Here, we present developmental phenotyping data on individuals with Bohring-Optiz Syndrome (BOS – ASXL1) and Bainbridge-Ropers Syndrome (BRS – ASXL3) related disorders, two CMDs highly penetrant for motor and developmental delays. This evidence concerns the gene ASXL3 and Severe feeding difficulties - failure to thrive - microcephaly due to ASXL3 deficiency.