A novel mutation in fibroblast growth factor 23 gene as a cause of tumoral calcinosis.
BACKGROUND
Tumoral calcinosis is a disease characterized by ectopic calcification and hyperphosphatemia due to enhanced renal tubular phosphate reabsorption. Fibroblast growth factor (FGF)23 was identified as a responsible factor in hypophosphatemic diseases caused by renal phosphate leak.


OBJECTIVE
The objective of the study was to analyze the involvement of FGF23 in the development of tumoral calcinosis.


METHODS
Serum FGF23 level was evaluated in a patient with tumoral calcinosis by two kinds of ELISA: full-length assay that detects only full-length FGF23 with phosphate-lowering activity and C-terminal assay that measures full-length as well as C-terminal fragment of FGF23. FGF23 gene was analyzed by direct sequencing of PCR products, and mutant FGF23 was analyzed by Western blotting after expression in mammalian cells.


METHODS
A family of tumoral calcinosis patients were studied.


RESULTS
Serum FGF23 was extremely high when measured by C-terminal assay. In contrast, it was low normal by full-length assay. Analysis of FGF23 gene detected a serine to phenylalanine mutation in codon 129. No wild-type allele of this codon was found in the patient. The brother of the proband showed the same base change. When this mutant FGF23 was expressed in vitro, full-length and N-terminal fragments were barely detectable by Western blotting, whereas C-terminal fragment with the same molecular weight as that from wild-type FGF23 could be detected.


CONCLUSIONS
The production and serum level of C-terminal fragment of FGF23 are increased in this patient with tumoral calcinosis. Together with the recent similar report of FGF23 mutation, impaired action of full-length FGF23 seems to result in tumoral calcinosis.
Araya
Kaori
K
Department of Pediatrics, University of Tokyo Hospital, 3-28-6, Bunkyo-ku, Tokyo 113-8655, Japan.
Fukumoto
Seiji
S
Backenroth
Rebecca
R
Takeuchi
Yasuhiro
Y
Nakayama
Kounosuke
K
Ito
Nobuaki
N
Yoshii
Nozomi
N
Yamazaki
Yuji
Y
Yamashita
Takeyoshi
T
Silver
Justin
J
Igarashi
Takashi
T
Fujita
Toshiro
T
D000328:Adult; D015153:Blotting, Western; D002114:Calcinosis / Q000209:etiology* / Q000235:genetics*; D002478:Cells, Cultured; D017077:Culture Media, Conditioned; D016373:DNA, Antisense / Q000235:genetics; D018076:DNA, Complementary / Q000096:biosynthesis / Q000235:genetics; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000235:genetics*; D006801:Humans; D008970:Molecular Weight; D009154:Mutation / Q000502:physiology*; D009369:Neoplasms / Q000150:complications* / Q000235:genetics*; D010375:Pedigree; D010710:Phosphates / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014807:Vitamin D / Q000378:metabolism
D017077:Culture Media, Conditioned; D016373:DNA, Antisense; D018076:DNA, Complementary; C000717427:FGF23 protein, human; D010710:Phosphates; D014807:Vitamin D; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23