, according to Zelma Chiesa Fuxench, MD.
This gene codes for profilaggrin, a protein, which is then cleaved to form filaggrin, which helps to organize the cytoskeleton of the skin and is an important structural component of the skin. The understanding is that patients who have filaggrin mutations tend to have earlier onset and more persistent disease, Dr. Chiesa Fuxench, of the department of dermatology at the University of Pennsylvania, Philadelphia, said during the Revolutionizing Atopic Dermatitis virtual symposium.
“Prior studies have shown that mutations in the FLG gene can confer a risk of developed AD that is two- to sevenfold with variants R501X and the 22804del4 frequently described. It is important to note that most of these findings have been described primarily in populations of European descent, with other variants being found in populations of African nation descent, and seem to be more prevalent in populations with early onset disease.”
Environmental factors
Other AD-related risk factors that have been previously described in the literature include environmental factors such as climate, diet, breastfeeding, obesity, pollution, tobacco smoke, pet ownership, and microbiome or gut microflora. “The list of culprits is ever increasing,” she said. “However, it’s important to recognize that data to support some of these associations are lacking, and oftentimes, a lot of the results are contradictory.”
As part of the International Study of Asthma and Allergies in Childhood, researchers evaluated the association between climate factors with the 12-month period prevalence rates of symptoms of atopic eczema in children. They found that patients who lived at higher latitudes and those who lived in areas where there were lower mean outdoor temperatures tended to have a higher prevalence of eczema symptoms. Worldwide, they found that symptoms of eczema were also prevalent in areas where there was lower indoor humidity.
“The authors concluded that they can’t really demonstrate a cause and effect, and that while latitude and temperature changes appear to affect the prevalence of eczema, they may do so indirectly, perhaps to changes in behavior and differences in sun exposure,” said Dr. Chiesa Fuxench, who was not involved with the study. “For example, we know that vitamin D is a protective risk factor for AD. Low vitamin D has been associated with more severe disease in some studies. We also know that UV exposure leads to the conversion of filaggrin degradation products such as trans-urocanic acid into cis-urocanic acid, which has been demonstrated to have immunosuppressive effects.”
A systematic review and meta-analysis of nine articles found small associations, which were significant, between being born in the winter (odds ratio, 1.15) and fall (OR, 1.16) and the risk of developing AD, compared with being born in the spring and summer. However, an analysis of satellite-derived data on air temperature across the United States from 1993 to 2011 found that as ambient air temperature increases, so did the risk for an ambulatory visit for AD to physicians from the National Ambulatory Medical Care Survey.
In all areas but the south, the largest number of AD visits occur in the spring. In the south, more AD visits occur in the summer. “This raises the point that we don’t really know everything when it comes to the influence of temperature and climate change on AD,” Dr. Chiesa Fuxench said.
Several maternal and neonatal risk factors for AD have been described in the literature, including the effect of prenatal exposure to antibiotics. In one large analysis, investigators assessed the association among 18-month-old children in the Danish National Birth Cohort, which included 62,560 mother-child pairs. They found that prenatal antibiotic use was associated with an increased odds of AD among children born to atopic mothers but only when used during all three trimesters (adjusted OR, 1.45). When they further stratified these analyses by type of birth (vaginal versus C-section), the association persisted in both groups, but was stronger among those delivered by C-section.