Impaired reciprocal social interaction is one of the core features of autism. 
While its determinants are complex, one biomolecular pathway that clearly 
influences social behavior is the arginine-vasopressin (AVP) system. The 
behavioral effects of AVP are mediated through the AVP receptor 1a (AVPR1a), 
making the AVPR1a gene a reasonable candidate for autism susceptibility. We 
tested the gene's contribution to autism by screening its exons in 125 
independent autistic probands and genotyping two promoter polymorphisms in 65 
autism affected sibling pair (ASP) families. While we found no nonconservative 
coding sequence changes, we did identify evidence of linkage and of linkage 
disequilibrium. These results were most pronounced in a subset of the ASP 
families with relatively less severe impairment of language. Thus, though we did 
not demonstrate a disease-causing variant in the coding sequence, numerous 
nontraditional disease-causing genetic abnormalities are known to exist that 
would escape detection by traditional gene screening methods. Given the emerging 
biological, animal model, and now genetic data, AVPR1a and genes in the AVP 
system remain strong candidates for involvement in autism susceptibility and 
deserve continued scrutiny.