TCF20 and neurodevelopmental disorder: This hypothesis predicts that TCF20 duplications are expected to cause similar neurodevelopmental defects as observed in the deletions, which is supported by the observation of TCF20 duplications from anonymized individuals with neurodevelopmental disorders, some of which are de novo (Fig. 2 and Additional file 1: Figure S1); additionally, one may speculate that specific phenotypes caused by TCF20 duplication may present mirror trait compared to those associated with the deletions, such as underweight versus overweight and schizophrenia spectrum disorders versus autism spectrum disorders.