Autism Spectrum Disorder 57
Genetic and physiological. Heritability estimates for au tism spectrum disorder have
ranged from 37% to higher than 90%, based on  twin concordance rates. Currently, as many
as 15% of cases of autism spec trum disorder appear  to be associated with a known genetic
mutation, with different  de novo copy number variants or de novo mutations in specific
genes associated with the disorder in differ ent families. However, even when an autism
spectrum disorder is associated with a know n genetic mutation, it does not appear to be
fully penetrant. Risk for the remainder of case s appears to be polygenic, with perhaps hun-
dreds of genetic loci making relatively small contributions.
Culture-Related Diagnostic Issues 
Cultural differences will exist in norms for social interaction, no nverbal communication,
and relationships, but individuals with auti sm spectrum disorder are markedly impaired
against the norms for their cultural context. Cultural and socioeconomic factors may affect
age at recognition or diagnosis; for example, in the United Stat es, late or underdiagnosis of
autism spectrum disorder among Af rican American children may occur.
Gender-Related Diagnostic Issues
Autism spectrum disorder is di agnosed four times more often in males than in females. In
clinic samples, females tend to be more li kely to show accompanying intellectual disabil-
ity, suggesting that girls without accompan ying intellectual impairments or language
delays may go unrecognized, perhaps because of subtler manifestatio n of social and com-
munication difficulties.
Functional Consequences of  Autism Spectrum Disorder
In young children with autism spectrum diso rder, lack of social and communication abil-
ities may hamper learning, especially learning through social interaction or in settings