Refining the dermatological spectrum in primary immunodeficiency: mucosa-associated lymphoid tissue lymphoma translocation protein 1 deficiency mimicking Netherton/Omenn syndromes

Skin manifestations of inborn errors of NF-κB

More than 400 single gene defects have been identified as inborn errors of immunity, including many arising from genes encoding proteins that affect NF-κB activity. We summarise the skin phenotypes in this subset of disorders and provide an overview of pathogenic mechanisms. NF-κB acts cell-intrinsically in basal epithelial cells during differentiation of skin appendages, influences keratinocyte proliferation and survival, and both responses to and amplification of inflammation, particularly TNF. Skin phenotypes include ectodermal dysplasia, reduction and hyperproliferation of keratinocytes, and aberrant recruitment of inflammatory cells, which often occur in combination. Phenotypes conferred by these rare monogenic syndromes often resemble those observed with more common defects. This includes oral and perineal ulceration and pustular skin disease as occurs with Behcet's disease, hyperkeratosis with microabscess formation similar to psoriasis, and atopic dermatitis. Thus, these genotype-phenotype relations provide diagnostic clues for this subset of IEIs, and also provide insights into mechanisms of more common forms of skin disease.

Progressive B cell depletion in human MALT1 deficiency

Mucosa-associated lymphoid tissue lymphoma-translocation gene 1 (MALT1)-deficiency is a rare combined immunodeficiency characterized by recurrent infections, dermatitis and enteropathy. We herein investigate the immunological profiles of our patient and previously reported children with MALT1-deficiency. A mutation analysis was performed by targeted panel sequencing for primary immunodeficiency. Lymphocyte subset, activation and B cell differentiation were analyzed by flow cytometry and t-distributed stochastic neighbor embedding. Pneumocystis pneumonia developed in a 6-month-old Japanese infant with atopic dermatitis, enteritis and growth restriction. This infant showed agammaglobulinemia without lymphopenia. At 8 years of age, the genetic diagnosis of MALT1-deficiency was confirmed on a novel homozygous mutation of c.1102G>T, p.E368X. T cell stimulation tests showed impairments in the production of interleukin-2, phosphorylation of nuclear factor kappa B (NF-κB) p65 and differentiation of B cells. In combination with the literature data, we found that the number of circulatory B cells, but not T cells, were inversely correlated with the age of patients. The hematopoietic cell transplantation (HCT) successfully reconstituted the differentiation of mature B cells and T cells. These data conceptualize that patients with complete MALT1-deficiency show aberrant differentiation and depletion of B cells. The early diagnosis and HCT lead to a cure of the disease phenotype associated with the loss-of-function mutations in human CARD11.

MALT1-Deficient Mice Develop Atopic-Like Dermatitis Upon Aging

MALT1 plays an important role in innate and adaptive immune signaling by acting as a scaffold protein that mediates NF-κB signaling. In addition, MALT1 is a cysteine protease that further fine tunes proinflammatory signaling by cleaving specific substrates. Deregulated MALT1 activity has been associated with immunodeficiency, autoimmunity, and cancer in mice and humans. Genetically engineered mice expressing catalytically inactive MALT1, still exerting its scaffold function, were previously shown to spontaneously develop autoimmunity due to a decrease in Tregs associated with increased effector T cell activation. In contrast, complete absence of MALT1 does not lead to autoimmunity, which has been explained by the impaired effector T cell activation due to the absence of MALT1-mediated signaling. However, here we report that MALT1-deficient mice develop atopic-like dermatitis upon aging, which is preceded by Th2 skewing, an increase in serum IgE, and a decrease in Treg frequency and surface expression of the Treg functionality marker CTLA-4.