We calculate the masses of the QQ(q)(q) (Q =c,b;q =u,d,s) tetraquark states with the aid of heavy diquark-antiquark symmetry (HDAS) and the chromomagnetic interaction (CMI) model.The masses of the highestspin (J =2) tetraquarks that have only the (QQ)(3)c((q)(q))3ccolor structure are related with those of conventional hadrons using HDAS.Thereafter,the masses of their partner states are determined with the mass splittings in the CMI model.Our numerical results reveal that (i) the lightest cc(n)(n) (n =u,d) is an I(JP) =0(1+) state around 3929 MeV (53 MeV above the DD* threshold),and none of the double-charm tetraquarks are stable;(ii) the stable double-bottom tetraquarks are the lowest 0(1+) bb(n)(n) around 10488 MeV (≈ 116 MeV below the-B-B* threshold)and the lowest 1/2(1+) bb(n)(s) around 10671 MeV (≈ 20 MeV below the (B)(B)*s/(B)s(B)* threshold);and (iii) the two lowest bc(n)(n) tetraquarks,namely the lowest 0(0+) around 7167 MeV and the lowest 0(1+) around 7223 MeV,are in the nearthreshold states.Moreover,we discuss the constraints on the masses of double-heavy hadrons.Specifically,for the lowest nonstrange tetraquarks,we obtain Tcc ＜ 3965 MeV,Tbb ＜ 10627 MeV,and Tbc ＜ 7199 MeV.