Novel Heterozygous Mutation in NFKB2 Is Associated With Early Onset CVID and a Functional Defect in NK Cells Complicated by Disseminated CMV Infection and Severe Nephrotic Syndrome

Abstract

Nuclear factor kappa-B subunit 2 (NF-κB2/p100/p52), encoded by NFKB2 (MIM: 164012) belongs to the NF-κB family of transcription factors that play a critical role in inflammation, immunity, cell proliferation, differentiation and survival. Heterozygous C-terminal mutations in NFKB2 have been associated with early-onset common variable immunodeficiency (CVID), central adrenal insufficiency and ectodermal dysplasia. Only two previously reported cases have documented decreased natural killer (NK) cell cytotoxicity, and little is known about the role of NF-κB2 in NK cell maturation and function. Here we report a 13-year-old female that presented at 6 years of age with a history of early onset recurrent sinopulmonary infections, progressive hair loss, and hypogamaglobulinemia consistent with a clinical diagnosis of CVID. At 9 years of age she had cytomegalovirus (CMV) pneumonia that responded to ganciclovir treatment. Functional NK cell testing demonstrated decreased NK cell cytotoxicity despite normal NK cell numbers, consistent with a greater susceptibility to systemic CMV infection. Research exome sequencing (ES) was performed and revealed a novel de novo heterozygous nonsense mutation in NFKB2 (c.2611C>T, p.Gln871^*) that was not carried by either of her parents. The variant was Sanger sequenced and confirmed to be de novo in the patient. At age 12, she presented with a reactivation of the systemic CMV infection that was associated with severe and progressive nephrotic syndrome with histologic evidence of pedicellar effacement and negative immunofluorescence. To our knowledge, this is the third NF-κB2 deficient patient in which an abnormal NK cell function has been observed, suggesting a role for non-canonical NF-κB2 signaling in NK cell cytotoxicity. NK cell function should be assessed in patients with mutations in the non-canonical NF-κB pathway to explore the risk for systemic viral infections that may lead to severe complications and impact patient survival. Similarly NF-κB2 should be considered in patients with combined immunodeficiency who have aberrant NK cell function. Further studies are needed to characterize the role of NF-κB2 in NK cell cytotoxic function.

Keywords: NF-κB2; NK cell deficiency; common variable immunodeficiency (CVID); nephrotic syndrome; pituitary deficiency; primary immunodeficiency; systemic cytomegalovirus.

Figure 1

Patient clinical presentation. (A) Left picture shows the face of the patient with alopecia totalis, edema and Cushingoid facies due to prolonged steroid treatment. Right picture shows trachyonychia of the toenails. (B) Pedigree of the family showing two healthy non-consanguineous parents and the patient (arrow) with c.2611C>T mutation in NFKB2. Sanger tracings of each individual in the family are presented. (C) NK cell cytotoxic function measured by ⁵¹Cr release assay. Left graph shows antibody dependent cellular cytotoxicity (ADCC) measured against Raji B cell targets in in the presence (dashed line) and absence (solid line) of rituximab. Right shows natural cytotoxicity against K562 targets in the presence (dashed line) and absence (solid line) of IL-2 stimulation. Due to sample availability and transport limitations this demonstrates a single assay performed in triplicate. (D) Electron microscopy of renal biopsy showing pedicellar effacement and few mesangial deposits (E) Left picture shows a chest X ray and chest CT scan taken during the patient's final stage of disease showing multiple bilateral foci of alveolar compromise with extensive consolidation of bilateral basal lobes, superior left lobe and medial lobe. (F) Graphic representation showing variations in CMV titers in blood (in blue) and proteinuria (in orange), Black arrows indicate nephrotic syndrome (NS) reactivations. Immunosuppressive and antiviral treatments are indicated in colored boxes as they were administered during the course of disease.

Figure 2

(A) Flow cytometry dot plots showing T cell memory subsets in total CD3⁺ T cells as well as in CD4⁺ and CD8⁺ subsets. (B) Flow cytometry dot plots showing patient and control NK CD56⁺ NK cells and gating on CD56^Dim and CD56^Bright NK cells. (C) 5 panels showing mean fluorescence intensity and percent of positive cells for different NK cell markers and receptors within CD56 ^Dim and CD56 ^Bright NK cells. Low percentages of cells compared to healthy donor are marked in red.

Figure 3

Representation of different variants in NFKB2 that have been associated to disease color-coded with the different clinical manifestations including defects in NK cell function.