GRM5 and atypical Rett syndrome: In support of our data, abnormal mGluR5 expression levels and function have been found in syndromic and non-syndromic forms of intellectual disability and ASD [Fragile X Syndrome (Bear et al., 2004), macrocephaly associated autism (Takeuchi et al., 2013), Rett Syndrome (Tao et al., 2016), and PMDS (Verpelli et al., 2011; Wang et al., 2016; Vicidomini et al., 2017)].