DNA-Binding domain mutations confer severe outcome at an early age among STAT1 gain-of-function patients

BACKGROUND

STAT1 gain-of-function (GOF) is an immune dysregulatory disorder with poorly studied genotype-phenotype correlation, impeding prognostication and early intervention. Given previous mechanistic studies, as well as anecdotal clinical reports, we sought to systematically determine whether DNA-binding domain (DBD) mutations in STAT1 result in a different phenotype than mutations in other gene domains.

METHODS

Negative prognostic features previously identified by the International STAT1 GOF Study Group (invasive infections, intracranial aneurysms, and malignancy), as well as other clinical features and mortality, were compared within a cohort of 30 patients with STAT1 GOF diagnosed at our center, consisting of 9 patients with DBD mutations and 21 patients with non-DBD mutations. We subsequently re-analyzed mortality data from a large, previously-published 274-patient cohort by the International STAT1 GOF Study Group.

RESULTS

While no differences were noted with respect to malignancy or symptomatic aneurysms, invasive /opportunistic infections were substantially more common among DBD patients, as were sinopulmonary infections, bronchiectasis, enteropathy, endocrinopathies, lymphoproliferative manifestations, and recurrent fevers/HLH. DBD patients also had a lower probability of survival and younger age of mortality compared with non-DBD patients. Our re-evaluation of the published data from the International STAT1 GOF Study Group revealed a similar finding of earlier mortality among patients harboring DBD mutations.

CONCLUSION

We report that STAT1 GOF patients with DBD mutations may be regarded as a unique subgroup, impacted more by early-onset profound combined immunodeficiency and with earlier mortality. These findings may impact clinical decision making with respect to early intervention, and in particular hematopoietic stem cell transplant considerations, in such patients.

A gain-of-function mutation of STAT1: A novel genetic factor contributing to chronic mucocutaneous candidiasis

Heterozygous gain-of-function (GOF) mutations in the signal transducer and activator of transcription 1 (STAT1) have increasingly been identified as a genetic cause of autosomal-dominant (AD) chronic mucocutaneous candidiasis (CMC). In this article, we describe a 33-year-old man who experienced chronic refractory candidiasis, recurrent otitis media, and pneumonia resulting in bronchiectasis, severe oral and esophageal candidiases with strictures associated with hypothyroidism and immune hemolytic anemia. His son also suffered from persistent candidiasis, chronic diarrhea, poor weight gain, and pneumonia that resulted in his demise because of sepsis. The immunological workup showed that an inverse CD4/CD8 ratio and serum immunoglobulins were all within normal ranges. The laboratory data revealed failure in response to Candida lymphocyte transformation test. In addition, by Sanger sequencing method, we found a heterozygous mutation, Thr385Met (T385M), located in the DNA-binding domain of STAT1, which was previously shown to be GOF. These findings illustrate the broad and variable clinical phenotype of heterozygous STAT1 GOF mutations. However, more clinical information and phenotype-genotype studies are required to define the clinical phenotype caused by AD STAT1 GOF.

Ruxolitinib reverses dysregulated T helper cell responses and controls autoimmunity caused by a novel signal transducer and activator of transcription 1 (STAT1) gain-of-function mutation

BACKGROUND

Gain-of-function (GOF) mutations in the human signal transducer and activator of transcription 1 (STAT1) manifest in immunodeficiency and autoimmunity with impaired T_H17 cell differentiation and exaggerated responsiveness to type I and II interferons. Allogeneic bone marrow transplantation has been attempted in severely affected patients, but outcomes have been poor.

OBJECTIVE

We sought to define the effect of increased STAT1 activity on T helper cell polarization and to investigate the therapeutic potential of ruxolitinib in treating autoimmunity secondary to STAT1 GOF mutations.

METHODS

We used in vitro polarization assays, as well as phenotypic and functional analysis of STAT1-mutated patient cells.

RESULTS

We report a child with a novel mutation in the linker domain of STAT1 who had life-threatening autoimmune cytopenias and chronic mucocutaneous candidiasis. Naive lymphocytes from the affected patient displayed increased T_H1 and follicular T helper cell and suppressed T_H17 cell responses. The mutation augmented cytokine-induced STAT1 phosphorylation without affecting dephosphorylation kinetics. Treatment with the Janus kinase 1/2 inhibitor ruxolitinib reduced hyperresponsiveness to type I and II interferons, normalized T_H1 and follicular T helper cell responses, improved T_H17 differentiation, cured mucocutaneous candidiasis, and maintained remission of immune-mediated cytopenias.

CONCLUSIONS

Autoimmunity and infection caused by STAT1 GOF mutations are the result of dysregulated T helper cell responses. Janus kinase inhibitor therapy could represent an effective targeted treatment for long-term disease control in severely affected patients for whom hematopoietic stem cell transplantation is not available.

Autosomal dominant transmission of signal transduction and activator of transcription 1 (STAT1) mutation (Thr385Met) and extended lifespan

Introduction: Heterozygous mutations in signal transducer and activator of transcription 1 (STAT1) have been associated with selective deficiencies to mycobacterial or fungal infections. Recent reports revealed that patients found to carry de novo heterozygous mutations in STAT1 encoding specific amino acid substitutions can go on to develop progressive combined immunodeficiency, distinct from the limited susceptibilities to infection previously reported for heterozygous STAT1 mutations.

Objectives: We present a case of a mother and her son with chronic mucocutaneous candidiasis and T-cell dysfunction, both of whom lived longer than projected life expectancy with a heterozygous STAT1 mutation. The son lived to the age of 20 years and the mother to the age of 32 years.

Methods: The son's blood sequencing of STAT1 was performed on a pure T-cell lineage at The Hospital for Sick Children and the Canadian Center for Primary Immunodeficiency, Toronto, Ontario.

Results: STAT1 analysis revealed a heterozygous DNA binding domain mutation at Thr385Met. The patient proceeded to develop fulminant progressive multifocal leukoencephalopathy that ultimately led to his death. The patient's mother, although never confirmed to have STAT1 mutation with formal blood sequencing, had multiple comorbidities including progressive lymphopenia, hypogammaglobulinemia, recurrent Pseudomonas pneumonias with associated bronchiectasis, end-stage kidney disease requiring hemodialysis, and ultimately death due to multiple end organ failure associated sepsis.

Conclusion: This is the first autosomal dominant transmission of the STAT1 DNA binding domain Thr385Met mutation with an extended lifespan.

Statement of Novelty: Previous patients found to have heterozygous mutations of STAT1 that were associated with progressive combined immunodeficiency, arose de novo in each case. Presumed autosomal dominant transmission of a heterozygous STAT1 DNA binding domain Thr385Met mutation has not been reported.

The effects of STAT1 dysfunction on the gut

Introduction: Mutations in the signal transducer and activator of transcription1 (STAT1) have been associated with a variety of clinical patterns. Interestingly patients with heterozygous mutations in the DNA binding domain (DBD) of STAT1 suffer acute and chronic colitis.

Methods: To further analyze the role of STAT1 deficiency in intestinal inflammation, we employed protein expression analysis of total and activated STAT1 in intestinal biopsy samples from 2 patients with heterozygous mutations in the DBD of the STAT1 gene.

Results: Both patients showed clinical and histological features of colitis. Total and activated STAT1 were decreased in duodenal and colonic enterocytes, and total STAT1 was found to be mislocalized in aggregates subapically. In addition, intestinal biopsy samples showed decreased numbers of lymphocytes. Patient-derived lymphoblasts demonstrated lack of viability and high susceptibility for cell death.

Conclusion: STAT1 expression and distribution in the gut of patients with mutations in the DBD are abnormal, suggesting a primary role of STAT1 dysfunction in enterocytes in addition to the secondary effect of aberrant inflammation.

Statement of novelty: Colitis associated with STAT1 mutations appears to have unique features distinct from typical inflammatory bowel disease.