24-Week Study to Assess the PD, Safety, Tolerability, and PK of GLM101 in Participants with PMM2-CDG

Inclusion Criteria:

• Is male or female, 18 to 65 years of age, inclusive, at Screening (Cohorts 1-3, 7), 12-17 years of age, inclusive, at Screening (Cohort 4) or 2-11 years of age,inclusive, at Screening (Cohorts 5 and 6);

• Molecularly confirmed diagnosis of PMM2-CDG. Diagnosis is defined as biallelicpathogenic and/or likely pathogenic variants, or, in the case of variants ofuncertain pathogenicity, demonstration of bi-allelic variants ANDphosphomannomutase-2 (PMM2) enzyme activity consistent with a diagnosis of PMM2-CDG.Historical diagnosis with lab report(s) on file is permitted;

• If the participant is a female of childbearing potential (i.e. fertile, followingmenarche and until becoming post-menopausal unless permanently sterile (permanentsterilization methods include hysterectomy, bilateral salpingectomy and bilateraloophorectomy)) she must not be pregnant (confirmed by a negative serum pregnancytest), is using a medically accepted method of contraception (abstinence, a hormonalcontraceptive associated with inhibition of ovulation in conjunction with a barriermethod, or use of an intrauterine device), and must agree to continue using thismethod for 50 days after the last infusion of GLM101; Note: sexual abstinence isconsidered a highly effective method only if defined as refraining from heterosexualintercourse during the entire period of risk associated with the study treatments.The reliability of sexual abstinence needs to be evaluated in relation to theduration of the clinical trial and the preferred and usual lifestyle of the subject.Periodic abstinence (calendar, symptothermal, post-ovulation methods) is not anacceptable method of contraception;

• If the participant is a female of non-childbearing potential, she must bepre-pubertal, surgically sterile, or must have an ovarian dysfunction confirmed by afollicle stimulating hormone (FSH) >40 IU/L and absence of menses for 12 monthswithout an alternative medical cause;

• If the participant is a sexually active male with female partners, the sexuallymature, nonsterile male participant agrees to use a medically acceptable method ofcontraception (abstinence, the partner taking a hormonal contraceptive inconjunction with a male condom, or use by the partner of an intrauterine device witha male condom) and agrees to continue using this method for 50 days after the lastinfusion of GLM101. Males are considered surgically sterile if they have undergonebilateral orchiectomy or vasectomy at least 3 months prior to Screening;

• If the participant is male, he must agree to refrain from donating sperm during thestudy and 50 days after the last infusion of GLM101;

• Is willing and able to provide informed consent/assent, directly or through his/herlegally authorized representative.

Exclusion Criteria:

• Diagnosis of congenital disorder of glycosylation (CDG) other than PMM2; Diagnosisis defined as biallelic pathogenic and/or likely pathogenic variants, or, in thecase of variants of uncertain pathogenicity, demonstration of bi-allelic variantsAND the defined CDG enzyme activity consistent with a diagnosis of the CDG otherthan PMM2 CDG.

• Has an active infection requiring parenteral antibiotics, antivirals, or antifungalsor treatment with systemic steroids within 7 days prior to Screening;

• Has confirmed active coronavirus disease-2019 (COVID-19) or tests positive forsevere acute respiratory syndrome coronavirus 2 (SARS CoV 2) at Screening or checkin to the clinical site;

• ALT or AST >3× ULN OR total bilirubin >2× ULN or INR >1.5

• Has a history of a severe allergic reaction to any drug or excipients of GLM101 (aslisted in the GLM101 Investigator's Brochure);

• Has a known history of poor venous access;

• Has a history of liver transplant;

• Has a history of drug or alcohol use disorder within 12 months prior to Screening;

• Has had a major surgical procedure within 30 days prior to Screening;

• Has Screening or eligibility confirmation laboratory value(s) outside the laboratoryreference range considered clinically significant and not related to PMM2-CDG;

• If female, has a positive serum pregnancy test during Screening;

• If female, must not be breastfeeding;

• Has serology positive for hepatitis B surface antigen or hepatitis C antibody duringScreening;

• Has history or presence, upon clinical evaluation, of any illness that might impactthe safety of GLM101 infusion or evaluability of drug effect based on theInvestigator's and Medical Monitor's discretion;

• Has a QTc ≥ 450 ms, or other clinically significant ECG abnormalities;

• Has uncontrolled cardiovascular, hepatic, pulmonary, gastro-intestinal, endocrine,metabolic, ophthalmologic, immunologic, psychiatric or other significant disease;

• Is currently participating in another interventional clinical study or has completedanother clinical study with an investigational drug or device within 30 days or 5half-lives before GLM101 infusion.

• Weight exceeds 75 kg.