So far clinical trials using LV transduced HSCs are ongoing in patients with adrenoleukodystrophy (ALD), metachromatic leukodystrophy (MLD), β-thalassemia, Wiskott-Aldrich syndrome (WAS), severe combined immunodeficiency (SCID) caused by adenosine deaminase (ADA) deficiency (ADA-SCID), X-linked SCID (X1-SCID) and chronic granulomatous disease (CGD) (Cicalese and Aiuti 2015, Aubourg 2016). The gene discussed is ADA; the disease is X-linked adrenoleukodystrophy.