Bone Abstracts

Background: The impact of X-linked hypophosphataemia (XLH) is poorly understood, previous studies have shown contradictory BMD levels in XLH at different sites. High levels of bone turnover markers and obesity have also been described in XLH. Whole body DXA scans can evaluate both bone density and body composition including fat mass and distribution. The aim of this service evaluation was to determine if whole body bone mineral density (WB BMD) of value in the management of XLH patients.

Methods: XLH patients attending a hospital metabolic unit for assessment of suitability for Burosomab treatment were included in the service evaluation. Whole body DXA scans were carried using a GE iDXA scanner. PINP, CTX and BAP were measured using an i-SYS autoanalyzer (IDS Ltd) following the standard protocol. Routine biochemistry was also obtained.

Results: 18 patients (8 f, 10 m; aged 20-73) were included. We were unable to conduct the DXA scan on one patient due to positioning issues. WB BMD was increased in XLH patients (T-Score 2.4±2.5). BMD levels were significantly correlated at all sites measured (P 0.001). BMD values were significantly lower in females than males at all sites but not WB T-scores (1.6±2.5 vs 3.1±2.5; P 0.217). Bone turnover markers were elevated in this cohort with 61.1% of PINP values were above the upper limit of normal (ULN), 27.8% of CTX and 42.9% of BAP. There were no differences in bone markers between males and females. 42.8% of subjects were obese according to both BMI and fat mass index (FMI). 64.7% of subjects had an android/gynoid fat (A/G) ratio 1 and 47% had a visceral adipose tissue area 100cm². The ratio of VAT to subcutaneous adipose tissue (SAT) was 0.4 in 58.8% of subjects but HB1Ac levels were within normal levels in all subjects.

Conclusion: WB scans were well tolerated, and WB BMD levels were raised in XLH patients. Bone markers were also elevated in a high proportion of subjects suggesting increased bone remodelling. WB scans indicated higher levels of fat mass particularly in the android region in a large proportion of patients despite normal HBA1c levels.