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Hypoplastic amelogenesis imperfecta, bilateral nephrolithiasis and FGF-23-mediated hypophosphataemia: a triad of FAM20A-related enamel renal syndrome
  1. Neeti Agrawal,
  2. Avivar Awasthi,
  3. Partha Pratim Chakraborty and
  4. Animesh Maiti
  1. Endocrinology & Metabolism, Medical College and Hospital, Kolkata, West Bengal, India
  1. Correspondence to Dr Partha Pratim Chakraborty; docparthapc{at}


Enamel renal syndrome (ERS) due to loss of function (LOF) mutation of FAM20A gene typically consists of hypoplastic amelogenesis imperfecta (AI) and bilateral nephrolithiasis/nephrocalcinosis. Recent evidence suggests that FAM20A interacts with FAM20C and increases its activity; thus LOF mutation of FAM20A leads to impaired FAM20C action. FAM20C, a golgi casein kinase, phosphorylates fibroblast growth factor (FGF)-23, prevents its glycosylation and makes it more susceptible to degradation by furine proteases. Consequently, inactivating mutations of FAM20C lead to increased concentration of bioactive and intact FGF-23 in circulation and resultant hypophosphataemia. LOF mutation of FAM20A, thus, might also be associated with FGF-23-mediated hypophosphataemia; however, such an association has never been reported in the literature. We describe, for the first time, a triad of AI, bilateral nephrolithiasis and FGF-23-mediated hypophosphataemia in LOF mutation of FAM20A. We suggest that serum phosphate should be measured in all patients with ERS to avoid metabolic and skeletal complications of undiagnosed, hence untreated hypophosphataemia.

  • Calcium and bone
  • Urology
  • General practice / family medicine
  • Endocrinology

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  • Contributors NA, AA, PPC and AM were involved in diagnosis and management of the patient. NA, AA and PPC did the literature search. NA wrote the manuscript and AA created figure 4. PPC finalised the manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Case reports provide a valuable learning resource for the scientific community and can indicate areas of interest for future research. They should not be used in isolation to guide treatment choices or public health policy.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.