Carbonic Anhydrase II Deficiency: Unusual Presentation of the Arabic Mutation. A Case Report

Carbonic anhydrase II deficiency is an extremely rare inborn error of metabolism that constitutes a triad osteopetrosis, renal tubular acidosis and intracerebral calcification. Unlike other subtypes of osteopetrosis, the presence of developmental delay and relative infrequency of skeletal fractures may not be a typical signs of symptoms indolent trajectory. This case report demonstrates a 11-year-old boy who had a bilateral midshaft tibial fracture despite low mechanism of injury. He was found to have severe respiratory distress with hypokalemia shortly after arriving to the emergency department venous blood gas (VBG) showed moderate metabolic acidosis. Potassium was corrected but he persistently had low potassium level despite frequent corrections. He was then started on sodium bicarbonate boluses. Whole exome sequencing (WES) was sent, and result was consistent with autosomal recessive osteopetrosis type III with renal tubular acidosis (RTA) evident by pathologic variant on CA2 gene confirming the diagnosis of carbonic anhydrase II (CA II) deficiency consistent with the unique Arabic mutation. Conversely, low mechanism of fracture injury in the context of severe form of fracture type should raise the concern of (CA II) deficiency especially in a pediatric patient who show no signs of developmental of cognitive delay.