Plasma LysoHexCer is reported to be correlated with chitotriosidase activity [30,35], but is more reliable as 6–8% of patients present chitotriosidase deficiency (due to a homozygous 24-bp duplication in the CHIT1 gene) and about 35% are heterozygous for this duplication [36], hampering the interpretation of chitotriosidase levels. The gene discussed is CHIT1; the disease is chitotriosidase deficiency.