ENPP2 and Hurler syndrome: Since the activities, levels or functions of proteins encoded by these transcripts are related to the levels of metal ions, mostly Ca2+ (MMP12, CAPG, CDH2, STK32B, SAR1A, CRELD1, PLCB4, ENPP2, TMEM38B), Zn2+ (MMP12, WTIP, FHL3, USP12, ENPP2) and Fe2+ (HEPH), we decided to test the concentrations of these three metal ions in cell cultures, using fibroblasts derived from a patient with MPS type I, revealing a severe phenotype (Hurler syndrome).