Calcium pyrophosphate deposition disease revealing a hypersensitivity to vitamin D.

OBJECTIVE: 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.

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

RESULTS: 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.

CONCLUSION: 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.