CYTH2 and Dravet syndrome: Among the genes with DS-DM in fetal DS brains are several of the above, plus AMIGO3, encoding a membrane protein essential for correct axon tract development [19], BRSK2, encoding the SAD1B kinase that plays a role in polarization of cortical neurons [67, 68], CYTH2, coding for an Arf6 guanine-nucleotide exchange factor, cytohesin-2, with a role in neurite extension [24], and GLI4, which is known to be expressed in the brain based on microarray data [25] and, by analogy to the other GLI family members, is predicted to control cell differentiation.