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

The adaptor protein-2 sigma subunit (AP2σ2) is pivotal for clathrin-mediated endocytosis of plasma membrane constituents such as the calcium-sensing receptor (CaSR). Mutations of the AP2σ2 Arg15 residue result in familial hypocalciuric hypercalcaemia type 3 (FHH3), a disorder of extracellular calcium (Ca(2+) o) homeostasis. To elucidate the role of AP2σ2 in Ca(2+) o regulation, we investigated 65 FHH probands, without other FHH-associated mutations, for AP2σ2 mutations, characterized their functional consequences and investigated the genetic mechanisms leading to FHH3. AP2σ2 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 AP2σ2 mutations impaired CaSR signal transduction in a dominant-negative manner. Mutational bias was observed at the AP2σ2 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 × sMg/100 × CCCR, which was ≥ 5.0, had a diagnostic sensitivity and specificity of 83 and 86%, respectively, for FHH3. Thus, our studies demonstrate AP2σ2 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

The broad phenotypic spectrum of 17α-hydroxylase/ 17,20-lyase (CYP17A1) deficiency: a case series.

CONTEXT 17α-hydroxylase/17,20-lyase deficiency (17OHD) caused by mutations in the CYP17A1 gene is a rare form of congenital adrenal hyperplasia typically characterized by cortisol deficiency, mineralocorticoid excess and sex steroid deficiency. OBJECTIVE To examine the phenotypic spectrum of 17OHD by clinical and biochemical assessment and corresponding in silico and in vitro functional analysis. DESIGN Case series Patients and Results: We assessed eight patients with 17OHD, including four with extreme 17OHD phenotypes: two siblings presented with failure to thrive in early infancy and two with isolated sex steroid deficiency and normal cortisol reserve. Diagnosis was established by mass spectrometry-based urinary steroid profiling and confirmed by genetic CYP17A1 analysis, revealing homozygous and compound heterozygous sequence variants. We found novel (p.Gly111Val, p.Ala398Glu, p.Ile371Thr), and previously described sequence variants (p.Pro409Leu, p.Arg347His, p.Gly436Arg, p.Phe53/54del, p.Tyr60IlefsLys88X). In vitro functional studies employing an overexpression system in HEK293 cells showed that 17,20-lyase activity was invariably decreased while mutant 17α-hydroxylase activity retained up to 14% of wild-type activity in the two patients with intact cortisol reserve. A ratio of urinary corticosterone over cortisol metabolites reflective of 17α-hydroxylase activity correlated well with clinical phenotype severity. CONCLUSION Our findings illustrate the broad phenotypic spectrum of 17OHD. Isolated sex steroid deficiency with normal stimulated cortisol have not been reported before. Attenuation of 17α-hydroxylase activity is readily detected by urinary steroid profiling and predicts phenotype severity

Raised Intracranial Pressure (Pseudotumour Cerebri) Associated With Severe Acute Respiratory Syndrome Coronavirus 2

Several neurological sequelae of coronavirus disease 2019 (Covid-19), the disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), are now described. We describe a pair of cases demonstrating a novel association between Covid-19 and severely raised intracranial pressure (ICP). Patient 2 is included as part of a summary of 43 cases of Covid-19 neurology