Background: Globotriaosylceramide (Gb3) was assessed as a surrogate marker to predict change from baseline after 12 months of agalsidase alfa (agalα) treatment (CFB-M12) in estimated glomerular filtration rate (eGFR) and left ventricular mass index (LVMI) using pooled data from three 24-week, randomized, placebo-controlled trials (RCTs; TKT003/ TKT005/TKT010) and their open-label extension studies (EXT; TKT006/ TKT007/TKT013/TKT015) of patients with Fabry disease (FD). Methods: Males (≥18-year-old) with confirmed FD received agalα (0.2 mg/kg every other week) for 12 months. A backward elimination approach evaluated potential predictors (baseline and CFB-M12 Gb3 [urine; plasma], urine protein; baseline eGFR; age at first dose; baseline LVMI). Subgroups included patients randomized to placebo during RCTs (pbo->agalα) or to agalα (agalα->agalα), or with stage 2/3 chronic kidney disease (CKD2/3). Results: In the analysis population (n=73), eGFR (baseline) and plasma Gb3 (baseline; CFB-M12) significantly predicted CFB-M12 eGFR (all P< 0.05). No predictors of CFB-M12 LVMI were significant (n=39). In the pbo->agalα subgroup (n=36), only plasma Gb3 (baseline; CFB-M12) significantly predicted CFB-M12 eGFR (P<0.05). No significant predictors were found in other subgroups. Conclusion: Urinary and plasma Gb3 concentrations were not useful biomarkers for FD progression in agalα-treated patients. Conflict of Interest declared. Bioavailability was ≥50%; food reduced bioavailability by 40%. Plasma levels increased proportionally up to 1250 mg; no further increase was observed at 2000 mg. Steady-state was achieved within 5 days; accumulation ratios were 1.2 to 1.8. Unchanged drug was eliminated by the kidney with a half-life of 4 hours. Dose-related increases in WBC α-Gal A activity were observed after 7 days of dosing. AT1001 was well tolerated, with dizziness, headache and skin irritation the most commonly reported adverse effects. Conclusion: Migalastat was rapidly absorbed and exhibited linear pharmacokinetics. Dose-related increases in α-Gal A activity in PBMCs were observed. Conflict of Interest declared. Background: Fabry disease is caused by mutations in the gene (GLA) that encodes alpha-galactosidase A (alpha-Gal A). The iminosugar AT1001 (GR181413A, migalastat hydrochloride, 1-deoxygalactonojirimycin) is an orally-available pharmacological chaperone that selectively binds and stabilizes alpha-Gal A, increasing total cellular levels and activity for some mutant forms. AT1001 is currently under clinical development for the treatment of Fabry disease. Methods: A validated, transient transfection-based assay was developed in HEK-293 cells to test 460+ Fabry disease-causing mutant forms (predominantly missense) for response to AT1001. Responses were measured by enzyme assay and western blot. Transfection efficiencies across independent assays and mutations were assessed by quantitative real-time PCR. Results: Increases in both alpha-Gal A protein level and enzyme activity were seen for~60% of the mutant forms. Importantly, the HEK-293 cell responses of 19 alpha-Gal A mutant forms to a clinically-achievable concentration of AT1001 (10 μM) were generally consistent with observed increases in alpha-Gal A activity in peripheral blood mononuclear cells from male Fabry patients administered AT1001 during Phase 2 clinical studies. Conclusions: These results suggest that the alpha-Gal A increase in cultured cells may be used to identify Fabry patients that could benefit from AT1001 therapy. Conflict of Interest declared.