[en] The problem of the realization of Wigner spin-isospin SU(4) symmetry in nuclei is analyzed on the basis of available experimental data on nuclide masses in the mass-number range 1 ≤ A ≤ 257. Empirical expressions are obtained for the universal functions in the Wigner mass formula. The experimental values of the energy of spin-orbit interaction are determined for the aforementioned nuclides. An alternative mechanism of the origin of the odd-even effect in nuclei having an even mass number associated with a specific property of the Casimir operator is proposed. The results obtained in this study suggest that SU(4) symmetry is broken predominantly by spin-orbit interaction.