Fig. 17. Rhodopsin mutations that cause autosomal dominant retinitis pigmentosa (ADRP) and related diseases. Currently 104 different mutations in the opsin gene are thought to cause either night blindness or retinitis pigmentosa. Of these, 89 are nucleotide substitutions causing missense or nonsense changes. Four of the mutations cause splicing defects in the opsin mRNA. Seven mutations are small deletions, and one is a small insertion. One each is from a gross deletion, a gross insertion or duplication, and one is a complex rearrangement. Some loops have comparatively fewer retinitis pigmentosa mutations; for example, the third cytosolic loop (positions 231 to 252) has no ADRP mutations and lacked a consistent structure by X-ray diffraction analysis. This may suggest that this sequence can vary to a limited extent without causing disease. All the transmembrane helices contain ADRP mutations, suggesting that these residues are critical for folding, assembly, retinoid interaction, and interhelix interactions. (This figure was created by Dr. Markus Preising. His group has assembled a collection of rhodopsin mutants at http://www.retina-international.com/sci-news/rhomut.htm. Another site that provides up-to-date information about rhodopsin gene lesions is at available at http://archive.uwcm.ac.uk/uwcm/mg/ns/1/120347.html.)