CLOCK and mucopolysaccharidosis type 2: Accordingly, the evaluation by qRT-PCR of clock gene expression upon synchronization through serum shock of normal fibroblasts and fibroblasts of patients affected by Hunter syndrome before and after 24 hours of idursulfase treatment evidenced a statistically significant effect on the expression levels of ARNTL2, PER1 and PER2, but only at the earlier time points examined, with advance of the phase of oscillation of gene expression.