MEN1 and Down syndrome: In an MEN1 haploid KO (Men1+/-) mouse model, a model similar to patients with the MEN1 syndrome, 65% of mice with MEN1 germline mutations developed naturally occurring tumours at 20 months of age; in the intervention group taking leflunomide from 6 months of age, the incidence was reduced to 5%.10 The results of the study demonstrate that leflunomide may be an effective drug for the treatment of MEN1-mutated tumours.