Isolated microphthalmia with coloboma in Soft Coated Wheaten Terriers

Microphthalmia is an eye defect characterized by a marked under-development of the entire eye. In this case it is associated with another defect - coloboma, representing a cleft defect of the iris and sometimes other parts of the eye (ciliary body, choroid or optic nerve). The manifestation is visual disturbances of varying severity, often myopia.

The disease is caused by mutation c.90_92del in the RBP4 gene, which encodes the retinol-binding protein 4.

Pedigree analysis suggests an autosomal recessive mode of inheritance, but it was found that the disease only appears in homozygous offspring from a homozygous mother. It is therefore a recessive defect with maternal transmission. The maternal effect arises from an impairment in the sequential transfer of retinol across the placenta via RBP4 encoded by maternal and fetal genomes.

The genetic test can clearly reveal the genotype of the animal and is a useful tool for breeders to prevent unintentional breeding of affected puppies.

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References:

Kaukonen, M., Woods, S., Ahonen, S., Lemberg, S., Hellman, M., Hytönen, M.K., Permi, P., Glaser, T., Lohi, H. : Maternal inheritance of a recessive RBP4 defect in canine congenital eye disease. Cell Rep 23:2643-2652, 2018. Pubmed reference: 29847795