Loss of DIAPH1 causes SCBMS, combined immunodeficiency, and mitochondrial dysfunction

Abstract

Background: Homozygous loss of DIAPH1 results in seizures, cortical blindness, and microcephaly syndrome (SCBMS). We studied 5 Finnish and 2 Omani patients with loss of DIAPH1 presenting with SCBMS, mitochondrial dysfunction, and immunodeficiency. Objective: We sought to further characterize phenotypes and disease mechanisms associated with loss of DIAPH1. Methods: Exome sequencing, genotyping and haplotype analysis, B-and T-cell phenotyping, in vitro lymphocyte stimulation assays, analyses of mitochondrial function, immunofluorescence staining for cytoskeletal proteins and mitochondria, and CRISPR-Cas9 DIAPH1 knockout in heathy donor PBMCs were used. Results: Genetic analyses found all Finnish patients homozygous for a rare DIAPH1 splice-variant (NM_005219:c.68411G>A) enriched in the Finnish population, and Omani patients homozygous for a previously described pathogenic DIAPH1 frameshift-variant (NM_005219:c.2769delT;p.F923fs). In addition to microcephaly, epilepsy, and cortical blindness characteristic to SCBMS, the patients presented with infection susceptibility due to defective lymphocyte maturation and 3 patients developed B-cell lymphoma. Patients' immunophenotype was characterized by poor lymphocyte activation and proliferation, defective B-cell maturation, and lack of naive T cells. CRISPR-Cas9 knockout of DIAPH1 in PBMCs from healthy donors replicated the T-cell activation defect. Patient-derived peripheral blood T cells exhibited impaired adhesion and inefficient microtubule-organizing center repositioning to the immunologic synapse. The clinical symptoms and laboratory tests also suggested mitochondrial dysfunction. Experiments with immortalized, patient-derived fibroblasts indicated that DIAPH1 affects the amount of complex IV of the mitochondrial respiratory chain. Conclusions: Our data demonstrate that individuals with SCBMS can have combined immune deficiency and implicate defective cytoskeletal organization and mitochondrial dysfunction in SCBMS pathogenesis. (J Allergy Clin Immunol 2021;nnn:nnn-nnn.)

Formins in Human Disease

“…Specific mutations of DIAPH1 cause seizures, cortical blindness (vision loss due to a damage or malfunction in the part of the brain cortex responsible for processing visual information), and microcephaly syndrome (SCBMS, MIM: 616632) (Figure 2, Supplementary Table S3). In contrast to DFNA1-related mutations, SCBMS-associated DIAPH1 mutations are generally of the nonsense type that affects the FH2 domain, are found in homozygosity, and are inherited with an autosomal recessive pattern, suggesting that they produce loss-of-function of DIAPH1 activity [10,14,16,17]. mDia1 KO mice are not microcephalic but, instead, some mice present unilateral dilatation of the ventricles, indicating that the effect of these mutations is species-specific [14].…”

“…The alteration of the actin cytoskeleton affecting the adherens junctions and progenitors' polarity seems to be the cause of the ectopic proliferation of neural stem cells in the double-KO mice. In addition to the characteristic SCBMS symptoms, some patients present pathologies related to immunodeficiency, such as recurrent infections, especially respiratory, bronchiectasis (enlargement of parts of the airways of the lung) and lymphoma [10,14,16]. Given that (i) mDia1 KO mice show defects in T cell migration and activation [140,141], (ii) DIAPH1 mutations are associated with mitochondrial dysfunction [10], and (iii) fibroblasts and some lymphocytes from SCBMS patients present mitochondrial alterations [10], it has been proposed that these additional symptoms are due to a defect in the mechanism of T cell activation [10].…”

Actin Dynamics at the T Cell Synapse as Revealed by Immune-Related Actinopathies

“…There is to date no reported PID entity that would be caused by genetic alterations in genes encoding formins. However, homozygous loss of DIAPH1 (the gene that encodes DIAPH1/mDIA1), which was initially reported to cause is causing seizures, cortical blindness, and microcephaly syndrome in humans ( Ercan-Sencicek et al, 2015 ), has recently been reported to be associated with lymphocyte maturation and function impairments, as well as increased risk of B cell lymphoma ( Kaustio et al, 2021 ). The immune cell defects included defective T cell IS assembly, in particular MTOC polarization, in agreement with earlier cell biology studies.…”

Molecular Tuning of Actin Dynamics in Leukocyte Migration as Revealed by Immune-Related Actinopathies

“…In particular, FMNL1 was shown to promote actin polymerization at the back of the cell to enable translation of the rigid nucleus through restrictive barriers of extracellular matrix. DIAPH1, a formin highly expressed in leukocytes, has recently been shown to be associated to immune cell defects in humans when mutated ( 32 ). Whether DIAPH1 also contributes to nucleus squeezing has not yet been investigated.…”