ESPE Abstracts

Introduction and Aims: Autosomal dominant hypocalcemia or type V Bartter syndrome is characterized by hypocalcemia, low parathyroid hormone (PTH), and calciuria, which marks its prognosis due to the risk of nephrocalcinosis. It is caused by activating mutations in the calcium-sensing receptor (CASR) gene (3q21.1), which is expressed in the parathyroid and renal tubules, causing salt and potassium loss, due to the inhibition of the ROMK and NKCC2 channels. We show an early-onset refractory hypocalcemia case with polyuria and hypokalemia, in order to disseminate its knowledge.

Clinical Case: We show a 22-day-old neonate with generalized tetany, irritability and seizures due to severe hypocalcemia: 6.4 mg/dl, hyperphosphatemia: 10.7 mg/dl, hypomagnesemia: 1.2 mg/dl, undetectable PTH, normal levels of calcidiol: 27 ng/ml and elevated levels of calcitriol: 86 pg/ml. He also showed metabolic acidosis and hypokalemia. In order to stop seizures, he required bolus and continuous intravenous infusion of calcium gluconate associated to phenobarbital. During his evolution because of persistent hypertonia instead of intravenous calcium, he required low phosphorus diet and supplementation with magnesium, oral calcitriol, acetazolamide, hyperhydration and furosemide. With all of this, he got stabilization of calcium and phosphorus levels, and he could advance to oral treatment with calcium, magnesium, and calcitriol. But he also needed to associate calcidiol because of a new seizure. In addition, he had a tendency to hypokalemia and moderate hypercalciuria, so we added hydrochlorothiazide, spironolactone and high fluid intake to treatment. The brain resonance, renal ultrasound, echocardiography, lumbar puncture, and eyes fundus were normal. The electroencephalogram showed continuous cerebral bioelectrical activity with a mixture of diffuse theta-delta rhythms. In genetic study it was detected two heterozygous variants of uncertain significance in the CASR gene, compatible with autosomal dominant hypocalcemia with hypercalciuria or type V Bartter: -CASR NM_000388.3Chr3:g.122257242C>A c.347C>A; p.Ala116Asp(De Novo Mutation) -CASR NM_000388.3Chr3:g.122284925A>C c.2971A>C; p.Asn991His (Inherited from father) After diagnosis, he required one more admission for calcium decompensation in context of pharyngotonsillitis and vomits, in which he needed intravenous calcium. After that, he has remained stable.

Conclusion: Bartter V syndrome is a rare disease, but it should be suspected in cases of hypokalemia associated with hypocalcemia. Gain-of-function CASR mutations inhibit PTH secretion. It is important to ensure adequate levels of calcium, magnesium and phosphorus, but avoiding hypercalciuria. Oral calcitriol can regulate these levels, but it could increase the risk of nephrocalcinosis.