Among the few gene therapies that have obtained FDA approval are HEMGENIX for the treatment of adults with congenital Factor IX deficiency (Hemophilia B), LUXTURNA for the treatment of adults with retinal dystrophy caused by biallelic RPE65 mutations, ZYNGEGLO for the treatment of adults with beta-thalasemia, and ZOLGENSMA for treatment of children less than 2 years with spinal muscular atrophy caused by biallelic SMN1 mutations. The gene discussed is SMN1; the disease is hemophilia B.