Many of the end-organ effects of
cystinosis are known to be risk factors for
osteopenia; these include deposition of
cystine crystals in bone,
hypothyroidism,
diabetes mellitus, primary
hypogonadism, urinary
phosphate wasting, and
chronic renal failure. While
transplantation may correct the latter, it exposes the child to other risk factors for diminished bone mass, notably the use of high-dose
glucocorticoids. Our objective was to determine if these multiple risk factors translate into an increased occurrence of
osteopenia, as measured by dual-energy X-ray absorptiometry (DEXA), and/or fractures in this population. We examined the charts, X-rays, and bone mineral density (BMD) of all cystinotic patients post renal transplant for whom this information was available. Lumbar spine BMD was measured by DEXA scan (Hologic 4500). Z-scores were corrected for growth parameters using previously published reference data. Fracture history and pertinent
serum markers of bone metabolism were also analyzed. Of the 63 renal transplants performed at our institution, 11 children were transplanted due to
cystinosis. Nine of these patients, 5 male and 4 female, had had BMD evaluations, with an average age of 14.3 years (range 5-17 years) at the time of initial BMD post transplant. The mean interval between transplant and BMD evaluation was 39 months (range 3-90 months). Surprisingly, 7 of 9 patients had normal uncorrected BMD values (z-scores -1.92 to +0.02) and 7 of 9 patients had normal corrected values (z-scores -1.20 to +1.93). Three patients suffered from a total of eight fractures. Of the 3 fracture patients, 2 had normal BMD. All patients maintained good graft function and had normal
calcium/phosphate mineral status. Of note, 3 of 5 male patients had evidence of primary testicular failure at earlier ages than often described, and this may be an unrecognized risk factor for
bone disease in this population. Despite the numerous risk factors for developing
osteopenia, these results suggest that the majority of cystinotic patients post renal transplant do not experience reduced bone mineral content as measured by DEXA. However, the significant fracture history among these patients demonstrates that DEXA cannot be used to assess fracture risk in patients with
nephropathic cystinosis.