Maternal autoimmune diseases significantly increased the risk of ADHD in children, based on data from a large cohort study of more than 800,000 mothers and children and a subsequent meta-analysis.
“There is growing evidence that immune-related cells and proteins play a role in brain development and function and that maternal immune activation, including infection, autoimmune disease, and chronic inflammation during pregnancy, increases the risk of neurodevelopmental disorders among children,” wrote Timothy C. Nielsen, MPH, of the University of Sydney, and colleagues.
Previous research has examined a link between maternal autoimmune disorders and autism spectrum disorders in children, but associations with ADHD have not been well studied, they said.
In a population-based cohort study published in JAMA Pediatrics, the researchers identified 831,718 mothers and their 831,718 singleton infants in Australia. A total of 12,787 infants were born to mothers with an autoimmune diagnosis; 12,610 of them were matched to 50,440 control infants. ADHD was determined based on prescription for a stimulant treatment or a hospital diagnosis; children with a first ADHD event younger than 3 years were excluded.
In the total cohort of 63,050 infants, the presence of any maternal autoimmune disease was associated with a significantly increased risk of ADHD (hazard ratio, 1.30) as was the presence of several specific conditions: type 1 diabetes (HR, 2.23), psoriasis (HR, 1.66), and rheumatic fever or rheumatic carditis (HR, 1.75).
In addition, the researchers conducted a meta-analysis of the current study and four additional studies that yielded similar results. In the meta-analysis, the risk of ADHD was significantly associated with any maternal autoimmune disease in two studies (HR, 1.20); with maternal type 1 diabetes in four studies (HR, 1.53); with maternal hyperthyroidism in three studies (HR 1.15); and with maternal psoriasis in two studies (HR, 1.31).
Type 1 diabetes (T1D) had the highest HR and was the most often studied condition. However, “the observed association may also be related to nonimmune aspects of T1D, such as glycemic control, as nonautoimmune diabetes has been associated with ADHD among children,” the researchers wrote.
The study findings were limited by several factors, including the lack of outpatient and primary care records to identify maternal autoimmune disease, and lack of data on any medication used to managed diseases during pregnancy, as well as a lack of data on children with ADHD who might not have been treated with medication, the researchers noted. In addition, “given differences in study design and definitions, the pooled HRs presented in the meta-analysis need to be treated cautiously.”
However, the results were strengthened by the hybrid study design and large study population, and were generally consistent with previous research supporting an effect of maternal immune function on fetal neurodevelopment, they noted.
“Our study provides justification for future studies that examine the effect of maternal autoimmune diseases, including biomarkers, condition severity, and management in pregnancy and in the periconception period, on neurodevelopmental disorders in children,” they concluded.
Studies need to explore mechanism of action
The current study, with its hybrid design, adds support to the evidence of an association between any maternal autoimmune disease and ADHD in children, as well as an association between the specific conditions of type 1 diabetes, hyperthyroidism, and psoriasis in mothers and ADHD in children, Søren Dalsgaard, MD, of Aarhus (Denmark) University, wrote in an accompanying editorial.
“Importantly, Nielsen et al. emphasized in their article that, for the many different autoimmune diseases, different underlying mechanisms for the associations with disorders of the central nervous system were likely. They mentioned that, for T1D, low glycemic control may play a role, as type 2 diabetes has been associated with ADHD,” said Dr. Dalsgaard.
“Overall, these mechanisms are thought to include shared genetic and environmental risk factors or direct effects of maternal autoantibodies or cytokines crossing the placenta and altering the fetal immune response, which in turns leads to changes in the central nervous system,” Dr. Dalsgaard explained. However, the current study and previous studies have not identified the mechanisms to explain the association between ADHD in children and maternal autoimmune disease.
“To understand more about these associations, future studies should include researchers and data from different scientific disciplines, such as epidemiology, animal modeling, genetics, and neuroimmunology,” he concluded.
Association is not causality
Overall, the study findings add to the evidence of a correlation between autoimmune diseases and neurologic disease, said Herschel Lessin, MD, of Children’s Medical Group, Poughkeepsie, N.Y., in an interview. “Anything that might contribute to behavioral problems is worth investigating.” However, it is important to remember that association is not causation.
Dr. Herschel Lessin
“There is some literature and evidence that autoimmune disease is associated with mental health issues, but the mechanisms of action are unknown,” said Dr. Lessin. ADHD is highly heritable, so the association may be caused by a similar genetic predisposition, or it may be something related to autoimmunity that is impacting the fetus by passing through the placenta.
The current study’s strengths include the large size and hybrid design, but limitations such as the identification of ADHD based on medication prescriptions may have led to underreporting, and identifying maternal autoimmune disease via inpatient hospital diagnosis could have selected for more severe disease, he said.
From a clinical standpoint, the study suggests a correlation that should be noted in a family history and potentially used to inform a diagnosis, especially in cases of type 1 diabetes where the association was strongest, Dr. Lessin said. The findings also support the value of further research to look for mechanisms that might explain whether the association between autoimmune disease and ADHD is autoimmune system causality or shared genetic susceptibility.
The study received no outside funding. One coauthor disclosed receiving grants from the National Blood Authority Australia and the Australian National Health and Medical Research Council during the conduct of the study. Dr. Dalsgaard had no financial conflicts to disclose. Dr. Lessin disclosed serving as editor of the ADHD toolkit for the American Academy of Pediatrics and coauthor of the current ADHD clinical guidelines. He also serves in advisory capacity to Cognoa, a company involved in diagnosis of autism, and Corium/KemPharm, companies involved in the development of ADHD treatments.