Therapeutical success has been obtained in pioneer trials using genetically corrected human bone marrow stem cells to treat patients suffering from X-linked severe combined immunodeficiency (SCID) (Hacein-Bey-Abina et al, 2002), X-linked adrenoleukodystrophy (ALD) (Cartier et al, 2009) and SCID-adenosine deaminase (ADA-SCID) (Aiuti et al, 2009). The gene discussed is ADA; the disease is X-linked adrenoleukodystrophy.