  The self-consistent random phase approximation (RPA) approach with the
residual interaction derived from a relativistic point-coupling energy
functional is applied to evaluate the isospin symmetry-breaking corrections
{\delta}c for the 0+\to0+ superallowed Fermi transitions. With these {\delta}c
values, together with the available experimental ft values and the improved
radiative corrections, the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM)
matrix is examined. Even with the consideration of uncertainty, the sum of
squared top-row elements has been shown to deviate from the unitarity condition
by 0.1% for all the employed relativistic energy functionals.
