Inclusion Criteria:
* definitive diagnosis of FSHD1 or FSHD2, confirmed by clinical findings and prior genetic testing results
* presence of weakness in upper limbs at Screening, defined as a Brooke score ≥ 2
* presence of weakness in a lower limb at Screening, defined as a MRC score of ≤4 on ankle dorsiflexion
* ambulatory at Screening
* if taking herbal remedies and supplements which can impact muscle strength and function, must maintain a stable regimen for the duration of the trial
* if taking prescription medicines, over-the-counter medicines and/or herbal supplements for supportive care, doses should be stable for ≥ 1 month prior to the Screening Visit and remain stable for the duration of the trial
* if on a physical therapy/strength training regimen, the regimen must be stable for ≥ 2 months prior to the Screening Visit and remain stable for the duration of the trial
* ability to provide written informed consent
* all participants, if sexually active, agree to follow the contraception requirements and sperm donation limitations
Exclusion Criteria:
* ambulatory participants expected to experience loss of ambulation within ≤ 12 months
* medical condition, other than FSHD, that would impact ambulation or ability to perform the functional assessments
* presence of acute or chronic illness, or history of chronic illness (other than FSHD)
* prior or ongoing medical condition, medical history, physical examination findings, ECG findings, or laboratory abnormality that, in the Investigator's opinion, could adversely affect the safety of the participant
* evidence of renal impairment at Screening, including renal impairment demonstrated by cystatin C-based estimated glomerular filtration rate (eGFR) \<60 mL/min/1.73m², a history of clinically significant renal disease, or current acute kidney injury or acute kidney injury
* evidence of significant hepatic dysfunction, defined as glutamate dehydrogenase (GLDH) \>2× upper limit of normal (ULN) at the Screening Visit, or known hepatic impairment classified as Child-Pugh Class B (moderate) or Child-Pugh Class C (severe)
* history of seizures or seizure-like events
* surgery (e.g., stomach bypass) or medical condition that might affect absorption of medicines
* acute gastrointestinal symptoms (e.g., nausea, vomiting, diarrhea, heartburn) or acute infection (such as influenza) or a significant infection or known inflammatory process at Screening
* presence or history of severe adverse reaction to any excipients in the study drug tablets
* treatment with another investigational drug or biological agent within 30 days or 5 half-lives of the investigational drug or biological agent
* received SAT-3247 in another study
* positive test for hepatitis B surface antigen (HBsAg), hepatitis C (HCV) antibody or Human Immunodeficiency Virus (HIV)
* current or expected use during the study of any medications that are known to be strong or moderate inhibitors of Cytochrome P450 isoform 3A4 (CYP3A4)
* treatment with a glucagon-like peptide-1 (GLP-1) receptor agonist or dual glucose-dependent insulinotropic polypeptide (GIP)/GLP-1 receptor agonist within 3 months prior to Screening
* consumption of grapefruit, grapefruit juice, and grapefruit-containing products
* employee, contractors, or consultants of the Sponsor, the contract research organization (CRO), and/or study site or their relatives
