Session: FRI 368-390-Metabolic Bone Disease Case Reports (posters)
Poster Board FRI 376
Clinical case: A 27 year-old man was referred to the Endocrinology Clinic after a diagnosis of hypophosphatemic rickets in early childhood, when he was treated with oral phosphorus and calcitriol, with suboptimal control. After puberty, he lost follow-up and remained untreated, with worsening of bone disease. He was the youngest of an offspring of twelve, born after an uneventful pregnancy of healthy non-consanguineous parents. Since birth, multiple right-side linear epidermal nevi along Blaschko’s lines were noted, which progressed lifelong. He also had right hemihypoplasia and dysplastic bone lesions on skeletal radiographs. He had no apparent neurologic abnormality, but was restricted to a wheelchair and developed severe restrictive lung disease consequent to thoracic deformity. He had an extremely low serum phosphorus level (0.94mg/dL, normal range [NR] 2.5-4.8), associated with very low serum 25-alpha–hydroxi-vitamin D (6.39 ng/mL) and mild hypocalcemia (8.4mg/dL, NR 8.8-11.0). PTH and alkaline phosphatase were high (347.8pg/mL, NR 10-69 and 396U/L, NR53-128U/L, respectively). Phosphate tubular resorption fraction was 55%, indicating urinary phosphate loss. Serum FGF23 was elevated (169.7kRU/L, NR 34 - 96kRU/L). Skeletal X-ray revealed innumerous deformities and severe osteomalacia. Calcitriol and phosphorous replacement were re-introduced with partial biochemical improvement. A skin biopsy of a lesion in the trunk was consistent with epidermal nevus, with a positive immunostaining for FGF23. However, no expression of FGF23 mRNA was detected by qPCR, using GAPDH and B2M genes as control.
Conclusion: This case illustrates the occurrence of FGF23 mediated–hypophosphatemia in ENS, which persisted during adulthood leading to severely disabling osteomalacia. Although expression of FGF23 in the skin lesion was not detected, positive immunostaining for FGF23 was shown. This finding may be associated with interactions of FGF23 and ubiquitously expressed isoforms of FGF receptors in skin (1,2). Recently, somatic activating RAS mutations have been described in this syndrome (3). Further studies are needed to clarify the molecular defects underlying the phenotypic features of this case.
Nothing to Disclose: LPV, DRC, ADLRF, AL
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