MERIT40 is a recently identified BRCA1 and RAP80 interacting protein that is essential for protein-protein interactions of a BRCA1 complex also containing Abraxas, BRCC36 and BRCC45. It is a mediator of checkpoint functions and DNA damage signaling through a (de)ubiquitination cascade. Based on its interaction with BRCA1 and its role in genome integrity maintenance, MERIT40 is a novel candidate gene for being involved in hereditary susceptibility to breast cancer. Here, we report to our knowledge the first comprehensive mutation screening of this gene in affected cases of breast cancer families. Only a number of sequence variants were found, four of which are novel. None of the observed variants appeared to be disease related, suggesting that germline mutations in MERIT40 are rare or absent in familial breast cancer patients.