Cardiometabolic phenotyping of patients with familial hypocalcuric hypercalcemia

Heterozygous inactivating mutations of the calcium-sensing receptor (CaSR) gene cause alterations in calcium metabolism [familial hypocalciuric hypercalcemia (FHH)]. In addition, calcium-sensing receptor is expressed in the myocardium and endocrine cells including pancreatic islets, enteroendocrine cells, and adipose tissue.

To discern whether FHH is associated with cardiometabolic alterations of clinical significance, endocrine responses to systemic calcium stimulation and oral glucose tolerance tests were performed. Ectopic lipid deposition and heart function were assessed using magnetic resonance spectroscopy/imaging.

Eight FHH patients and nine controls matched for anthropometric characteristics (age 45 ± 18 y; body mass index 29 ± 4 vs 29 ± 6 kg/m(2)) were studied to determine cardiac function, ectopic and visceral lipid content, and insulin sensitivity and secretion.

Insulin sensitivity (clamp-like index: 4.5 ± 0.6 vs 4.3 ± 0.4 mg/kg · min), basal (insulin secretion rate: 266 ± 33 vs 218 ± 25 pmol/min), and glucose-stimulated β-cell function (adaptation index: 180.2 ± 12.2 vs 176.2 ± 17.4) as well as calcium-stimulated insulin secretion were comparable between FHH and controls, respectively. Ectopic lipid content in liver [3.75% (1.4%; 34%) vs 4.18% (0.9%; 28%)], soleus muscle (1.07% ± 0.38% vs 1.02% ± 0.56 %), and myocardium (0.39% ± 0.3% vs 0.32% ± 0.1 %), visceral and sc adipose tissue distribution (0.51 ± 0.16 vs 0.47 ± 0.17) as well as heart function (ejection fraction: 71.5% ± 8% vs 72.8% ± 8 %; E to A ratio: 1.4% ± 0.6% vs 1.3% ± 0.7%) were not different between the groups.

Despite comprehensive cardiometabolic phenotyping, no alterations in myocardial function, lipid distribution, or glucose metabolism were observed in FHH. Thus, FHH might reflect a laboratory finding without any relevant cardiometabolic alterations.