“…The etiology is suggested to be multifactorial, involving both genetic and environmental factors. Among nongenetic risk factors that have been mentioned are maternal smoking, use of certain drugs like some anticonvulsants and corticosteroids, organic solvent exposure, and folic acid deficiency (Wyszynski and Beaty, 1996;Wyszynski et al, 1997). In Sweden maternal drug use during pregnancy apparently plays a minor role (Källén, 2003).…”