Microphthalmia / blindness (RBP4-related) - Irish Soft Coated Wheaten Terrier

What does this test analyse?

This genetic test analyses the RBP4 c.90_92del deletion in the Irish Soft Coated Wheaten Terrier. The condition is named microphthalmia, isolated microphthalmia with coloboma and congenital eye malformation with risk of blindness.

RBP4 encodes retinol-binding protein 4, which transports vitamin A to tissues including the placenta and developing eye. The deletion disrupts this transport and can affect eye development during gestation.

What does this condition mean?

Microphthalmia means that one or both eyes are abnormally small or incompletely developed. This form can also involve coloboma, retinal or choroidal abnormalities, cataract-like changes and reduced vision. The abnormalities become visible shortly after the eyes open and can have a major impact on welfare, selection and breeding plans.

Inheritance and result

The variant is inherited as autosomal recessive, but with a specific maternal influence and incomplete penetrance. Puppies mainly develop microphthalmia when both the dam and the puppy are homozygous for the deletion; dam genotype information is therefore especially important.

Practical value of this test

• The test distinguishes clear dogs, carriers and dogs with the relevant genetic risk genotype.
• The result helps breeders plan matings deliberately and avoid risk pairings.
• Variant status can be documented clearly within lines, families and breeding advice.
• The test is especially useful for identifying bitches with two copies of the deletion, because their genotype directly contributes to puppy risk.
• Males and young dogs can also be used more deliberately when their clear, carrier or high-risk status is known.
• In lines with eye abnormalities, the result helps actively reduce microphthalmia, coloboma and blindness risk.

For this condition, the tested dog’s genotype is not the only relevant factor; the dam’s role during pregnancy is also important. Testing potential breeding bitches and planned pairings is therefore more practical than only assessing puppies afterwards.