ABSTRACT
Introduction
Inborn errors of immunity (IEI) are a heterogenous group of disorders that lead to impairment and dysfunction of one or more parts of the immune system. Autoimmunity and autoimmune cytopenias have increasingly been recognized as early markers of IEI. This study describes the type, severity and range of cytopenias in children with IEI of varying immunophenotypes at a single Canadian centre.
Methods
A retrospective chart review was completed of children with IEI followed at the Stollery Children’s Hospital in Edmonton, Alberta from January 2015 to December 2022. Patients were included if they received a diagnosis of an IEI and had single or multi-lineage cytopenia(s). The IEI diagnoses were grouped into immunophenotypic categories and cytopenias were compared using descriptive statistics.
Results
Immune cytopenias were common in all phenotypic categories, though there was variability in the type and severity. Thrombocytopenia was most likely to be seen in combined (53.8%), syndromic (59%) and immune regulatory disorders (63.6%). Neutropenia was most common in phagocytic (71.4%), immune regulatory (63.7%) and humoral disorders (52.6%). Multi-lineage cytopenias were present in 67.2% of cases and 10.4% had persistent cytopenias.
Conclusions
Immune cytopenias are common in varying types of IEI and are not isolated to a specific disease category. When seeing a patient with concerns for IEI, providers should investigate both for features of immunodeficiency and autoimmunity, in particular autoimmune cytopenias. The pattern of cytopenia may favour specific immunophenotypes and help prioritize further testing and timely referral.
Keywords: Inborn error of immunity, Immunodeficiency, Cytopenia, Autoimmunity
Introduction
Inborn errors of immunity (IEI) are a heterogeneous group of disorders, most of which arise from monogenic germline mutations that lead to impairment and dysfunction of one or more parts of the immune system. The prevalence of IEI is rising in Canada. The Canadian IEI National Registry estimates that 29,000 Canadians live with IEI and notes unique founder mutations in specific populations including First Nations, Inuit, Métis, Mennonite and some immigrant communities (1). The International Union of Immunological Societies (IUIS) classifies IEI into nine categories based on immunologic phenotype (2). Each of the nine categories has different clinical features, patterns of infections, laboratory findings and long-term risks. Although select disorders are now captured in many provincial newborn screening programs, notably severe combined immunodeficiency (SCID), most conditions require astute recognition of early symptoms and laboratory findings to diagnose. General practitioners should be familiar with the key features of IEI to initiate prompt work-ups and referrals to subspecialists.
Susceptibility to infections is the most well-recognized manifestation of IEI. The Jeffrey Model Foundation popularized 10 warning signs of immunodeficiency in children, which include recurrent bacterial infections (e.g., ear, sinopulmonary, abscesses and deep-seated infections), presence of atypical infections (persistent thrush or cutaneous fungal infections and recurrent abscesses), need for antibiotics to clear infections, history of failure to thrive and a positive family history of immunodeficiency (3). However, immune dysregulation and autoimmunity have increasingly been recognized as common findings in IEI. Peripheral blood cytopenias may be a presenting feature of IEI or occur during follow-up as a secondary autoimmune phenomenon. In 2017, the IUIS updated the categories of IEI to include those with predominant autoimmunity and immune dysregulation reflecting the evolving recognition of this phenotype (2).
Though there is emerging evidence of cytopenias as a marker of underlying immunodeficiency, there is limited data characterizing cytopenias across categories of IEI with varying immunophenotypes. This study will describe the severity and range of cytopenias in children with IEI followed at the Stollery Children’s Hospital. We highlight a rare, but important, group of conditions associated with laboratory abnormalities commonly encountered in general paediatric practices to aid in early work-up, diagnosis, and referral of children with IEI.
METHODS
Study design
We completed a retrospective cross-sectional study to describe cytopenias in children with known or suspected IEI followed at the Stollery Children’s Hospital, in Edmonton, Alberta.
The electronic medical records of all patients aged 0 to 17 years followed in the Paediatric Immunology and/or combined Paediatric Hematology and Immunology programs between January 2015 and December 2022 were reviewed for inclusion. Patients were selected based on two criteria: that they received a diagnosis of IEI, and that they had single or multi-lineage cytopenia(s) at presentation or during diagnostic evaluation.
The presence of IEI was based on a review of clinical documentation and laboratory studies, including genetic testing. Those with secondary causes for immunodeficiency were excluded. Autoimmune cytopenias were assessed by review of diagnostic testing and clinical courses, including positive direct antiglobulin test (DAT) for cases of anemia and response to therapy for cases of Immune thrombocytopenia (ITP). Anti-neutrophil antibodies are not available at our centre. The nature of cytopenia(s) was also assessed for clear alternative explanations such as iron deficiency anemia, medication-related, or marrow failure based on chart review. The study was approved by the Alberta Research Information Services (study ID MS4_Pro00109063). Consent was waived due to the retrospective and anonymized nature of the data.
Statistical analysis
The primary endpoint was the frequency and severity of cytopenias by immunophenotype. Each patient was categorized by the IUIS immunophenotypes: (1) humoral and/or antibody deficiencies, (2) combined immunodeficiency, (3) immunodeficiency with syndromic features, (4) primary immune regulatory disorders, (5) phenocopies of primary immunodeficiencies, (6) phagocytic and innate immunodeficiencies, (7) complement disorders. Examples of disorders seen in each category are listed in Table 1.
Table 1.
Diagnostic categories.
| Phenotypic Categories | Select examples of common diagnoses | Code | Count |
|---|---|---|---|
| Humoral and/or antibody deficiency | Hypogammaglobulinaemia, X-linked agammaglobulinaemia (XLA) | 1 | 19 |
| Combined immunodeficiency | Common variable immunodeficiency (CVID), severe combined immunodeficiency (SCID), hyper IgM syndrome | 2 | 13 |
| Immunodeficiencies with syndromic features | STAT3 deficiency/Hyper IgE syndrome, Wiskott–Aldrich syndrome, 22q11 microdeletion syndrome/ DiGeorge syndrome | 3 | 14 |
| Primary immune regulatory disorders | Autoimmune lymphoproliferative syndrome (ALPS), Tregopathies, Chediak-Higashi syndrome | 4 | 11 |
| Phenocopies of primary immunodeficiencies | Ras-Associated Lymphoproliferative Disorder (RALD) | 5 | 1 |
| Phagocytic and innate defects | Congenital Granulomatous Disease, G6PC3 deficiency | 6 | 7 |
| Complement deficiencies | Autosomal or X-linked recessive forms | 7 | 2 |
Complete blood cell counts for each patient were assessed for the minimum and maximum value of hemoglobin, leukocytes, neutrophils and platelets during the study period. The patient’s age at the time of collection was also recorded. Cytopenia was defined as a value below age-based normal ranges. Frequency distributions were computed for cytopenias of hemoglobin, leukocytes, neutrophils and platelets for each IEI category. Descriptive numerical data for the range of cytopenias was summarized using boxplot analysis. Our sample was not powered for comparative statistical analysis.
To better describe our population, demographic information including sex, age at referral and age at diagnosis, and reason for referral were assessed using descriptive statistics. Immunophenotypic data were collected for all patients for whom the laboratory tests had been performed on a clinical basis.
RESULTS
We screened 387 patients seen by the Paediatric Immunology and/or combined Paediatric Hematology-Immunology programs over the 7-year study period, of whom 67 met the inclusion criteria. Using clinical and laboratory data, we classified cases into seven diagnostic categories derived from the IUIS classification (Table 1). Our population represented a variety of IEI diagnoses. The most common categories were humoral and antibody defects, immunodeficiencies with syndromic causes, and combined immunodeficiencies, respectively.
Demographics
Our population had a slight male predominance (n = 42, 62.7%). The median age at presentation to Paediatric Immunology was 4.75 years (range 0.5 to 11.8 years), and the median age of diagnosis with an IEI was 5.6 years (range 0.5 to 12.3 years). The most common reason for referral was for severe and/or recurrent infections (n = 21, 31.3%). A smaller proportion (n = 8, 11.9%) were referred for autoimmunity, including autoimmune cytopenias.
Cytopenias were seen in all phenotypic categories of IEI (Table 2). Across all IEI categories, leukopenia (70.6%) and anemia (61.8%) were the most common cytopenias. Thrombocytopenia was most likely to be seen in combined (53.8%), syndromic (59%) and immune regulatory disorders (63.6%). Neutropenia was most common in phagocytic (71.4%), immune regulatory (63.7%) and humoral disorders (52.6%).
Table 2.
Frequency of cytopenia by inborn errors of immunity (IEI) category.
| IEI category | 1. Humoral antibody deficiency (n = 19) | 2. Combined (n = 13) | 3.Syndromic features (n = 14) | 4. Primary immune regulatory disorder (n = 11) | 5. Phenocopies (n = 1) | 6. Phagocytic and innate defects (n = 7) | 7. Complement disorders (n = 2) | Total (n = 67) |
|---|---|---|---|---|---|---|---|---|
| Anemia | 9 (47.4%) | 9 (69.2%) | 4 (28.6%) | 10 (90.9%) | 1 (100.0%) | 7 (100.0%) | 1 (50.0%) | 42 (62.7%) |
| Thrombocytopenia | 6 (31.6%) | 7 (53.8%) | 7 (50.0%) | 7 (63.6%) | 1 (100.0%) | 3 (42.9%) | 0 (0.0%) | 31 (46.2%) |
| Leukopenia | 12 (63.2%) | 12 (92.3%) | 8 (57.1%) | 9 (81.8%) | 1 (100.0%) | 6 (85.7%) | 0 (0.0%) | 48 (71.6%) |
| Neutropenia | 10 (52.6%) | 5 (38.5%) | 5 (35.7%) | 7 (63.7%) | 1 (100.0%) | 5 (71.4%) | 0 (0.0%) | 33 (49.2%) |
| Multi-lineage | 13 (68.2%) | 9 (69.2%) | 7 (50.0%) | 9 (81.8%) | 1 (100.0%) | 6 (85.7%) | 0 (0.0%) | 45 (67.2%) |
The minimum values for hemoglobin, platelets, leukocytes and neutrophils by immunophenotypic category are presented in Figure 1A–1D. There was variability in the range and severity of cytopenias across categories.
Figures 1.
(A). Box plots of minimum values for hemoglobin in children with inborn errors of immunity (IEI) followed at the Stollery Children’s Hospital between January 2015 and December 2022. Each data point represents the lowest value of the respective blood cell line seen in each child during the study period. Within each box, horizontal black lines denote median values; boxes extend from the 25th to the 75th percentile for each group’s distribution of values; vertical lines denote the upper and lower values of the data sets. (B) Box plots of minimum values for platelets in children with IEI followed at the Stollery Children’s Hospital between January 2015 and December 2022. Each data point represents the lowest value of the respective blood cell line seen in each child during the study period. Within each box, horizontal black lines denote median values; boxes extend from the 25th to the 75th percentile for each group’s distribution of values; vertical lines denote the upper and lower values of the data sets. (C) Box plots of minimum values for leukocytes in children with IEI followed at the Stollery Children’s Hospital between January 2015 and December 2022. Each data point represents the lowest value of the respective blood cell line seen in each child during the study period. Within each box, horizontal black lines denote median values; boxes extend from the 25th to the 75th percentile for each group’s distribution of values; vertical lines denote the upper and lower values of the data sets. (D) Box plots of minimum values for neutrophils in children with IEI followed at the Stollery Children’s Hospital between January 2015 and December 2022. Each data point represents the lowest value of the respective blood cell line seen in each child during the study period. Within each box, horizontal black lines denote median values; boxes extend from the 25th to the 75th percentile for each group’s distribution of values; vertical lines denote the upper and lower values of the data sets. Outer dots are outliers.
Sixty-seven percent of cases (n = 45) in our study had multiple cell lines involved. Multi-lineage cytopenias were seen in all diagnostic categories except for complement disorders and were most frequently observed in phagocytic disorders (n = 6, 85.7%) and immune regulatory disorders (n = 9, 81.8%). Counts were persistently low for the duration of the study period in nine cases (13.4%) and included examples of each blood cell line. Persistent cytopenias were seen in humoral (n = 2, 10.5%), syndromic (n = 2, 14.3%), immune regulatory (n = 2, 18.2%) and combined (n = 1, 7.8%) disorders.
A DAT was performed in 18 (26.9%) of patients and was positive in eight cases. Anti-neutrophil antibodies are not available at our centre.
During the study period, many patients required immunosuppressive therapies or other supportive care treatment of cytopenias or the underlying IEI. Twenty-three (34.3%) were treated with IVIG, 19 for replacement of deficiencies and three with high-dose IVIG for immunosuppression. Other immunosuppressive therapies were used in 14 (20.9%) patients including high-dose steroids, Rituximab, Sirolimus, Sulfasalazine, MMF, Anakinra, Cyclosporin, Adalimumab and Thrombopoietin-receptor agonists. For treatment of an underlying IEI, seven children underwent stem cell transplantation, two received gene therapy, three received G-CSF and 17 required antibiotics and/or antifungal prophylaxis.
DISCUSSION
Population data have shown that autoimmune cytopenias are common in patients with IEI. In recent retrospective studies of national immunodeficiency registries, 26% to 62% of patients had autoimmune cytopenias at presentation (4,5). However, autoimmunity and autoimmune cytopenia seem to remain under-recognized in IEI and are not a common reason for referral. In our population, 11.8% of patients were referred to Immunology for concerns of autoimmunity and/or autoimmune cytopenias. We hope to increase recognition of autoimmunity as an important feature of IEI to guide diagnostic evaluation and timely referral.
In this single-centre study that examined 67 patients with seven types of immunodeficiencies, we found at least one type of cytopenia in each phenotypic category of IEI. The cytopenias in children with IEI often reached moderate to severe levels though there was variability between categories. Multi-lineage cytopenias were present in 66% of patients and 13% had persistent cytopenias. These findings are supported by the literature documenting that cytopenias associated with IEI tend to be early-onset, multi-lineage and have poor response to initial treatments (6).
Autoimmune cytopenias can be challenging to diagnose. In some cases, laboratory tests can confirm autoimmunity, for example, DAT-positive anemia which was the case in a minority of patients in our cohort. Anti-neutrophil antibodies are not available at our centre, so the diagnosis of autoimmune neutropenia was based on clinical documentation and natural history. ITP is a clinical diagnosis based on history and response to treatment. Other important explanations for cytopenias in patients with IEI include myelosuppressive therapies for those who undergo transplant and marrow failure. These cases were excluded from our cohort based on clinical chart review. However, we may overestimate the instances of autoimmune cytopenia, in part due to the limitations of our retrospective methodology. We could only exclude cytopenias due to secondary causes (e.g., iron deficiency, medications and marrow failure) if it was documented in the chart, evident in laboratory work-up and explored by the clinical team.
Anemia was the most common cytopenia overall in our population and was seen with varying severity across categories. Children with immune dysregulation and humoral and antibody disorder had the most severe anemia. The severity of leukopenia and neutropenia was also variable. In some patients, we saw that leukocyte counts remained elevated through the study period (i.e., the minimum value was in fact not a cytopenia). This may be explained by inflammatory reactions during acute infections but does not exclude an underlying immunodeficiency or autoimmune process.
We saw high rates of all types of cytopenias in humoral and antibody disorders, immune regulatory disorders, and phagocytic and innate disorders. Combined immunodeficiencies had predominant leukopenia, though all types of cytopenias were seen. Syndromic disorders most notably had moderate to severe thrombocytopenia. Wiskott–Aldrich syndrome and 22q11.2 deletion syndrome, the most common syndromes in our population, are known to be associated with micro- and macrothrombocytopenia, respectively. The incidence of thrombocytopenia in our cohort was similar to that described in previous literature (8).
While our data set looked at the pattern of cytopenias in patients with known IEI, the following clinical features were more commonly seen in our cohort and as such should raise suspicion for IEI in any patient with cytopenias (Table 3). This corroborates with previous studies that have also found these clinical features in patients with cytopenias who were eventually diagnosed with IEI (5–7). Some initial investigations that can be pursued by front-line providers are also included to guide work-up when IEI is suspected. Our study adds to the existing literature that cytopenias appear to be common across IEI phenotypes and are not isolated to single disease entities.
Table 3.
Clinical features suspicious for underlying inborn errors of immunity (IEI) and initial investigations.
| Clinical feature |
|---|
| Early-onset cytopenias |
| Multiple immune cytopenias |
| >1 autoimmune disorder |
| Dysmorphic features (microcephaly, low set ears, facial dysmorphisms, defective tooth development) |
| Short stature |
| Developmental delay |
| Severe, recurrent, unusual infections |
| Further testing for autoimmunity and immune function |
| Quantitative serum immunoglobulins |
| Lymphocytes subsets including total lymphocyte count, T lymphocytes (CD3, CD4 and CD8), B lymphocytes (CD19 and CD20), CD4/CD8 ratio |
| Vaccine titers |
The presence of cytopenia in immune regulatory disorders has been well described. Autoimmune lymphoproliferative disorder (ALPS), for example, is a rare genetic disorder with lymphoproliferation, elevated levels of double-negative T cells, and antibody-mediated destruction of blood cells (including autoimmune anemia, thrombocytopenia and neutropenia). Autoimmune cytopenias are also an established feature of antibody disorders, namely combined variable immunodeficiency (CVID). Autoimmune manifestations in patients with CVID have been reported in 22% to 48% of cases with similar rates and distributions of cytopenias as in our population (7).
There are no limitations to our study. The small sample size of our single-centre study limits the power and generalizability of our findings. Given that there were only two cases of complement disorders in our population, it was not possible to draw substantial conclusions about this group. Additionally, the understanding and testing for IEI have changed significantly over the study period. The availability of new testing modalities and awareness of autoimmunity as a feature of IEI may influence diagnoses and laboratory work-ups. We did not collect data on the time of onset of cytopenias (at the time of diagnosis of IEI or during the course of underlying disease) which could be explored in future studies and help understand the natural history of autoimmunity and immune dysregulation in these patients. Further research could compare the characteristics of children with IEI with and without cytopenias. Collaboration across centres and with other subspecialists involved in the care of these patients would enhance our understanding of these rare diseases.
IEI are an important group of disorders with varied presentations most well-known for symptoms of severe, recurrent and unusual infections. However, there is increasing knowledge of the role of immune dysregulation and autoimmunity in IEI which often presents as autoimmune cytopenia. The children with confirmed IEI in our cohort and in wider literature often have multi-lineage and persistent cytopenias. When seeing a patient with concerns for IEI, providers should investigate for both susceptibility to infection and autoimmunity, in particular autoimmune cytopenias. The pattern of cytopenia in a patient suspected of IEI may favor specific immunophenotypes and help prioritize further diagnostic testing and timely referrals.
Contributor Information
Julia Lew, Division of Pediatric Haematology and Oncology, Hospital for Sick Children, Toronto, Ontario, Canada.
Sneha Suresh,, Pediatric Immunology and Infectious Disease, University of Alberta, Edmonton, Alberta, Canada.
Catherine Corriveau-Bourque,, Division of Pediatric Hematology, University of Alberta, Edmonton, Alberta, Canada.
Potential conflicts of interest
All authors have no conflicts of interest to disclose.
Ethics approval
The study was approved by the Alberta Research Information Services (study ID MS4_Pro00109063).
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