INTRODUCTION
Down syndrome (DS) is associated with trisomy of chromosome 21 and has an estimated prevalence of 1 in 1,000 live births [1]. It is the most common chromosomal disorder among live newborns [2]. Numerous comorbid conditions associated with DS have been identified, including developmental delay, congenital heart diseases, gastrointestinal anomalies, an increased risk of hematological malignancies, and various autoimmune diseases [3].
DS is also the most common genetic syndrome associated with immunodeficiency, involving both innate immune defects and impaired adaptive immune responses [4]. Defects in immunological parameters have been described in DS and have been proposed as a cause for the increased severity of infections observed in children with DS [5, 6]. The immunological defects that contribute to heightened susceptibility to such infections may include hypogammaglobulinemia due to decreased levels of immunoglobulin (Ig) G subclasses (IgG2, IgG4) as well as reduced IgA and IgM isotypes; diminished antibody responses to vaccinations; decreased B cell proliferation; reductions in the numbers of total and memory B cells; impaired neutrophil chemotaxis; and reduced absolute NK cell counts [6–11].
The aim of this study is to evaluate the causes and status of immunodeficiency in children with DS receiving intravenous immunoglobulin (IVIG) therapy, which is being followed up in the pediatric immunology department of our hospital.
CASE REPORTS
In this study, we present a case series of all patients with DS and immunodeficiency who were evaluated at the pediatric immunology department of a university training/research hospital from May 2013 to May 2023. As this is a retrospective case series, no ethical committee approval was required. However, informed consent was obtained from each patient for inclusion in this study.
Clinical presentation and laboratory tests, including complete blood count, immunoglobulin quantification by nephelometry, antibody response by ELISA, and lymphocyte phenotyping by flow cytometry, were evaluated. Cellular immunity was quantitatively assessed based on the levels of CD3+, CD4+, and CD8+- T cells, B lymphocytes, and NK cells. The collected data were compared with reference values for age-specific normal ranges [12]. Impaired humoral immunity was determined based on immunoglobulin (IgG, IgA, and IgM) levels, with hypogammaglobulinemia defined as values below the 95% confidence interval for age [13]. Additionally, humoral immunity was qualitatively assessed by evaluating specific antibody responses to various protein antigens, including antibodies against hepatitis B, Rubella, and Cytomegalovirus, as well as isohemagglutinin titers of the patients.
The clinical and laboratory characteristics of the cases are briefly described individually below.
CASE 1
A 4-year-old male patient was referred from the general pediatrics department to the pediatric immunology department at 15 months of age due to low IgG and IgA levels. Initial laboratory results showed IgG: 460 mg/dl (normal range: 748.2–851.4), IgA: 38 mg/dl (42.9–52.6), and IgM: 99 mg/dl (96.3–117.7). Based on these findings, the patient was diagnosed with transient hypogammaglobulinemia of infancy (THI), and prophylactic trimethoprim-sulfamethoxazole treatment was initiated, with a follow-up scheduled for 3 months later. At the follow-up 4 months later, laboratory tests for IgG, IgA, IgM, total IgE, and IgG subclasses were repeated. Results were as follows: IgG: 551 (748–851) mg/dl, IgA: 18 (42.9–52.6) mg/dl, IgM: 59 (96.3–117.7) mg/dl, IgG1: 357 (702–844) mg/dl, IgG2: 112 (92–116) mg/dl, IgG3: 12 (37–49) mg/dl and IgG4: 9 (18–26) mg/dl. Flow cytometry findings were normal. Due to the continuation of frequent infections despite prophylactic treatment, IVIG replacement therapy was initiated.
CASE 2
A 19-year-old male patient was referred to the pediatric immunology department 5 years ago due to recurrent infections and a diagnosis of low IgM levels during evaluation in the general pediatrics department. Laboratory assessments, including IgG, IgA, IgM, IgG subclasses, flow cytometry, and antibody responses (anti-HBs, anti-Rubella IgG, anti-CMV IgG, and isohemagglutinin titers for anti-A/-B), were performed. The results were as follows: IgG: 1840 (1014–1209) mg/dl, IgA: 200 (118–159) mg/dl, IgM: 30 (110–147) mg/dl, anti-HBs: 0.6 IU/ml, anti-Rubella IgG: 3.1 IU/ml, anti-A/-B isohemagglutinin titers: 1/16–1/2, IgG1: 1120 (711–956) mg/dl, IgG2: 230 (214–292) mg/dl, IgG3: 43.6 (51–73) mg/dl, and IgG4: 90.7 (30–72) mg/dl. Flow cytometry findings were normal. Due to the findings of low IgM and IgG3 levels, along with impaired antibody responses to immunization and isohemagglutinins, IVIG replacement therapy was initiated.
CASE 3
An 8.5-year-old male patient presented to the pediatric immunology department 2 years ago with complaints of recurrent sinus infections and frequent upper respiratory tract infections. Laboratory evaluations, including IgG, IgA, IgM, IgG subclasses, flow cytometry, and antibody responses (anti-HBs, anti-Rubella IgG, anti-CMV IgG, and isohemagglutinin titers for anti-A/-B), were performed. The results were as follows: IgG: 1220 (1011–1111) mg/dl, IgA: 200 (105–127) mg/dl, IgM: 98 (95–116) mg/dl, anti-HBs: 1.25 IU/ml, anti-Rubella IgG: 84.9 IU/ml, anti-A/-B isohemagglutinin titers: 1/64–1/8, IgG1: 958 (778–920) mg/dl, IgG2: 174 (193–245) mg/dl, IgG3: 25 (51–73) mg/dl, and IgG4: 54 (49–72) mg/dl. Flow cytometry findings were normal. Due to the IgG subclass deficiency and reduced CD19+-B cell counts, IVIG replacement therapy was initiated.
CASE 4
A patient referred to the pediatric immunology department from the pediatric hematology-oncology department had been followed for transient myeloproliferative disease and received chemotherapy at 16 months of age. The patient reported no complaints other than nasal congestion and sneezing persisting for 3 months. Laboratory evaluations, including IgG, IgA, IgM, flow cytometry, and antibody responses (anti-HBs, anti-Rubella IgG, anti-CMV IgG, and isohemagglutinin titers for anti-A/-B), were conducted. Results were as follows: IgG: 859 (748–851) mg/dl, IgA: 39 (42.9–52.6) mg/dl, IgM: 38 (96.3–117.7) mg/dl, anti-HBs: 59.65 IU/ml, anti-Rubella IgG: 34.2 IU/ml, and anti-A/-B isohemagglutinin titers: 1/256–1/256. The patient, with low serum IgM and IgA levels, was diagnosed with “unclassified antibody deficiency” and has been receiving IVIG replacement therapy for 1.5 years.
CASE 5
A 4-year and 3-month-old male patient was referred to the pediatric immunology department from the general pediatrics department 9 months ago due to frequent illnesses during the winter months. Laboratory evaluations, including IgG, IgA, IgM, flow cytometry, and antibody responses (anti-HBs, anti-Rubella IgG, anti-CMV IgG, and isohemagglutinin titers for anti-A/-B), were conducted. The results were as follows IgG: 1040 (844–944) mg/dl, IgA: 96 (64.8–79.2) mg/dl, and IgM: 72 (80.9–104) mg/dl. Specific antibody responses showed anti-HBs: 0 IU/ml (negative), anti-Rubella IgG: 31.8 IU/ml, and an anti-A isohemagglutinin titer of 1/32. IgG subclass analysis showed IgG1: 985 (726–867) mg/dl, IgG2: 280 (155–211) mg/dl, IgG3: 28 (35–50) mg/dl, and IgG4: 14 (27–48) mg/dl. Flow cytometry revealed CD3+: 84.1% (43–76), CD3+-CD4+: 25.4% (23–48), CD3+-CD8+: 57% (14–33), CD19+: 3.4% (14–44), and CD16+56: 0.44% (0.9–2.9). Due to the findings of CD19+- B cell deficiency and IgG subclass deficiency, IVIG replacement therapy was initiated.
CASE 6
A 4-year-old female patient presented to the pediatric immunology department with complaints of frequent illnesses during the winter months and persistent cough. Laboratory evaluations, including serum IgG, IgA, IgM, and specific antibody responses (anti-HBs, anti-Rubella IgG, anti-CMV IgG, and isohemagglutinin titers for anti-A/-B), were conducted. The results showed IgG: 622 (844–944) mg/dl, IgA: 60.2 (64.8–79.2) mg/dl, IgM: 36 (80.9–104) mg/dl, anti-HBs: 206.26 IU/ml, anti-Rubella IgG: 98.1 IU/ml, and an anti-A isohemagglutinin titer of 1/32. IgG subclass analysis revealed IgG1: 438 (726–867) mg/dl, IgG2: 379 (155–211) mg/dl, IgG3: 68 (35–50) mg/dl, and IgG4: 82 (27–48) mg/dl. Based on the findings of low serum IgG, IgM, and IgG1 levels, the patient was diagnosed with THI, and IVIG replacement therapy was initiated.
RESULTS
Of the patients, 4 were male and 2 were female, with an average age of diagnosis of 59 months. Five of the patients had comorbid conditions (Table 1). Two patients were diagnosed with THI. The most frequently observed deficiencies among the patients were IgG3 (4 patients) and IgM (5 patients), followed by IgA deficiency (3 patients). The least common deficiency was IgG2 (1 patient), while deficiencies in IgG, IgG1, and IgG4 were each identified in 2 patients (Table 2).
Table 1
Demographic characteristics and comorbidities
Table 2
Serum immunoglobulin isotypes and IgG subgroup levels*
Anti-HBs were negative in 4 patients, and anti-Rubella IgG was negative in 1 patient. Low isohemagglutinin titers were observed in 2 patients (Table 3). Flow cytometric evaluation was performed in 5 out of 6 patients. All patients demonstrated reduced absolute counts of CD19+- B cells, while 4 cases showed percentages below the reference range. Reduced percentages of CD4+- T cells and CD16+/56+- NK cells were observed in 1 patient, and an inverted CD4/CD8 ratio was noted in 2 patients (Table 4).
Table 3
Specific antibody responses and isohemagglutinin titer levels
Table 4
Peripheral lymphocyte subgroup values*
DISCUSSION
DS represents the most common genetic syndrome associated with immune dysregulation. Evidence regarding genetic abnormalities affecting the immune system due to trisomy of chromosome 21 remains limited. In recent years, the increased life expectancy in these patients has shifted focus toward the long-term complications of comorbidities (Table 1), infection risk and autoimmunity, which can significantly reduce their quality of life.
Immune system abnormalities associated with DS include a marked reduction in naive lymphocytes, impaired specific antibody responses, defects in neutrophil chemotaxis, and mild to moderate T and B cell lymphopenia. Kusters et al. reported lymphocyte subsets in 95 children with DS. In their study, the number and percentage of naive T cells were found to be reduced by approximately half compared to non-DS children across all age groups. In the same DS cohort, the researchers compared various maturation stages of peripheral blood B cells with those of normal children and found a reduction in all B cell stages, particularly naive B cells [14]. In our study, although the naive B cell counts could not be evaluated, reductions in CD19+- cells were identified (Table 4).
In a study conducted by Selikowitz, IgG2 deficiency was reported as the most common IgG subclass deficiency [15]. However, in our study, among the 6 patients receiving IVIG replacement therapy, IgG3 deficiency was observed in 4 patients (IgG1: 2 patients, IgG2: 1 patient, IgG3: 4 patients, IgG4: 2 patients) (Table 2).
Research indicates that individuals with DS exhibit alterations in NK cell populations, characterized by reduced numbers and impaired functionality. For instance, studies have shown that NK cells in DS often display decreased expression of activating receptors and increased expression of inhibitory receptors, leading to diminished cytotoxic activity against target cells [16]. In our study, a reduced NK cell percentage was observed in 1 patient (Table 4).
This dysfunction may be exacerbated by the presence of other immune deficiencies common in this population, such as T cell and B cell abnormalities [17]. Additionally, 1 of our patients exhibited a decreased CD4+- T cell percentage and absolute counts, and 2 patients showed an inverted CD4/CD8 ratio [18] (Table 4).
In Down syndrome patients with antibody and/or cellular immune system deficiency, prophylactic antibiotic and IVIG treatment may need to be initiated to prevent fatal lower respiratory tract or similar infections or infections that may develop after certain operations such as tooth extraction [19, 20]. Although other comorbid conditions associated with Down syndrome are well known, the association with primary immunodeficiency disorders is not well known. Awareness on this issue will increase thanks to this article [21].
Our patients exhibited B cell lymphopenia. It is becoming evident that immune disorders are an additional concern apart from the well-defined systemic comorbidities in patients with DS [5–11]. We recommend flow cytometric analysis of lymphocytes in DS patients with recurrent infections.
