Bulldog Dwarfism (Chondrodysplasia) in Miniature Zebus
Bulldog dwarfism is a lethal genetic defect of Miniature Zebu cattle. Affected fetuses have disproportionate dwarfism, a short and compressed vertebral column, a large head, short, stocky limbs, and are naturally aborted around seven months of gestation. The mutation that causes this defect is specific to Zebu cattle and is different from the Dexter mutations.
Phenotype: Bulldog dwarfism in Miniature Zebu is a cartilage disorder characterized by disproportionate dwarfism, short, compressed vertebral column, a large head, and short, stocky limbs. Fetuses with this genetic defect are naturally aborted around the seventh month of gestation.
Mode of Inheritance: Autosomal recessive
Alleles: N = Normal/Unaffected, BDz = Bulldog dwarfism
Breeds appropriate for testing: Miniature Zebu, Dahomey
Explanation of Results:
Cattle with N/N genotype will not have bulldog dwarfism and cannot transmit this bulldog dwarfism variant to their offspring.
Cattle with N/BDz genotype will not be affected by bulldog dwarfism, but are carriers. They will transmit this bulldog dwarfism variant to 50% of their offspring. Matings between two carriers result in a 25% chance of producing a calf with bulldog dwarfism.
Cattle with BDz/BDz genotype will have bulldog dwarfism. Fetuses with this genotype are expected to naturally abort.
Inheritance of a form of generalized chondrodysplasia known as bulldog dwarfism has been documented in several breeds of cattle including Miniature Zebus. Among other defects, affected fetuses have severe disproportionate dwarfism, a short and compressed vertebral column, a large head, and short, stocky limbs. Fetuses with this genetic defect are naturally aborted around the seventh month of gestation.
A mutation in the cartilage development gene Aggrecan (ACAN) was identified as the cause of bulldog dwarfism in Miniature Zebu cattle. The mutation is one base pair insertion (ACAN:c.5686insC) in the sequence of exon 12 of the gene which results in production of truncated protein and loss of its critical function needed for normal bone and cartilage development. This mutation (named here BDzfor simplicity) has an autosomalrecessive lethal mode of inheritance. This means that both males and females are equally affected and that affected fetuses are not viable and are aborted later in pregnancy. Two other mutations (BD1 and BD2) in the same gene are responsible for bulldog dwarfism in Dexter cattle.
Testing for this bulldog dwarfism variant in miniature Zebus can help breeders determine if carriers are present among breeding stock and to use mating strategies to avoid producing affected calves. Breeding carrier animals together is not advised because this type of mating has a 25% chance of producing affected calves. The test can also be used by veterinarians to confirm bulldog dwarfism diagnosis of aborted fetuses.
Normal. No copies of the BDz mutation are present.
Carrier. 1 copy of the BDz mutation is present. Animal is normal but can produce affected offspring if bred to another carrier.
Affected. 2 copies of the BDz mutation.
Cavanagh, J. A. L., Tammen, I., Windsor, P. A., Bateman, J. F., Savarirayan, R., Nicholas, F. W., & Raadsma, H. W. (2007). Bulldog dwarfism in Dexter cattle is caused by mutations in ACAN. Mammalian Genome18(11), 808-814. doi: 10.1007/s00335-007-9066-9
Struck, A-K., Dierks, C., Braun, M., Hellige, M., Wagner, A., Oelmaier, B., Beineke, A., Metzger, J., & Distl, O. (2018). A recessive lethal chondrodysplasia in a miniature zebu family results from an insertion affecting the chondroitin sulfate domain of aggrecan. BMC Genetics, 19(1), 91. doi: 10.1186/s12863-018-0678-8