Abstract
Objective
The cryopyrinopathies are a group of rare autoinflammatory disorders that are caused by mutations in CIAS1, encoding the cryopyrin protein. However, cryopyrin mutations are found only in 50% of patients with clinically diagnosed cryopyrinopathies. This study was undertaken to investigate the structural effect of disease‐causing mutations on cryopyrin, in order to gain better understanding of the impact of disease‐associated mutations on protein function.
Methods
We tested for CIAS1 mutations in 22 patients with neonatal‐onset multisystem inflammatory disease/chronic infantile neurologic, cutaneous, articular syndrome, 12 with Muckle‐Wells syndrome (MWS), 18 with familial cold‐induced autoinflammatory syndrome (FCAS), and 3 probands with MWS/FCAS. In a subset of mutation‐negative patients, we screened for mutations in proteins that are either homologous to cryopyrin or involved in the caspase 1/interleukin‐1β signaling pathway. CIAS1 and other candidate genes were sequenced, models of cryopyrin domains were constructed using structurally homologous proteins as templates, and disease‐causing mutations were mapped.
Results
Forty patients were mutation positive, and 7 novel mutations, V262A, C259W, L264F, V351L, F443L, F523C, and Y563N, were found in 9 patients. No mutations in any candidate genes were identified. Most mutations mapped to an inner surface of the hexameric ring in the cryopyrin model, consistent with the hypothesis that the mutations disrupt a closed form of cryopyrin, thus potentiating inflammasome assembly. Disease‐causing mutations correlated with disease severity only for a subset of known mutations.
Conclusion
Our modeling provides insight into potential molecular mechanisms by which cryopyrin mutations can inappropriately activate an inflammatory response. A significant number of patients who are clinically diagnosed as having cryopyrinopathies do not have identifiable disease‐associated mutations.