Cryopyrin-associated periodic syndrome (CAPS) is caused by gain-of-function NLRP3 mutations. Recently, somatic NLRP3 mosaicism has been reported in some CAPS patients who were previously classified as “mutation-negative.” We describe here the clinical and laboratory findings in eight British adult patients who presented with symptoms typical of CAPS other than an onset in mid-late adulthood. All patients underwent comprehensive clinical and laboratory investigations, including analysis of the NLRP3 gene using Sanger and amplicon-based deep sequencing (ADS) along with measurements of extracellular apoptosis-associated speck-like protein with CARD domain (ASC) aggregates. The clinical phenotype in all subjects was consistent with mid-spectrum CAPS, except a median age at disease onset of 50 years. Sanger sequencing of NLRP3 was non-diagnostic but ADS detected a somatic NLRP3 mutation in each case. In one patient, DNA isolated from blood demonstrated an increase in the mutant allele from 5 to 45% over 12 years. ASC aggregates in patients’ serum measured during active disease were significantly higher than healthy controls. This series represents 8% of CAPS patients diagnosed in a single center, suggesting that acquired NLRP3 mutations may not be an uncommon cause of the syndrome and should be sought in all patients with late-onset symptoms otherwise compatible with CAPS. Steadily worsening CAPS symptoms in one patient were associated with clonal expansion of the mutant allele predominantly affecting myeloid cells. Two patients developed AA amyloidosis, which previously has only been reported in CAPS in association with life-long germline NLRP3 mutations.

Key Points We found no evidence of somatic NLRP3 mosaicism in the pathogenesis of Schnitzler syndrome. Pathogenic inflammasome activation is supported by increased ASC, IL-18, IL-6, and anakinra response.

IntroductionMutations in the NLRP3 gene are associated with the dominantly inherited cryopyrin-associated periodic syndrome (CAPS). The significance of the V198M variant is unclear; it has been reported in association with various CAPS phenotypes and as a variant of uncertain consequence. The aim of this study was to characterize the clinical phenotypes and treatments in individuals with V198M assessed in a single UK center.MethodsDNA samples from 830 subjects with fever syndromes or a family history of CAPS were screened for mutations in the NLRP3 gene with polymerase chain reaction (PCR) and sequencing. A detailed medical history was available in all cases. Inflammatory disease activity was monitored monthly with measurements of serum amyloid A protein (SAA) and C-reactive protein (CRP) in symptomatic individuals.ResultsNLRP3 V198M was identified in 19 subjects. It was found in association with CAPS in five cases, in one patient with Schnitzler syndrome, in three patients who also had a nucleotide alteration in another fever gene, and in three other patients with evidence of an autoinflammatory phenotype. Seven asymptomatic individuals were detected during screening of family members.ConclusionsThe NLRP3 V198M variant shows variable expressivity and reduced penetrance. It may be associated with classical inherited or apparently sporadic CAPS and with atypical autoinflammatory disease of varying severity, intriguingly including Schnitzler syndrome. The factors that influence the pathogenic consequences of this variant remain unknown. However, the remarkable response to interleukin 1 (IL-1) blockade in all but one individual in our series confirms that their clinical features are indeed mediated by IL-1.

Objective To investigate the molecular cause of persistent fevers in a patient returning from working overseas, in whom investigations for tropical diseases yielded negative results. Methods DNA was extracted from the patient's whole blood, leukocyte subpopulations, saliva, hair root, and sperm. The TNFRSF1A gene was analyzed by polymerase chain reaction (PCR), allele‐specific PCR, Sanger sequencing, and next‐generation sequencing. In silico molecular modeling was performed to predict the structural and functional consequences of the tumor necrosis factor receptor (TNFR) type I protein mutation in the extracellular domain. Results Sanger sequencing corroborated by allele‐specific PCR detected a novel in‐frame deletion of 24 nucleotides (c.255_278del) in the TNFRSF1A gene, and this was subsequently confirmed using next‐generation sequencing methods (targeted sequencing and amplicon‐based deep sequencing). Results of amplicon‐based deep sequencing revealed variable frequency of the mutant allele among different cell lines, including sperm, thus supporting the presence of gonosomal TNFRSF1A mosaicism. The patient had a complete response to treatment with interleukin‐1 (IL‐1) blockade, with resolution of symptoms and normalization of acute‐phase protein levels. Conclusion We describe the first case of gonosomal TNFRSF1A mosaicism in a patient with TNFR‐associated periodic syndrome (TRAPS), which was attributable to a novel, somatic 24‐nucleotide in‐frame deletion. The clinical picture in this patient, including the complete response to IL‐1 blockade, was typical of that found in TRAPS. This case adds TRAPS to the list of dominantly inherited autoinflammatory diseases reported to be caused by somatic (or postzygotic) mutation.

Transthyretin amyloidosis (ATTR) is caused by deposition of either wild-type (ATTRwt) or variant (ATTRm) transthyretin. ATTRwt presents with restrictive cardiomyopathy, while ATTRm displays a range of organ involvement. This retrospective analysis includes all patients referred to a single UK center in the last 25 years for clinical and laboratory assessment of known or suspected amyloidosis who underwent TTR gene sequencing. A total of 4459 patients were included in this study; 37% had final diagnosis of ATTR amyloidosis; 27% light chain amyloidosis; 0.7% other types of amyloidosis; 21.3% had no amyloid and 14% had no data. TTR variants were found in 770 (17%) cases; the most prevalent were p.V142I, p.T80A, and p.V50M identified in 42, 25, and 16%, respectively. The median age at referral in each group was: 76 (range 47-93), 66 (40-81), and 45 years (21-86), respectively. Overall 42 rare or novel variants were identified. Forty-two percent patients with ATTRm died at a median age of 73 years (33-89) with a median survival from diagnosis of 50 months. ATTRwt was the final diagnosis in 20% of patients undergoing genetic testing. Our findings of TTR variants in 17% of screened patients highlight the need for routine genetic testing in the evaluation of suspected ATTR amyloidosis.