Ethical approvals for the use of clinical notes and for the research study were obtained from The

Gambian Government/MRC Laboratories Joint Ethics Committee. Written informed consent was obtained from the family. The father did not participate in the study. A detailed clinical assessment was conducted to identify the presence of any clinical signs and symptoms of rickets including; enlarged wrists or ankles, leg pain, difficulty walking and bow-leg or windswept deformity, and to discount other diseases associated with bone deformities. Bilateral radiographs were taken of knees and wrists of the affected children and were scored by a consultant paediatrician (JMP) using a 10-point scoring system developed by Thacher et al. [6]. Standard anthropometry was conducted which included weight (wt) and standing height (ht). An overnight-fasted, 2 h urine (u) sample was collected between BI 6727 manufacturer the hours of 07.00 and 09.00. Acidified (HCl 10 μL/mL, laboratory reagent grade SD 1.18, Fisher Scientific UK Ltd., Loughborough, UK) urine aliquots were stored at − 20 °C DAPT mouse and then later transported frozen on dry ice to MRC Human Nutrition Research (HNR), Cambridge, UK for analysis. A fasting, venous blood sample was collected, in the middle of the 2 h urine collection, transferred to lithium heparin (LiHep) and EDTA-coated tubes, plasma separated by centrifugation at

4 °C and frozen at − 20 °C, and later transported frozen on dry ice to MRC HNR, where the plasma samples and the blood cell pellets were stored at − 80 °C until analysis. The plasma samples were

analysed for markers of vitamin D, Ca and P metabolism using commercially-available methods according to the manufacturers’ instructions: intact PTH (Immunoradiometric assay; DiaSorin Ltd., Berks, UK), FGF23 (C-terminal ELISA; Immutopics Inc., CA, USA), 25OHD and 1,25(OH)2D (radioimmunoassay DiaSorin, Vasopressin Receptor MN, USA and IDS, Tyne and Wear, UK respectively). The following colorimetric methods (Cobras Fara, Roche Products Ltd, UK and Konelab™ Analyser 20i, Finland) were used to determine plasma analytes: total calcium (TCa) by methylthymol blue (Roche Unit-Kit II) and arsenazo III (Konelab™ 981367); P, ammonium molybdate (Roche Unit-Kit II and Konelab™ 981890); and total alkaline phosphatase (TALP), p-nitrophenyl phosphate at 37 °C (Roche Alp MPR2 and Konelab™ 981832). For FGF23, > 125 RU/mL was used as an upper-limit cut-off of normality. Acidified urine was used to determine urinary (u) uCa and uP employing the same colorimetric methods as for plasma and uCr was determined using the Jaffe method (Konelab™ 981832). uCa excretion was expressed as a molar ratio with uCr. Tubular maximal reabsorption of phosphate (TmP:GFR) (mmol/L) was determined in the following way: Tubular reabsorption of phosphate (TRP) = 1 − (uP/P) × (Cr/uCr), if TRP < 0.86 then TmP:GFR = TRP × P mmol/L, if TRP > 0.86 then TmP:GFR = (0.3 × TRP/1 − (0.8 × TRP)) × P mmol/L [7].