An infant with ZAP-70 deficiency with disseminated mycobacterial disease

Rare Biallelic Variants Affecting the Interdomain B Region of Zeta-Chain Associated Protein Kinase 70 (ZAP70) Protein in a Sudanese Patient: Case Report

Introduction

A class of disorders known as inborn errors of immunity (IEI) is defined by a compromised or missing immune response, which increases the vulnerability to infections, immunological dysregulation, and cancer. Severe combined immunodeficiencies (SCIDs), affecting both T and B-cell function are rare but often severe diseases. In this report, we describe a 10-month-old SCID patient from Sudan with disseminated BCG infection.

Case Presentation

A 10-month-old boy whose parents were first degree relatives, presented with a six-month history of repeated chest infections and fever. Physical examination revealed a very ill-looking boy with respiratory distress dependent on oxygen, had slight abdominal distention and hepatomegaly. Investigations revealed positive polymerase chain reaction (PCR) for M. tuberculosis complex infection and low CD4+ and CD8+ cells. Genetic testing showed compound heterozygosity in trans for two variants in the Zeta-chain Associated Protein Kinase 70 (ZAP70) gene associated with autosomal recessive SCID. The patient was started on BCG-related infection treatment, intravenous immunoglobulin (IVIG) replacement and trimethoprim/sulfamethoxazole prophylaxis with an excellent response and the patient responded well to the treatment.

Conclusion

SCIDs are rare, and early management is crucial. In this case, a diagnosis of ZAP70 deficiency was based on next-generation sequencing and inhouse bioinformatic computational analysis of the ZAP70 gene, highlighting the importance of genetic testing in the workup of immunodeficiencies in low resource settings.

Novel Compound Heterozygous ZAP70 R37G A507T Mutations in Infant with Severe Immunodeficiency

Zeta-chain associated protein kinase 70 kDa (ZAP70) combined immunodeficiency (CID) is an autosomal recessive severe immunodeficiency that is characterized by abnormal T-cell receptor signaling. Children with the disorder typically present during the first year of life with diarrhea, failure to thrive, and recurrent bacterial, viral, or opportunistic infections. To date, the only potential cure is hematopoietic stem cell transplant (HSCT). The majority of described mutations causing disease occur in the homozygous state, though heterozygotes are reported without a clear understanding as to how the individual mutations interact to cause disease. This case describes an infant with novel ZAP-70 deficiency mutations involving the SH2 and kinase domains cured with allogeneic HSCT utilizing a reduced-intensity conditioning regimen and graft manipulation. We then were able to further elucidate the molecular signaling alterations imparted by these mutations that lead to altered immune function. In order to examine the effect of these novel compound ZAP70 heterozygous mutations on T cells, Jurkat CD4+ T cells were transfected with either wild type, or with individual ZAP70 R37G and A507T mutant constructs. Downstream TCR signaling events and protein localization results link these novel mutations to the expected immunological outcome as seen in the patient's primary cells. This study further characterizes mutations in the ZAP70 gene as combined immunodeficiency and the clinical phenotype.

Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review

Background: Zeta-Chain Associated Protein Kinase 70 kDa (ZAP-70) deficiency is a rare combined immunodeficiency (CID) caused by recessive homozygous/compound heterozygous loss-of-function mutations in the ZAP70 gene. Patients with ZAP-70 deficiency present with a variety of clinical manifestations, particularly recurrent respiratory infections and cutaneous involvements. Therefore, a systematic review of ZAP-70 deficiency is helpful to achieve a comprehensive view of this disease.

Methods: We searched PubMed, Web of Science, and Scopus databases for all reported ZAP-70 deficient patients and screened against the described eligibility criteria. A total of 49 ZAP-70 deficient patients were identified from 33 articles. For all patients, demographic, clinical, immunologic, and molecular data were collected.

Results: ZAP-70 deficient patients have been reported in the literature with a broad spectrum of clinical manifestations including recurrent respiratory infections (81.8%), cutaneous involvement (57.9%), lymphoproliferation (32.4%), autoimmunity (19.4%), enteropathy (18.4%), and increased risk of malignancies (8.1%). The predominant immunologic phenotype was low CD8+ T cell counts (97.9%). Immunologic profiling showed defective antibody production (57%) and decreased lymphocyte responses to mitogenic stimuli such as phytohemagglutinin (PHA) (95%). Mutations of the ZAP70 gene were located throughout the gene, and there was no mutational hotspot. However, most of the mutations were located in the kinase domain. Hematopoietic stem cell transplantation (HSCT) was applied as the major curative treatment in 25 (51%) of the patients, 18 patients survived transplantation, while two patients died and three required a second transplant in order to achieve full remission.

Conclusion: Newborns with consanguineous parents, positive family history of CID, and low CD8+ T cell counts should be considered for ZAP-70 deficiency screening, since early diagnosis and treatment with HSCT can lead to a more favorable outcome. Based on the current evidence, there is no genotype-phenotype correlation in ZAP-70 deficient patients.

Novel compound heterozygous mutations in ZAP70 in a Chinese patient with leaky severe combined immunodeficiency disorder

In humans, the complete lack of tyrosine kinase ZAP70 function results in combined immunodeficiency (CID), with abnormal thymic development and defective T cell receptor (TCR) signaling of peripheral T cells, characterized by the selective absence of CD8⁺ T cells. So far, 15 unique ZAP70 mutations have been identified in approximately 20 patients with CID, with variable clinical presentations. Herein, we report the first case from China of novel compound heterozygous mutations in ZAP70 (c.598-599delCT, p.L200fsX28; c.847 C>T, R283H). The patient suffered from early-onset and recurrent infections, but showed normal growth and development without signs of failure to thrive, thus presenting as leaky SCID. The patient also had clinical manifestations of autoimmunity, such as eczematous skin lesion, inflammatory bowel disease (IBD), and intractable diarrhea, suggesting compromised T cell tolerogenic functions. Residual ZAP70 expression was identified. Immunological analysis revealed the selective absence of CD8⁺ T cells in the periphery and the presence of CD4⁺ T cells that failed to respond to phytohemagglutinin. Stimulation with lectin from pokeweed mitogen also failed to stimulate B cell proliferation in the patient. The frequency of Tfhs and Tregs in the patient was lower compared with the normal reference. Compared with the age-matched healthy control, the level of IL-17 was higher and the levels of IFN-γ, IL-4, and IL-21 were lower. Infants with selected CD8 deficiency and severe autoimmune disorders or exaggerated inflammation should be screened for ZAP70 deficiency.

Long-Term Outcomes of Hematopoietic Stem Cell Transplantation for ZAP70 Deficiency

ZAP70 deficiency is a rare T + B + NK+ combined immunodeficiency with limited outcome data to help guide decisions around hematopoietic stem cell transplant (HSCT). We sought to understand the long-term clinical and immunologic outcomes of both conditioned and unconditioned HSCT for ZAP70 deficiency following transplant from a variety of graft sources. We performed a retrospective, single center review of all cases of HSCT for genetically confirmed ZAP70 deficiency since 1992. At a median of 13.5-year post-HSCT, 8/8 (100 %) patients are alive. Three received unconditioned bone marrow transplants from human leukocyte antigen (HLA)-matched siblings and achieved stable mixed donor-recipient T cell chimerism but low B cell (4-9 %) and absent to near-absent myeloid donor engraftment. Despite this, all three have normal immunoglobulin levels, have developed specific protective antibody responses to post-HSCT vaccinations, and have discontinued immunoglobulin replacement. Five patients received myeloablative conditioning (three T cell-depleted haploidentical and two unrelated cord blood) and have full donor chimerism for T and B cells and myeloid lineages. One patient experienced primary graft failure after serotherapy only. CD8 T cell count is normal in 5/8, high in 1/8, and low in 2/8. Infectious complications in 5/5 and autoimmune thrombocytopenia in one patient resolved post-HSCT. Mitogen proliferation to phytohemagglutinin was normal after HSCT in 8/8 patients. In total, seven have discontinued immunoglobulin replacement. In conclusion, HSCT using a variety of graft sources and approaches, including unconditioned matched sibling donor transplant, is a life-saving therapy for ZAP70 deficiency, providing excellent long-term immune function and resolution of clinical problems.