New variants of the MRTFA gene broaden the spectrum of actinopathy with low white blood cell counts and inflammation

Article title: Des nouveaux variants de MRTFA expandent le phénotype de cette actinopathie avec neutropénie et manifestations autoinflammatoires

First author: Wendao Li

Journal: Pediatric Allergy and Immunology

Link to the article: https://pubmed.ncbi.nlm.nih.gov/40808667/

Author of the abstract: Philippe Mertz

Three key points to remember:

1. MKL1 deficiency was known to cause major disruption of the actin cytoskeleton and severe primary immunodeficiency with phagocyte defects.

2. The authors report here the first case of composite heterozygous variants in MRTFA, broadening the known phenotypic spectrum with major autoinflammatory manifestations and abnormalities in neutrophil number and function at the forefront.

3. As illustrated here, the full phenotype of actinopathies remains to be discovered, highlighting the importance of accurate diagnosis and in-depth functional investigations.

The MRTFA gene encodes the Megakaryoblastic Leukemia 1 (MKL1) protein, a regulator of the SRF transcription factor that induces the transcription of genes involved in actin cytoskeleton homeostasis, cell migration, and adhesion in multiple cell types. Normally, G-actin polymerization releases MKL1, allowing it to enter the nucleus to coactivate SRF-targeted genes.

The MKL1 defect was initially described in 2015 in three patients who presented with a phenotype of actinopathy with combined immunodeficiency, including a defect in the number and function of phagocytes. These earlier cases, from consanguineous families, had homozygous variants leading to the complete absence of the MKL1 protein. The classic clinical picture included increased susceptibility to severe bacterial infections, poor wound healing, and thrombocytopenia.

This article reports the fourth patient with MKL1 deficiency and the first reported case associated with composite heterozygous variants in the MRTFA gene (NM_020831; p.Q377X/p.C684X). These two variants are located in critical domains of the MKL1 protein, resulting in the complete absence of the protein in PBMCs and neutrophils, and therefore of its function as a regulator of actin metabolism gene transcription factors.

The patient, aged 3 years and from a non-consanguineous family, presented her first symptoms at the age of 2 months. She suffered from early infections, intermittent neutropenia, and thrombocytopenia, with a nadir of 55 G/L. Unlike the cases initially described in the literature, the infections observed in this patient were relatively less severe. However, she had marked autoinflammatory manifestations, characterized by recurrent febrile episodes associated with multiple erythematous and papular skin lesions affecting the face and limbs, as well as swelling of the hands and feet. She also had intermittent bloody diarrhea, rectal ulcers, colitis, and colonic lymphoid follicular hyperplasia, as confirmed by endoscopy.

Figure extraite de l’article

The authors conducted several functional explorations to understand the impact of these variants:

The absence of MKL1 caused marked dysfunction of the actin cytoskeleton, characteristic of actinopathies. A significant reduction in filamentous actin (F-actin) content was observed in neutrophils, monocytes, and, to a lesser extent, T and B lymphocytes. Similarly, F-actin polymerization in response to stimulation (fMLF) was reduced.

Major neutrophil dysfunction:

Migration: greatly reduced chemotactic response

ROS production and oxidative burst: The production of ROS (reactive oxygen species), whether intracellular or extracellular, and the production of H₂O₂ (assessed by DHR) were reduced in response to stimulation. This contrasts with previous reports that did not note any defects in ROS production.

NETs (Neutrophil Extracellular Traps): The formation of NETs, a crucial immune defense mechanism requiring intact actin cytoskeleton rearrangement, was impaired.

Transcriptomic analysis of neutrophils provided support for the clinical inflammatory observations, revealing downregulation of cytoskeletal genes but, concomitantly, upregulation of inflammatory pathways, including the NFkB pathway, TNFα, and a signature typical of inflammatory bowel disease (IBD). These results may partly explain the inflammatory manifestations observed in the patient.

In conclusion, the authors report here the first case of MKL1 deficiency associated with composite heterozygous variants, significantly broadening the known phenotypic spectrum. The association of a marked autoinflammatory phenotype with a less severe immune deficiency highlights the diversity and complexity of actinopathies. As illustrated here, the full phenotype of these diseases probably remains to be discovered, justifying further clinical and functional investigations.

Pediatric Allergy Immunology - 2025 - Li - Novel compound heterozygous MRTFA gene variants.

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Discovery of a new actinopathy linked to the CCDC88A gene, associated with neurological and immune disorders

Article title: Genome sequencing reveals CCDC88A variants in malformations of cortical development and immune dysfunction

First author:Johanna Lehtonen

Journal: Human Molecular Genetics

Link to the article: https://pubmed.ncbi.nlm.nih.gov/40401444/

Author of the abstract: Philippe Mertz

Three key points to remember:

1. Two new variants of CCDC88A have been identified in two full-term children born to unrelated parents of Finnish origin, who suffer from cortical malformations, microcephaly, and epilepsy. This gene encodes the protein girdin, which can bind to actin and acts as a regulator of the actin cytoskeleton.

2. Their fibroblasts show qualitative and functional abnormalities of the actin cytoskeleton.

3. This actinopathy is associated with immune disorders, including an associated immune deficiency, and probably also with inflammatory disorders (inflammatory colitis in one of the two patients).

Actinopathies are a group of rare genetic diseases in which abnormalities in the dynamics of the actin cytoskeleton disrupt various cellular functions, particularly in the immune and nervous systems. They are associated with complex clinical phenotypes, which may include manifestations such as malformations and dysmorphic syndrome, neurodevelopmental delay, manifestations such as primary immunodeficiency, or autoimmune and autoinflammatory manifestations.

The CCDC88A gene encodes the protein girdin, a protein capable of binding directly to actin and participating in the regulation of its functions. It acts as a multifunctional adapter essential for the organization of the actin cytoskeleton, PI3K-AKT signaling, cell migration, and the regulation of the balance between proliferation and migration. Girdin also interacts with many proteins, including EGFR, and is involved in the formation of the immunological synapse, autophagy, and vesicular trafficking.

In this study, the authors report on two patients, a brother and sister, born to two unrelated parents of Finnish origin, who suffered from cortical developmental malformations, postnatal microcephaly, severe epilepsy, profound intellectual disability, and increased susceptibility to infections. Whole genome sequencing revealed composite heterozygous variants of CCDC88A in both children, including a missense mutation (p.Asp310Ala) and an intragenic deletion of three exons (p.E508*), which had not been reported previously. Simple heterozygous carriage of these variants was detected in asymptomatic individuals in the family.

Functional analysis of patients' fibroblasts has enabled the cellular consequences of girdin deficiency to be characterized for the first time. The mutated cells show increased proliferation, decreased migration, reduced cell size, disorganization of the actin cytoskeleton (elongated, aggregated, and poorly reticulated bundles), decreased focal adhesions, and perinuclear accumulation of endolysosomal organelles. These phenotypes were reproduced in fibroblast lines knocked out for CCDC88A by CRISPR-Cas9, confirming that this is an actinopathy associated with loss of girdin function.

Immunologically, girdin is mainly expressed by monocytes, macrophages, and dendritic cells, and less so by T lymphocytes. Patients showed marked susceptibility to respiratory infections, defective vaccine response, moderate B lymphopenia, reduced numbers of monocyte-like and plasmacytoid dendritic cells, and decreased regulatory T cells. One patient also had chronic inflammatory bowel disease diagnosed on the basis of compatible abdominal symptoms and elevated fecal calprotectin. Interestingly, girdin deficiency leads to a hyperreactive immune response by macrophages in the mouse model of dextran sodium sulfate-induced colitis (a model that also presents with a shortened colon and significant weight loss). These data support the existence of a combined immune deficiency affecting innate and adaptive immunity, and associated inflammatory manifestations.

CCDC88A had already been implicated in neurodevelopmental encephalopathies caused by homozygous truncating variants, but this is the first time that an immune dysfunction phenotype has been authenticated in patients carrying mutations in this gene. It is also the first study to demonstrate, through functional approaches on primary cells and CRISPR models, that CCDC88A variants induce true immunoactinopathy.

Genome sequencing reveals CCDC88A variants.pdf

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VEXAS syndrome: what can we learn from France's experience with azacitidine?

Article title: Efficacy and safety of azacitidine for VEXAS syndrome: a large-scale retrospective study from FRENVEX

First author: Vincent Jachiet

Journal: Blood

Link to the article: https://pubmed.ncbi.nlm.nih.gov/40373272/

Author of the abstract: Philippe Mertz

Three key points to remember:

1. Azacitidine is an effective treatment option for VEXAS syndrome even without associated myelodysplasia, with simultaneous effects on inflammation, cytopenias, and the UBA1 clone.

2. The response is often delayed and requires prolonged exposure (≥6 cycles) before evaluation. Adverse effects, particularly infectious ones, occur mainly in the first 3 cycles of treatment. Discontinuation of AZA leads to relapse in the majority of cases, suggesting a suspensive rather than curative effect.

3. Molecular monitoring (UBA1 VAF) allows for objective assessment of clonal response and could become a biomarker for monitoring this disease.

   
   

VEXAS syndrome is an acquired monogenic autoinflammatory disease associated with somatic mutations in the UBA1 gene. Patients present with a wide spectrum of severe inflammatory manifestations and cytopenias, which may be associated with myelodysplastic syndrome (MDS). Treatment is mainly based on corticosteroids, with frequent corticosteroid dependence despite associated sparing therapy with targeted therapies (anti-IL-6, anti-JAK, etc.) that have inconsistent efficacy. Azacitidine (AZA), a hypomethylating agent used in MDS, has shown potential in VEXAS, but published data remain limited.

This is a retrospective multicenter study conducted in France by the FRENVEX group, including 88 patients with genetically confirmed VEXAS who received at least one cycle of AZA between 2009 and 2024.

In this study, inflammatory response was defined as both clinical and biological improvement in systemic manifestations, including reduction in inflammatory symptoms and sustained decrease in biological markers such as CRP. The hematologic response followed the 2018 International Working Group criteria for MDS and corresponded to a significant improvement in cytopenias, including an increase in hemoglobin, platelets, or neutrophils, or a reduction in transfusion requirements. Finally, the molecular response was established on the basis of at least a 25% reduction in the mutational burden (VAF) of the UBA1 variant, assessed by targeted sequencing during treatment. Treatment side effects were described according to the Common Terminology Criteria for Adverse Events (version 5.0).

Inflammatory, hematological, and molecular responses were evaluated, as well as tolerance, regardless of the presence of associated MDS (present in 80%).

The main results of this study show:

• A partial or complete inflammatory response observed in 61% of patients (41% at 6 months, 54% at 12 months). The median response time was sometimes delayed (>6 cycles).

• A hematological response with improvement in hemoglobin in 65% and platelet count in 77%, with clinical benefit in terms of cytopenias and transfusion requirements.

• A molecular response with at least a 25% reduction in UBA1 mutation burden was observed in 65% of patients, correlating with the clinical response.

• Severe adverse events (grade III and IV) occurred in 60% of patients, mainly infections (34%) and cytopenias (36%), occurring predominantly in the first 3 cycles.

• 75% of patients relapse after stopping AZA (median duration of treatment-free period of 3.1 years), but resumption of treatment is effective in 80% of cases.

This study supports the use of AZA as first-line treatment in patients with VEXAS syndrome and severe cytopenias, or as second-line treatment in cases of failure of anti-inflammatory biotherapies, even in the absence of associated MDS. Treatment-related adverse effects, particularly infections, appear to occur mainly during the first 3 cycles of treatment. Prospective studies are needed to confirm its positioning and optimize the therapeutic strategy.