Tritanopia

A number sign (#) is used with this entry because tritanopia is caused by heterozygous mutation in the OPN1SW gene (613522) on chromosome 7q32.

Description

Tritanopia is an autosomal dominant disorder of human vision characterized by a selective deficiency of blue spectral sensitivity (Weitz et al., 1992).

Clinical Features

The first report of tritan defects was that of Wright (1952) and related to a 'confusion chart' which had appeared in an article in a Netherlands illustrated paper, Picture Post, in 1951. Affected individuals lack blue and yellow sensory mechanisms while retaining those for red and green. Defective blue vision is characteristic.

Went and Pronk (1985) found 7 males with both tritan and red-green defects.

Inheritance

Kalmus (1955) concluded that tritanopia is autosomal dominant with incomplete manifestation.

Went and Pronk (1985) found tritan color vision defects in 79 persons in 6 families with autosomal dominant inheritance and wide variability in test results within families.

Population Genetics

Went and Pronk (1985) estimated the frequency of tritanopia at 2 per 1,000; Kalmus (1955) had suggested a much lower frequency, about 1 in 20,000, and Wright (1952) had estimated the frequency in Great Britain as 'between 1 in 13,000 and 1 in 65,000, the higher frequency probably being the more likely.'

Molecular Genetics

Using PCR and denaturing gradient gel electrophoresis (DGGE), Weitz et al. (1992) detected point mutations in the BCP gene (613522.0001, 613522.0002) in 5 individuals with tritanopia. The dominant inheritance of these mutations suggested that the aberrant gene products actively interfere with the viability or fidelity of blue-sensitive cone photoreceptors.

History

Kalmus (1965) concluded that there is an X-linked form of tritanopia.

Krill et al. (1971) suggested that congenital tritanopia and hereditary dominant optic atrophy are identical conditions, i.e., tritanopia is merely a manifestation of optic atrophy (165500). The view of Krill et al. (1971) was discredited by studies of Smith et al. (1973) and several other groups. Miyake et al. (1985) found that the blue cone electroretinogram permits differentiation of congenital tritanopia and dominantly inherited juvenile optic atrophy (DIJOA). The blue cone ERG was unrecordable in patients with congenital tritanopia but within the normal range in those with DIJOA.