Clinical and Outcome Comparison of Genetically Positive Vs. Negative Patients in a Large Cohort of Suspected Familial Hypocalciuric Hypercalcemia

Objective Biochemical suspicion of familial hypocalciuric hypercalcemia (FHH) might provide with a negative (FHH-negative) or positive (FHH-positive) genetic result. Understanding the differences between both groups may refine the identification of those with a positive genetic evaluation, aid management decisions and prospective surveillance. We aimed to compare FHH-positive and FHH-negative patients, and to identify predictive variables for FHH-positive cases. Design Retrospective, national multi-centre study of patients with suspected FHH and genetic testing of the CASR , AP2S1 and GNA11 genes. Methods Clinical, biochemical, radiological and treatment data were collected. We established a prediction model for the identification of FHH-positive cases by logistic regression analysis and area under the ROC curve (AUROC) was estimated. Results We included 66 index cases, of which 30 (45.5%) had a pathogenic variant. FHH-positive cases were younger ( p = 0.029), reported more frequently a positive family history ( p < 0.001), presented higher magnesium ( p < 0.001) and lower parathormone levels ( p < 0.001) and were less often treated for hypercalcemia ( p = 0.017) in comparison to FHH-negative cases. Magnesium levels showed the highest AUROC (0.825, 95%CI: 0.709–0.941). The multivariate analysis revealed that family history and magnesium levels were independent predictors of a positive genetic result. The predictive model showed an AUROC of 0.909 (95%CI: 0.826–0.991). Conclusions The combination of magnesium and a positive family history offered a good diagnostic accuracy to predict a positive genetic result. Therefore, the inclusion of magnesium measurement in the routine evaluation of patients with suspected FHH might provide insight into the identification of a positive genetic result of any of the CaSR-related genes.