RTL4 and autism spectrum disorder: Among the 11 RTL genes, PEG10 [1,2], RTL1 (also known as PEG11) [10,11] and Leucine zipper down-regulated in cancer 1 (LDOC1, also known as SIRH7 and RTL7) [12,13,14] play essential but different roles in the placenta while RTL4 (also known as SIRH11 and Zinc finger CCHC domain-containing 16 (ZCCHC16)) plays an important role in controlling impulsivity in the brain [14,15] and is recognized as a causative gene in autism spectrum disorders [16].