Mutational analysis of Kabuki Syndrome patients and functional dissection of KMT2D mutations

The discovery of histone methyltransferase KMT2D and demethylase KDM6A genetic alterations in Kabuki Syndrome (KS) expanded and highlighted the role of histone modifiers in causing congenital anomalies and intellectual disability syndromes. KS is a rare autosomal dominant condition characterized by facial features, various organ malformations, postnatal growth deficiency, and intellectual disability. Since 2011 we performed a mutational screening of our KS cohort, that includes now 505 KS patients, by Sanger sequencing and MLPA of KMT2D, followed by KDM6A analysis in those patients resulted as KMT2Dnegative. Of these 505 patients, we identified 196/505 (39%) patients with KMT2D variants and 208 different KMT2D variations; of them 37/208 (18%) never described before. The majority of KS patients carry nonsense and splicesite variants, suggesting the loss of function, and therefore haploinsufficiency, as the likely mechanism for the KS phenotype. RT-PCR and direct sequencing on cDNA from Kabuki patients carrying KMT2D splice site variants demonstrated that these cause aberrant splicing of the corresponding transcript, resulting in a truncating and not functional translated protein. Molecular assays also showed that KMT2D mRNAs bearing premature stop codon are degraded by the nonsense mediated mRNA decay, contributing to KMT2D protein haploinsufficiency. We hypothesized that KS patients may benefit from a readthrough therapy that mediates translational suppression of nonsense variants, restoring the physiologically levels of endogenous KMT2D protein. Fourteen KMT2D nonsense variants were tested for their response to readthrough treatment through an in vitro dual reporter luciferase vector system, identifying 11/14 variants that displayed high levels of readthrough in response to gentamicin treatment. Among our cohort we identified three new cases with a mosaic variants in KMT2D gene, consisting in single nucleotide change resulting in two already reported nonsense variants, the c.13450C=/>T (p.R4484X) and the c.15061C=/>T (p.R5021X) and in a new frameshift variant, the c.3596_3597=/del (p.L1199HfsX7) KMT2D, respectively. Moreover, relevant for diagnostic and counselling purposes, we implemented a number of bioinformatics tools to assess the pathogenicity of 69 KMT2D missense variants, found overall in our cohort of 505 KS patients, and for 14 of them we adopted a combination of biochemical and cellular approaches to investigate their role and characterize their functional impact in the pathogenesis of the disease. We found 9/14 missense variants showing altered H3K4 methylation activity. We additionally assessed the impact on complex formation with WRAD protein complex, and we found that the reduced methyltransferase activity could be a consequence of lack of interaction

Expression analysis of miRNA hsa-let7b-5p in naso-oropharyngeal swabs of COVID-19 patients supports its role in regulating ACE2 and DPP4 receptors

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) is the novel coronavirus responsible for worldwide coronavirus disease (COVID-19). We previously observed that Angiotensin-converting enzyme 2 (ACE2) and Dipeptidyl peptidase-4 (DPP4) are significantly overexpressed in naso-oropharyngeal swabs (NPS) of COVID-19 patients, suggesting their putative functional role in the disease progression. ACE2 and DPP4 overexpression in COVID-19 patients may be associated to epigenetic mechanism, such as miRNA differential expression. We investigated if hsa-let7b-5p, reported to target both ACE2 and DPP4 transcripts, could be involved in the regulation of these genes. We verified that the inhibition and overexpression of hsa-let7b-5p matched to a modulation of both ACE2 and DPP4 levels. Then, we observed a statistically significant downregulation (FC = -1.5; p < 0.05) of hsa-let7b-5p in the same COVID-19 and control samples of our previous study. This is the first study that shows hsa-let7b-5p low expression in naso-oropharyngeal swabs of COVID-19 patients and demonstrates a functional role of this miR in regulating ACE2 and DPP4 levels. These data suggest the involvement of hsa-let7b-5p in the regulation of genes necessary for SARS-CoV-2 infections and its putative role as a therapeutic target for COVID-19

Genomic and Genetic Disorders Biobank

The Genomic and Genetic Disorders Biobank (GGDB, formerly Genomic Disorders Biobank) was established in 2006 as an internal bioresource supported by own database, to collect and store biospecimens from genomic-disorder (e.g. microdeletion and duplication syndromes) affected individuals. Since 2009 the Bioresource has joined the Telethon Network of Genetic Biobanks and has expanded the collection to include also genetic mendelian diseases. The GGDB gathers wholly annotated clinical and longitudinal data and biological samples from affected and healthy donors, according to standard ethical principles. Biospecimens are available to the international scientific community for research projects in the field of the pathologies collected and stored in GGDB.</p

Analysis of ACE2 genetic variants in 131 Italian SARS-CoV-2-positive patients

Coronaviruses (CoV) are a large family of viruses that are common in humans and many animal species. Animal coronaviruses rarely infect humans with the exceptions of the Middle East respiratory syndrome ( MERS-CoV ), the severe acute respiratory syndrome corona virus (SARS-CoV), and now SARS-CoV-2, which is the cause of the ongoing pandemic of coronavirus disease 2019 (COVID-19). Several studies suggested that genetic variants in the ACE2 gene may influence the host susceptibility or resistance to SARS-CoV-2 infection according to the functional role of ACE2 in human pathophysiology. However, many of these studies have been conducted in silico based on epidemiological and population data. We therefore investigated the occurrence of ACE2 variants in a cohort of 131 Italian unrelated individuals clinically diagnosed with COVID-19 and in an Italian control population, to evaluate a possible allelic association with COVID-19, by direct DNA analysis

Poking COVID-19: Insights on Genomic Constraints among Immune-Related Genes between Qatari and Italian Populations

Host genomic information, specifically genomic variations, may characterize susceptibility to disease and identify people with a higher risk of harm, leading to better targeting of care and vaccination. Italy was the epicentre for the spread of COVID-19 in Europe, the first country to go into a national lockdown and has one of the highest COVID-19 associated mortality rates. Qatar, on the other hand has a very low mortality rate. In this study, we compared whole-genome sequencing data of 14398 adults and Qatari-national to 925 Italian individuals. We also included in the comparison whole-exome sequence data from 189 Italian laboratory-confirmed COVID-19 cases. We focused our study on a curated list of 3619 candidate genes involved in innate immunity and host-pathogen interaction. Two population-gene metric scores, the Delta Singleton-Cohort variant score (DSC) and Sum Singleton-Cohort variant score (SSC), were applied to estimate the presence of selective constraints in the Qatari population and in the Italian cohorts. Results based on DSC and SSC metrics demonstrated a different selective pressure on three genes (MUC5AC, ABCA7, FLNA) between Qatari and Italian populations. This study highlighted the genetic differences between Qatari and Italian populations and identified a subset of genes involved in innate immunity and host-pathogen interaction

Clinical and Neurobehavioral Features of Three Novel Kabuki Syndrome Patients with Mosaic KMT2D Mutations and a Review of Literature

Kabuki syndrome (KS) is a rare disorder characterized by multiple congenital anomalies and variable intellectual disability caused by mutations in KMT2D/MLL2 and KDM6A/UTX, two interacting chromatin modifier responsible respectively for 56–75% and 5–8% of the cases. To date, three KS patients with mosaic KMT2D deletions in blood lymphocytes have been described. We report on three additional subjects displaying KMT2D gene mosaics including one in which a single nucleotide change results in a new frameshift mutation (p.L1199HfsX7), and two with already-known nonsense mutations (p.R4484X and p.R5021X). Consistent with previously published cases, mosaic KMT2D mutations may result in mild KS facial dysmorphisms and clinical and neurobehavioral features, suggesting that these characteristics could represent the handles for genetic testing of individuals with slight KS-like traits

COL1‐related overlap disorder: A novel connective tissue disorder incorporating the osteogenesis imperfecta/Ehlers‐Danlos syndrome overlap

The 2017 classification of Ehlers‐Danlos syndromes (EDS) identifies three types associated with causative variants in COL1A1/COL1A2 and distinct from osteogenesis imperfecta (OI). Previously, patients have been described with variable features of both disorders, and causative variants in COL1A1/COL1A2; but this phenotype has not been included in the current classification. Here, we expand and re‐define this OI/EDS overlap as a missing EDS type. Twenty‐one individuals from 13 families were reported, in whom COL1A1/COL1A2 variants were found after a suspicion of EDS. None of them could be classified as affected by OI or by any of the three recognized EDS variants associated with COL1A1/COL1A2. This phenotype is dominated by EDS‐related features. OI‐related features were limited to mildly reduced bone mass, occasional fractures and short stature. Eight COL1A1/COL1A2 variants were novel and five recurrent with a predominance of glycine substitutions affecting residues within the procollagen N‐proteinase cleavage site of α1(I) and α2(I) procollagens. Selected variants were investigated by biochemical, ultrastructural and immunofluorescence studies. The pattern of observed changes in the dermis and in vitro for selected variants was more typical of EDS rather than OI. Our findings indicate the existence of a wider recognizable spectrum associated with COL1A1/COL1A2