For X-linked and autosomal recessive retinitis pigmentosa, which account for approximately 40% of patients with identified mutations, achieving over 50% photoreceptor transduction may be seen as a threshold for halting disease progression, since female carriers of X-linked mutations are usually minimally affected (e.g., choroideremia, X-linked retinitis pigmentosa associated with mutations in RPGR or RP2). The gene discussed is RP2; the disease is autosomal recessive retinitis pigmentosa.