Have you ever wondered why some people tend to get sick while others seem to be immune to a variety of infections? It's one of the most perplexing questions with respect to public health. Several theories have emerged such as age, lifestyle choices and the environment. While these may influence the likelihood for exposure, they do not always offer an explanation as to why certain individuals are just more likely to become ill.
One of the more compelling reasons to come out over the years has dealt not with the world around us, but inside us. Researchers have theorized our genetic makeup may be an unavoidable factor in determining whether we end up suffering from certain types of infections. In essence, we could be born with a higher risk for one or more diseases.
The basis for this concept is the fact every single one of us has a unique genetic sequence. While we all share the same genes, the actual DNA sequence may differ in certain places. These alterations, known as single nucleotide polymorphisms, or SNPs (pronounced "snips"), can change the way certain genes function in the body. Most of the time, these SNPs have no effect — but over the last decade, several have been associated with diseases, including diabetes, kidney disease, cardiovascular disease and cancer.
The first links between SNPs and infectious disease happened in 2004 when it became clear certain SNPs could increase the chances for the potentially fatal infection known as sepsis. Soon after, a link between these minor changes in genetic sequence and hepatitis C virus infection were determined. These discoveries promoted researchers to start "gene fishing" in the hopes of finding more possible genetic predispositions to infectious diseases.
It was only a matter of time before researchers began to search for SNPs linked to infectious disease.
During this time, the ability to sequence an individual's genetic sequence became much easier and cheaper to perform. Companies emerged from this new reality all aiming to help people learn more about their genes. As this happened, a database of information became available. It was only a matter of time before researchers began to search for SNPs linked to infectious disease.
Last week, a team of American researchers did just that. They examined a rather large database of human genetic sequences and tried to match them to individuals suffering from various infections. The results revealed how SNPs can make a person more susceptible to certain diseases and how in the case of some infections, the genetic makeup has no effect on the risk for troubles.
The team tested over 200,000 samples of individuals with a European ancestry. Each one had donated a sample for genetic sequencing and also had answered a survey regarding the occurrence of infections. The team tried to link SNPs to 23 different conditions. Some were routine illnesses such as strep throat, warts, ear infections and the common cold, while others were specific such as tuberculosis, meningitis, mononucleosis and shingles.
After the analysis was complete the team was pleased to see 17 out of the 23 diseases could be linked to at least one SNP. Most of the SNPs represented a slight increase in the likelihood of infection. But a few revealed greater than a 50 per cent increase in vulnerability for diseases such as mumps and meningitis.
As one might expect, several of the identified SNPs occurred in genes known to be involved in the immune response. Others were involved in maintenance of the body's ability to maintain and heal itself. For example, one particular gene identified as being involved in ear infections is known as plasminogen. It's known for helping to protect the mucous membranes in the ear. Deficiency — and possibly loss of proper function due to a SNP — is known to be involved in a higher chance of ear infections.
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There was one unexpected result. In some infections, no association with SNPs could be made. The list included measles, rubella, sinus infection, rheumatic fever and the common cold. All of these infections are known to be easily transmitted and can cause widespread outbreaks in non-vaccinated populations. The lack of any link to our genes suggests these pathogens have no need for an advantage from a weakened genetic position. They work perfectly fine on their own.
The results of this study reveal the importance of SNPs in public health. By learning more about the meaning behind these minor changes in our genetic makeup, we may be able identify individuals with a higher risk for a variety of illnesses. Granted, much more work needs to be done in this regard before we will be able to perform genetic diagnostics. Yet, as time moves on we may be able to include genetics as a risk factor along with the usual suspects of dietary and lifestyle choices, and the environment.
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