A rapid screening of a recurrent CYP24A1 pathogenic variant opens the way to molecular testing for Idiopathic Infantile Hypercalcemia (IIH)

Introduction: Loss-of-function mutations in cytochrome P450 family 24 subfamily A member 1 (CYP24A1) gene are associated with Idiopathic Infantile Hypercalcemia (IIH) and adult kidney stone disease. The enzyme deficiency leads to an impaired vitamin D catabolism pathway, resulting in a syndrome characterized by recurrent hypercalcemia, hypercalciuria and suppressed parathyroid hormone (PTH) levels. In these patients, the genetic evaluation of CYP24A1 is an important diagnostic tool, allowing the definitive diagnosis of IIH. Methods: A rapid CYP24A1 gene testing based on High Resolution Melting Analysis (HRMA) was designed in order to detect the CYP24A1 c.428_430delAAG (p.Glu143del), a recurrent IIH-associated variant. Results: HRMA method was able to identify c.428_430delAAG genotypes evaluating melting curve shape and melting temperature (Tm). Heterozygous samples exhibited a typical melting profile while homozygous samples showed a specific Tmshift. Conclusions: We provide evidence about application of HRMA in unambiguous genotyping of the CYP24A1 c.428_430delAAG variant, making this method useful in clinical molecular diagnostics. This approach opens the way to a helpful molecular analysis of CYP24A1 gene in IIH diagnosis, to an improved pharmacological treatment strategy and to a reduced risk of recurrent stones and worsening nephrocalcinosis.