An Association of Hereditary Eye Defects with White Spotting

Abstract

An asymmetrical effect on eye color in the house mouse, previously ascribed to the gene for ruby eye (ru), was later found to be due to specific defects of the iris, which in turn were due to a gene, s, for spotting or piebald. Animals were observed at weaning time (3-4 weeks of age), and two strains were used in studying the eye defects. In one strain, An (aniridia or absence of the iris), ru (ruby eyes), s (piebald), many mice showed deviations from ruby eye color, and ophthalmoscopic examinations showed in general an enlarged pupil (anisocoria) accompanied by reduction in amt. of pigment in the iris. Of 133 animals examined, the iris defect was expressed in about 80% of the individuals and in about 63% of the eyes. Another strain (Anophthalmic), which lacked the piebald gene, carried a gene or genes which caused a defect of the bulbus and/or cornea varying from bilateral anophthalmia to unilateral staphyloma. Approximately 65% of the individuals were affected. When these two strains were crossed the 26 F1 animals were all non-piebald with normal irides. 14 F1 animals were backcrossed to the An piebald strain and gave 120 non-piebald to 115 piebald animals. Approx. 37% of the piebald animals had iris abnormalities whereas only 3.3% of the non-piebald animals had any iris abnormalities. Among 212 black-eyed animals of 4 other spotted strains, 18 cases of iris defects were observed indicating that the ru gene does not need to be present. Crosses between one of these strains and the An strain indicated a similar genetic basis for Anisocoria. 176 self-colored animals from several strains did not have anisocoria, but among 100 albinos 15 cases of iris defects were found which differed from the anisocoria associated with piebald. A new occurrence of aniridia was also found in several related animals from a mixed stock. It is suggested that the genotype for piebald spotting increases the probability of death or failure to function of the pigment cells (melanophores) and that, since the normal development of the iris depends upon contributions by these cells, their abnormal functioning increases the probability that the structure or pigment of the stroma of the iris will fail to develop. Similar cases of aniridia and spotting are also known in man.