A Null mutation in the rhodopsin gene causes rod photoreceptor dysfunction and autosomal recessive retinitis pigmentosa

Small eye (Sey) in mouse is a semidominant mutation which in the homozygous condition results in the complete lack of eyes and nasal primordia. On the basis of comparative mapping studies and on phenotypic similarities, Sey has been suggested to be homologous to congenital aniridia (lack of iris) in human. A candidate gene for the aniridia (AN) locus at 11p13 has been isolated by positional cloning and its sequence and that of the mouse homologue has been established (C.T., manuscript in preparation). This gene belongs to the paired-like class of developmental genes first described in Drosophila which contain two highly conserved motifs, the paired box and the homeobox. In vertebrates, genes which encode the single paired domain as well as those which express both motifs have been described as the Pax multigene family. A Pax gene recently described as Pax-6 is identical to the mouse homologue of the candidate aniridia gene. Here we report the analysis of three independent Sey alleles and show that indeed this gene is mutated and that the mutations would predictably interrupt gene function.

Night blindness is an early symptom of retinitis pigmentosa. The rod photoreceptors are responsible for night vision and use rhodopsin as the photosensitive pigment. We found three mutations in the human rhodopsin gene; each occurred exclusively in the affected members of some families with autosomal dominant retinitis pigmentosa. Two mutations were C-to-T transitions involving separate nucleotides of codon 347; the third was a C-to-G transversion in codon 58. Each mutation corresponded to a change in one amino acid residue in the rhodopsin molecule. None of these mutations were found in 106 unrelated normal subjects who served as controls. When the incidence of these three mutations was added to that of a previously reported mutation involving codon 23, 27 of 150 unrelated patients with autosomal dominant retinitis pigmentosa (18 percent) were found to carry one of these four defects in the rhodopsin gene. All 27 patients had abnormal rod function on monitoring of their electroretinograms. It appears that patients with the mutation involving codon 23 probably descend from a single ancestor. In some patients with autosomal dominant retinitis pigmentosa, the disease is caused by one of a variety of mutations of the rhodopsin gene.