Pattern recognition receptors (PRRs) play a key role in innate immunity as dedicated sensors for the detection of pathogen-associated molecular pattern (PAMPs) such as viral RNA. Immunodeficiencies or autoimmune diseases associated with PRRs are often related to misrecognition between self and non-self i.e., foreign molecules. MDA5 is the main PRR dedicated to the detection of dsRNA upon viral infections. Three MDA5 single nucleotide polymorphisms (MDA5-Δ8, MDA5-Δ14 and MDA5-ΔCTD) previously reported as loss-of-function variants were associated with a dominant negative phenotype in heterozygous children developing hypersusceptibilities upon RSV infection. To decipher the dominant negative effect, we further characterized at first each variant independently. We then mimicked heterozygosity in vitro combining both WT and variant proteins. This work allowed us to specify the molecular bases at the origin of the negative interference and to build different models to explain the mechanism behind the dominant negative phenotype.