GSTM1 and autism: It has the advantage that it can be used with complete and incomplete trios as well as independent cases and controls With respect to the association study of the GSTM1 locus with autism, both the traditional case-control analysis and the 1-df likelihood ratio test (utilizing controls) support (at p = 0.028 and p = 0.046, respectively) the association of the homozygous GSTM1 deletion genotype with an increased risk of autism.