A Study to Learn About the Safety and Effects of the Study Drug PRX-102 in Children and Adolescents With Fabry Disease

Prior treatment

• Initiation of treatment with an angiotensin-converting enzyme inhibitor (ACEi) or angiotensin II receptor blocker (ARB) or a dose change in ongoing treatment in the four weeks before screening.
• Currently taking another investigational drug for any condition.
• History of acute kidney injury in the 12 months before screening, including specific kidney diseases (e.g., acute interstitial nephritis, acute glomerular and vasculitic renal diseases); non-specific conditions (e.g., ischaemia, toxic injury); or extrarenal pathology (e.g., prerenal azotaemia, acute postrenal obstructive nephropathy).
• Severe cardiomyopathy or significant unstable cardiac disease within six months before screening.
• A positive test for Severe Acute Respiratory Syndrome-Coronavirus 2 (SARS-CoV-2) within three months before screening.
• Receipt of treatment for Fabry disease within six months before screening
• Positive for anti-PRX-102 antibodies at screening
  • Additional Exclusion Criteria for Subjects in Stage II (i.e., non-treatment naïve males or females):

Other illness

• History of type I hypersensitivity reactions (anaphylactic or anaphylactoid life-threatening reaction) to other ERT treatment for Fabry disease or any component of the study drug.
• History of renal dialysis or kidney transplantation.
• History of or current malignancy requiring treatment.
• Presence of any medical, emotional, behavioural, or psychological condition that, in the Investigator's judgement, could interfere with the subject's compliance with the requirements of the study.
  • Additional Exclusion Criteria for Subjects Enrolled in Stage I:
• Non-classic form of Fabry disease
• Unwilling to discontinue current ERT treatment for Fabry disease before baseline.

Lab values

• Estimated glomerular filtration rate (eGFR) at screening \< 80 mL/min/1.73 m2.
• Urine protein to creatinine ratio (UPCR) \> 0.5 g/g (0.5 mg/mg or 500 mg/g) if not treated with an ACE inhibitor or ARB.

Other

• All Subjects:
• Female
• Females: Pregnant or lactating, or of childbearing potential with a fertile male partner and unwilling to use a highly reliable method of contraception from the informed consent signature until 30 days after the last infusion.

• Participants with the provision of informed consent from their legal guardians
• Boys and girls aged 2 to 7 years (Cohort A), 8 to 12 years (Cohort B), or 13 to \<18 years (Cohort C).
• Confirmed diagnosis of Fabry disease
• Presence of at least one of the following characteristic features of Fabry disease: neuropathic pain, cornea verticillata, and/or clustered angiokeratoma.
• History of Fabry pain: Fabry crises OR chronic pain.
• Clinical condition that, in the investigator's opinion, requires ERT treatment.