The RP1 gene has been localized to chromosome 8q11.2-q12.1.  This gene encodes a member of the doublecortin family.  It has two doublecortin domains, which bind microtubules and regulate microtubule polymerization. The protein encoded by RP1 is a photoreceptor microtubule-associated protein and is required for regulating the stability and length of the microtubule-based axoneme of photoreceptors.  The RP1 protein and the RP1L1 protein play essential and synergistic roles in affecting photosensitivity and outer segment morphogenesis of rod photoreceptors, ensuring the correct orientation and higher-order stacking of outer segment disks along the photoreceptor axoneme.  Defects in this protein are the cause of retinitis pigmentosa 1 (RP1), a retinal dystrophy characterized by retinal pigment deposits visible on fundus examination and primary loss of rod photoreceptor cells followed by secondary loss of cone photoreceptors.