The heart tilts to the left, the liver is on the right, the gut always coils in the same direction and the lungs have neither the same shape nor number of lobes. This internal organization is invisible from the outside and develops in the embryo's very first days of life, and the heart depends on it for its double blood circulatory system.

When this fails, the child is born with a rare disease, heterotaxy syndrome, a condition where the organs are arranged independently of each other with no connection between them. The syndrome affects roughly one in 10,000 births and in the vast majority of cases involves severe heart defects. Rather than the arrangement of organs, these defects are what put the child's life at risk. Currently, a genetic cause is only identified in one in five patients.

In a study published in Science Advances, Sigolène Meilhac's team (Inserm, Imagine Institute, Institut Pasteur, Université Paris Cité) showed in a mouse model that the mechanism long held as the foundational event of left-right asymmetry – cilia-driven fluid flow – is not behind this; it serves merely to direct it. A second previously unsuspected mechanism involving one of the major communication pathways between cells during development – the Wnt pathway – supplements the first.

Find out more (English version coming soon)