Progressive Retinal Atrophy (PRA)
A TEST FOR PRA IN OLD ENGLISH SHEEPDOGS
By Dr. Simon Petersen-Jones
What is PRA?
PRA (progressive retinal atropy) is a common cause of blindness that affects several different breeds of dog. It is actually several different conditions that all result in similar changes in the eye leading to blindness. It is an inherited condition; in most breeds it is recessive condition meaning that to develop PRA a dog must receive two of the abnormal (PRA causing) genes. Dogs that receive one normal gene and one abnormal (PRA causing gene) are called carriers. Carrier dogs do not themselves develop the condition but can produce offspring with the disease.
At Michigan State University we are funded by The American Kennel Club Canine Health Foundation and the Old English Sheepdog Club of America to try and find the PRA causing gene in Old English Sheepdogs. The approach that we are using is called a Candidate Gene Approach. This involves identifying a list of genes that potentially could cause PRA. We then make DNA markers specific for that gene by identifying naturally occurring variations in the gene sequence. These variations between DNA of individuals occurs regularly along the length of DNA. Many of these DNA differences are in the portions of DNA that do not code for proteins and do not alter the function of any gene. These are known as polymorphisms. Some of these differences occur in the coding portion of genes and account for the difference between individuals. Others occur in genes and alter the function of a gene in a harmful way causing disease (e.g. PRA). Such DNA changes that cause disease are called mutations. We can use the naturally occurring polymorphisms as markers for the portion of DNA they occur in, in this case the Candidate Gene we have selected. We can investigate theses polymorphic markers in a breed with PRA and see if the Candidate Gene in which we have found a marker is positioned very close to the gene mutation which is causing PRA. This is called association analysis and has been successful in identifying the gene for PRA in other breeds.
Progress made and your help requested.
We have already screened several candidate genes in Old English Sheepdogs with PRA and also screened gene loci which cause PRA in other breeds. So far we have ruled out several genes but not identified a marker linked to PRA in the Old English Sheepdog. We are currently working very hard to develop markers in several more genes that we will also test in the Old English Sheepdog. However we really do need your help: we need more samples from PRA-affected Old English Sheepdogs and as many related dogs as possible. Without these samples finding the PRA gene and developing a DNA test for PRA in Old English Sheepdog is more difficult. Although we have done a lot of work with the samples that we have had we are limited in what further work we can do. Please support our attempts to help your breed by sending us blood samples from all dogs with PRA and their immediate relatives. The information that is provided to us is treated in confidence. Please do not hesitate to contact us for more details.
Assistant Professor, Comparative Ophthalmology
Michigan State University
Phone: (517) 353-3278
Fax: (517) 355-5164