Activating mutations in the calcium-sensing receptor: genetic and clinical spectrum in 25 patients with autosomal dominant hypocalcaemia - a German survey

Objective Autosomal dominant hypocalcaemia or hypoparathyroidism is caused by activating mutations of the calcium-sensing receptor (CaSR). Treatment with calcium and vitamin D often worsens hypercalciuria and nephrocalcinosis, and renal impairment can result. Our aim was to describe the phenotypic variance of this rare disorder in a large series and to evaluate the outcome after long-term treatment. Design Nationwide retrospective collaborative study. Patients We describe 25 patients (14 men and 11 women), 20 belonging to 11 families and five single cases. Measurements Activating CaSR mutations and clinical and biochemical findings were evaluated. Results Nine different missense mutations of the CaSR, including one novel variant (M734T), were found. Twelve patients (50%) were symptomatic, 9 (36%) had basal ganglia calcifications and 3 (12%) had nephrocalcinosis. Serum calcium was decreased (1·87 ± 0·13 mm), and PTH was decreased (n = 19) or inappropriately low (n = 4). The occurrence of hypocalcaemic symptoms at diagnosis was related to the degree of hypocalcaemia. The occurrence of features like calcification of basal ganglia or kidney calcification did not correlate with the severity of hypocalcaemia or the age at diagnosis. The most common treatment was calcitriol (median dosage 0·6 μg/day), and the mean duration of therapy was 7·1 years (max. 26 years). Hypercalcaemic episodes rarely occurred, and the rate of kidney calcifications was remarkably low (12%). Conclusion This series increases the limited knowledge of mutations and phenotypes of this rare disorder. Mutation analysis of the CaSR gene facilitates patient and family management. Low dosages of calcitriol resulted in less frequent renal calcifications.