The tonsils, along with the appendix and spleen appear to be unnecessary. Now Danish researchers have not only mapped out a genetic link from inflamed tonsils to the human genome. They have also shown that this genetic link protects against developing inflammatory bowel diseases.
Incredible pain and eating ice cream are what most people remember from having their tonsils removed. Although the procedure is carried out less often than before, it is still one of the most common operations for children. Danish researchers have learned much more about which children are more likely to get tonsillitis after studying the genetic data from 16,000 people.
“We have looked at data from the past 40 years in Denmark’s population-based health registries and identified the children who underwent tonsillectomy. Comparing genetic data from some of these children with data from other children showed that children with tonsillitis were genetically similar in some parts of the genome. In particular, we saw a very clear genetic pattern in one gene on chromosome 22: children with tonsillitis more often had a specific genetic variant than other children,” explains senior scientist at Statens Serum Institut, Bjarke Feenstra, who led the study.
The vast majority of the approximately 3 billion base pairs in the human genome are identical for everyone. However, all humans also have small variations in their DNA. Today, these can be analysed in detail through genome-wide association studies – and researchers can thereby investigate whether single nucleotide polymorphisms (SNPs), the most common type of genetic variation, are linked to specific diseases.
Diseases are linked
Unsurprisingly, the children with tonsillitis have some genetic variations in their genome in common. The interesting thing is that the genetic variation found in the study also appears to influence other diseases.
It is interesting that we find a place in the genome that is linked to other diseases. The genetic variant we discovered for tonsillitis is already known for increasing the risk of developing a rare form of nephritis and for preventing inflammatory bowel diseases.
Previous research have not revealed any importance of the tonsils after children turn 3 years old as children whose tonsils have been removed don’t appear to have reduced immune response later in life. The genetic link between these three diseases is especially interesting because imbalances in the immune response play a major role in all three diseases.
“Valuable information related to the link in the immune system response is therefore presumably available at precisely this location of the genome. The tonsils are part of the immune system. Some people react very strongly to an infection with very enlarged tonsils; others do not. The genetic link we have discovered may turn out to be a marker for how the body copes with infections.”
The inexhaustible biobank
Bjarke Feenstra’s research group at Statens Serum Institut has focused on genome-wide association studies for 10 years and has discovered many genetic variants that influence diseases, particularly diseases in children.
“This investigation was very cost-effective because of Denmark’s population-based health registries and access to genetic data. The study included 13,000 people for whom we already had existing genetic data from previous studies. Using the health registries, we were easily able to identify the 1500 people who had undergone tonsillectomy. We then began to analyse the data to see whether there was a pattern. Once genetic data has been generated, they can then be used for other important studies of other diseases.”
These studies are only possible because Denmark has built up unique nationwide population-based registries over many years with information on everyone living in the country. In addition, biological material has been collected routinely from a large number of people. The creation of the Danish National Biobank at Statens Serum Institut in 2012 enabled researchers to get an overview and access to the millions of biological samples from Denmark’s healthcare system.
“This provides new opportunities to conduct research on the causes of diseases and how to prevent and treat them. For example, our next study will link birth weight to the genetic data from the child’s mother to determine whether the mother’s genome affects foetal growth.”
“Genome-wide association study identifies variants in HORMAD2 associated with tonsillectomy” has been published in the Journal of Medical Genetics. In 2014, the Novo Nordisk Foundation awarded a grant to senior scientist Bjarke Feenstra. In 2009, the Novo Nordisk Foundation awarded a 10-year grant to the Danish National Biobank at Statens Serum Institut.