Molecular basis of abnormal red-green color vision: a family with three types of color vision defects

The molecular nature of three different types of X-linked color-vision defects, protanomaly, deuteranomaly, and protanopia, in a large 3-generation family was determined. In the protanomalous and protanopic males the normal red pigment gene was replaced by a 5' red-3' green fusion gene. The protanomalous male had more red pigment DNA in his fusion gene than did the more severely affected protanopic individual. The deuteranomalous individual had four green pigment genes and one 5' green-3' red fusion gene. These results extend those of Nathans et al., who proposed that most red-green color-vision defects arise as a result of unequal crossing-over between the red and green pigment genes. The various data suggest that differences in severity of color-vision defects associated with fusion genes are caused by differences in crossover sites between the red and green pigment genes. Currently used molecular methodology is not sufficiently sensitive to define these fusion points accurately, and the specific color-vision defect within the deutan or protan class cannot be predicted. The DNA patterns for color-vision genes of female heterozygotes have not previously been described. Patterns of heterozygotes may not be distinguishable from those of normals. However, a definite assignment of the various color pigment gene arrays could be carried out by family study. Two compound heterozygotes for color-vision defects who tested as normal by anomaloscopy were found to carry abnormal fusion genes. In addition, a normal red pigment gene was present on one chromosome and at least one normal green pigment gene was present on the other.(ABSTRACT TRUNCATED AT 250 WORDS)