Study to Assess the Safety, Tolerability, PK and PD of ABX1100

Parts A-B Inclusion Criteria:

• Body mass index (BMI) between 18.0 and 32.0 kg/m2, inclusive and weight between 50and 90 kg, inclusive.

• Agree not to have a tattoo or body piercing until the end of the study.

• Agree not to receive COVID-19 vaccination from 7 days prior to first study drugadministration until at least 7 days after the last study drug administration.

• Agree not to receive a vaccination (live attenuated vaccine) during the study anduntil 60 days after the study has ended (last study procedure).

• Willing to undergo needle muscle biopsies.

• Willing to avoid strenuous activities 48 hours before needle muscle biopsy andthroughout the study.

• Female participants who are sexually active with a non-sterilized partner must benon-pregnant and non-lactating and agree to use a highly effective method ofcontraception.

• Males of childbearing potential must agree to use a highly effective method ofcontraception with female sexual partners of childbearing potential and not donatesperm during study participation and for 90 days after last administration of studydrug ABX1100 or placebo.

Parts A-B Exclusion Criteria:

• Known history or presence of any clinically significant hepatic,renal/genitourinary, gastrointestinal, cardiovascular, cerebrovascular, pulmonary,endocrine, immunological, musculoskeletal, neurological, psychiatric, dermatologicalor hematological disease or condition.

• History of any inherited or acquired skeletal muscle diseases (for example, DuchenneMuscular Dystrophy (DMD), Becker Muscular Dystrophy (BMD), Limb-Girdle MuscularDystrophy (LGMD), Myotonic Dystrophy, Spinal Muscular Atrophy (SMA), Polymyositis,Rhabdomyolysis and Inclusion Body Myositis (IBM).

• History of any inherited or acquired cardiac disease including congestive heartfailure, ischemic heart disease, or arrhythmias; an abnormal ECG.

• History of cancer within past 5 years, with the exception of treated or excised skinbasal cell carcinoma.

• Any clinically significant illness, medical/surgical procedure, or trauma within 4weeks prior to the screening visit

• Presence of any significant physical or organ abnormality.

• Major surgery within 6 months prior to the start of the study.

• Current smoker, recent history of smoking and/or use of any nicotine-containingproducts (within past 6 months).

• A known history or positive test result for hepatitis B surface antigen (HBsAg),hepatitis C antibody or human immunodeficiency virus (HIV) infection.

• Currently participating in another investigational trial or have received anyinvestigational drug within the past 30 days.

Part C Key Inclusion criteria

• Male or female LOPD patients aged ≥ 18 years (inclusive) of age, at the time ofinformed consent.

• Body mass index (BMI) between 18.0 and 35.0 kg/m2, inclusive and weight >50 kg.

• Agree not to receive COVID-19 vaccination from 7 days prior to first study drugadministration until at least 7 days after the last study drug administration orafter the final study procedure, whichever is later.

• Agree not to receive a vaccination (live attenuated vaccine) during the study anduntil 60 days after the study has ended (last study procedure).

• Willing to undergo needle muscle biopsies.

• Documented Acid alpha-glucosidase (GAA) deficiency and mutation analysis from blood,skin, or muscle tissue for confirmation of diagnosis of LOPD.

• Currently receiving a stable dose of standard of care enzyme replacement therapy (ERT) regularly for a minimum of 6 months immediately prior to study entry

• Capable of walking 50 meters with or without an assistive device.

• Predicted upright Forced Vital Capacity (FVC) >= 30% within the past year prior tostudy entry, not requiring invasive mechanical ventilation. Non-invasive, temporary,respiratory support is acceptable

• Female participants who are sexually active with a non-sterilized partner must benon-pregnant and non-lactating and agree to use a highly effective method ofcontraception.

• Males of childbearing potential must agree to use a highly effective method ofcontraception with female sexual partners of childbearing potential and not donatesperm during study participation and for 90 days after last administration of studydrug ABX1100.

Part C Key Exclusion criteria

• History of muscle biopsy within 1 month of Day 1 or planning to undergo non-studyrelated muscle biopsies during study period.

• History of coronary artery disease or cardiovascular disease.

• History or presence of gastrointestinal, renal, or hepatic disease or any othercondition known to interfere with absorption, distribution, metabolism, or excretionof drugs.

• Presence of any significant physical or organ abnormality as determined by thePI/Sub-Investigator.

• Resting seated blood pressure < 90/40 mmHg or > 140/90 mmHg , unless deemed notclinically significant by the PI/Sub-Investigator.

• Resting seated heart rate < 45 bpm or > 99 bpm, unless deemed not clinicallysignificant by the PI/Sub-Investigator.

• Intolerance to and/or difficulty with blood sampling through venipuncture.

• Positive pregnancy test for female participants.

• Currently participating in another investigational trial or have received anyinvestigational drug within the past 30 days or 5 elimination half-lives of theinvestigational drug, whichever is longer, prior to dosing.

• Requires a wheelchair or invasive ventilation.

• Fridericia's corrected QT (QTcF) > 450 ms for participants or history of QT intervalprolongation unless deemed not clinically significant by the PI/Sub-Investigator.

• Uncontrolled diabetes (Hemoglobin A1c [HbA1c] equal to or higher than 7.5%).

• A known history or positive test result for hepatitis B surface antigen (HBsAg),hepatitis C antibody or human immunodeficiency virus (HIV) infection.