Orbifolded SU(7) and unification of families
  A 5D SU(7) family unification model with two spinor representations of SO(14) is presented. The fifth dimension is compactified on $S^1/Z_2\times Z_2'$. The orbifolding is used to obtain 4D SO(10) chiral fermions. The 4D grand unification group is the flipped $SU(5)\times U(1)$. The doublet-triplet splitting through the missing partner mechanism is achieved. Also, fermion mass matrices are considered. 
Kyuwan Hwang and Jihn E. Kim