GSTM1 and autism: Moreover it could find a support in a genetic study on this enzyme which revealed that M1 (GSTM1), is reduced or absent in individuals carrying the GSTM1*0 (null) allele, increasing their sensitivity to xenobiotics [46] In addition, two recent studies have reported an association between the null allele and autism suggesting that GST contributes to the risk of oxidative stress and autism [46,47].