Background/Purpose

To identify the cause of disease in an adult patient who presented with recurrent fevers and urticaria which responded to IL-1 inhibition with anakinra. She was negative for NLRP3 mutations based on conventional sequencing

Methods

A 52 year-old perimenopausal pediatrician presented to the NIH with new-onset episodes of urticarial rash, fever, chills, fatigue, arthralgia, and myalgia.  A skin biopsy revealed neutrophilic infiltrates.  She recalled a similar urticarial rash as a child, which resolved at puberty.  Prior treatments included colchicine, prednisone, IVIG, antihistamines, H2 blockers, high dose aspirin, and hydroxychloroquine, without significant benefit. The patient was started on anakinra 100 mg daily, and eventually increased to 300 mg daily. Frequency and duration of flares and diagnostic biomarkers, including CRP, ESR, and WBC, were recorded before starting anakinra and for eleven years afterwards. Whole-exome sequencing, targeted deep resequencing of NLRP3 in peripheral blood and buccal cells, and mutational screening in subcloned amplicons from skin fibroblasts, buccal cells, and flow-sorted monocytes, granulocytes, T lymphocytes, and B lymphocytes, was performed to interrogate the possibility of somatic mutations in NLRP3.

Results

Prior to starting anakinra, flares occurred every 2-3 days lasting less than 24 hours. A stress-induced erythematous rash was the predominant symptom during flares, along with constitutional symptoms, arthralgia, and myalgia. During flares the CRP was elevated at 16.5 mg/L, and the WBC was slightly elevated at 9.860 K/uL. After starting anakinra, there was immediate resolution of rash, constitutional symptoms and normalization of inflammatory markers. WBC also normalized at 5.060 K/uL. Whole- exome sequencing identified a previously reported CAPS-associated mutation, p.Tyr570Cys, with a mutant allele ratio of 15% in whole blood. Targeted deep sequencing of NLRP3 in blood and buccal cells demonstrated similar levels of mosaicism, but only in the peripheral blood.  We then analyzed 192 colonies each from subcloned amplicons derived from monocytes, granulocytes, T lymphocytes, B lymphocytes, fibroblasts, and buccal cells. This confirmed the presence of the mosaic mutation at a ratio similar to the exome data in monocytes and granulocytes but not in lymphocytes, cultured fibroblasts, or buccal cells.

Conclusion

To our knowledge this abstract represents the first report documenting lineage-specific NLRP3 mosaicism, established by subcloning amplicons from six different cell types. The patient’s initial presentation of urticarial rash before puberty and reoccurrence during menopause along with constitutional symptoms, arthralgia and myalgia was not classic for Muckle-Wells syndrome, however the clinical presentation was suggestive of a cryopyronpathy. The molecular demonstration of lineage-specific NLRP3 mosaicism, taken together with the clinical response to anakinra, confirm the diagnosis of cryopyrinopathy, and underscore the emerging role of massively-parallel sequencing in clinical diagnosis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/cryopyrinopathy-with-a-myeloid-specific-nlrp3-mutation/