X chromosome that is not on the Y that is involved with the sex bias of ASD. In another study, it has been found that the gene called NLGN4, when mutated, can cause ASD. This gene and other NLGN genes are important for neuron communications. This NLGN4 gene is found on both the X (NLGN4X) and the Y (NLGN4Y) chromosome. The sex chromosomes are 97% identical. It has been determined that most of the mutations that occur are located on the NLGN4X gene. Research into the differences between NLGN4X and NLGN4Y found that the NLGN4Y protein has poor surface expectations and poor synapses regulations, leading to poor neuron communication. Researchers concluded that males have a higher incidence of autism when the mechanism is NLGN4X-associated. This association was concluded since females have two X chromosomes; if there is a mutation in a gene on an X chromosome, the other X chromosome can be used to compensate for the mutation. Whereas males have only one X chromosome, meaning that if there is a mutation in a gene on an X chromosome, then that is the only copy of the gene and it will be used. The genomic difference between males and females is one mechanism that leads to the higher incidence of ASD in males. Candidate gene loci Known genetic syndromes, mutations, and metabolic diseases account for up to 20% of autism cases. A number of alleles have been shown to have strong linkage to the autism phenotype. In many cases the findings are inconclusive, with some studies showing no linkage. Alleles linked so far strongly support the assertion that there is a large number of genotypes that are manifested as the autism phenotype. At least some of the alleles associated with autism are fairly prevalent in the general population, which indicates they are not rare pathogenic mutations. This also presents some challenges in identifying all the rare allele combinations involved in the etiology of autism. A 2008 study compared genes linked with autism to those of other neurological diseases, and found that more than half of known autism genes are implicated in other disorders, suggesting that the other disorders may share molecular mechanisms with autism. Primary Others There is a large number of other candidate loci which either should be looked at or have been shown to be promising. Several genome-wide scans have been performed identifying markers across many chromosomes. A