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Abstract: SA-PO274

Nephropathic Cystinosis: A Distinct Model of CKD-MBD

Session Information

Category: Bone and Mineral Metabolism

  • 402 Bone and Mineral Metabolism: Clinical

Authors

  • Florenzano, Pablo, Pontificia Universidad Catolica de Chile, Santiago, Chile
  • Ferreira, Carlos R., NHGRI, Bethesda, Maryland, United States
  • Jimenez, Macarena, Pontificia Universidad Católica de Chile, Santiago, Chile
  • Tella, Sri harsha, University of South Carolina, Columbia, South Carolina, United States
  • Gafni, Rachel, NIH, Bethesda, Maryland, United States
  • Wolf, Myles, Duke University, Durham, North Carolina, United States
  • Gahl, William, National Institutes of Health, Bethesda, Maryland, United States
  • Salusky, Isidro B., Mattel Children's Hospital, Los Angeles, California, United States
  • Collins, Michael, NIHI, Bethesda, Maryland, United States
Background

Cystinosis is a rare autosomal recessive lysosomal storage disorder. Nephropathic cystinosis (NC) presents with Fanconi syndrome and CKD. Persistent phosphate wasting is a prominent feature; however, its impact on CKD-MBD has not been described. Thus, we compare CKD-MBD in NC (n=53) vs. non-NC (n=97).

Methods

eGFR, Ca, P, PTH, 1,25D, FGF23, and TRP were assessed. C-terminal FGF23 was measured by ELISA (Quidel), S-PTH and 1,25D by immunoassay. Subjects were grouped according to CKD stage; CKD 4 and 5 were analyzed together. Dialysis pts. were excluded. All NC patients were treated with cysteamine, phosphate supplementation, and 1,25D; non-NC with 1,25D and binders as needed. Statistical analysis included Spearman correlations and the Mann-Whitney U test.

Results

Age and eGFR were similar between the groups (Table). In NC across all CKD stages, TRP and FGF23 were lower, and 1,25D higher (Figure). PTH and S-PO4 were lower in NC stage 3. In NC, FGF23 was inversely associated with eGFR (r=-0.30, p<0.05) and positively associated with S-PO4(r=0.53, p<0.001). All hypophosphatemic NC subjects had normal FGF23 levels, independent of eGFR.

Conclusion

NC is characterized by a distinct CKD-MBD, with lower FGF23 and higher 1,25D levels. Persistent phosphate wasting may lead to this phenotype. Such findings may: 1) explain the long-term musculoskeletal complications and 2) support the concept for induction of phosphate excretion in non-NC pts. to lower FGF23 and raise 1,25D levels.

Funding

  • NIDDK Support