Many Genes Commonly Implicated in Long QT Syndrome May Not Actually be Related

The Problem with Identifying the Genes that Cause a Genetic Disorder

from In The Cloud Copy

When it comes to genetic disorders, it can be very difficult to pinpoint exactly what gene or genes may be causing a disease’s symptoms. It turns out that identifying any specific gene, disease-causing or otherwise, is a tricky task. Each of a person’s 46 chromosomes contains thousands of genes all linked together in a single, very long molecule of DNA. Visually, it all looks pretty much the same, so geneticists have to look for specific markers on the DNA strand that may identify the start and end of separate genes.

Despite the difficulty, geneticists have made huge strides in mapping the human genome in the last few decades. Their success has led to improved testing for and treatment of genetic conditions. One example of this is the discovery of mutations in the BRCA1 and BRCA2 genes, mutations that greatly increase the likelihood of breast and ovarian cancers. Women with a family history of these cancers can now be tested for the mutations and take extra precautions if they have them.

Long QT Syndrome

Long QT syndrome (LQTS) is a heart condition that can cause erratic variations in the rhythm of a person’s heartbeat. In a person with LQTS, the heart’s electrical system doesn’t function properly.

When any human heart is beating, the heart’s electrical system fires as the cardiac muscles contract, then recharges while they recover. That time it takes for the system to recharge is shown on an electrocardiogram as the Q-T interval. In long QT syndrome, this recovery time takes longer than it should, which can lead the heart to beat irregularly and inefficiently.

Some people with long QT syndrome don’t show symptoms or even know they have it. Others find out only after symptoms like fainting or seizures lead to medical testing. The medical community knows that there is a genetic component to LQTS but identifying the exact genes that cause it hasn’t been easy.

Variations in 17 genes have been presented as being tied to long QT syndrome. A team of experts recently published their analysis after examining the evidence for each of these 17 genes and their relationship to LQTS. They reported that, of the 17 genes:

  • 9 lack sufficient evidence to be considered to cause the disorder.
  • 3 show enough evidence to be considered definitively related.
  • 4 show very strong causal evidence in less-common variations of LQTS.
  • 1 shows moderate evidence in a related syndrome.

Why Do These Results Matter?

While identifying the gene that causes a disease doesn’t automatically lead to a cure, it can help patients get an accurate diagnosis and therefore, treatment, when doctors are trying to identify the cause of their symptoms.

Researchers believe that some of the over-identification of related genes in LQTS comes because of a flawed approach to one method for analyzing genes that cause a disorder. The so-called “candidate gene” approach only looks at certain areas of the genome in people with the disease and doesn’t adequately compare them to the genomes of people who don’t have the disease. This can lead to the thinking that variations in certain genes must be related to the disease, even though those same differences might appear in a person without it.

Researchers and doctors hope that this work will encourage those who provide genetic tests to be more selective in the genes they screen for so that patients can have more accurate results when trying to identify the cause of their symptoms.

Check out the source article here.


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