School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, Australia
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Progressive retinal degeneration in the Australian Cattle Dog

Progressive retinal degeneration (PRD) is an inherited disease that causes blindness in many breeds of dogs. It was first discovered in 1911 in Gordon Settlers. Prcd is a form of this disease, which is found in Australian Cattle Dogs. It has been shown that dogs can adapt to the decrease in vision ability as it deteriorates but not if they are in a situation where they are required to have excellent vision. This is certainly the case for Australian Cattle Dogs where the work they do requires excellent vision. Prcd is believed to be inherited from simple Mendelian recessive genetics because most forms of PRA are inherited in this manner, however the inheritance of prcd is well known to be breed specific. For example, it to be inherited as a dominant disorder in the Bull mastiff and the English mastiff while it shows distortion of segregation in the miniature poodles.


Prcd can cause blindness in dogs from the age of 5 but often does not develop until they are 6 or 7 years old, therefore it is termed as a late onset disorder. As it is a late onset disorder it is difficult to eliminate. Most bitches have already had their first litter by the age of 5. The first stage of the disease is the degeneration of the “rod” cells, the cells in the back of the eye, which causes night blindness. This is followed by loss of function of the “cone” cells which means the eyes no longer function even in full light conditions.


In dogs most DNA is diploid and not haploid. This means that one chromosome is inherited from the sire and the other chromosome from the dam. If a disease is inherited as a recessive trait it means that both chromosomes (or more specifically the prcd mutation in this case) must have the mutation for the disease to be observed. A pattern C dog has both chromosomes with the disease mutation and is termed “affected” (high probability of becoming blind). If a dog has one chromosome with the disease mutation and one that is normal it is called a pattern B dog or a “carrier”. If both chromosomes are normal it is called a pattern A or “unaffected”.

 

 

Zangerl B, Goldstein O, Philp AR, Lindauer SJ, Pearce-Kelling SE, Mullins RF, Graphodatsky AS, Ripoll D, Felix JS, Stone EM, Acland GM, Aguirre GD.2006. Genomics. 2006 Nov;88(5):551-63.

ABSTRACT:

Progressive rod-cone degeneration (prcd) is a late-onset, autosomal recessive photoreceptor degeneration of dogs and a homolog for some forms of human retinitis pigmentosa (RP). Previously, the disease-relevant interval was reduced to a 106-kb region on CFA9, and a common phenotype-specific haplotype was identified in all affected dogs from several different breeds and breed varieties. Screening of a canine retinal EST library identified partial cDNAs for novel candidate genes in the disease-relevant interval. The complete cDNA of one of these, PRCD, was cloned in dog, human, and mouse. The gene codes for a 54-amino-acid (aa) protein in dog and human and a 53-aa protein in the mouse; the first 24 aa, coded for by exon 1, are highly conserved in 14 vertebrate species. A homozygous mutation (TGC --> TAC) in the second codon shows complete concordance with the disorder in 18 different dog breeds/breed varieties tested. The same homozygous mutation was identified in a human patient from Bangladesh with autosomal recessive RP. Expression studies support the predominant expression of this gene in the retina, with equal expression in the retinal pigment epithelium, photoreceptor, and ganglion cell layers. This study provides strong evidence that a mutation in the novel gene PRCD is the cause of autosomal recessive retinal degeneration in both dogs and humans.

 

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