Nephrocalcinosis often occurs in
infants and is caused by excessive
calcium or
vitamin D supplementation, neonatal
primary hyperparathyroidism, and
genetic disorders. Idiopathic infantile
hypercalcemia (IIH), a rare cause of
nephrocalcinosis, results from genetic defects in
CYP24A1 or SLC34A1.
Mutations in
CYP24A1, which encodes 25-hydroxyvitamin D 24-
hydroxylase, disrupt active
vitamin D degradation. IIH clinically manifests as
failure to thrive and
hypercalcemia within the first year of
life and usually remits spontaneously. Herein, we present a case of IIH wih
CYP24A1 mutations.An 11-month-old
girl visited our
hospital with incidental
hypercalcemia. She showed
failure to thrive, and her oral intake had decreased over
time since the age of 6 months. Her initial
serum parathyroid hormone level was low, 25-OH
vitamin D and 1,25-OH
vitamin D levels were normal, and renal
ultrasonography showed bilateral
nephrocalcinosis. Whole-
exome sequencing revealed compound heterozygous variants in
CYP24A1 (NM_000782.4c.376C>T [p.Pro126Ser] and c.1310C>A [p.Pro437His]). Although her
hypercalcemia and poor oral intake spontaneously resolved in approximately 8 months, we suggested that her
nephrocalcinosis and renal function be regularly checked in consideration of potential asymptomatic renal damage.
Hypercalcemia caused by IIH should be suspected in
infants with severe
nephrocalcinosis, especially when presenting with
failure to thrive.