Identification of a bovine β-mannosidosis mutation and detection of two β-mannosidase pseudogenes

Abstract.

β-Mannosidase deficiency results in β-mannosidosis, a severe neurodegenerative lysosomal storage disease identified in cattle, goats, and humans. To more fully understand the molecular pathology of this disease, the mutation associated with bovine β-mannosidosis was identified by sequence analysis of cDNA from an affected calf. A transition mutation of G to A at position 2574 of the cDNA coding sequence creates a premature stop codon near the 3′ end of the protein coding region. To aid commercial breeders of Salers cattle, a PCR-based test was developed to detect the mutation for β-mannosidosis carrier screening. Application of this test also revealed the presence of two β-mannosidase pseudogenes. Portions of the pseudogenes were amplified with allele-specific primers and then sequenced. One pseudogene was highly homologous (>99% sequence identity) to the expressed cDNA sequence over the 1292 bp that were sequenced, while the other showed more divergence (83% sequence identity) in the 477 bp that were sequenced. Both are processed pseudogenes that are not expressed. The severity of the bovine β-mannosidosis phenotype suggests that the 22 C-terminal amino acids of β-mannosidase play an important role in the function of this enzyme.