Fig. 1.

Identification of the TCF3DN variant. (A) Family pedigree of the patient. The arrow indicates the affected patient. WT, wild-type; Mut, mutant; E?, unknown genotype. (B) Facial features of the patient. (C) Sanger sequencing shows the heterozygous single base substitution c.1663 G>A; p.E555K (E47) in TCF3. (D) Schematic diagram of the TCF3 gene (top), and the primary structure (middle) and secondary structure (bottom) of the E47 protein (residues S530–R604). Exon 18b, which is specific to the E47 isoform, consists of 75 amino acids and contains a basic helix-loop-helix (bHLH) domain. (E) 3D structural model of the E47 monomer (left) and the homodimer bound to the E-box sequence (center and right). The area highlighted in blue represents the basic region