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Ras-related C3 botulinum toxin substrate 2 (RAC2) is a small guanine nucleotide binding molecule that is exclusively expressed in hematopoietic cell lineages as a switcher. Based on in vivo and/or in vitro model experiments, RAC2 plays important roles in different cells through proliferation, secretion, and phagocytosis. It also performs a suppressing function in immunoglobulin (Ig) switching in Rac2-/- animals or cells. Several RAC2 natural mutations have been described in patients with primary immunodeficiency. RAC2 mutations can be classified into loss-of-function inactivating (LoF-I) and gain-of-function activating mutations according to their functional effects. Only two LoF-I mutations on RAC2 have been reported, including a dominant D57N mutation in several cases that exhibit granulocyte function defects and a recessive D56X mutation in cases with common variable immunodeficiency. Regardless of the type of mutation, most of the reported RAC2 mutant cases have shown reduced IgG, IgA, and IgM levels. Herein, we report on a family with three members that suffer from persistent HPV infection, recurrent respiratory infections, bronchiectasis, and autoimmune disease. The immunologic profile suggests that the family was affected by combined immunodeficiency (CID) with increased serum levels of IgG, IgA, and IgE. Exome sequencing identified a de novo RAC2 mutation (c.44G > A/p.G15D) that was co-segregated with the disease in the family. Gene functional experiments identified that such mutation results in reduced guanosine triphosphate binding activity and RAC2 protein expression. In patients’ lymphocytes, impaired aggregation and proliferation effects, decreased mitochondrial membrane potential, and increased levels of cell apoptosis were observed, although no functional abnormalities were detected in neutrophils. To our knowledge, this study was the first to identify a LoF-I mutation of RAC2 affecting lymphocyte function that consequently led to CID and increased levels of serum IgG, IgE, and IgA. This study presents a novel subtype of RAC2-related immune disorder.

PMID:36459342 | DOI:10.1007/s10875-022-01411-5

Retrospective evaluation of adults with primary immunodeficiency disease

December 2, 2022 By Manish Butte

Postepy Dermatol Alergol. 2022 Oct;39(5):976-979. doi: 10.5114/ada.2022.120887. Epub 2022 Nov 9.

ABSTRACT

INTRODUCTION: Primary immunodeficiency diseases (PIDs) are a group of heterogeneous disorders that result from one or more immune system abnormalities and have a wide range of clinical manifestations.

AIM: To evaluate the demographic, clinical, and radiological features of adult patients with PID.

MATERIAL AND METHODS: We retrospectively reviewed the data of adult patients with PID who had been receiving immunoglobulin therapy at the adult allergy and immunology outpatient clinic between November 2017 and April 2022.

RESULTS: Of the 23 patients included, 4 (17.4%) were females and 19 (82.6%) were males. The mean age was 38.7 ±16.2 (range: 18-75) years. Time of delay in the diagnosis of immunodeficiency was 14.9 ±15.7 (range: 0.5-49) years. The most common complaint on admission was sinopulmonary infection, and 65% of the patients had bronchiectasis. A total of 6 patients had a history of lymphoma, and 3 of them were diagnosed during the study period. Recurrence of lymphoma was observed in 1 patient.

CONCLUSIONS: Patients with PID frequently have findings related to more than one organ system, and the diagnosis is often delayed in adults. Recognition and increased awareness of these manifestations is essential for early diagnosis and reducing morbidity and mortality.

PMID:36457675 | PMC:PMC9704451 | DOI:10.5114/ada.2022.120887

The diagnosis of severe combined immunodeficiency (SCID): The Primary Immune Deficiency Treatment Consortium (PIDTC) 2022 Definitions

December 1, 2022 By Manish Butte

J Allergy Clin Immunol. 2022 Nov 28:S0091-6749(22)01479-8. doi: 10.1016/j.jaci.2022.10.022. Online ahead of print.

ABSTRACT

Severe combined immunodeficiency (SCID) results from defects in the differentiation of hematopoietic stem cells into mature T lymphocytes, with additional lymphoid lineages affected in particular genotypes. In 2014, the Primary Immune Deficiency Treatment Consortium published criteria for diagnosing SCID, which are now revised to incorporate contemporary approaches. Patients with typical SCID must have less than 0.05 × 10⁹ autologous T cells/L on repetitive testing, with either pathogenic variant(s) in a SCID-associated gene, very low/undetectable T-cell receptor excision circles or less than 20% of CD4 T cells expressing naive markers, and/or transplacental maternally engrafted T cells. Patients with less profoundly impaired autologous T-cell differentiation are designated as having leaky/atypical SCID, with 2 or more of these: low T-cell numbers, oligoclonal T cells, low T-cell receptor excision circles, and less than 20% of CD4 T cells expressing naive markers. These patients must also have either pathogenic variant(s) in a SCID-associated gene or reduced T-cell proliferation to certain mitogens. Omenn syndrome requires a generalized erythematous rash, absent transplacentally acquired maternal engraftment, and 2 or more of these: eosinophilia, elevated IgE, lymphadenopathy, hepatosplenomegaly. Thymic stromal defects and other causes of secondary T-cell deficiency are excluded from the definition of SCID. Application of these revised Primary Immune Deficiency Treatment Consortium 2022 Definitions permits precise categorization of patients with T-cell defects but does not imply a preferred treatment strategy.

PMID:36456361 | DOI:10.1016/j.jaci.2022.10.022

The diagnosis of severe combined immunodeficiency: Implementation of the PIDTC 2022 Definitions

December 1, 2022 By Manish Butte

J Allergy Clin Immunol. 2022 Nov 28:S0091-6749(22)01478-6. doi: 10.1016/j.jaci.2022.10.021. Online ahead of print.

ABSTRACT

BACKGROUND: Shearer et al in 2014 articulated well-defined criteria for the diagnosis and classification of severe combined immunodeficiency (SCID) as part of the Primary Immune Deficiency Treatment Consortium’s (PIDTC’s) prospective and retrospective studies of SCID.

OBJECTIVE: Because of the advent of newborn screening for SCID and expanded availability of genetic sequencing, revision of the PIDTC 2014 Criteria was needed.

METHODS: We developed and tested updated PIDTC 2022 SCID Definitions by analyzing 379 patients proposed for prospective enrollment into Protocol 6901, focusing on the ability to distinguish patients with various SCID subtypes.

RESULTS: According to PIDTC 2022 Definitions, 18 of 353 patients eligible per 2014 Criteria were considered not to have SCID, whereas 11 of 26 patients ineligible per 2014 Criteria were determined to have SCID. Of note, very low numbers of autologous T cells (<0.05 × 10⁹/L) characterized typical SCID under the 2022 Definitions. Pathogenic variant(s) in SCID-associated genes was identified in 93% of patients, with 7 genes (IL2RG, RAG1, ADA, IL7R, DCLRE1C, JAK3, and RAG2) accounting for 89% of typical SCID. Three genotypes (RAG1, ADA, and RMRP) accounted for 57% of cases of leaky/atypical SCID; there were 13 other rare genotypes. Patients with leaky/atypical SCID were more likely to be diagnosed at more than age 1 year than those with typical SCID lacking maternal T cells: 20% versus 1% (P < .001). Although repeat testing proved important, an initial CD3 T-cell count of less than 0.05 × 10⁹/L differentiated cases of typical SCID lacking maternal cells from leaky/atypical SCID: 97% versus 7% (P < .001).

CONCLUSIONS: The PIDTC 2022 Definitions describe SCID and its subtypes more precisely than before, facilitating analyses of SCID characteristics and outcomes.

PMID:36456360 | DOI:10.1016/j.jaci.2022.10.021