PAX3 and Hydrocephalus: Although heterozygous mutations of either Pax3 or Pax7 do not cause hydrocephalus and, along with the close relationship and overlapping expression pattern of the two Pax members in early cranial neuroepithelium (Figure 7), we questioned whether loss of one copy of Pax7 would result in hydrocephalus within Pax3+/Δ5 heterozygotes.