Genetics of a cow gone mad
Mad cow disease, also known as Bovine Spongiform Encephalopathy (BSE) is termed a prion disease and variants of this abnormal protein occur in humans through consumption of contaminated meat as well as other livestock. As the term prion suggests, this disease is a result of polymorphisms in the coding and regulatory regions of the normal prion protein (PRNP) gene localized on chromosome BTA 13 at position q17.
BSE is not a viral or bacterial infection because the alteration in the DNA sequence is brought about by an infectious prion protein acquired primarily from contaminated feed. Furthermore, scientists have proven that only cows which are genetically susceptible are affected. So far, studies have shown that this susceptibility factor is highly associated with the expression of other genes in chromosomes 5, 10 and 20 in addition to the PRNP locus.
In a case study where they compared the genes of healthy and infected cattle, they found that diseased cattle across different breeds were characterized by a higher frequency of insertion/deletion polymorphism within the open reading frame of the PRNP gene.
The body naturally has normal prion proteins within its cells which the infectious prion converts into a form identical to its own after entering. The accumulation of these indigestible proteins leads to chronic degeneration of the central nervous system. Clinical symptoms include ‘nervousness’, kicking, abnormal walking and pelvic limb ataxia.
Despite these advances, scientists are still working to uncover the puzzling mechanism behind the concept of an infectious ‘protein’.
References
Primary source –
Zhang, C., de Koning, D-L., Hernandez-Sanchez, J., Haley, C.S., Williams, J.L. & Wiener, P. 2004, ‘Mapping of Quantitative trait loci affecting Bovine Spongiform Encephalopathy’, Genetics Society of America [online] Available at: http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&TermToSearch=15342524 (accessed 28/05/07)
Secondary source –
Czarnik U, Zabolewicz T, Strychalski J, Grzybowski G, Bogusz M, Walawski K. 2005, Deletion/insertion polymorphism of the prion protein gene (PRNP) in Polish Holstein-Friesian cattle [online] Available at: http://www.ncbi.nlm.nih.gov/sites/entrez
Jeong BH, Sohn HJ, Lee JO, Kim NH, Kim JI, Lee SY, Cho IS, Joo YS, Carp RI, Kim YS. 2005, ‘Polymorphisms of the prion protein gene (PRNP) in Hanwoo (Bos taurus coreanae) and Holstein cattle’, Ilsong Institute of Life Science [online] Available at: http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&TermToSearch=16284424 (accessed 28/05/07)
For more information -
http://www.mad-cow-facts.com/about.htm
http://www.cbc.ca/news/background/madcow/science.html
http://science-education.nih.gov/home2.nsf/Educational+Resources/Resource+Formats/Online+Resources/+High+School/D07612181A4E785B85256CCD0064857B
by Agnes Meredith
41099744
