X chromosome
Based on the results of a study on females with Turner syndrome, a hypothesis involving epigenetic mechanisms was proposed to help describe the gender bias of ASD. Turner syndrome patients have only one X chromosome which can be either maternal or paternal in origin. When 80 females with monosomy X were tested for measures of social cognition, the patients with a paternally derived X chromosome performed better than those with a maternally derived X chromosome. Males have only one X chromosome, derived from their mother. If a gene on the paternal X chromosome confers improved social skills, males are deficient in the gene. This could explain why males are more likely to be diagnosed with ASD.