Calcium pyrophosphate deposition disease revealing a hypersensitivity to vitamin D

Hypersensitivity to vitamin D (HVD) due to a loss of function mutation of the CYP24A1 gene, which encodes vitamin D catabolizing enzyme was initially described as a cause of acute hypercalcemia in children and chronic renal diseases in adults.

We describe the first case of a patient presenting a calcium pyrophosphate deposition disease (CPDD) revealing a HVD.

An abnormality of phospho-calcic metabolism was discovered during the course of an etiological workup for CPDD in a 52-year-old patient. Laboratory tests revealed a blood calcium level at the upper limit of normal range, a markedly low parathormone level, a 25-hydroxyvitamin D level within the upper level of normal, an elevated 1,25-dihydroxyvitamin D level and an elevated urine calcium level. CYP24A1 gene sequencing analysis revealed two mutations in a heterozygous state. The study of the 25-hydroxyvitamin D₃: 24,25-dihydroxyvitamin D₃ ratio, two metabolites of vitamin D confirmed the enzyme deficiency in vivo. Our observation suggests that this disease could correspond to a rare cause of CPDD.

In cases of CPDD associated with calcium values within the upper limit of normal range (or hypercalcemia) with an abnormally low PTH, one could suggest searching for HVD.