Safety, Pharmacokinetics, Pharmacodynamics, and Efficacy of Migalastat in Pediatric Subjects (Aged 12 to <18 Years)

This is a Phase 3b, 2-stage, open-label, uncontrolled, multicenter study to evaluate the
safety, pharmacokinetics, pharmacodynamics, and efficacy of migalastat treatment in pediatric
subjects 12 to <18 years of age and weighing ≥ 45 kg (99 pounds) with Fabry disease and with
amenable GLA variants. Subjects must be either naïve to enzyme replacement therapy (ERT) or
have stopped ERT at least 14 days at the time of screening.

Stage 1 will be a treatment period of approximately 1 month (4 weeks); Stage 2 will be a
treatment period of 11 months and a 30-day (untreated) safety follow-up period. There will be
no break in treatment between Stages 1 and 2. Prior to Stage 1, there will be a screening
period lasting at least 14 days and up to 30 days (or more, if GLA genotyping is required).
Stage 1 and 2 together will consist of a 12-month treatment period, and a 30-day safety
follow-up period, for a total of approximately 13 months. Subjects may have the option to
enroll in a long-term extension study conducted under a separate protocol.

Subjects will be randomly assigned 1:1:1 to 1 of 3 PK sampling groups using interactive
response technology (IRT). Four blood samples for determination of migalastat concentrations
in plasma will be collected on any one 24 hour period between Day 15 and Day 30 of study drug
administration and again at Months 6 and 12.

Inclusion Criteria

- Willing and able to provide written consent or assent (subject and parent/legal
guardian, as applicable)

- Male or female between 12 and <18 years of age diagnosed with Fabry disease

- Confirmed GLA variant that has shown to be responsive to AT1001 in vivo

- Subject weighs at least 45 kg (99 pounds) at screening

- Subject has never been treated with ERT or has not received ERT for 14 days prior to
screening

- Subject has at least one complication (ie, laboratory abnormality and/or sign/symptom)
of Fabry disease

- Subject is able to swallow study medication whole

- Women/girls who can become pregnant and all males agree to be sexually abstinent or
use medically accepted methods of birth control during the study and for 30 days after
study completion

Exclusion Criteria

- Has moderate or severe renal impairment (eGFR <60 ml/min/1.73 m2 at screening)

- Has advanced kidney disease requiring dialysis or kidney transplantation

- History of allergy or sensitivity to study medication (including excipients) or other
iminosugars (eg, miglustat, miglitol)

- Has received any gene therapy at any time or anticipates starting gene therapy during
the study period

- Requires treatment with Glyset (miglitol), Zavesca (miglustat) within 6 months before
screening or throughout the study

- Requires treatment with Replagal (agalsidase alfa), or Fabrazyme (agalsidase beta)
within 14 days before screening or throughout the study

- Subject is treated or has been treated with any investigational/experimental drug,
biologic or device within 30 days before screening

- Any intercurrent illness or condition or concomitant medication use considered to be a
contraindication at screening or baseline or that may preclude the subject from
fulfilling the protocol requirements or suggests to the investigator that the
potential subject may have an unacceptable risk by participating in this study

- Pregnant or breast-feeding

- Otherwise unsuitable for the study in the opinion of the investigator