Hypophosphatemic osteomalacia and bone sclerosis caused by a novel homozygous mutation of the FAM20C gene in an elderly man with a mild variant of raine syndrome

Shinji Takeyari, Takehisa Yamamoto, Yuka Kinoshita, Seiji Fukumoto, Francis H. Glorieux, Toshimi Michigami, Kosei Hasegawa, Taichi Kitaoka, Takuo Kubota, Yasuo Imanishi, Tsunesuke Shimotsuji, Keiichi Ozono

Research output: Contribution to journalArticlepeer-review

35 Citations (Scopus)

Abstract

Background: Hypophosphatemia and increased serum fibroblast growth factor 23 (FGF23) levels have been reported in young brothers with compound heterozygous mutations for the FAM20C gene however, rickets was not observed in these cases. We report an adult case of Raine syndrome accompanying hypophosphatemic osteomalacia with a homozygous FAM20C mutation (R408W) associated with increased periosteal bone formation in the long bones and an increase in bone mineral density in the femoral neck. Case: The patient, a 61-year-old man, was born from a cousin-to-cousin marriage. A short stature and severe dental demineralization were reported at an elementary school age. Hypophosphatemia was noted inadvertently at 27years old, at which time he started to take an active vitamin D metabolite (alphacalcidol) and phosphate. He also manifested ossification of the posterior longitudinal ligament. On bone biopsy performed at the age of 41years, we found severe osteomalacia surrounding osteocytes, which appeared to be an advanced form of periosteocytic hypomineralized lesions compared to those reported in patients with X-linked hypophosphatemic rickets. Laboratory data at 61years of age revealed markedly increased serum intact-FGF23 levels, which were likely to be the cause of hypophosphatemia and the decreased level of 1,25(OH)2D. We recently identified a homozygous FAM20C mutation, which was R408W, in this patient. When expressed in HEK293 cells, the R408W mutant protein exhibited impaired kinase activity and secretion. Discussion: Our findings suggest that certain homozygous FAM20C mutations can cause FGF23-related hypophosphatemic osteomalacia and indicate the multiple roles of FAM20C in bone.

Original languageEnglish
Pages (from-to)56-62
Number of pages7
JournalBone
Volume67
DOIs
Publication statusPublished - Oct 2014

Keywords

  • Cortical hyperostosis
  • FAM20C
  • FGF23
  • Hypophosphatemic rickets
  • Loss of teeth
  • OPLL

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Physiology
  • Histology

Fingerprint Dive into the research topics of 'Hypophosphatemic osteomalacia and bone sclerosis caused by a novel homozygous mutation of the FAM20C gene in an elderly man with a mild variant of raine syndrome'. Together they form a unique fingerprint.

Cite this