Identification of a heterozygous pathogenic variant in IRAK4 in an adult patient with pneumococcal sepsis, monoclonal gammopathy of uncertain significance, and idiopathic systemic capillary leak syndrome

Abstract

IRAK-4 haploinsufficiency can present with pneumococcal sepsis and poor pneumococcal vaccine response in adults. Further research can determine the significance of unrecognized pathogenic variants in IRAK4 in adults presenting with pneumococcal sepsis and the utility of immunoglobulin replacement in these patients.

IL-1 receptor–associated kinase (IRAK)-4 is a serine–threonine kinase that plays a critical role in innate immunity via its involvement in Toll-like receptor (TLR) and IL-1 receptor (IL-1R) signaling. TLRs sense microbial products, and members of the IL-1R family (IL-1R, IL-18R, and IL-33Rα) are critical mediators of host defense. IRAK-4 forms a complex consisting of 2 active kinases (IRAK-1 and IRAK-4) and 2 noncatalytic subunits (IRAK-2 and IRAK-3M). MyD88, a cytosolic adaptor molecule, provides a bridge from TLRs and IL-1Rs to the IRAK complex via a shared Toll and IL-1R (TIR) domain. For all human TLRs other than TLR3, signaling through the MyD88- and IRAK-4–dependent TIR pathway results in the synthesis of cytokines such as TNF-α, IFN-α/β, IFN-γ, IL-1β, IL-6, and IL-8.¹ Autosomal-recessive IRAK-4 deficiencies are inborn errors of immunity associated with recurrent or severe invasive pneumococcal disease, cutaneous staphylococcal infections, and sinopulmonary infections resulting from Pseudomonas aeruginosa.1, 2, 3

In a cohort of 48 patients with IRAK-4 deficiency, the mortality in childhood was 38% due to disseminated infections. These individuals tend to have weak signs of systemic inflammation and are not susceptible to mycobacterial, viral, parasitic, or fungal disease. To date, all reports of IRAK-4 deficiency have occurred in those with homozygous or compound heterozygous mutations. The majority of mutations in IRAK4 in this cohort were loss of expression and loss of function, creating premature termination codons or large deletions of the gene. Previous reports have denoted heterozygous carriers of variants in IRAK4 to be asymptomatic.⁴ Two patients had compound heterozygous mutations including c.1188+520A>G.

We identified a 62-year-old woman with a history of pneumococcal bacteremia and monoclonal gammopathy-associated idiopathic systemic capillary leak syndrome (ISCLS), also known as Clarkson disease, who carries this heterozygous variant with associated defects in TLR signaling. To our knowledge, this is the first description of a mutation in a single allele of IRAK4, causing clinical disease identified in an adult patient.

The patient gave consent for her clinical information to be shared for educational purposes and blood to be drawn for research under an approved institutional review board protocol. The patient was healthy as a child and young adult. She is white and of Italian ancestry. At age 49, she developed scleritis and was treated with rituximab. She was then diagnosed with IgGκ monoclonal gammopathy of uncertain significance (MGUS) during evaluation for an acute episode of lower extremity edema. At diagnosis, she had an M spike of 1.1 g/dL and total IgG of 1660 mg/dL, and bone marrow biopsy results demonstrated normocellularity with <3% κ-restricted plasma cells. At age 60, she had an episode of pneumococcal bacteremia with septic shock. She was then hospitalized at age 62 with coronavirus disease 2019 (COVID-19) complicated by a life-threatening episode of ISCLS with distributive shock, hemoconcentration (hemoglobin 16.4 g/dL), hypoalbuminemia (albumin 3.0 g/dL), and compartment syndrome of the bilateral upper extremities. She presented clinically with syncope and did not have preceding flulike symptoms, fever/chills, or respiratory involvement. No bacterial organism was identified, and there was no evidence of disease transformation to multiple myeloma. She had received her second dose of Pfizer/BioNTech mRNA vaccination 6 months before, and the most recent dose of rituximab had been administered 5 months before. Eventually the patient recovered, but she has experienced disfigurement and residual lymphedema as a result of 9 fasciotomies. Assessment revealed mildly low IgA (43 mg/dL), poorly protective postpneumococcal polysaccharide vaccination (PPSV23) titers to Streptococcus pneumoniae, reduced CD27⁺/IgD-switched memory B cells, and increased CD38^hiIgM^hi transitional B cells (Table I). Intravenous immunoglobulin therapy (initially 2 g/kg, then later 1.5 g/kg per month) was initiated to address specific antibody deficiency and as prophylaxis for ISCLS.

Table I.

Laboratory evaluation of patient with heterozygous IRAK4 mutation

Investigation	Result	Reference
White blood count	5.9 k/μL	4.0-10.5 k/μL
Hemoglobin	11.3 g/dL	12.5-16.0 g/dL
Platelets	473 k/μL	150-500 k/μL
Absolute neutrophil count	2.7 k/μL	2.3-6.7 k/μL
Absolute lymphocyte count	2.4 k/μL	0.8-3.2 k/μL
Absolute monocyte count	0.7 k/μL	0.4-0.9 k/μL
Absolute eosinophil count	0.2 k/μL	0.0-0.2 k/μL
Calcium	10.1 mg/dL	8.1-11.3 mg/dL
Alkaline phosphatase	135 U/L	32-92 U/L
Aspartate transaminase	28 U/L	10-40 U/L
Alanine transaminase	37 U/L	10-40 U/L
Creatinine	0.6 mg/dL	0.5-1.3 mg/dL
Total protein	7.6 g/dL	6.5-8.1 g/dL
Albumin	4.5 g/dL	3.5-5.0 g/dL
High-sensitivity C-reactive protein	0.76 mg/dL	0.0-0.4 mg/dL
Erythrocyte sedimentation rate	26 mm/h	0-30 mm/h
C3	74 mg/dL	66-162 mg/dL
C4	10.2 mg/dL	19.0-52.0 mg/dL
Alternative pathway (AH50)	104 U/mL	77-159 U/mL
Classical pathway (CH50)	101 U/mL	176-382 U/mL
IgG	1352 mg/dL	700-1620 mg/dL
IgA	43 mg/dL	50-462 mg/dL
IgM	80 mg/dL	44-266 mg/dL
IgE	2.27 kU/L	0-100 kU/L
IL-6	2.9 pg/mL	<2.0 pg/mL
IL-12	<3.20 pg/mL	0.00-8.40 pg/mL
TNF-α	12.93 pg/mL	0.00-22.30 pg/mL
IL-2	<3.20 pg/mL	0.00-60.80 pg/mL
IFN-γ	<3.20 pg/mL	0.00-24.10
Tetanus antitoxoid	1.06 IU/mL	>0.10 IU/mL
Varicella zoster IgM	0.45 ISR	<0.90 ISR
Cytomegalovirus PCR	Not detected	Not detected
HIV-1 nucleic acid amplification test	Not detected	Not detected
EBV
EBV-VCA Ab (IgM)	<36.00 U/mL	<36.00 U/mL
EBV-VCA Ab (IgG)	375.00 U/mL	<36.00 U/mL
EBV-EBNA Ab (IgG)	118.00 U/mL	<36.00 U/mL
Streptococcus pneumoniae IgG 23 serotypes (>6 weeks after PPSV23 vaccine)	3/23 to >9/23 (>1.3 μg/mL)	16/23 (>1.3 μg/mL)
Haemophilus influenzae type b IgG	0.53 μg/mL	>1.00 μg/mL
Semi-quant spike COVID-19 IgG	47.8 RU/mL; 153.0 BAU/mL	>11 RU/mL; >35.2 BAU/mL
DHR oxidative burst index	68.2	>30
CD19 percentage	4.9%	6.3-20.0%
CD19 absolute	116 cells/μL	96-515 cells/μL
CD27+/IgD+ (unswitched)	0.7%	3.8-52.7%
CD27+/IgD− (switched)	1.1%	1.9-30.4%
CD27−/IgD+ (naive)	97.2%	24.4-90.6%
CD38hi/IgMhi (transitional)	19.2%	0.3-9.2%
CD38hi/IgMlo (plasmablasts)	0.2%	0.1-4.7%
CD38lo/CD21lo (immature)	2.7%	0.5-8.0%
CD3 percentage	86.5%	62.0-88.0%
CD3 absolute	2052 cells/μL	678-2504 cells/μL
CD4 percentage	65.3%	35.3-61.1%
CD4 absolute	1549 cells/μL	414-1679 cells/μL
CD8 percentage	21.9%	11.2-37.3%
CD8 absolute	519 cells/μL	162-1038 cells/μL
CD4+/CD45RA+ (naive)	22.4%	32-73%
CD4+/CD45RO+ (memory)	77.4%	29-63%
CD16/56 percentage	7.6%	3.2-23.7%
CD16/56 absolute	180 cells/μL	45-523 cells/μL
Lymphocyte antigen stimulation	Candida–normal, tetanus–low	Normal
CD40 ligand assay	Normal expression	—
TH1 (IFN-γ)	20.4%	>5.3%
TH17 (IL-17)	0.5%	>0.3%

DHR, Drug hypersensitivity reaction; EBV, Epstein-Barr virus.

Targeted genetic panel testing identified a heterozygous intronic monoallelic variant in IRAK4 (c.1188+520A>G). Although the results of a commercially available TLR stimulation assay were normal, we suspected subtle TIR pathway defects. We found that peripheral blood mononuclear cells from the patient had significantly reduced IRAK-4 phosphorylation in response to IL-18, poly(I:C), and, to a lesser extent, IL-1β compared to healthy control cells (Fig 1, A and B). IL-6 and TNF-α secretion were normal in the patient’s cells in response to these stimuli, indicating an incomplete defect of IRAK-4 function with redundant mechanisms of cytokine production (Fig 1, C and D). More information is provided in the Methods section in this article’s Online Repository available at www.jaci-global.org.

Fig 1.

Defective TIR signaling in a patient with monoallelic IRAK4 mutation. (A and B) For Western blot test, peripheral blood mononuclear cells were cultured in complete RPMI 1640 medium alone or with IL-18, IL-1β, and poly(I:C) for 1 hour. Cell lysates were immunoblotted with phosphorylated IRAK-4 and β-actin antibodies. (C and D) IL-6 and TNF-α (DY210-05; R&D Systems) in culture supernatant were measured by ELISA kits as per the manufacturer’s instructions.

IRAK-4 is critical for pediatric immunity. Invasive bacterial infections in IRAK-4/MyD88-deficient individuals are rare after age 14.¹ This is unusual among primary immunodeficiencies and is a distinguishing feature of this group. The attenuation of the phenotype with age may be due to increase in adaptive T- and B-cell responses⁵ or a maturity of innate immune responses. It is possible that invasive bacterial infections could reemerge in older patients when the overall quantity and quality of adaptive immune responses decline.⁶ Similar to our patient, individuals with IRAK-4 deficiency show normal quantitative T-cell subsets and proliferation to phytohemagglutinin as well as normal total immunoglobulin levels. Many IRAK-4–deficient individuals do not mount protective antibody responses to S pneumoniae after polysaccharide pneumonia vaccination.¹ Individuals with IRAK-4 deficiencies also have fewer IgM⁺IgD⁺CD27⁺ B cells responsible for T-cell–independent antibody responses against bacterial antigens.⁷ Consistent with an incomplete defect in IRAK-4 function, our patient did not have a history of infection with Staphylococcus aureus or Pseudomonas aeruginosa, 2 common bacterial infections among IRAK-4–deficient patients after S pneumoniae.

There are a few features that distinguish our patient from previously described IRAK-4–deficient patients with homozygous mutations, namely MGUS, ISCLS, and previous treatment with rituximab. Multiple myeloma is associated with pneumococcal sepsis;⁸ however, in MGUS, there is a reported increase in bacterial infections and septicemia, although the organism has not been identified.⁹ Unfortunately, pneumococcal titers were not done during the patient’s prior presentation with pneumococcal sepsis, and it is not known if she was vaccinated during or shortly thereafter. Among patients with ISCLS, infection is one of the primary causes of flares; however, an increased risk of disseminated pneumococcus has not been specifically identified. In this patient, we cannot rule out the effect of rituximab, as CD20 blockade is known to impair pneumococcal immunity. Our patient had reduced switched-memory B cells. Prior reports demonstrate that IRAK-deficient patients have a decrease in unswitched memory B cells whereas switched memory B cells are preserved compared to controls.¹⁰ Last, the targeted genetic panel in this patient did identify 6 additional heterozygous variants (in NOD2, CD27, CD55, FCH01, IL10RA, SAR1B, and TGF3) that were classified as variants of uncertain significance and that we thought did not fit her phenotype.

To date, pathogenic IRAK-4 variants have not been associated with either ISCLS or MGUS. ISCLS is a rare disorder defined by recurrent episodes of hypotension/shock, hemoconcentration, and hypoalbuminemia resulting from fluid extravasation into tissues. Fatal exacerbations of ISCLS have been described in the setting of COVID-19, and flares have been described in the setting of COVID-19 vaccination.^11,12 High-dose indefinite intravenous immunoglobulin therapy improves survival.¹³ Our patient did not experience any adverse effects from COVID-19 vaccination or other vaccinations, although her third through fifth COVID-19 vaccinations were provided while the patient was receiving intravenous immunoglobulin. Most patients (>90%) with ISCLS have an MGUS, typically IgGκ. The mechanism of vascular leakage in ISCLS is unknown but may involve an aberrant endothelial response to inflammatory mediators. Likewise, the genetic susceptibility to ISCLS is undefined. Patients typically lack a family history and develop symptoms in midlife, suggesting complex inheritance.

Of note, our patient had a persistently low C4 level and low CH50. This is largely in part due to ongoing consumption rather than tissue extravasation resulting from ISCLS, given that her C1q binding was elevated at 10.1 μg Eq/mL (reference, 0-3.9 μg Eq/mL), indicative of circulating immune complexes. Low C4 levels have been implicated in monoclonal gammopathy of clinical significance, where tissue deposition may lead to organ damage.¹⁴ Our patient had normal C1 esterase inhibitor level and function, indicating that hereditary angioedema did not contribute to these abnormalities.

In summary, we have identified a 62-year-old woman with a heterozygous IRAK4 mutation. We believe that this mutation is likely pathogenic, given its association with pneumococcal sepsis and the fact that the mutant IRAK protein is poorly phosphorylated on stimulation with IL-18, an RNA viral mimic, and to a lesser extent IL-1β. The case is further complicated by 2 comorbid conditions: MGUS and ISCLS. The linkage of subclinical or subtle immunodeficiencies associated with haploinsufficiency of immunologic genes is a relatively novel concept in the field of primary immunodeficiencies but has been previously described. For example, single organ autoimmunity has been seen in carriers of dominant negative mutations in the gene AIRE that encodes the protein autoimmune regulator, which plays a critical role in central tolerance.¹⁵ Within the experimental system used in in this study, there was no evidence suggesting impaired cytokine production. Further transcriptional and cytokine profiling studies are necessary to analyze the extent of immune dysregulation in people with haploinsufficiency of IRAK-4. Further research will determine the significance of unrecognized pathogenic variants in IRAK4 among adults presenting with pneumococcal sepsis and the utility of immunoglobulin replacement in these patients.

Disclosure statement

Supported by National Institutes of Health grants RO1 AI165922, RO1 AI137970, and RO1 AI157138 to R.A.

Disclosure of potential conflict of interest: The authors declare that they have no relevant conflicts of interest.