TB Susceptibility Marker #1: rs11031731Edit
A study published in Nature Genetics compared 2,100 TB-infected individuals with 5,600 unaffected individuals. The study looked at exclusively people of African descent in Ghana.
It was found that individuals with a GG genotype at the marker site, 11p13 downstream of the WT1 (Wilms Tumor 1) gene had a 1.3 times greater chance of developing TB, and those with an AA genotype at that marker had a 1.3 times decreased chance of developing TB, and finally, those with an AG genotype who had typical odds of developing TB (2). It is interesting to note that the WT1 gene is known to have a role in Vitamin D Receptor (VDR) activation and in mice, suppression of Interleukin-10 (IL-10), both of which (VDR and IL-10) play roles in TB: VDR is involved in TB pathophysiology (4) and IL-10 in TB suceptibility(5).
TB Susceptibility Marker #2: rs4804803Edit
A second study published by PLoS ONE compared 1,262 TB-infected people to 914 unaffected individuals. They were specifically interested in SNPs for the CD209 gene, which is known to encode a receptor capable of bringing Mycobacterium tuberculosis into cells and internalizing it. Also, previous studies indicated that the SNP -336A/G affects CD209 expression (the -336G allele variant is associated with protection against TB) (2).
It was found that an AA genotype at the marker was associated with a 1.16 times greater chance of developing TB, individuals with an AG genotype had typical odds of developing TB, andthose with a GG genotype had a 1.16 times decreased odds of developing TB. It was also shown by this study that GG inidividuals at this particular marker who did develop TB had decreased liklihood of developing the severe form of TB, known as cavitory TB.
Lessons Learned from GenotypeEdit
At both markers, Professor Burke is expected to have slightly higher odds (1.3 times higher odds for marker 1, 1.16 time higher odds for marker 2) of developing TB. Howevver, both studies looked at invidiauls of only African descent and thus may not be valuable representations of the true risk that Professor Burke has of developing tuberculosis. TB is also a pathogen and thus requires contact to contract the disease, so if Professor Burke is not immunocompromised and doesn't come into contact with someone affected with TB, he will not develop the disease.
1. Centers for Disease Control: Tuberculosis (http://www.cdc.gov/TB/)
2. Thye T et. al. (2012). "Common variants at 11p13 are associated with suceptibility to tuberculosis" Nature Genetics.
3. Vannberg FO et. al. (2008). "CD209 genetic polymorphism and tubersulosis disease" PLoS ONE 3(1):e1388.
4. Flynn JL, Chan J. Immunology of tuberculosis. Annu Rev Immunol. 2001;19:93–129. [Pubmed].
5. Ottenhoff TH, Verreck FA, Hoeve MA, van de Vosse E. Control of human host immunity to mycobacteria. Tuberculosis. 2005;85:53–64. [PubMed].