• Safety and tolerability of 3 dose levels of oral AT1001
  

• Pharmacokinetics of 3 dose levels of oral AT1001
  
• Pharmacodynamic effects of oral AT1001 (effects on enzyme and substrate levels, cardiac function, renal function, and nerve conduction)
  

This open-label study will be conducted in up to 20 patients at five clinical sites in the United States. Patients will undergo a 28-day screening period, including a 14-day run-in with AT1001 to assess eligibility for the study. Patients receiving enzyme replacement therapy or substrate depletion therapy for Fabry disease must undergo a 2-week washout of prior therapy before the 28-day screening period. Patients will receive a daily dose of AT1001 for 12 weeks during the treatment phase. The pharmacokinetics of AT1001 in plasma and urine will be assessed at regular intervals. Safety will be evaluated throughout the treatment period. At the end of the 12-week treatment period, the effect of AT1001 on pharmacodynamic parameters (alpha-Gal A in leukocytes, GL-3 in plasma and urine, and alpha-Gal A and GL-3 in skin biopsy samples) and functional parameters (cardiac function as assessed by electrocardiogram, echocardiogram, and MRI, and renal function as assessed by blood and urine tests, and nerve conduction as assessed by QSART and CASE IV tests) will be evaluated. If the safety profile is acceptable, patients will be permitted to enter a 36-week treatment extension period and continue to receive AT1001, with safety, pharmacodynamic, and functional assessments performed at 12-week intervals.

Inclusion Criteria:

• Males between 18 and 55 years of age (inclusive)
• Hemizygous for Fabry disease
• Have a confirmed diagnosis of Fabry disease with a documented missense gene mutation (individual or familial)
• Have enhanceable enzyme activity
• In the judgment of the investigator, must either be able safely to suspend enzyme replacement therapy (ERT) for a minimum of 18 weeks throughout the study, or be ERT naive
• Agree to be sexually abstinent or use a condom with spermicide when engaging in sexual activity during the course of the study and for a period of 30 days following completion of the study
• Willing and able to sign an informed consent form

Exclusion Criteria:

• History of significant disease other than Fabry disease (eg, end-stage renal disease; Class III or IV heart disease [per the New York Heart Association classification]; current diagnosis of cancer, except for basal cell carcinoma of the skin; diabetes (unless HbA1c <= 8); or neurological disease that impairs the patient's ability to participate in the study
• History of organ transplant
• Serum creatinine greater than 2 on Day -2
• Screening 12-lead ECG demonstrating QTc > 450 msec prior to dosing
• Taking a medication prohibited by the protocol: Fabrazyme (agalsidase beta), Replagal (agalsidase alfa), Glyset (miglitol), Zavesca(miglustat), or any experimental therapy for any indication
• Participated in a previous clinical trial in the last 30 days
• Any other condition, which, in the opinion of the investigator, would jeopardize the safety of the patient or impact the validity of the study results