The developmental pathways disrupted by leflunomide are unknown but their elucidation could help understand the mechanism by which DHODH mutations cause malformations. In the liver of mice treated with leflunomide, TNF-α production is repressed by the direct inhibition of NF-κB activity26. Interruption of NF-κB signaling during development can result in disrupted cell migration, diminished cellular proliferation, and increased apoptosis27. Indeed, open eye is a defect observed in mice with targeted disruption of TNF-α28C. Furthermore, NF-κB plays an important role in limb morphogenesis, specifically as a transducer of signals that regulate Sonic hedgehog (Shh) expression. Shh controls, in part, anterior-posterior patterning of the digits and Shh-/- knockout mice fail to form digits 2-529. These observations suggest that the malformations observed in individuals with Miller syndrome could be caused by perturbed NF-κB signaling due to loss of DHODH function.
