Autosomal dominant hypocalcemia due to a truncation in the C-tail of the calcium-sensing receptor

- A new activating mutation of CASR gene leads to a truncated tail.
- The in-vitro study shows that mutated receptor is more active than the wild-type.
- The patient had a prolonged QTc, but no clinical signs of hypocalcemia.
- No nephrocalcinosis was present despite high renal calcium excretion.
- The treatment did not normalized serum calcium and renal calcium excretion.

Autosomal Dominant Hypocalcemia (ADH) is an endocrine disorder due to activating mutations of the calcium-sensing receptor (CASR) gene. We report on a young boy who presented low serum calcium with hypercalciuria, hyperphosphatemia and low serum concentration of parathyroid hormone, not accompanied by classic clinical signs of hypocalcemia. Treatment with calcitriol and calcium did not normalize serum calcium and renal calcium excretion. The use of thiazide diuretics slightly reduced calciuria. Despite high calcium excretion, no signs of nephrocalcinosis were detected. The patient had a prolonged Q-T interval at ECG, which did not normalize during treatment. PCR amplification of CASR coding sequence and direct sequencing of PCR products.showed a novel heterozygous deletion of a cytosine (c.2682delC), responsible for a frameshift (p.S895Pfs*44) and a premature stop codon resulting in a truncation of the CaSR's C-tail. Functional studies indicated increased activity of mutant receptor compared to the wild-type.