,14,15,16,17,18 Considering that the majority of GAGs are taken up by endocytosis and undergo degradation in endosomes and lysosomes,19 mutations in VPS33A, a subunit of the tethering complexes that regulates the endocytosis process, may cause the defects of endocytosed GAGs transportation or degradation in MPSPS patient cells. Here, VPS33A is linked to mucopolysaccharidosis-plus syndrome.