Diagnosis of inherited diseases

image of Diagnosis of inherited diseases
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It has long been recognized that some diseases in domestic animals are due wholly or partly to inheritance, with Darwin himself describing inherited conditions such as polydactyly in the dog and cat, and noting that there is a ‘unanimity of belief among veterinaries of all nations in the transmission of various morbid tendencies’ ( ). Since Darwin’s time, numerous inherited diseases have been described in companion animals. This chapter discusses the canine and feline genome, basic genetics, diagnosis of genetic disease and DNA testing. This section includes case examples.

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Image of 30.2
30.2 Blood smear from a dog with Pelger–Huet anomaly. All neutrophils have a band-shaped nucleus with mature chromatin. (Wright–Giemsa stain; original magnification X500). (Courtesy of S D’Agorne of Axiom Veterinary Laboratories)
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30.3 Restriction fragment length polymorphism (RFLP) analysis of the canine SOD-1:c.118G>A mutation in three German Shepherd Dogs (GSDs). DNA was extracted from ethylenediamine tetra-acetic acid (EDTA) blood and PCR used to amplify a specific product, using primers designed to flank the site of the mutation. Digestion (Dig) was then performed, in which an enzyme was used to digest the PCR product, and the results analysed by agarose gel electrophoresis. In an animal carrying normal genes, digestion occurs and the original PCR product of 292 base pairs (bp) is cut into two fragments, one of 230 bp and one of 62 bp. However, if the mutation is present, digestion does not occur. In the example shown here, a PCR product is seen in all three dogs at 292 bp. GSD 1 is unaffected (homozygous wild-type), so after digestion two fragments (230 bp and 62 bp) are seen; GSD 2 is affected (homozygous mutant) so bands are only seen at 292 bp, i.e. digestion has not occurred; and GSD 3 is a carrier (heterozygous), showing three bands after digestion at 292 bp (uncut), 230 bp and 62 bp (digestion fragments). (Courtesy of B Catchpole, Royal Veterinary College)
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30.6 T2-weighted transverse MR image of the brain, showing bilaterally symmetrical regions of hyperintensity.
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