Background/Purpose: Mutations in genes coding for 20S proteasome subunits or proteasome assembly helpers cause chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperatures (CANDLE) or proteasome-associated autoinflammatory syndromes (PRAAS). Patients with CANDLE/PRAAS present with chronically elevated type I interferon scores as consequence of increased proteotoxic stress by mechanisms that are only partially characterized. The purpose of this study is to report and functionally characterize eight disease-causing variants, six of which are novel variants, in four proteasome genes (PSMA5, PSMC5,PSMB10 and PSMB8) in five unrelated patients with CANDLE/PRAAS.

Methods: All patients (Pts) were enrolled into an IRB-approved protocol (NCT02974595). Whole exome sequencing was performed in all patients. Peripheral blood interferon response gene signature was determined by NanoString. The effects of the proteasome variants were investigated by transfection studies in HeLa cells.

Results: The five Pts presented in the first month of life with fever, systemic inflammation, and nodular or annular rash. Skin biopsies showed a neutrophilic dermatosis (Pts1, 2, 4 and 5) or a perivascular lymphocytic infiltrate (Pt3). One patient (Pt1) had additive loss-of-function variants in PSMB8/β5i (c.224C >T, p.T75M), and in 2 previously not disease-associated genes, PSMA5/α5 (c.502C >T, p.R168*, de novo), and PSMC5/Rtp6 (c.1080+1_1080+10del). Four patients had novel compound heterozygous variants in 2 known CANDLE/PRAAS-associated genes, PSMB8/β5i and PSMB10/β2i. Three Brazilian patients, Pts2-4, had the same PSMB10/β2i variant,c.40_42del, p.F14del, in combination with a different variant, c.500G >A p.G167D (Pt2); c.247_248insT, p.C83Lfs*123 (Pt3), and c.710+1G >C (Pt4). Pt5 was compound heterozygous for PSMB8/β5i variants c.163C >T, p.Q55* and c.352T >C, p.S118P. Pt1 is in clinical remission on treatment with tofacitinib in combination with tocilizumab; Pt2 responded partially and Pt5 responded fully to tofacitinib; and Pts3 and 4 are in clinical remission on baricitinib. All five patients had a high type I interferon signature in peripheral blood. Transient transfection of mutant constructs PSMA5/α5 p.R168*, PSMB8/β5i p.Q55* or PSMB10/β2i p.C83Lfs*123 into HeLa cells result in mRNA nonsense mediated decay and no protein production, and mutant constructs PSMB10/β2i p.G167AD and p.F14del, and PSMB8/β5i p.S118P impair cleavage of the pro-peptide and prevent incorporation of the mutant proteasome component. PSMB10/β2i c.710+1G >C leads to exon skipping with no incorporation of the mutant protein. All but the PSMC5/Rtp6 variant were shown to substantially impact the steady-state expression of the affected proteasome subunits and/or their incorporation into mature 20S and/or 26S proteasomes.

Conclusion: Our observations expand the spectrum of CANDLE/PRAAS-causing genetic variants and will improve molecular diagnosis and genetic counseling of patients with autoinflammation.

This study was supported in part by the Intramural Research Program of NIAID, NIH.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/identification-and-functional-characterization-of-eight-candle-praas-causing-proteasome-variants-in-five-unrelated-patients/