Disclosed is a pharmaceutical composition comprising at least 50 mg/ml of a porphobilinogen deaminase polypeptide and functionally equivalent parts and analogues hereof, wherein said functionally equivalent parts and analogues hereof exerts substantially the same enzymatic activity as the full length enzyme, and wherein less than 5% of the total amount of porphobilinogen deaminase in said composition is present in the form of aggregates. Further disclosed is the use of a pharmaceutical composition comprising 50-300 mg/ml of a porphobilinogen deaminase polypeptide, and functionally equivalent parts and analogues hereof, in the manufacture of a medicament for the treatment of Acute Intermittent Porphyria, and wherein said functionally equivalent parts and analogues hereof exerts substantially the same enzymatic activity as the full length enzyme.
