NKX2-5 and thyroid gland disorder: While the phenotype of Nkx2-6 and Nkx2-3 null mice does not suggest a thyroid defect, Nkx2-5-null mice present with a small thyroid bud expressing Nkx2-1, Foxe1 and Pax8 at E9.5, pointing to a role for Nkx2-5 in thyroid organogenesis.