Despite the fact that about 6% of Caucasians have complete enzyme deficiency due to homozygosity to the 24-bp duplication mutation at exon 10 of the chitotriosidase gene (CHIT1) [13], plasma chitotriosidase activity has been established as a screening marker and therapeutic monitor for enzyme replacement therapy in Gaucher’s disease [14]. The gene discussed is CHIT1; the disease is Gaucher disease.