Mucolipidosis II (MLII) is a rare lysosomal storage disorder causing diverse clinical symptoms such as skeletal and craniofacial defects and heart abnormalities. Petrey et al. probe the molecular mechanisms underlying craniofacial defects that are recapitulated in a zebrafish model of MLII they developed previously. Analysis of chondrocyte-enriched populations shows that zebrafish MLII embryos have increased activity of several enzymes involved in remodelling of the extracellular matrix, particularly cathepsins L and K and matrix metalloproteinase 13. Exposure of MLII embryos to a cathepsin K inhibitor lessens the disease phenotype. These data pinpoint new players in MLII that will guide further studies of the disease. Page 177

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