0.05â¯mmol/L (95â¯% limits of agreement: -0.10 to 0.20). Furthermore, in 70â¯% (i.e., 14 patients out of 20) and 80â¯% (i.e., 16 patients out of 20) of cases the difference between TmP/GFR 2â¯h and TmP/GFR 24â¯h was within ±30â¯% and ±35â¯%, respectively. CONCLUSIONS: Despite TmP/GFR 2 and 24â¯h show a relatively suboptimal agreement, the difference between the two parameters appears to be small and not clinically significant in the setting of adult patients with FGF23-dependent urine phosphate wasting and secondary hypophosphatemia.
Asunto(s)
Factor-23 de Crecimiento de Fibroblastos , Osteomalacia , Fosfatos , Toma de Muestras de Orina , Adulto , Anciano , Femenino , Humanos , Masculino , Persona de Mediana Edad , Adulto Joven , Raquitismo Hipofosfatémico Familiar/orina , Raquitismo Hipofosfatémico Familiar/diagnóstico , Tasa de Filtración Glomerular , Hipofosfatemia/orina , Hipofosfatemia/diagnóstico , Túbulos Renales/metabolismo , Osteomalacia/orina , Osteomalacia/diagnóstico , Síndromes Paraneoplásicos/orina , Síndromes Paraneoplásicos/diagnóstico , Fosfatos/orina , Toma de Muestras de Orina/métodosRESUMEN
Vitamin D is a pro-hormone characterized by an intricate metabolism and regulation. It is well known for its role in calcium and phosphate metabolism, and in bone health. However, several studies have assessed a huge number of extra-skeletal functions, ranging from cell proliferation in some oncogenic pathways to antioxidant and immunomodulatory functions. Vitamin D exerts its role by binding to VDRs (vitamin D receptors), which are located in many different tissues. Moreover, VDRs are able to bind hundreds of genomic loci, modulating the expression of various primary target genes. Interestingly, plenty of gene polymorphisms regarding VDRs are described, each one carrying a potential influence against gene expression, with relapses in several chronic diseases and metabolic complications. In this review, we provide an overview of the genetic aspects of vitamin D and VDR, emphasizing the gene regulation of vitamin D, and the genetic modulation of VDR target genes. In addition, we briefly summarize the rare genetic disease linked to vitamin D metabolism.