This is a multicenter, randomized, double-blind, placebo-controlled, cross-over study to evaluate the efficacy and safety of AVTX-801 in subjects with SLC35A2-CDG

Inclusion Criteria

• Molecular confirmation of SLC35A2 genetic variant
• Age > 1 month
• Presence of seizures, chronic vomiting, chronic constipation, or chronic diarrhea
• A parent or legal guardian must be available and willing to provide consent on behalf of minor subjects or adult subjects who are unable to give informed consent due to developmental disabilities.
• Use of contraception in females > age 8 years
• Previously performed eye exam within last year

Exclusion Criteria

• Aldolase-B deficiency
• Galactosemia
• Hemolytic uremic syndrome
• Hemoglobin < 7 mg/dL
• LFTs > 3x ULN
• Previously experienced severe AEs from oral galactose (severe diarrhea, vomiting, constipation, galactosuria, or increased liver glycogen storage)
• Other history of galactose intolerance as determined by the investigator
• Currently treated with ketogenic diet
• Current enrollment in another trial involving investigational compounds
• Ongoing dietary D-galactose supplementation
• Use of investigational compounds
• Pregnancy