Olkhovych N.V. 1 , Pichkur N.O 1 , Ivanova T. P 1 , Grishchenko O.N. 1 , Nedoboy A.N. 1 , Gorovenko N.G. 2 , Trofimova N.S 1 1 National Children Hospital "OHMATDET", Kyiv, Ukraine 2 National Medical Academy of Postdiploma, Kyiv, Ukraine Introduction: Gaucher disease (GD) is an inherited glycolipid storage disorder resulting from the deficiency of glucocerebrosidase. The GD accounts for 71% of all lysosomal disorders diagnosed in Ukraine. Materials and methods: The 17 GD patients (7 children, 10 adults) have been treated with ERT and monitored since 2004. The diagnoses of all patients were established by clinical, laboratory and morphological ("Gaucher cells" in bone marrow) data. The mean activity of glucocerebrosidase deficiency in leukocytes was 2,7 ±1,4 nmol/h/mg protein (reference range-7,2±2,1 nmol/h/mg protein). All patients were screened for gene mutations in the GBA gene. Results: The regularity of ERT with the recombinant glucocerebrosidase has reduced manifestations of hepatosplenomegaly and pancytopenia, bone pain and bone crises in the most GD patients, and led to significant improvements. The chitotriosidase activity has decreased from 4552-29614 nmol/h/ml pl (before the ERT) to 870-4897 nmol/h/ml pl (after the ERT). Conclusions: The efficacy of treatment depends on the regularity, the dose and the severity of the disease at the beginning of therapy. Background: In GD1, certain disease-related biomarkers (GL-1, GM3) have been identified that reflect perturbation of the glycosphingolipid metabolic pathway caused by acid beta-glucosidase deficiency, whereas others (chitotriosidase, CCL18, ACE, TRAP) represent secondary effects on tissues. Various biomarkers in GD1 are responsive to imiglucerase enzyme replacement therapy and are used clinically to monitor patients. Eliglustat, a novel, small molecule inhibitor of glucosylceramide synthase (GCS), is under development as an oral substrate reduction therapy for GD1. Objectives: Evaluate biomarker responses to eliglustat in GD1 patients. Methods: A Phase 2 study enrolled 26 adult patients with GD1 not on treatment; 19 completed 3 years of treatment with eliglustat. Plasma levels of GL-1, GM3, chitotriosidase, CCL18, ACE, and TRAP were measured periodically throughout the study. Results: GD1 biomarkers were elevated in most patients pre-treatment. Statistically significant decreases (P<.0001) following eliglustat treatment were seen in median plasma GL-1 and GM3 (80% and 64%, respectively), which normalized; and median chitotriosidase, CCL-18, and ACE (80%, 73%, and 62%, respectively), which all remained above normal. Two-year median TRAP decreased by 51% (P<.0020), but remained above normal. Conclusions: Eliglustat treatment led to reductions in GD1-related biomarkers that reflect both primary and secondary effects of the underlying enzyme deficiency. Conflict of Interest declared.