NRXN1 and autism: Decreased penetrance and variable phenotypic expression have been observed for other genes in which rare variants are reported to be associated with autism [Abrahams and Geschwind, 2008; State, 2010] such as SHANK3 [Moessner et al., 2007], NRXN1 [Kim et al., 2008], and CNTNAP2 [Bakkaloglu et al., 2008].