Structural Biochemistry/Genetic Variants

Genetic Variant

A genetic variant is a different version of a gene, one that has a slightly different sequence of nucleotides.

Types

Genetic variant may refer to:

• A single-nucleotide polymorphism (SNP), in case it is a common genetic variant
• A mutation, in case it is a rare genetic variant
• A copy-number variation

AIDS

Some people that are exposed to HIV, never end up developing AIDS, this leads to the question of why that happens? Researchers discovered a rare genetic variant that protects people from getting AIDS. Scientists think that the rare variant of a gene called CCR5 originally may have been selected during evolution because it made people resistant to an organism unrelated to HIV. However, CCR5 gene variant’s ability to protect against AIDS may contribute to keeping it in the human gene pool in terms of evolution.

The CCR5-delta32 gene codes for protection against the HIV virus in the human blood. The HIV virus binds to blood cells that have normal receptors on the surface. The CCR5-delta32 gene protects by changing the receptors into a smaller version that is in the inside. This makes the HIV virus unable to bind to the blood cell and is therefore rendered useless. The fact that almost 20% of Caucasians have one copy of the CCR5-delta32 gene shows that it is selected for evolutionarily. The gene came out of mutation, but became fixed in the gene pool due to a benefit. Resistance to HIV is not logical because HIV is a relatively new phenomenon, and therefore can not be the cause of this evolutionary selection. The current thought is that the CCR5-delta32 gene provided protection from previous epidemics. That would explain why it has such a high prevalence in northern Europe. Also, there is almost no CCR5 gene in the Asian or African population. This suggests that the CCR5-delta32 gene was not for the prevention of HIV due to high prevalence populations lacking the gene.

References

• U.S. Department of Health and Human Services. The New Genetics. October 2006.<http://www.nigms.nih.gov>.
• "Genetic Variant Wikipedia Page. ".<http://en.wikipedia.org/wiki/Genetic_variant>.