Gaucher's disease is due to glucocerebrosidase deficiency which is responsible 
for the accumulation of non degraded glucosylceramide within the lysosomes of 
macrophages: these "Gaucher cells", overloaded and alternatively activated, 
release in patient's plasma numerous compounds (cytokines, chemokines, 
hydrolases...) some of which contribute to the various tissue damages. Some of 
these compounds are surrogate biomarkers which contribute to the evaluation of 
disease severity, progression and stabilisation or regression during treatment. 
To date, the most interesting biomarkers are chitotriosidase and the chemokine 
CCL18/PARC, especially in chitotriosidase deficient patients. These biomarkers 
together with the clinical evaluation help to therapeutic choice (treatment by 
enzyme replacement therapy or substrate reduction therapy) and initiation 
decision, response follow-up and dose adjustments. Biomarkers should be assessed 
every 12 months together with clinical evaluation in patients not receiving 
specific treatments. An assessment every 3 months is recommended during the 
first year of treatment. Then when clinical goals have been achieved, the 
frequency can be reduced to every 12 months if the therapeutic scheme is not 
modified.