Microphthalmia (RBP4)

Microphthalmia is characterized by an incomplete or unusually small development of one or both eyes. \nA genetic variant that causes a prenatal vitamin A deficiency can be responsible for the onset of the disease in the breed Irish Soft Coated Wheaten Terrier. Affected puppies only develop symptoms of microphthalmia, if their dam is affected by this disease, too. The disrupted transfer of vitamin A begins in the hepatic store of the mother and continues at the placenta. The puppies will most likely show no symptoms, if their dam is heterozygous for the genetic variant. Therefore, the maternal genotype influences the inheritance of the disease besides the autosomal recessive trait of this genetic variant.\nA genetic variant in the DNAJC21 gene causing microphthalmia with haematopoietic defects has been identified in Portuguese Water Dogs. Affected dogs show bilateral or unilateral microphthalmia with eyes being less than 50% of normal size. In addition, other ocular defects such as cataract, corneal dystrophy, microphakia/aphakia, glaucoma, retinal lesions and persistent pupillary membranes can be observed in some dogs. Non-ocular findings include dental enamel abnormalities, growth retardation and thrombocytopenia with anaemia. It has been reported that erythrocyte counts and haematocrits can improve with age, while platelet counts remain low.