Controlling Progressive Retinal Atrophy in a Labrador Retriever Breeding Colony
E.A. Leighton and D.H. Holle
In 1992, a four-year-old working dog guide and his full-sister, a breeder, were diagnosed with progressive retinal atrophy (PRA). To halt further spread of this inherited autosomal recessive disease, The Seeing Eye ultimately employed three tools. First, traditional test matings were done whereby young males of unknown genetic composition were mated with known carriers or with PRA affected mates. The progeny were monitored to see if any PRA affected offspring were produced. Second, a computer program was written to calculate the probability that a young breeding candidate of unknown genetic composition was a heterozygous carrier, based on all information known about related animals in the breeding colony. These calculated probabilities helped guide breeder selection decisions in the absence of a DNA marker-based test that would otherwise have separated heterozygous carriers from homozygous normal dogs. Third, a major research initiative was funded to develop a DNA test that uses either markers or identifies the actual gene. Using tools one and two, the disease was controlled by 1997, when the last of 38 confirmed cases was born. This date coincided, approximately, with release of the first version of a DNA marker test that could be used to identify heterozygous carriers. In early 2005, the marker test became a gene based test. The Seeing Eye invested almost $800,000 in the research project that eventually led to this DNA marker test, but this was less than half of total funding required to complete the project.