Background Systemic autoinflammatory diseases (SAIDs) are a rare, heterogeneous group of disorders caused by dysregulated innate immune activation. Objective To characterize the phenotype and clinical features of two unrelated cases with SAID suspicion, each carrying a heterozygous NLRP12 variant of uncertain significance (VUS)—one previously reported and one newly identified in Europeans—and to evaluate their functional and genetic relevance. Methods We analyzed clinical and genetic findings from two individuals harboring distinct heterozygous NLRP12 variants not associated with Familial Cold Autoinflammatory Syndrome type 2 (FCAS2). Functional assays using peripheral blood mononuclear cells (PBMCs) were performed to assess the impact of these variants on cytokine production. Clinical features were compared among affected and unaffected family members and correlated with molecular findings. Results Genetic screening revealed two different single nucleotide variants (SNVs) in NLRP12 gene. The first, c.2854GA (p.Asp952Asn), previously reported but still classified as a VUS, substitutes a negatively charged aspartic acid with an uncharged asparagine at residue 952. Structural modeling suggested disruption of local interactions between the pyrin domain (PYD) and leucine-rich repeat (LRR) domains, potentially impairing protein activation. The second variant, c.616CG (p.Arg206Gly), represents a novel finding in Europeans, replacing a large positively charged arginine with a small, flexible glycine at residue 206. Modeling predicted destabilization of a loop near the nucleotide oligomerization core domain (NACHT) and loss of key interactions. Despite their classification as VUS according to the American College of Medical Genetics and Genomics (ACMG) criteria, both variants demonstrated functional impact. Carriers of p.Asp952Asn (index case, mother, and sibling) showed a marked, generalized increase in proinflammatory cytokines, particularly IL-1β, TNF-α, and IL-17A. The index case exhibited exceptionally high basal IL-1β levels, consistent with an activated inflammatory state, and clinical data confirmed elevated C-reactive protein (CRP) levels. In contrast, the individual carrying p.Arg206Gly displayed a selective inflammatory response characterized by increases in IL-1β and TNF-α only after lipopolysaccharide (LPS) stimulation, not after muramyl dipeptide (MDP), with no elevation in IL-10 or IL-17A. Conclusion Functional data support that both NLRP12 variants affect inflammatory cytokine production, though with distinct patterns: p.Asp952Asn induces broad hyperinflammation, whereas p.Arg206Gly results in stimulus-specific dysregulation. These findings highlight the importance of integrating genetic, structural, and functional evidence for the interpretation of NLRP12 VUS in the context of Human Inborn Errors of Immunity and primary immunodeficiencies.
Lizama-Muñoz et al. (Wed,) studied this question.