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Adaptor protein-2 sigma subunit mutations causing familial hypocalciuric hypercalcaemia type 3 (FHH3) demonstrate genotype-phenotype correlations, codon bias and dominant-negative effects

Lookup NU author(s): Professor Simon Pearce

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Abstract

The adaptor protein-2 sigma subunit (AP2G2) is pivotal for clathrin-mediated endocytosis of plasma membrane constituents such as the calcium-sensing receptor (CaSR). Mutations of the AP2 sigma 2 Arg15 residue result in familial hypo calciuric hypercalcaemia type 3 (FHH3), a disorder of extracellular calcium (Ca-o(2+)) homeostasis. To elucidate the role of AP2G2 in Ca-o(2+) regulation, we investigated 65 FHH probands, without other FHH-associated mutations, for AP2G2 mutations, characterized their functional consequences and investigated the genetic mechanisms leading to FHH3. AP2 sigma 2 mutations were identified in 17 probands, comprising 5 Arg15Cys, 4 Arg15His and 8 Arg15Leu mutations. A genotype-phenotype correlation was observed with the Arg15Leu mutation leading to marked hypercalcaemia. FHH3 probands harboured additional phenotypes such as cognitive dysfunction. All three FHH3-causing AP2 sigma 2 mutations impaired CaSR signal transduction in a dominant-negative manner. Mutational bias was observed at the AP2 sigma 2 Arg15 residue as other predicted missense substitutions (Arg15Gly, Arg15Pro and Arg15Ser), which also caused CaSR loss-of-function, were not detected in FHH probands, and these mutations were found to reduce the numbers of CaSR-expressing cells. FHH3 probands had significantly greater serum calcium (sCa) and magnesium (sMg) concentrations with reduced urinary calcium to creatinine clearance ratios (CCCR) in comparison with FHH1 probands with CaSR mutations, and a calculated index of sCa x 5Mg/100 x CCCR, which was >= 5.0, had a diagnostic sensitivity and specificity of 83 and 86%, respectively, for FHH3. Thus, our studies demonstrate AP2 sigma 2 mutations to result in a more severe FHH phenotype with genotype-phenotype correlations, and a dominant-negative mechanism of action with mutational bias at the Arg15 residue.


Publication metadata

Author(s): Hannan FM, Howles SA, Rogers A, Cranston T, Gorvin CM, Babinsky VN, Reed AA, Thakker CE, Bockenhauer D, Brown RS, Connell JM, Cook J, Darzy K, Ehtisham S, Graham U, Hulse T, Hunter SJ, Izatt L, Kumar D, McKenna MJ, McKnight JA, Morrison PJ, Mughal MZ, O'Halloran D, Pearce SH, Porteous ME, Rahman M, Richardson T, Robinson R, Scheers I, Siddique H, Van't Hoff WG, Wang T, Whyte MP, Nesbit MA, Thakker RV

Publication type: Article

Publication status: Published

Journal: Human Molecular Genetics

Year: 2015

Volume: 24

Issue: 18

Pages: 5079-5092

Print publication date: 15/09/2015

Online publication date: 16/06/2015

Acceptance date: 12/06/2015

Date deposited: 16/06/2016

ISSN (print): 0964-6906

ISSN (electronic): 1460-2083

Publisher: Oxford University Press

URL: http://dx.doi.org/10.1093/hmg/ddv226

DOI: 10.1093/hmg/ddv226


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