A gene therapy medical product is defined by the European Medicines Agency (EMA) as having two characteristics: (a) it comprises an active substance that contains or consists of a recombinant nucleic acid utilized in or provided to human beings with a view to regulating, correcting, replacing, or adding or deleting a genetic sequence; and (b) its therapeutic, prophylactic, or diagnostic impact relates directly to the recombinant nucleic acid. Vaccines against infectious illnesses are not permitted in gene therapy ,however clinical successes in 2009-2011 have bolstered new optimism in the promise of gene therapy. These include successful treatment of patients with the retinal disease Leber congenital amaurosis X linked SCID, ADA-SCID, adrenoleukodystrophy, and Parkinson's disease,