Late-Onset Non-HLH Presentations of Growth Arrest, Inflammatory Arachnoiditis, and Severe Infectious Mononucleosis, in Siblings with Hypomorphic Defects in UNC13D

Filaggrin-Associated Atopic Skin, Eye, Airways, and Gut Disease, Modifying the Presentation of X-Linked Reticular Pigmentary Disorder (XLPDR)

BACKGROUND

X-linked reticular pigmentary disorder (XLPDR) is a rare condition characterized by skin hyperpigmentation, ectodermal features, multiorgan inflammation, and recurrent infections. All probands identified to date share the same intronic hemizygous POLA1 hypomorphic variant (NM_001330360.2(POLA1):c.1393-354A > G) on the X chromosome. Previous studies have supported excessive type 1 interferon (IFN) inflammation and natural killer (NK) cell dysfunction in disease pathogenesis. Common null polymorphisms in filaggrin (FLG) gene underlie ichthyosis vulgaris and atopic predisposition.

CASE

A 9-year-old boy born to non-consanguineous parents developed eczema with reticular skin hyperpigmentation in early infancy. He suffered recurrent chest infections with chronic cough, clubbing, and asthma, moderate allergic rhinoconjunctivitis with keratitis, multiple food allergies, and vomiting with growth failure. Imaging demonstrated bronchiectasis, while gastroscopy identified chronic eosinophilic gastroduodenitis. Interestingly, growth failure and bronchiectasis improved over time without specific treatment.

METHODS

Whole-genome sequencing (WGS) using Illumina short-read sequencing was followed by both manual and orthogonal automated bioinformatic analyses for single-nucleotide variants, small insertions/deletions (indels), and larger copy number variations. NK cell cytotoxic function was assessed using 51Cr release and degranulation assays. The presence of an interferon signature was investigated using a panel of six interferon-stimulated genes (ISGs) by QPCR.

RESULTS

WGS identified a de novo hemizygous intronic variant in POLA1 (NM_001330360.2(POLA1):c.1393-354A > G) giving a diagnosis of XLPDR, as well as a heterozygous nonsense FLG variant (NM_002016.2(FLG):c.441del, NP_0020.1:p.(Arg151Glyfs*43)). Compared to healthy controls, the IFN signature was elevated although the degree moderated over time with the improvement in his chest disease. NK cell functional studies showed normal cytotoxicity and degranulation.

CONCLUSION

This patient had multiple atopic manifestations affecting eye, skin, chest, and gut, complicating the presentation of XLPDR. This highlights that common FLG polymorphisms should always be considered when assessing genotype-phenotype correlations of other genetic variation in patients with atopic symptoms. Additionally, while the patient exhibited an enhanced IFN signature, he does not have an NK cell defect, suggesting this may not be a constant feature of XLPDR.

The leptomeninges as a critical organ for normal CNS development and function: First patient and public involved systematic review of arachnoiditis (chronic meningitis)

BACKGROUND & IMPORTANCE

This patient and public-involved systematic review originally focused on arachnoiditis, a supposedly rare "iatrogenic chronic meningitis" causing permanent neurologic damage and intractable pain. We sought to prove disease existence, causation, symptoms, and inform future directions. After 63 terms for the same pathology were found, the study was renamed Diseases of the Leptomeninges (DLMs). We present results that nullify traditional clinical thinking about DLMs, answer study questions, and create a unified path forward.

METHODS

The prospective PRISMA protocol is published at Arcsology.org. We used four platforms, 10 sources, extraction software, and critical review with ≥2 researchers at each phase. All human sources to 12/6/2020 were eligible for qualitative synthesis utilizing R. Weekly updates since cutoff strengthen conclusions.

RESULTS

Included were 887/14286 sources containing 12721 DLMs patients. Pathology involves the subarachnoid space (SAS) and pia. DLMs occurred in all countries as a contributor to the top 10 causes of disability-adjusted life years lost, with communicable diseases (CDs) predominating. In the USA, the ratio of CDs to iatrogenic causes is 2.4:1, contradicting arachnoiditis literature. Spinal fusion surgery comprised 54.7% of the iatrogenic category, with rhBMP-2 resulting in 2.4x more DLMs than no use (p<0.0001). Spinal injections and neuraxial anesthesia procedures cause 1.1%, and 0.2% permanent DLMs, respectively. Syringomyelia, hydrocephalus, and arachnoid cysts are complications caused by blocked CSF flow. CNS neuron death occurs due to insufficient arterial supply from compromised vasculature and nerves traversing the SAS. Contrast MRI is currently the diagnostic test of choice. Lack of radiologist recognition is problematic.

DISCUSSION & CONCLUSION

DLMs are common. The LM clinically functions as an organ with critical CNS-sustaining roles involving the SAS-pia structure, enclosed cells, lymphatics, and biologic pathways. Cases involve all specialties. Causes are numerous, symptoms predictable, and outcomes dependent on time to treatment and extent of residual SAS damage. An international disease classification and possible treatment trials are proposed.

Severely impaired CTL killing is a feature of the neurological disorder Niemann-Pick Syndrome type C1

Niemann-Pick disease type C1 (NP-C1) is a rare lysosomal storage disorder resulting from mutations in an endo-lysosomal cholesterol transporter, NPC1. Despite typically presenting with pronounced neurological manifestations, NP-C1 also resembles long-term congenital immunodeficiencies that arise due to impairment of cytotoxic T lymphocyte (CTL) effector function. CTLs kill their targets through exocytosis of the contents of lysosome-like secretory cytotoxic granules (CGs) that store, and ultimately release the essential pore-forming protein perforin and pro-apoptotic serine proteases, granzymes, into the synapse formed between the CTL and a target cell. We have discovered that NPC1 deficiency increases CG lipid burden, impairs autophagic flux due to stalled trafficking of the transcription factor EB (TFEB), and dramatically reduces CTL cytotoxicity. Using a variety of immunological and cell biology techniques, we show that the cytotoxic defect arises specifically due to impaired perforin pore-formation. We demonstrated defects of CTL function of varying severity in NP-C1 patients, with the greatest loss of function associated with the most florid and/or earliest disease presentations. Remarkably, perforin function and CTL cytotoxicity were restored in vitro by promoting lipid clearance with therapeutic 2-hydroxypropyl-b-cyclodextrin (HPbCD), whereas restoring autophagy through TFEB over-expression was ineffective. Overall, our study revealed that NPC1 deficiency has a deleterious impact on CTL (but not natural killer cell) cytotoxicity that, in the long term, may predispose NP-C1 patients to atypical infections and impaired immune surveillance more generally.

Neuroinflammation Associated With Inborn Errors of Immunity

The advent of high-throughput sequencing has facilitated genotype-phenotype correlations in congenital diseases. This has provided molecular diagnosis and benefited patient management but has also revealed substantial phenotypic heterogeneity. Although distinct neuroinflammatory diseases are scarce among the several thousands of established congenital diseases, elements of neuroinflammation are increasingly recognized in a substantial proportion of inborn errors of immunity, where it may even dominate the clinical picture at initial presentation. Although each disease entity is rare, they collectively can constitute a significant proportion of neuropediatric patients in tertiary care and may occasionally also explain adult neurology patients. We focus this review on the signs and symptoms of neuroinflammation that have been reported in association with established pathogenic variants in immune genes and suggest the following subdivision based on proposed underlying mechanisms: autoinflammatory disorders, tolerance defects, and immunodeficiency disorders. The large group of autoinflammatory disorders is further subdivided into IL-1β-mediated disorders, NF-κB dysregulation, type I interferonopathies, and hemophagocytic syndromes. We delineate emerging pathogenic themes underlying neuroinflammation in monogenic diseases and describe the breadth of the clinical spectrum to support decisions to screen for a genetic diagnosis and encourage further research on a neglected phenomenon.

MRI Patterns in Pediatric CNS Hemophagocytic Lymphohistiocytosis

BACKGROUND AND PURPOSE

Neuroimaging has an important role in detecting CNS involvement in children with systemic or CNS isolated hemophagocytic lymphohistiocytosis. We characterized a cohort of pediatric patients with CNS hemophagocytic lymphohistiocytosis focusing on neuroradiologic features and assessed whether distinct MR imaging patterns and genotype correlations can be recognized.

MATERIALS AND METHODS

We retrospectively enrolled consecutive pediatric patients diagnosed with hemophagocytic lymphohistiocytosis with CNS involvement treated at 2 pediatric neurology centers between 2010 and 2018. Clinical and MR imaging data were analyzed.

RESULTS

Fifty-seven children (40 primary, 70%) with a median age of 36 months (interquartile range, 5.5-80.8 months) were included. One hundred twenty-three MR imaging studies were assessed, and 2 broad imaging patterns were identified. Pattern 1 (significant parenchymal disease, 32/57, 56%) was seen in older children (P = .004) with worse clinical profiles. It had 3 onset subpatterns: multifocal white matter lesions (21/32, 66%), brainstem predominant disease (5, 15%), and cerebellitis (6, 19%). All patients with the brainstem pattern failed to meet the radiologic criteria for chronic lymphocytic inflammation with pontine perivascular enhancement responsive to steroids. An attenuated imaging phenotype (pattern 2) was seen in 25 patients (44%, 30 studies) and was associated with younger age.

CONCLUSIONS

Distinct MR imaging patterns correlating with clinical phenotypes and possible genetic underpinnings were recognized in this cohort of pediatric CNS hemophagocytic lymphohistiocytosis. Disruptive mutations and missense mutations with absent protein expression correlate with a younger onset age. Children with brainstem and cerebellitis patterns and a negative etiologic work-up require directed assessment for CNS hemophagocytic lymphohistiocytosis.

NBAS Variants Are Associated with Quantitative and Qualitative NK and B Cell Deficiency

PURPOSE

Biallelic pathogenic NBAS variants manifest as a multisystem disorder with heterogeneous clinical phenotypes such as recurrent acute liver failure, growth retardation, and susceptibility to infections. This study explores how NBAS-associated disease affects cells of the innate and adaptive immune system.

METHODS

Clinical and laboratory parameters were combined with functional multi-parametric immunophenotyping methods in fifteen NBAS-deficient patients to discover possible alterations in their immune system.

RESULTS

Our study revealed reduced absolute numbers of mature CD56dim natural killer (NK) cells. Notably, the residual NK cell population in NBAS-deficient patients exerted a lower potential for activation and degranulation in response to K562 target cells, suggesting an NK cell-intrinsic role for NBAS in the release of cytotoxic granules. NBAS-deficient NK cell activation and degranulation was normalized upon pre-activation by IL-2 in vitro, suggesting that functional impairment was reversible. In addition, we observed a reduced number of naïve B cells in the peripheral blood associated with hypogammaglobulinemia.

CONCLUSION

In summary, we demonstrate that pathogenic biallelic variants in NBAS are associated with dysfunctional NK cells as well as impaired adaptive humoral immunity.

Dilemmas in the diagnosis and pathogenesis of atypical late-onset familial haemophagocytic lymphohistiocytosis

Objectives

A congenital loss of cytotoxic lymphocyte activity leads to a potentially fatal immune dysregulation, familial haemophagocytic lymphohistiocytosis. Until recently, this disease was uniformly associated with infants or very young children, but it appears now that the onset may be delayed for decades. As a result, some adults are being mis‐ or under‐diagnosed because of their ‘atypical’ symptoms that are not recognised as immunodeficiency. The clinical picture and histopathology can overlap with those of haematologic malignancy, further complicating the diagnostic thought process. The spectrum of atypical symptoms is poorly defined, and therefore, it is important to describe these cases and the attendant immunological and cellular changes associated with familial haemophagocytic lymphohistiocytosis, in order to improve diagnosis and prevent unintended consequences of symptomatic therapies.

Methods

A 45‐year‐old patient presented with suspected T‐cell lymphoma and was treated with combination chemotherapy (cyclophosphamide, doxorubicin, vincristine, prednisolone) supplemented with granulocyte‐colony stimulating factor (G‐CSF). To mobilise stem cells for autologous transplantation, the patient was then treated with high‐dose G‐CSF and rapidly developed haemophagocytic lymphohistiocytosis. Symptoms resolved temporarily with intensive immunosuppression with alemtuzumab and durably with a subsequent allograft.

Results

The patient was found to be a carrier of bi‐allelic mutations in the STXBP2 protein that is essential for cytotoxic lymphocyte function, and the initial diagnosis has been revised as familial haemophagocytic lymphohistiocytosis.

Conclusion

This case highlights the difficulty in distinguishing atypical/late‐onset familial haemophagocytic lymphohistiocytosis from a malignant process as well as a possible exacerbation of the disease with G‐CSF therapy.

Hematopoietic stem cell transplant effectively rescues lymphocyte differentiation and function in DOCK8-deficient patients

Bi-allelic inactivating mutations in DOCK8 cause a combined immunodeficiency characterised by severe pathogen infections, eczema, allergies, malignancy and impaired humoral responses. These clinical features result from functional defects in most lymphocyte lineages. Thus, DOCK8 plays a key role in immune cell function. Hematopoietic stem cell transplantation (HSCT) is curative for DOCK8 deficiency. While previous reports have described clinical outcomes for DOCK8 deficiency following HSCT, the effect on lymphocyte reconstitution and function has not been investigated. Our study determined whether defects in lymphocyte differentiation and function in DOCK8-deficient patients were restored following HSCT. DOCK8-deficient T and B lymphocytes exhibited aberrant activation and effector function in vivo and in vitro. Frequencies of αβ T and MAIT cells were reduced while γδT cells were increased in DOCK8-deficient patients. HSCT improved, abnormal lymphocyte function in DOCK8-deficient patients. Elevated total and allergen-specific IgE in DOCK8-deficient patients decreased over time following HSCT. Our results document the extensive catalogue of cellular defects in DOCK8-deficient patients, and the efficacy of HSCT to correct these defects, concurrent with improvements in clinical phenotypes. Overall, our findings provide mechanisms at a functional cellular level for improvements in clinical features of DOCK8 deficiency post-HSCT, identify biomarkers that correlate with improved clinical outcomes, and inform the general dynamics of immune reconstitution in patients with monogenic immune disorders following HSCT.

Neonatal Cytomegalovirus Palatal Ulceration and Bocavirus Pneumonitis Associated With a Defect of Lymphocyte Cytotoxicity Caused by Mutations in UNC13D

Single gene defects that impair lymphocyte cytotoxicity can predispose to severe viral infection that normally remains subclinical. The classic severe presentation is hemophagocytic lymphohistiocytosis. Here, we report the case of a neonate who presented with cytomegalovirus palatal ulceration and bocavirus pneumonitis secondary to impaired cytotoxicity caused by biallelic mutations in the UNC13D gene.

Two Brothers with Atypical UNC13D-Related Hemophagocytic Lymphohistiocytosis Characterized by Massive Lung and Brain Involvement

Hemophagocytic lymphohistiocytosis (HLH) is a potentially fatal hyperinflammatory condition. Variants in different genes have been associated with the familial forms of the syndrome (FHL), usually presenting within the first 2 years of life. Due to increasing awareness of the signs and symptoms of HLH and a better understanding of the genetic basis of the disease, FHL has been increasingly diagnosed in patients presenting beyond infancy. Here, we report on two brothers with atypical, late-onset HLH in which whole exome sequencing revealed a homozygous pathogenic UNC13D variant. In the first brother, the clinical phenotype was dominated by a massive lung involvement. In the second brother a progressive neurological deterioration was observed. In both cases, the clinical manifestations at symptom onset were misleading, making the diagnosis difficult to achieve. This report expands the spectrum of clinical presentations of FLH3. Moreover, it highlights the importance to warn clinicians to keep a high level of suspicion in patients presenting with fever, cytopenia, splenomegaly of unknown origin, and unresponsiveness to conventional treatment even beyond early childhood. Moreover, this report emphasizes that insidious neurologic symptoms may represent the initial or sole presenting sign of FHL, even in the absence of peripheral signs of activation.