Heterozygous loss of function (LOF) mutations in EXT1 and EXT2 are known to be involved in the development of hereditary multiple exostoses (HME) syndrome [10], a disorder with a reported prevalence of 1/50.000 individuals [11], and have been shown to lead to both locally (exostosis plate) [12] and systemically [13] altered heparan sulfate composition. Here, EXT2 is linked to hereditary multiple exostoses.