Severe combined immune deficiency (SCID) encompasses a spectrum of disease states characterized by depleted or dysfunctional T-cells, B-cells, and NK cells. These defects severely hamper adaptive immune response and can result in diminished serum immunoglobulins. Although the genetic abnormalities underlying SCID are heterogeneous, the clinical presentation typically involves opportunistic infections and failure to thrive during infancy.1 Mutations involving the zeta chain associated protein kinase 70 (ZAP70), which is involved in T-cell receptor(TCR) signaling, can induce a SCID state through disruptions in T-cell differentiation and function. The mutations are characterized by CD8+ T cell lymphopenia and anergic CD4+ T cells that fail to respond to mitogen stimulation.2,3,4 The prevalence of ZAP70 mutations is relatively low, with about 20 affected individuals identified/reported. These individuals represent a diagnostic challenge due to the clinical heterogeneity of their presentation.1,5
We report a case of a 7-month-old infant who presented with recurrent fevers, skin rash, and gastrointestinal symptoms (diarrhea). He was initially treated for incomplete (atypical) Kawasaki disease before the diagnosis of SCID with underlying ZAP70 deficiency was made. This case report demonstrated the value of flow cytometric analysis performed on peripheral blood as a diagnostic tool in this rare condition. In this case, timely diagnosis resulted in the initiation of appropriate treatment early in the course of the disease. This report also serves as a teaching case in recognizing SCID and suspecting a ZAP70 defect as an underlying cause.
The patient was a Caucasian male born at term with a normal birth weight following an uneventful pregnancy. There were neither known maternal risk factors nor significant family medical history. He was developing normally until 7 months of age when he presented with two weeks of cough, diarrhea, vomiting, and fevers up to 40°C. Initial laboratory evaluation revealed elevated WBC count (33.5 K/µL) and C-reactive protein (CRP) (132 mg/L) with chest X-ray features suggestive of viral infection [Table 1]. On hospital day 3 infectious causes were ruled out and the symptoms, which included submental lymphadenopathy and erythematous feet in addition to persistent fever and elevated CRP, were interpreted as incomplete Kawasaki disease. Given this diagnosis, treatment with a single dose of IVIG in conjunction with 72 hours of high dose aspirin was initiated. Further workup with echocardiogram failed to demonstrate any pathology involving the coronary arteries. By hospital day 5, the patient’s fevers had subsided and laboratory values were normalizing, resulting in hospital discharge.
Laboratory values during initial presentation at 7 months old.
|WBC (6.2-14.5) k/µL||33.5||Blood urea nitrogen (5-17) mg/dL||3|
|RBC (4.1-5.0) M/µL||3.45||Creatinine (0.57-1.3) mg/dL||0.33|
|HGB (10.3-12.4) g/dL||9.0||Sodium (135-145) meq/L||141|
|HCT (30.9-37.0) %||26.6||Potassium (3.6-5.1) meq/L||3.0|
|Platelets (219-452) k/µL||288||Chloride (98-110) meq/L||109|
|MCV (70.5-81.2) FL||77.1||Aspartate Aminotranferase (20-60) IU/L||34|
|RDW (13.1-15.6) %||18.0||Lactate Dehydrogenase (120-220) IU/L||459|
|Segmented Neutrophil %||55||Alkaline Phosphatase (145-320) IU/L||116|
|Lymphocyte %||41||Bilirubin total (0.2-1.1) mg/dL||0.4|
|Monocyte %||3||C-Reactive Protein (CRP) (0.00-7.48) mg/L||132.30|
|Eosinophil %||0||Iron (49-181) µg/dL||13|
|Basophil %||0||% Iron Saturation (25-72) %||5|
|Band Neutrophil %||1||Ferritin (22-227) ng/mL||732|
|Reticulocyte Count (08.-2.0) %||0.6||Transferrin (181-331) mg/dL||190|
Shortly thereafter, the patient experienced persistent leukocytosis (WBC 19.2 K/µL), night time cough, and perioral erythema without fever or signs of infection. He also developed a varicella infection, immediately following vaccination, that necessitated a 5 day course of acyclovir. He was admitted again at 17 months with acute otitis media, three weeks of fever and a pruritic, erythematous rash on the face and extremities. Immunoglobulin levels were within normal limits aside from a mildly depressed IgM. He received a 600 mg/kg dose of IVIG; on this admission laboratory evaluation of the peripheral blood smear revealed atypical lymphocytes (Figure 1). Flow cytometric evaluation of peripheral blood was performed and demonstrated a markedly reduced CD8 count and a significantly increased CD4:CD8 ratio of 40:1. Based on this finding ZAP70 deficiency was suspected. Subsequent testing including mitogen stimulation (conducted at Cincinnati Children’s Hospital) revealed markedly decreased response to phytohemagglutinin, concanavalin A and pokeweed mitogens. Immunologic studies revealed that ZAP70 expression was not detected in the patient’s T or NK cell populations by flow cytometry. These findings were indicative of ZAP70 deficiency, and the patient was transferred to Boston Children’s Hospital for hematopoietic stem cell transplantation (HSCT). He is currently doing well, apart from mild GVHD, 2 years post-transplant.
Peripheral blood findings in the patient with ZAP70 related SCID. Atypical lymphocyte is noted (arrow). Wright-Giemsa stain at x1000 magnification.
Unlike other forms of SCID, ZAP70 deficiency does not present with thymic dysfunction. While ZAP70 is critical for CD8+ T-cell selection and peripheral CD4+ T-cell function, its absence does not prevent CD4+ T-cell section in the thymus. This results in low to absent CD8+ T-cell counts and normal to increased CD4+ T-cell counts. The exact mechanism by which ZAP70 deficiency interferes with positive selection of CD8+ thymocytes remains unclear. Spleen tyrosine kinase (SyK), which is down-regulated in mature peripheral T-cells, is thought to compensate for ZAP70 signaling in thymocyte CD4+ lineage selection. Peripheral CD4+ T-cell dysfunction manifests as a failure to proliferate or produce IL-2 in response to stimulation by mitogens. This occurs due to impaired ZAP70 mediated signaling downstream of the T-cell receptor.6
The initial presentation of this patient’s ZAP70 deficiency highlights the clinical heterogeneity present within ZAP70 related SCID that other authors have previously commented on.1,2 Among the clinical presentations previously reported include a classic SCID presentation, Omenn phenotype following BCG vaccination, disseminated mycobacterial infections and cerebral infarction.7 The patient in this study did not present with classic SCID symptoms. Instead, the defining features of the patient’s initial presentation were persistent leukocytosis, intractable fever, lymphadenopathy and rash. These findings, in conjunction with a lack of a definitive infectious etiology, lead to the initial diagnosis of incomplete Kawasaki disease.
Kawasaki disease is a medium sized vessel vasculitis that manifests as an acute febrile illness. Due to a tendency to involve coronary arteries, cardiac sequelae such as coronary artery aneurysms are associated with the disease. The diagnosis is based on clinical criteria. The most common symptoms include an uncontrollable fever lasting at least 4 days in conjunction with four principle criteria including cervical lymphadenopathy, conjunctival injection, polymorphous exanthema, and changes to the oral cavity and extremities. Incomplete Kawasaki disease encompasses a subset of patients that display some of the classical symptoms of Kawasaki disease without meeting enough of the principle criteria to be diagnosed with Kawasaki disease.8 The diagnosis of incomplete Kawasaki disease is not specific and can represent the initial manifestation of congenital immunodeficiency disorders such as ZAP70 deficiency. Complete immunologic workup can be helpful, but it is usually not performed as a part of initial evaluation. Flow cytometry, on the contrary can easily identify major immune cell subsets. In our case, the absence of CD8 cells lead to suspicion of ZAP70 deficiency and to a complete immunodeficiency workup. Due to the rarity of ZAP70 deficiency, this entity is rarely suspected. However, immunodeficiency needs to be suspected with recurrent infections where a definitive infectious etiology is not identified. This case highlights the clinical heterogeneity of ZAP70 deficiency at initial presentation and illustrates utility of routine flow cytometric analysis as a diagnostic tool to investigate the presence of ZAP70 deficiency.