Atrial fibrillation (AF) is the most common irregular heart rhythm, affecting one in four people over the age of 40. While not usually life-threatening on its own, individuals with the condition are at increased risk of stroke and heart failure. AF appears most frequently in older, male individuals with a history of obesity or cardiovascular problems, but some people develop it at a young age and with no obvious heart disease. This type of AF, known as “lone” AF, tends to run in families but is otherwise difficult to diagnose.

Previous studies covered by The Spittoon have linked common genetic variants to AF, but these studies have focused mainly on the typical, later-onset type of AF. Led by Patrick Ellinor and Stefan Kaab, a group of researchers from the United States and Europe investigated the genetic basis for lone AF in a group of about 1,300 people of European ancestry with the condition and more than 12,000 people without AF. Their study, published this week in Nature Genetics, connected the genetic variant rs13376333 with increased risk of lone AF.

In their analysis, each copy of the T version of rs13376333 increased the odds of lone AF by 1.52 times compared to two copies of the C version. The T version was also associated with an increased risk of typical AF, but the effect was smaller – only 1.13 times higher odds of having the condition for each copy.

(23andMe Complete Edition customers can check their data for rs13376333 using the Browse Raw Data feature.)

The variant is located near KCNN3, a gene that codes for an ion channel responsible for controlling the movement of potassium in and out of cells. KCNN3 ion channels in particular are found in “excitable” tissues such as the brain and heart. In mice, abnormalities in the behavior of the KCNN3 gene have been associated with increased blood pressure, but the exact role of KCNN3 in the human heart is unclear. Further research is needed to explore whether KCNN3 may have therapeutic applications for treatment of AF.

SNPwatch gives you the latest news about research linking various traits and conditions to individual genetic variations. These studies are exciting because they offer a glimpse into how genetics may affect our bodies and health; but in most cases, more work is needed before this research can provide information of value to individuals. For that reason it is important to remember that like all information we provide, the studies we describe in SNPwatch are for research and educational purposes only. SNPwatch is not intended to be a substitute for professional medical advice; you should always seek the advice of your physician or other appropriate healthcare professional with any questions you may have regarding diagnosis, cure, treatment or prevention of any disease or other medical condition.

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Researchers have identified a genetic variant that increases risk of atrial fibrillation (AF), an electrical disorder of the heart, which in turn increases risk of stroke.

AF affects one in four people over 40 years old, and stroke is the third leading cause of death in the United States.

In one of two studies, scientists scanned the genomes of 5,806 people from the United States, Iceland and Norway to look for genetic variations associated with AF. The other study combined data from several large studies comprising almost 47,000 people of European ancestry.

Their results, published online this month in Nature Genetics, newly linked one SNP to slightly elevated risk for developing AF in European populations.

Most strokes are caused by a blood clot that blocks circulation to the brain. Because AF causes ineffective beating of the heart, blood can pool and clot in the upper chambers, resulting in stroke if a clot leaves the heart and lodges in the brain. AF increases the risk of stroke four to five times across all age groups and is the cause behind 10 to 15 percent of all blood clot-related strokes.

In the first study, Gudbjartsson et al. studied people of European descent from the United States, Iceland and Norway to reveal that the T version of rs7193343, a SNP on chromosome 16, is associated with 1.21 times increased odds of AF. This SNP was also associated with 1.11 times increased odds of ischemic stroke and 1.22 increased odds for cardioembolic stroke.

In the second study, Benjamin et al. associated AF with another SNP near rs7193343. Both SNPs are likely to be marking a third genetic variation that actually has a functional effect on AF. Further research will be necessary to identify both the variation and its effect.

(23andMe customers can check their data for rs7193343 using the Browse Raw Data feature.)

Gudbjartsson et al. also assessed the association of AF with the T version of rs7193343 in more than 3,000 Han Chinese, but the association was not significant. They noted that the T allele of this SNP is much more frequent in Han Chinese than in European populations.

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