SNPwatch: New Genetic Insight into the Causes of Eczema

By Bethann Hromatka, Ph.D.

Sometimes called the “itch that rashes”, atopic dermatitis, or eczema, is a relatively common condition, affecting up to one in five children and one in 30 adults (many people outgrow it by early adulthood).

It can be both physically painful and emotionally difficult to live with since it’s not a disorder that hides inside of you. Although atopic dermatitis appears to run in families, the genetics underlying this condition are not well understood and up until recently only a few genetic variants had been linked to it.

New findings published in December in Nature Genetics by lead author Lavinia Paternoster now add more genetic variants to the picture. This study, performed in conjunction with researchers from around the world, analyzed data from over 50,000 people with European ancestry, roughly 11,000 of whom had atopic dermatitis. In addition to confirming previously discovered associations with atopic dermatitis – with functional variants of the filaggrin gene, which are present in 25-50% of people with this disorder, and in a region of chromosome 11 – the findings also provide further genetic evidence that this condition likely results from defects in immunological and skin barrier pathways.

The Link Between Atopic Dermatitis, Asthma and Allergies
Many people with atopic dermatitis also suffer from asthma or allergies (hay fever and food allergies), but there isn’t a 1:1 correlation. Environmental factors that exacerbate atopic dermatitis – allergens in the air, some chemicals, and emotional stress – can also trigger asthma. People with atopic dermatitis may also react positively on skin allergy tests. On the genetic side of the equation, these conditions tend to run together in families and although a number of studies have implicated functional variants of the filiggrin gene in all of them, researchers are still teasing out the details. 23andMe does not report on these relatively rare variants.

One of the SNPs newly associated with atopic dermatitis, is located in the OVOL1 gene, which encodes a protein that plays important roles in skin cells. Another SNP is located near a group of immune system genes on chromosome 5 that have been tied to other immune diseases like psoriasis, Crohn’s disease and asthma.

When the researchers looked in more detail at genetic variants involved in the immune system, they found an even stronger association at another SNP located in the IL13 gene. Their in-depth analysis suggests that the associations on chromosome 5 are centered on the immune genes IL13 and IL4, which encode cytokines –  small molecules that circulate in the body and regulate the immune system.

Although the causes of atopic dermatitis are still a puzzle, scientists are beginning to learn more about the genetic components and their relationship to environmental factors. Future research may follow up on the immune system and skin-related pathways identified by Paternoster and colleagues and perhaps further determine if atopic dermatitis, asthma and allergies are genetically linked.