Pregnant women who don't make nearly enough thyroid hormone are nearly 4 times likelier to produce autistic children than healthy women, report scientists... The association emerged from a study of more than 4,000 Dutch mothers and their children, and it supports a growing view that autism spectrum disorders can be caused by a lack of maternal thyroid hormone, which past studies have shown is crucial to the migration of fetal brain cells during embryo development. "It is increasingly apparent to us that autism is caused by environmental factors in most cases, not by genetics," said lead author Gustavo Román, M.D.,...