Genotyping Brahman cattle for generalised glycogenosis

To develop procedures for genotyping Brahman cattle for loss-of-function alleles within the acidic alpha-glucosidase gene and to assess the risk of generalised glycogenosis in Australian Brahman cattle.

PCR assays for three loss-of-function alleles were designed to exploit internal restriction sites within acidic alpha-glucosidase amplicons that are independent of allelic variants at the mutant sites.

Genotyping 8529 clinically normal Brahmans between August 1996 and August 2001 revealed 16.4% were heterozygous for the more common of the two mutations (1057deltaTA, often referred to as the 'E7' mutation) that cause generalised glycogenosis in this breed. The less common 1783T mutation (often referred to as the 'E13' mutation) was restricted to descendants of one imported bull, and was not detected in 600 randomly selected Brahmans. Prior to definition of these two disease-causing mutations, 640 (18%), and 14 (0.4%), of 3559 clinically normal Brahmans analysed between January 1994 and December 1996, were heterozygous, and homozygous, respectively, for a silent polymorphism (2223G-->A) that is associated with generalised glycogenosis. In addition to the 1057deltaTA and 1783T mutations, approximately 15% of Brahmans were found to be heterozygous for a single base substitution in exon 9 (1351T, commonly referred to as the 'E9' mutation) that significantly reduces acidic alpha-glucosidase activity, but has not been associated with clinical disease. These three loss-of-function alleles were found in Brahmans imported, or selected for import, from the USA.

The PCR procedures reported here represent a significant improvement in reliability and accuracy over previous published methods. Utilisation of these PCR/restriction enzyme based assays will facilitate precise selection against the 1057deltaTA and 1783T alleles, and consequently reduce the incidence of generalised glycogenosis in registered and commercial Brahman herds.