To explore the in vitro functions of the c.403G>A (p.Asp135Asn) mutation in BARD1, reconstitution with wild-type BARD1 (BARD1WTres) and mutant BARD1 (BARD1D135Nres) was conducted in two BARD1 knockout breast cancer cells (T47D and MDA-MA-468) by the CRISPR-Cas9 system. The gene discussed is BARD1; the disease is breast cancer.