Autism spectrum disorder (ASD) is a complex neurodevelopmental condition. Genetic, environmental, and epigenetic variables are all likely to have a role in the occurrence of ASD. This systematic review was done to determine the implications of genetic factors and modifiers in ASD. Our results show that nearly all human chromosomes have one or more genes susceptible to autism including X and Y chromosomes. In majority of the studies, different genes like MTHFR, A1298C, KDM5B, AIM2, AMPD1-NRAS, TRIM33, and TRIM33-BCAS2 located on chromosome number 1 were found to have high association with ASD. It is concluded that genes on approximately all human chromosomes have association with the risk of ASD. Given the possible involvement of epigenetic processes in the development of autism and the ability of environmental variables to change gene expression, it seems essential to investigate a variety of factors, particularly interaction between gene and environment.