CYFIP1 and Intellectual disability: In humans, either increases or decreases in CYFIP1 gene dosage are risk factors for intellectual disability, autism, and schizophrenia (Chai et al., 2003; Kirov et al., 2009; van der Zwaag et al., 2010; Leblond et al., 2012; De Rubeis et al., 2014; Kushima et al., 2018), and deletions in chromosome 15 that include CYFIP1 are associated with increased symptom severity in Prader–Willi and Angelman syndromes (Chai et al., 2003; Butler et al., 2004; Bittel et al., 2006; Sahoo et al., 2006).