Nine-year cinacalcet monotherapy in a child with neonatal severe hyperparathyroidism caused by compound heterozygous <i>CASR</i> mutations

Abstract Objectives Neonatal severe primary hyperparathyroidism (NSHPT) is a rare, potentially life-threatening disorder caused by loss-of-function mutations in the CASR gene. Treatment traditionally includes hydration, diuretics, bisphosphonates, and parathyroidectomy. Long-term data on pharmacological therapy with cinacalcet are limited. Case presentation We report a female infant with NSHPT due to compound heterozygous CASR variants (c.893C&gt;T, p.Ala298Val; c.2414A&gt;C, p.Lys805Thr). Initial therapy with bisphosphonates provided transient calcium reduction. Cinacalcet monotherapy was started in the third week of life, with empirically guided dose titration. Follow-up over nine years showed stable mild hypercalcemia (approximately 3 mmol/L), normal or slightly elevated PTH, normal growth and cognitive development, absence of nephrocalcinosis, and preserved bone mineral density. This case suggests that long-term cinacalcet therapy may provide sustained biochemical control in selected patients with NSHPT carrying CASR variants with residual receptor function. Conclusions Long-term cinacalcet monotherapy may provide sustained biochemical control and normal development in selected patients with NSHPT carrying CASR variants with residual receptor function.