Marta Rusmini

Severe COVID-19 displays substantial inter-individual variability that cannot be fully explained by common genetic variants, suggesting a contribution of rare functional variation. We performed whole-genome sequencing in 191 Italian patients (96 moderate, 95 severe) to investigate rare coding variants (minor allele frequency EIF4G3, GTF2F2, LY96, COX6A1, and STK11, which are involved in transcriptional and translational regulation, innate immune signaling, and mitochondrial function. Unsupervised biclustering significantly stratified patients by severity, and a decision tree model highlighted the burden of DOCK10 variants as a key discriminator between phenotypes. Convergence between the network-based and machine learning results further supported the robustness of the identified signals. Overall, our integrative framework underscores the contribution of rare variants to COVID-19 severity and highlights the coordinated perturbation of interconnected molecular pathways as a determinant of clinical outcome.

The X-linked G-protein coupled receptor GPR174 is highly expressed in T and B lymphocytes and has immunoregulatory roles in mice, but its function in humans is unknown. We describe a cohort of six individuals who have function-disrupting variants in GPR174 and a clinical phenotype of lymphadenopathy and autoimmunity. Histological analysis of two patient lymph nodes revealed necrotizing lymphadenitis and lymphoproliferation resembling Kikuchi-Fujimoto disease. In-depth analysis of three patients and related carriers revealed overaccumulation of CD8 terminally differentiated effector memory cells re-expressing CD45RA (T _EMRA ). Patient cells and GPR174- deficient CD8 T cells generated from controls showed less repression of proliferation by the GPR174 ligand lysophosphatidylserine (lysoPS) and an effector-biased gene expression program. GPR174-deficient CD4 T cells were resistant to lysoPS-mediated suppression of IL2 production. In mice, chronic viral infection led to over-accumulation of GPR174-deficient effector CD8 T cells. We describe an inborn error of immunity associated with dysregulated lymphocyte responses that we propose predisposes to exaggerated lymphoproliferation and autoimmunity following viral infection. Summary: Six individuals with function-disrupting variants in the G-protein coupled receptor GPR174 provide insight into its immunoregulatory role. GPR174 loss emerges as a potential genetic risk factor for histiocytic necrotizing lymphadenitis (Kikuchi-Fujimoto disease) and autoimmunity via defects in T cell regulation.

Background: Heterozygosity for pathogenic variants in the ABCC6 gene has been associated with an increased incidence of cerebrovascular diseases. This study aims to characterize the prevalence and clinical and neuroradiological phenotypes associated with monoallelic and biallelic ABCC6 variants in pediatric and adult patients presenting with arterial ischemic stroke or cerebral small vessel disease (CSVD). Methods: We conducted a retrospective observational study on 143 consecutive patients (48 pediatric, 24 juvenile, 71 adult) diagnosed with ischemic stroke or CSVD of unknown etiology. Clinical and neuroradiological data were collected and analyzed in relation to the identified genetic variants through next-generation sequencing. Results: Among the patients, 16 (11.2%) tested positive for causative variants in the ABCC6 gene, with 11 subjects carrying monoallelic variants and 5 carrying biallelic variants. Patients with biallelic variants exhibited severe and complex vasculopathy, with a high incidence of early ischemic events. In contrast, monoallelic carriers predominantly presented with microvascular disease manifestations, including lacunar strokes and signs of CSVD. Conclusions: The results suggest a significant age-dependent phenotypic divergence in patients with ABCC6 variants, highlighting the impact of heterozygosity on cerebrovascular health. Identifying these variants may enhance risk stratification and inform management strategies in patients with traditional vascular risk factors.

Non-remitting neutropenia in children and chronic idiopathic neutropenia (CIN) in adults have been described previously as peculiar subgroups of neutropenic patients carrying similar clinical and immunological features. The present collection comprising 25 subjects (16 adults and 9 children) mostly affected with mild (84%) and moderate (16%) neutropenia aimed to identify the underlying (possibly common) genetic background. The phenotype of these patients resemble the one described previously: no severe infections, presence of rheumathological signs, leukopenia in almost all patients and lymphocytopenia in one-third of the cohort. The pediatric patients did not share common genes with the adults, based on the results of the multisample test, while some singular variants in neutropenia potentially associated with immune dysregulation likely consistent with the phenotype were found. SPINK5, RELA and CARD11 were retrieved and seem to be consistent with the clinical picture characterized by neutropenia associated to immune dysregulation. The enrichment and burden tests performed in comparison with a control group underline that the products of expression by the variants involved belong to the autoimmunity and immune regulation pathways (i.e., SPINK5, PTPN22 and PSMB9). Even with the limitation of this study’s low number of patients, these results may suggest that non-remitting neutropenia and CIN in adults deserve deep genetic study and enlarged consideration in comparison with classical neutropenia.

Serine/arginine-rich splicing factors (SRSFs) are a family of proteins involved in RNA metabolism, including pre-mRNA constitutive and alternative splicing. The role of SRSF proteins in regulating mitochondrial activity has already been shown for SRSF6, but SRSF4 altered expression has never been reported as a cause of bone marrow failure. An 8-year-old patient admitted to the hematology unit because of leukopenia, lymphopenia, and neutropenia showed a missense variant of unknown significance of the SRSF4 gene (p.R235W) found via whole genome sequencing analysis and inherited from the mother who suffered from mild leuko-neutropenia. Both patients showed lower SRSF4 protein expression and altered mitochondrial function and energetic metabolism in primary lymphocytes and Epstein–Barr-virus (EBV)-immortalized lymphoblasts compared to healthy donor (HD) cells, which appeared associated with low mTOR phosphorylation and an imbalance in the proteins regulating mitochondrial biogenesis (i.e., CLUH) and dynamics (i.e., DRP1 and OPA1). Transfection with the wtSRSF4 gene restored mitochondrial function. In conclusion, this study shows that the described variant of the SRSF4 gene is pathogenetic and causes reduced SRSF4 protein expression, which leads to mitochondrial dysfunction. Since mitochondrial function is crucial for hematopoietic stem cell maintenance and some genetic bone marrow failure syndromes display mitochondrial defects, the SRSF4 mutation could have substantially contributed to the clinical phenotype of our patient.

Serine/arginine-rich splicing factors (SRSF) are a family of proteins involved in RNA metabolism, including pre-mRNA constitutive and alternative splicing. The role of SRSF proteins on mitochondria activity has already been shown for SRSF6 but SRSF4 altered expression has never been reported as disease causing. An 8-year-old patient admitted to the Hematology Unit because of leukopenia, lymphopenia, and neutropenia showed a missense variant of unknown significance on the SRSF4 gene (p.R235W) found by Whole Genome Sequencing analysis and inherited by the mother who suffered from mild leuko-neutropenia. Both patients showed lower SRSF4 protein expression compared to HD and altered mitochondrial function and energetic metabolism, which appeared associated with low mTOR phosphorylation and an imbalance in proteins regulating biogenesis (i.e., CLUH) and mitochondrial dynamics (i.e., DRP1, OPA1). Transfection with the wt-SRSF4 gene restored the mitochondrial function. In conclusion, this study shows that the de-scribed variant of the SRSF4 gene is pathogenetic and causes reduced SRSF4 protein expression, which leads to cells’ mitochondrial function impairment. Since mitochondrial function is crucial for hematopoietic stem cells maintenance and some genetic bone marrow failure syndromes display mitochondrial defects, SRSF4 mutation could have substantially contribute to the clinical phenotype of our patient.

Editorial: Elucidation of the causes of human disease by multi-omics integration

The advent of Whole Genome Sequencing (WGS) broadened the genetic variation detection range, revealing the presence of variants even in non-coding regions of the genome, which would have been missed using targeted approaches. One of the most challenging issues in WGS analysis regards the interpretation of annotated variants. This review focuses on tools suitable for the functional annotation of variants falling into non-coding regions. It couples the description of non-coding genomic areas with the results and performance of existing tools for a functional interpretation of the effect of variants in these regions. Tools were tested in a controlled genomic scenario, representing the ground-truth and allowing us to determine software performance.

Hirschsprung disease (HSCR, OMIM 142623) involves congenital intestinal obstruction caused by dysfunction of neural crest cells and their progeny during enteric nervous system (ENS) development. HSCR is a multifactorial disorder; pathogenetic variants accounting for disease phenotype are identified only in a minority of cases, and the identification of novel disease-relevant genes remains challenging. In order to identify and to validate a potential disease-causing relevance of novel HSCR candidate genes, we established a complementary study approach, combining whole exome sequencing (WES) with transcriptome analysis of murine embryonic ENS-related tissues, literature and database searches,in siliconetwork analyses, and functional readouts using candidate gene-specific genome-edited cell clones. WES datasets of two patients with HSCR and their non-affected parents were analysed, and four novel HSCR candidate genes could be identified:ATP7A,SREBF1,ABCD1andPIAS2. Further rare variants in these genes were identified in additional HSCR patients, suggesting disease relevance. Transcriptomics revealed that these genes are expressed in embryonic and fetal gastrointestinal tissues. Knockout of these genes in neuronal cells demonstrated impaired cell differentiation, proliferation and/or survival. Our approach identified and validated candidate HSCR genes and provided further insight into the underlying pathomechanisms of HSCR.