A novel intronic splice site deletion of the IL-2 receptor common gamma chain results in expression of a dysfunctional protein and T-cell-positive X-linked Severe combined immunodeficiency

Trends in the Epidemiology of Pneumocystis Pneumonia in Immunocompromised Patients without HIV Infection

The increasing morbidity and mortality of life-threatening Pneumocystis pneumonia (PCP) in immunocompromised people poses a global concern, prompting the World Health Organization to list it as one of the 19 priority invasive fungal diseases, calling for increased research and public health action. In response to this initiative, we provide this review on the epidemiology of PCP in non-HIV patients with various immunodeficient conditions, including the use of immunosuppressive agents, cancer therapies, solid organ and stem cell transplantation, autoimmune and inflammatory diseases, inherited or primary immunodeficiencies, and COVID-19. Special attention is given to the molecular epidemiology of PCP outbreaks in solid organ transplant recipients; the risk of PCP associated with the increasing use of immunodepleting monoclonal antibodies and a wide range of genetic defects causing primary immunodeficiency; the trend of concurrent infection of PCP in COVID-19; the prevalence of colonization; and the rising evidence supporting de novo infection rather than reactivation of latent infection in the pathogenesis of PCP. Additionally, we provide a concise discussion of the varying effects of different immunodeficient conditions on distinct components of the immune system. The objective of this review is to increase awareness and knowledge of PCP in non-HIV patients, thereby improving the early identification and treatment of patients susceptible to PCP.

Hemophagocytic syndrome associated with Mycobacterium bovis in a patient with X-SCID: a case report

Background

Mycobacterium bovis could infect patients with immunodeficiency or immunosuppressive conditions via Bacillus Calmette-Guérin (BCG) vaccination. Tuberculosis-related hemophagocytic syndrome (HPS) is reported, but not HPS caused by Mycobacterium bovis in children.

Case presentation

A 4-month Chinese boy presented fever and cough. The initial laboratory investigation showed the lymphocyte count of 0.97 × 10⁹/L, which decreased gradually. HPS was diagnosed based on the test results that fulfilled the HLH-2004 criteria. In addition, Mycobacterium tuberculosis complex was detected from his peripheral blood via metagenomic next-generation sequencing (mNGS) and M. bovis was identified by polymerase chain reaction-reverse dot blot (PCR-RDB). Thus, the patient was treated with Isoniazid, Rifampin, and Pyrazinamide, but not improved. However, parents refused to accept further therapy, and was discharged on the day 12 of admission. To confirm the pathogenesis, genetic analysis was performed. Mutation in the interleukin-2 receptor subunit gamma gene: Exon 6: c.854G > A; p. Arg285Gln was detected in the patient and the mother, which could underlie X-linked severe combined immunodeficiency.

Conclusions

A boy with X-SCID was diagnosed with M. bovis-associated HPS, emphasizing that X-SCID should be considered when M. bovis is detected in a male infant with low lymphocyte counts.

A synonymous splice site mutation in IL2RG gene causes late-onset combined immunodeficiency

X-Linked severe combined immunodeficiency (X-SCID) is a severe form of primary immunodeficiency characterized by absence of T cells and NK cells. X-SCID is caused by a loss-of-function mutation in the IL2RG gene that encodes common gamma chain (γc), which plays an essential role in lymphocyte development. We report the first case of hypomorphic X-SCID caused by a synonymous mutation in the IL2RG gene leading to a splice anomaly, in a family including two patients with diffuse cutaneous warts, recurrent molluscum contagiosum, and mild respiratory infections. The mutation caused aberrant splicing of IL2RG mRNA, subsequently resulted in reduced γc expression. The leaky production of normally spliced IL2RG mRNA produced undamaged protein; thus, T cells and NK cells were generated in the patients. Functional assays of the patients' T cells and NK cells revealed diminished cytokine response in the T cells and absent cytokine response in the NK cells. In addition, the TCR repertoire in these patients was limited. These data suggest that a fine balance between aberrant splicing and leaky production of normally spliced IL2RG mRNA resulted in late-onset combined immunodeficiency in these patients.

Two Unique Cases of X-linked SCID: A Diagnostic Challenge in the Era of Newborn Screening

In the era of newborn screening (NBS) for severe combined immunodeficiency (SCID) and the possibility of gene therapy (GT), it is important to link SCID phenotype to the underlying genetic disease. In western countries, X-linked interleukin 2 receptor gamma chain (IL2RG) and adenosine deaminase (ADA) deficiency SCID are two of the most common types of SCID and can be treated by GT. As a challenge, both IL2RG and ADA genes are highly polymorphic and a gene-based diagnosis may be difficult if the variant is of unknown significance or if it is located in non-coding areas of the genes that are not routinely evaluated with exon-based genetic testing (e.g., introns, promoters, and the 5'and 3' untranslated regions). Therefore, it is important to extend evaluation to non-coding areas of a SCID gene if the exon-based sequencing is inconclusive and there is strong suspicion that a variant in that gene is the cause for disease. Functional studies are often required in these cases to confirm a pathogenic variant. We present here two unique examples of X-linked SCID with variable immune phenotypes, where IL2R gamma chain expression was detected and no pathogenic variant was identified on initial genetic testing. Pathogenic IL2RG variants were subsequently confirmed by functional assay of gamma chain signaling and maternal X-inactivation studies. We propose that such tests can facilitate confirmation of suspected cases of X-linked SCID in newborns when initial genetic testing is inconclusive. Early identification of pathogenic IL2RG variants is especially important to ensure eligibility for gene therapy.