Hydrolysis of unsulfated alpha-L-iduronosidic linkages in dermatan sulfate. Monomer. Detected in testis (at protein level). Expressed ubiquitously. A smaller 63 kDa protein probably arises from IDUA protein by proteolytic cleavage. N-glycosylation contributes to substrate binding and is required for full enzymatic activity. Defects in IDUA are the cause of mucopolysaccharidosis type I (MPS I). Belongs to the glycosyl hydrolase 39 family.