Rare hereditary recessive diseases were thought to be expressed in offspring only when both parents carry a mutation in the causal gene, but a new study is changing this paradigm. An international research team led by scientists at the University of Lorraine in France along with McGill University and the Research Institute of the McGill University Health Centre (RI-MUHC) in Canada discovered a new cause of a rare condition known as cblC, that they named “epi-cblC”. They reported it in patients from Europe and the United States.