The possibility that a decrease in atRA signaling could account for TCDD-induced effects appears unlikely because the palatal malformations generated upon functional vitamin A deficiency or Rar gene ablations a) affect essentially the development of the primary palate and b) are never isolated, but instead occur as part of a holoprosencephaly syndrome (Lohnes et al. 1994). The gene discussed is RARA; the disease is vitamin A deficiency.