The aim of our study was to evaluate the functioning of the clock gene machinery in HS, and to address this issue we analyzed and compared mRNA expression levels of the core clock genes CLOCK, NPAS2, ARNTL1, ARNTL2, PER1, PER2, PER3, CRY1, CRY2, CSNK1D, CSNK1E, CSNK2A1, CSNK2A2,CSNK2B, NR1D1, NR1D2, RORA, SIRT1, TIMELESS, TIPIN, and a set of clock controlled genes in normal human fibroblasts and fibroblasts derived from subjects affected by Mucopolysaccharidosis type II. This evidence concerns the gene PER3 and mucopolysaccharidosis type 2.