Moreover, rapid desensitization has been used also in the case of allergy to recombinant enzymes in rare metabolic diseases, including allergy to Pegvaliase in phenylketonuria [43], allergy to elosulfase alfa in the Morquio syndorme [44] and allergy to idursulfase [45] and laronidase [9]. The gene discussed is IDS; the disease is phenylketonuria.