Abstract
Objective. To evaluate the rate of somatic NLRP3 mosaicism in an Italian cohort of mutation-negative patients with cryopyrin-associated periodic syndrome (CAPS).
Methods. The study enrolled 14 patients with a clinical phenotype consistent with CAPS in whom Sanger sequencing of the NLRP3 gene yielded negative results. Patients’ DNA were subjected to amplicon-based NLRP3 deep sequencing.
Results. Low-level somatic NLRP3 mosaicism has been detected in 4 patients, 3 affected with chronic infantile neurological cutaneous and articular syndrome and 1 with Muckle-Wells syndrome. Identified nucleotide substitutions encode for 4 different amino acid exchanges, with 2 of them being novel (p.Y563C and p.G564S). In vitro functional studies confirmed the deleterious behavior of the 4 somatic NLRP3 mutations. Among the different neurological manifestations detected, 1 patient displayed mild loss of white matter volume on brain magnetic resonance imaging.
Conclusion. The allele frequency of somatic NLRP3 mutations occurs generally under 15%, considered the threshold of detectability using the Sanger method of DNA sequencing. Consequently, routine genetic diagnostic of CAPS should be currently performed by next-generation techniques ensuring high coverage to identify also low-level mosaicism, whose actual frequency is yet unknown and probably underestimated.
Footnotes
Supported by Giovani Ricercatori–Ricerca Finalizzata grant no. GR-2010-2315933 to SB, and partially funded by the Italian Ministry of Health through both “Cinque per mille” and Ricerca Corrente to the Gaslini Institute, Ricerca Telethon GGP14144 to MG and CERCA Programme/Generalitat de Catalunya (JIA), SAF2015-68472-C2-1-R grant from the Spanish Ministry of Economy and Competitiveness and Fondo Europeo de Desarrollo Regional (JIA) and AC15/00027 grant from the Instituto de Salud Carlos III/Transnational Research Projects on Rare Diseases (JIA).
- Accepted for publication June 30, 2017.