Medical University of Vienna FGF23 in hypophosphatemic states lessons learnt from a unique patient Gabriele Haeusler, MD Medical University of Vienna Austria

Healthy until age 13 years Muscle weakness Bone pain Vasile-Joan B, born 1990 Healthy until age 13 years Muscle weakness Bone pain Severely disabled at age 15 years 16 yrs Laboratory findings: Alkaline phosphatase 1652 U/L (<200) Serum phosphate 0,31-0,55 mmol/l (>0,9) Serum calcium 2,44 mmol/l (>2,25) PTH 39,8 pg/ml (15-60) 25-OHVitD 67,8nmol/l (>50) 1,25-OH2VitD 9pg/ml (>25) Photograph shown with permisiion of patient/family Height 148 cm (<<3rd Pct) Puberty: Tanner V

within collagen-I fibers Rickets/ osteomalacia= Defect in mineralization Mineralization: Deposition of hydroxyapatite Ca 10(Po4)6 OH 2 within collagen-I fibers

PTH FGF-23 Vit-D bone Intracellular space serum phosphate reabsorption Mineralization Bone development Skeletal integrity Component of DNA,RNA Energy source (ATP) intestine kidney

Bhattacharyya N et al Trends Endocrinol Metab 23: 610-618 (2012) Farrow E & White K Nat Rev Nephrol 6:207-217 (2010) Jüppner-H et al J Bone Miner Res 25: 2091—2097 (2010) Sapir-Kohen & Livshits IBMS BoneKEy 8: 286-300 (2011)

Nat. Rev. Nephrol. doi:10.1038/nrneph.2010.17 Urakawa et al, Nature 2006 Kurosi et al,J Biol Chem 2006 Weinman, J Biol Chem 2011 Baum et al, Kidn Int 2005 Shimada et al JBMR 2004 JCI 2004 Farrow, E. G. & White, K. E. (2010) Recent advances in renal phosphate handling Nat. Rev. Nephrol. doi:10.1038/nrneph.2010.17

Figure 1 FGF23 regulatory systems in phosphate metabolism Farrow, E. G. & White, K. E. (2010) Recent advances in renal phosphate handling Nat. Rev. Nephrol. doi:10.1038/nrneph.2010.17 Sapir-Kohen et al, IBMR BoneKEy 2011

Osteocytes 90-95% of all bone cells Act as mechanosensors Communicators Orchestrators (bone remodelling) Regulators of calcium and phosphate homeostasis FGF-23 not highly expressed in OC under physiological conditions But excessive expression in hypophosphatemic patients and CKD FGF-23 production by osteocytes Bonewald& Wacker, Pediatr Nephrol 2013

Figure 1 FGF23 regulatory systems in phosphate metabolism Farrow, E. G. & White, K. E. (2010) Recent advances in renal phosphate handling Nat. Rev. Nephrol. doi:10.1038/nrneph.2010.17 Sapir-Kohen et al, IBMR BoneKEy 2011

Bhattacharyya N et al, Trends Endocrinology & Metabolism 2012

Bhattacharyya N et al, Trends Endocrinology & Metabolism 2012

Acquired forms Shimada T et al Recognition of a phosphaturic factor in 1959 by Prader et al Shimada T et al Cloning and characterization of FGF-23 as a causative factor of tumor-induced osteomalacia PNAS 98: 6500, 2001 Tumor induced rickets <20 cases Tumor induced osteomalacia (TIO) > 300 cases Folpe 2004, Chong 2011

TIO- Diagnosis/ Detection Histopathological entity (Folpe et al, 2004) PMTMCT phosphaturic mesenchymal tumor mixed connective tissue variant Variety of bone sites, size <1-14 cm Detection rate about 50% ( MRI) High resolution techniques (HR-MRI) Somatostatin receptor imaging (Scintigraphy 111 In-octreotide)

68-Gallium DOTATOC PET HE, 1:25 mixed connective tissue type JCEM 95; 4511-4517 (2010)

Komaba, H. & Fukagawa, M. Nat Rev Nephrol (2012) Serum FGF23 Komaba, H. & Fukagawa, M. Nat Rev Nephrol (2012)

surgery Immunohistochemistry FGF23 Oral Calcium 1-2g/d HE, 1:25 mixed connective tissue type JCEM 95; 4511-4517 (2010)

Photograph shown with permisiion of patient/family

JCEM 95; 4511-4517 (2010)

The porcine model for growth plate research Piglets 4-6 weeks Histo/cDNA Database Manual extraction total growth plates Whole explant culture Collagenase digestion Laser microdisection Density gradient centrifugation Monolayer culture 3D culture

Immunehistochemistry FGF23 Pig, 4 weeks Phalanx 10x 25x

Raimann et al, Conn Tiss 2012

Summary FGF-23 is a central regulator of phosphate metabolism FGF-23 is involved in hypophosphatemic rickets, both hereditary and acquired FGF-23 is the factor responsible for renal phosphate wasting in patients with TIO The source of FGF-23 is bone, where FGF-23 is produced by bone cells under physiological, and much more abundand, in pathological states In TIO, therapy consists of surgical removal of the tumor, which, if complete, results in healing and complete recovery In hereditary forms of hypophosphatemic rickets, therapy consists of oral phosphate and 1-25 OHD until new therapeutic agends are available

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