Inherited tritan color vision deficiency is caused by defects in the
function of the short-wavelength-sensitive (S) cones. This heterozygous
group of disorders has an autosomal dominant pattern of inheritance. Amino
acid variations of the S cone opsin are rare and all that have been
identified thus far are associated with inherited tritan color vision
defects. Here we report the identification of a 30-year-old male who made
errors on standard color vision tests consistent with the presence of a
mild tritan color vision deficiency. We tested the hypothesis that his
color vision impairment was due to a mutation in the S cone photopigment
gene. He was found to be heterozygous for a mutation that caused the amino
acid proline to be substituted in place of a highly conserved leucine at
amino acid position 56 in the S cone opsin. This mutation was absent in
564 S cone photopigment genes from 282 subjects who did not make tritan
errors. Thus, we conclude that this mutation disrupts the normal function
of S cones.