Late Onset Progressive Retinal Atrophy (PRA) in the Abyssinian and Somali Cat; Evaluation of Allele Frequency in Europe for the Causative Mutation
A recessively inherited late on-set type of PRA was described for the first time in Abyssinian cats in Sweden 25 years ago. A high frequency of the disease was observed; it was calculated that 45% of Abyssinian cats were affected by the progressively blinding disease, 44% were carriers and 11% were normal. Recently, the causative mutation for the defect was discovered; a single nucleotide polymorphism in the CEP290 gene, allowing for a mutation detection test to be developed. The present study was performed in order to elucidate the allele frequency in Europe for the causative mutation recently discovered, now not only in Abyssinian, but also in Somali cats.
The detection of the mutation was performed by a real-time Taq-Man PCR assay using fluorescence labeled probes specific for either the wildtype allele or the rdAc-mutation. Cheek swabs (sterile cotton swabs, Nerbe Plus) with air dried saliva obtained by the owners or EDTA-blood samples obtained by the veterinarian from individual Abyssinian and Somali cats were sent to the lab by regular mail or by courier service.
A total of 484 cheek swabs from Abyssinian and Somali cats from 14 different European countries were analyzed. Sixty one percent were found to be homozygous normal, 31% heterozygous and 4% homozygous affected for the causative mutation.
The calculated frequency of the mutant rdAc-allele of Abyssinian and Somali cats in 2007 is 19.6%.
The allele frequency 25 years ago in Europe outside of Sweden is not known. It is, however, probable that the frequency was high, since there was interaction between breeders of Abyssinian and Somali cats mainly in northern Europe and affected cats were observed at the time, also in Finland, Norway, Holland and Germany. It is thus encouraging that the number of affected cats has now become markedly reduced mainly by the use of non-affected animals (cats that are heterozygous or homozygous normal for the mutation) for breeding. The mutation detection test commercially available may allow for eradication of this specific gene defect.