一例联合免疫缺陷患者的 MALT1 功能缺失：一种新型致病性变异及免疫学见解

Clinical and laboratory records were reviewed. Patients underwent next-generation sequencing (NGS), and analysis of genomic DNA was performed on the patient and her parents. Lymphocyte subsets, MALT1 expression and NF-kB signaling was evaluated by flow cytometry, RT-PCR and immunoblotting.

The patient carried a novel pathogenic biallelic loss-of-function variant in MALT1 (c.1411G > A; p.D471N) located in the caspase-like domain, leading to severely reduced MALT1 protein expression. Impaired CBM-mediated NF- B activation was confirmed by reduced phosphorylation of the p65 subunit, resulting in deficient production of IL-2 and TNF- . This functional defect caused lower Tfr and Treg cells, a normal proportion of Tfh cells, with higher expression of activation markers PD-1 and ICOS. The patient displayed low NK cell and B cell counts, together with a developmental block at the transitional B cell stage. Additionally, the proportion of marginal zone-like B cells (MZB-like) was markedly decreased, indicating impaired B cell differentiation.

Human MALT1 deficiency causes profound CID by impairing CBM-mediated NF-kB signaling and MALT1-paracaspase activity. Consistent with the reported variants located in the caspase-like domain, our patient presented with an inflammatory phenotype, supporting the notion that the MALT1 D471N mutation phenocopies a partial loss of both MALT1 scaffolding function and paracaspase activity. Prompt hematopoietic stem cell transplantation (HSCT) is highly recommended as an effective therapy for MALT1 deficiency.