Chronic kidney disease (CKD) in children is associated with multiple skeletal complications and growth impairment. Increased fracture incidence often persists after transplantation and could be linked to alterations in bone material properties. Bone matrix mineralisation density distribution (BMDD) based on quantitative backscattered electron microscopy (qBEI) reflects bone turnover (average tissue age) and mineralisation kinetics of the bone matrix. We compared BMDD in transiliac bone biopsies obtained from patients 8.0±6.4 years after kidney transplantation (n=9, age 17.0±1.9 years, height Z-score -1.8±0.8, GFR (mL/1.73m2): 42.89±10.13, with a healthy paediatric reference cohort (n=54) and children with CKD on dialysis (n=18). None of the subjects was treated with bisphosphonates or growth-hormone. Bone histomorphometry of transplant recipients revealed low to normal bone turnover (MS/BS Z-score -1.0±1.4). Osteoid indices were normal but mineralisation lag time was increased. qBEI showed an increase in the most frequent calcium concentration (+3.4%;+4.7%) and the portion of fully mineralised bone (3-fold; 11-fold) in trabecular and cortical compartments respectively, versus healthy children. The amount of lowly mineralised bone packets was elevated in cancellous bone leading to a marked heterogeneity of matrix mineralisation. None of the BMDD parameters in the transplant recipients were significantly distinct from non-transplanted children on dialysis. In conclusion, the abnormally high bone matrix mineralisation in transplanted children is similar to non-transplanted CKD patients, suggesting a history of low bone turnover with accumulation of fully mineralised bone packets. Even though at the time of the biopsy histomorphometry revealed only marginally decreased bone turnover, it seems probable that BMDD alterations acquired during the decline of kidney function are not completely corrected. The observed delayed osteoid mineralisation and the increased portion of lowly mineralised bone packets suggest a slow-down in the onset and accumulation of mineral in the newly formed osteoid possibly linked to CKD and concomitant glucocorticoid and immunosuppressive medication.
Disclosure: The authors declared no competing interests.