According to researchers at Houston Methodist Neurological Institute and Erasmus Medical Centre, women who have deficiency of thyroid hormone have a four times higher risk of giving birth to children with autism than healthy women. This is the conclusion reached after researchers conducted a study on 4,000 Dutch mothers and their children. Previous studies have shown that thyroid hormones are essential for fetal brain cells migration during embryonic development and now the present study further confirms this idea.
Lead author Gustavo RomÃ¡n, MD, a neurologist and neuroepidemiologist who directs the Nantz National Alzheimer Center, believes that autism is not caused by genetic factors but by environmental factors, which means that it is possible to prevent the condition. Regarding the relationship between thyroid hormones and the risk of autism in offspring, the researchers found that children with autism have more pronounced symptoms if their mothers had severe deficiency of thyroxine (thyroid hormone T4). Mild T4 deficiencies in the mother resulted in an insignificant increase in autistic symptoms in children.
The most common cause of thyroid hormone deficiency is the lack of iodine in the diet because both thyroid hormones (both T3 and T4) contain this element. Iodine deficiency is quite common around the world, including in developed countries and the statistics show that 1 in 3 people are affected. Although it was considered that this problem was solved in the U.S. through salt iodization, a study conducted in 2005 showed that 1 in 7 Americans were deficient in iodine.
Researchers at Erasmus Medical Centre, Rotterdam, Netherlands, in collaboration with the scientists from Methodist Neurological Institute in Houston, conducted a study involving over 4,000 pregnant women in 2002-2006. In the 13th week of pregnancy, blood samples were taken to measure levels of T4 and of other two proteins that might indicate the cause of iodine deficiency. After six years, the women who participated in the study were asked to describe emotional and behavioral traits of their children using a standardized psychology checklist.
From a population of 4039, 80 children were considered “probable autistic”, 159 mothers were found to have severe deficiency of T4, and 136 were found to have mild deficiency of T4. Researchers found a weak association between mild deficit of T4 and the risk of having autistic children; however there was a strong association between severe deficiency of T4 and this risk. Therefore, the researchers advise women who are pregnant or planning to become pregnant to measure their level of urinary iodine and thyroid hormone levels.