5 cases (19%) were found to have previously described pathological mutations: 1 missense mutation in exon 4 c.137C > T; p.S46F in a MXLS that over-expressed MDM2 and MDMX; 3 missense mutations in exon 5 namely c.511G > A; p.E171K and c.392A > G; p.N131S in a WDLS case that had normal MDM2 and MDMX expression; and c.550G > A; p.D184N in two cases (MXLS and WDLS) that over-expressed both MDM2 and MDMX. This evidence concerns the gene MDM4 and well-differentiated liposarcoma.