Somatic reversion in dedicator of cytokinesis 8 immunodeficiency modulates disease phenotype.

BACKGROUND: Autosomal recessive loss-of-function mutations in dedicator of cytokinesis 8 (DOCK8) cause a combined immunodeficiency characterized by atopy, recurrent infections, and cancer susceptibility. A genotype-phenotype explanation for the variable disease expression is lacking. OBJECTIVE: We investigated whether reversions contributed to the variable disease expression. METHODS: Patients followed at the National Institutes of Health's Clinical Center were studied. We performed detailed genetic analyses and intracellular flow cytometry to detect DOCK8 protein expression within lymphocyte subsets. RESULTS: We identified 17 of 34 DOCK8-deficient patients who had germline mutations with variable degrees of reversion caused by somatic repair. Somatic repair of the DOCK8 mutations resulted from second-site mutation, original-site mutation, gene conversion, and intragenic crossover. Higher degrees of reversion were associated with recombination-mediated repair. DOCK8 expression was restored primarily within antigen-experienced T cells or natural killer cells but less so in naive T or B cells. Several patients exhibited multiple different repair events. Patients who had reversions were older and had less severe allergic disease, although infection susceptibility persisted. No patients were cured without hematopoietic cell transplantation. CONCLUSIONS: In patients with DOCK8 deficiency, only certain combinations of germline mutations supported secondary somatic repair. Those patients had an ameliorated disease course with longer survival but still had fatal complications or required hematopoietic cell transplantation. These observations support the concept that some DOCK8-immunodeficient patients have mutable mosaic genomes that can modulate disease phenotype over time.

The respiratory presentation of severe combined immunodeficiency in two Mennonite children at a tertiary centre highlighting the importance of recognizing this pediatric emergency.

Severe combined immunodeficiency (SCID) is considered to be a pediatric emergency, with respiratory distress being the most common presenting symptom. The authors present two cases of SCID in children <4 months of age with respiratory distress at a tertiary care centre due to a recently described homozygous CD3 delta mutation found only in the Mexican Mennonite population. Failure to respond to broad-spectrum antibiotics prompted investigation for possible SCID. Bronchial alveolar lavage fluid from both patients grew Pneumocystis jiroveci, and flow cytometry revealed absent T cells. The CD3 delta gene is believed to be important in T cell differentiation and maturation. The present article reminds pediatricians and pediatric respirologists that the key to diagnosing SCID is to have a high index of suspicion if there is poor response to conventional therapies.

Antibiotic skin testing accompanied by provocative challenges in children is a useful clinical tool.

BACKGROUND: Diagnostic testing to antibiotics other than to penicillin has not been widely available, making the diagnosis of antibiotic allergy difficult and often erroneous. There is often reluctance in performing challenges to antibiotics when standardized testing is lacking. However, while the immunogenic determinants are not known for most antibiotics, a skin reaction at a non-irritating concentration (NIC) may mean that antibodies to the native form are present in the circulation. While the NIC's for many non penicillin antibiotics have been determined in adults, the use of these concentrations for skin testing pediatric subjects prior to provocative challenge has not been done. Our objective was to determine if we could successfully uncover the true nature of antibiotic allergy in children using these concentrations for testing. METHODS: Children were included between 2003-2009 upon being referred to the Drug and Adverse Reaction/Toxicology (DART) clinic of the Hospital for Sick Children in Toronto, Ontario Canada. The referral needed to demonstrate that clinical care was being compromised by the limitation in antibiotic options or there was a significant medical condition for which the label of antibiotic allergy may prove detrimental. Patients were not seen if there was a suggestion of serum like sickness, Stevens Johnson Syndrome or Toxic Epidermal Necrolysis. Patients were excluded from testing if there was objective evidence of anaphylaxis. All other patients were consented to receive testing and/or challenges. A retrospective chart review was then performed of the results. RESULTS: We were able to exclude an antibiotic allergy in the majority of our patients who had a negative intradermal test result and were then challenged (>90%). Only one patient was challenged with a positive intradermal test to Cotrimoxazole because of a questionable history and this patient failed the provocative challenge. While we did not challenge more patients with positive testing, we did note that 10/11 (91%) patients with positive intradermal testing had some aspect of a Type 1 reaction in their history. CONCLUSIONS: Through testing with NIC's of various antibiotics in children and providing provocative challenges based on negative skin testing results, we were able to advance the medical care of the majority of our patients by increasing their antibiotic options in order to successfully treat future infections. While challenging patients with positive testing was not deemed ethically appropriate at this stage of our study, it would be a useful future step to reaching statistical validity of testing to these antibiotics.

Defining combined immunodeficiency.

BACKGROUND: Although the extreme condition of typical profound T-cell dysfunction (TD), severe combined immunodeficiency (SCID), has been carefully defined, we are currently in the process of better defining less typical T-cell deficiencies, which tend to present with autologous circulating T-cell combined immunodeficiency (CID). Because autologous cells might interfere with the outcome of bone marrow transplantation, protocols usually include conditioning regimens. Therefore it is important to define the numbers of autologous cells usually detected in patients with CID versus those with SCID. OBJECTIVES: We sought to determine the number of circulating T cells in patients with SCID as opposed to those with CID, to study their function, and to evaluate their possible detection during newborn screening using T-cell receptor excision circle (TREC) analysis. METHODS: Numbers of circulating CD3(+) T cells (as determined by means of flow cytometry), in vitro responses to PHA, and TREC levels, all measured at presentation, were compiled from the research charts of the entire cohort of patients followed prospectively for T-cell immunodeficiency at the Hospital for Sick Children. Clinical data were ascertained retrospectively from the patient's hospital charts. RESULTS: One hundred three patients had CD3(+) determinations, and 80 of them had a genetic diagnosis. All patients considered to have typical SCID had CD3(+) T-cell counts of fewer than 500 cells/µL. Some variability was observed among different genotypes. In vitro responses to PHA were recorded in 88 patients, of whom 68 had a genetic diagnosis. All patients with low CD3(+) T-cell numbers (<500 cells/µL) also had markedly decreased responses to PHA (typical SCIDs). However, responses ranged widely in the groups of patients with TD who had more than 500 CD3(+) autologous circulating T cells per microliter. Although patients with Omenn syndrome and ζ chain-associated protein, 70 kDa (ZAP70), and purine nucleoside phosphorylase (PNP) deficiencies had low responses, patients with the p.R222C mutation in the IL-2 receptor γ(IL2RG) gene as well as IL-10 receptor and CD40 ligand deficiencies had normal or near-normal mitogen responses. Finally, 51 patients had TREC levels measured. All patients with typical SCID, Omenn syndrome, and ZAP70 deficiency had low TREC levels. In contrast, patients with mutations in forkhead box protein 3 (FOXP3), CD40 ligand (CD40L), and IL-10 receptor α(IL10RA), as well as patients with the p.R222C mutation in the IL2RG gene, had normal TREC levels. CONCLUSION: Patients with typical SCID can be defined as having fewer than 500 circulating CD3(+) T cells. Most patients with autologous T cells still have profound TD, as defined by reduced in vitro function and thymus output. Some patients with conditions including TD have normal TREC levels and will therefore not be detected in a TREC-based newborn screening program.

Aplastic anemia following varicella vaccine.

Varicella zoster vaccine is a safe vaccine that is rarely associated with life-threatening complications. We describe an immunocompetent child who developed transient severe aplastic anemia concomitant with a typical clinical and laboratory-proven chickenpox syndrome 3 weeks after immunization. A causative association between the vaccine and the hematologic disease is possible, and pediatricians should be aware of this severe although rare adverse event.

Variability of clinical and laboratory features among patients with ribonuclease mitochondrial RNA processing endoribonuclease gene mutations.

BACKGROUND: Cartilage hair hypoplasia is an autosomal recessive type of metaphyseal chondrodysplasia, caused by mutations in the ribonuclease mitochondrial RNA processing (RMRP) gene. Typical features of cartilage hair hypoplasia include short stature, a predisposition to malignancy, and a variable degree of impairment of cellular immunity. OBJECTIVE: We sought to describe the heterogeneity of clinical and immunologic phenotype in 12 consecutive patients with RMRP mutations who were referred to 2 different institutions for immunologic evaluation. METHODS: We have retrospectively analyzed the clinical and laboratory features in 12 patients with molecular defects in the RMRP gene. T-cell repertoire was investigated by quantitating Vbeta families' expression and analyzing their diversity. T-cell receptor excision circle analysis was used to study thymic output. RESULTS: All 12 patients had significant immune abnormalities, leading to severe immune deficiency in 9. CD8 lymphocytopenia was identified as a novel phenotype associated with RMRP mutations. Significant, even intrafamilial, phenotypic heterogeneity was observed. In 3 cases, severe immunodeficiency was the only phenotypic manifestation associated with RMRP mutations, a novel finding. Mutations leading to significant immune defects were most often located in the promoter, and the first case of a compound heterozygote for 2 such mutations is reported. CONCLUSION: This report broadens the spectrum of phenotypes associated with RMRP mutations and suggests that mutations in this gene should be considered when evaluating patients with combined immune deficiency, regardless of the presence of other manifestations.

Acute neurological events associated with influenza vaccination: are the WHO criteria for assessing causality adequate?

We identified neurological admissions temporally associated with influenza vaccine to determine the likelihood of causality using World Health Organization (WHO) criteria. Although all cases were categorized as possibly related to the vaccine, most had a compelling alternative explanation. This observation suggests that the current WHO criteria may not be sufficient in determining if an adverse event is truly vaccine related.