Mass Matrix Model Broken From A4 To 2 $\leftrightarrow$ 3 Symmetry
  2$\leftrightarrow$3 symmetry is realized by the breaking from alterating group of degree 4 ($A4$) symmetry. $A4$ explains why the generation number is three. However the mass matrices are realized in the form of the breaking to $2\leftrightarrow 3$ symmetry $\times Z_3$, which leads us to $2\leftrightarrow 3$ symmetric mass matrix with vanishing (1,1) component. Thus the $3\times 3$ mass matrix model with $2\leftrightarrow 3$ symmetry and vanishing (1,1) component has the group theoretical background as the symmetry in GUT model. 
Takeshi Fukuyama