The invention relates to mRNA therapy for the treatment of Acute Intermittent Porphyria (AIP). mRNAs for use in the invention, when administered in vivo, encode human porphobilinogen deaminase (PBGD), isoforms thereof, functional fragments thereof, and fusion proteins comprising PBGD. mRNAs of the invention are preferably encapsulated in lipid nanoparticles (LNPs) to affect efficient delivery to cells and/or tissues in subjects, when administered thereto. mRNA therapies of the invention increase and/or restore deficient levels of PBGD expression and/or activity in subjects. mRNA therapies of the invention further decrease levels of toxic metabolites associated with deficient PBGD activity in subjects, namely porphobilinogen and aminolevulinate (PBG and ALA).
