RAI1 and Potocki-Lupski syndrome: It is tempting to hypothesize that dosage gain of TCF20 may also be disease causing, given the similar observation at the 17p11.2 locus, where copy number gain of RAI1 was found to cause PTLS, potentially presenting mirror trait endophenotypes in comparison to SMS (e.g., underweight versus overweight) [53, 54].