While there are over 100 distinct mutations in the
rhodopsin gene that are found in patients with the degenerative disease autosomal dominant
retinitis pigmentosa (ADRP), there are only four known mutations in the
rhodopsin gene found in patients with the dysfunction
congenital stationary night blindness (CSNB). CSNB patients have a much less severe phenotype than those with ADRP; the patients only lose rod function which affects their vision under dim light conditions, whereas their cone function remains relatively unchanged. The known
rhodopsin CSNB mutations are found clustered around the site of
retinal attachment. Two of the mutations encode replacements of
neutral amino acids with negatively charged ones (A292E and G90D), and the remaining two are neutral
amino acid replacements (T94I and A295V). All four of these mutations have been shown to constitutively activate the
apoprotein in vitro. The mechanisms by which these mutations lead to
night blindness are still not known with certainty, and remain the subject of some controversy. The dominant nature of these genetic defects, as well as the relative normalcy of vision in individuals with half the
complement of wild type
rhodopsin, suggest that it is an active property of the mutant
opsin proteins that leads to defective rod vision rather than a loss of some needed function. Herein, we review the known biochemical and electrophysiological data for the four known
rhodopsin mutations found in patients with CSNB.