Functional analysis of new Blau syndrome-associated CARD15 mutations

Blau ssyndrome (BS) is a very rare autosomal dominant syndrome characterized by early onset granulomatous arthritis, uveitis and skin rash, caused by high penetrance mutations in the CARD15 gene encoding a cytoplasmic receptor of bacterial peptidoglycan natural immunity . In contrast with the common Crohn’s disease-associated SNPs, which are located in the final ligand binding domain and impair ligand recognition, the identified Blau s. mutations are all in the central nucleotide binding domain and may activate ligand independent signals, in accordance with the lack of intestinal involvement. In an Italian BS family we recently described the CARD15 E383K mutation (van Duist et al. 2005). The position in the NBD close to a magnesium binding site, its segregation with the disease, its absence in 100 healthy controls and its conservation in other NBD containing genes and in homologous genes of different species, suggested this mutation to be pathogenic. Here we report the functional analysis of this variant by a gene reporter assay, that proved this mutation to be gain-of-function. The E383K variant showed a 3 fold increased NF-kB activity compared to the wild type protein, slightly lower than the previously identified mutations (R334Q/W, L469F = 4 fold). Similar investigation is underway for another never earlier described NBD variant W490L we identified in a BS affected child born from healthy parents (Patient from A.Martini and M.Gattorno, Gaslini Institute, Genova ).