No abstract

Adults with distal renal tubular acidosis (dRTA) commonly present with hypokalaemia (with/without paralysis), nephrolithiasis/nephrocalcinosis and vague musculoskeletal symptoms. All adults with dRTA should be thoroughly evaluated for systemic diseases, certain medications and toxins. The leading cause of acquired or secondary dRTA in adults is primary Sjögren syndrome (SS); however, other collagen vascular diseases (CVDs) including seronegative spondyloarthropathy (SSpA) may at times give rise to secondary dRTA. Metabolic bone disease is often encountered in adults with dRTA, and the list includes osteomalacia and secondary osteoporosis; sclerotic metabolic bone disease is an extremely rare manifestation of dRTA. Coexistence of dRTA and sclerotic bone disease is seen in primary dRTA due to mutation in CA2 gene and acquired dRTA secondary to systemic fluorosis. Primary SS and SSpA, rarely if ever, may also lead to both secondary dRTA and osteosclerosis. Circulating autoantibodies against carbonic anhydrase II and possibly calcium sensing receptor may explain both these features in patients with CVD.

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

Liquid chromatography–mass spectrometry, the gold standard method for cortisol measurement, is expensive and not widely available in the developing countries. Chemiluminescent immunoassay, commonly used for cortisol measurement is prone to clinically meaningful inter-assay variability in some analysers. This occurs due to non-specific nature of anticortisol antibodies used in different platforms, having cross reactivity with structurally similar cortisol precursors like 17α-hydroxyprogesterone (17OHP), 11-deoxycortisol and 21-deoxycortisol. In patients with 21-hydroxylase deficiency, where 17OHP and 21-deoxycortisol are significantly elevated, older generation machines like Siemens Advia Centaur XP provide spuriously high cortisol concentration compared with values measured by Roche Cobas e 411 or Siemens Immulite 1000. Diagnosis of potentially life-threatening salt-wasting 21-hydroxylase deficiency may be missed and treatment may be delayed due to such interference. Two children with classic 21-hydroxylase deficiency are being reported here, in whom high cortisol values were observed in Siemens Advia Centaur XP system.

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.