Researchers have described a novel primary immunodeficiency due to a mutation in AIOLOS. This acts through a novel pathogenic mechanism termed ‘heterodimeric interference’, whereby when two different proteins bind together in a heterodimer, the mutant protein hijacks the function of the normal protein. In a mouse model, they were able to restore some of the lost functions by interfering with the mutated protein, suggesting a possible therapeutic approach to disorders of this nature.