Mutations in Retinitis pigmentosa GTPase regulator gene (RPGR) are the most common cause of X-linked retinitis pigmentosa (RP). Almost 60% of disease-causing RPGR mutations are located in ORF-15 region which cannot be detected by Next Generation Sequencing (NGS) due to the existence of highly repetitive regions. An Iranian family with a priori diagnosis of autosomal dominant RP was studied by Sanger sequencing of ORF15 of RPGR gene after an inconclusive NGS result. A frameshift two-base-pair deletion (c.2323_2324del, p.Arg775Glufs*59) in this region was segregating in both affected hemizygous males and affected homozygous females. To our knowledge, this is the first example of homozygous females for RPGR -ORF15 mutations. • Mutations in Retinitis pigmentosa GTPase regulator gene (RPGR) are the most common cause of X-linked retinitis pigmentosa (RP). • Almost 60% of disease-causing RPGR mutations are located in ORF-15 region which cannot be detected by Next Generation Sequencing (NGS). • In this work, a molecular study of exon ORF-15 of RPGR gene was carried out after a NGS analysis. • A frameshift two-base-pair deletion (c.2323_2324del, p. Arg775Glufs*59) in the RPGR (ORF-15) gene was segregating in an Iranian family with a priori diagnosis of autosomal dominant RP in which several females were homozygous and clinically affected. [ABSTRACT FROM AUTHOR]