RP1 Dominant p.Ser740* Pathogenic Variant in 20 Knowingly Unrelated Families Affected by Rod-Cone Dystrophy: Potential Founder Effect in Western Sicily.

Background and Objectives. Retinitis pigmentosa (RP) is the most common inherited rod-cone dystrophy (RCD), resulting in nyctalopia, progressive visual field, and visual acuity decay in the late stages. The autosomal dominant form (ADRP) accounts for about 20% of RPs. Among the over 30 genes found to date related to ADRP, RP1 pathogenic variants have been identified in 5-10% of cases. In a cohort of RCD patients from the Palermo province on the island of Sicily, we identified a prevalent nonsense variant in RP1, which was associated with ADRP. The objective of our study was to analyse the clinical and molecular data of this patient cohort and to evaluate the potential presence of a founder effect. Materials and Methods. From 2005 to January 2023, 84 probands originating from Western Sicily (Italy) with a diagnosis of RCD or RP and their relatives underwent deep phenotyping, which was performed in various Italian clinical institutions. Molecular characterisation of patients and familial segregation of pathogenic variants were carried out in different laboratories using Sanger and/or next-generation sequencing (NGS). Results. Among 84 probands with RCD/RP, we found 28 heterozygotes for the RP1 variant c.2219C>G, p.Ser740* ((NM_006269.2)*, which was therefore significantly prevalent in this patient cohort. After a careful interview process, we ascertained that some of these patients shared the same pedigree. Therefore, we were ultimately able to define 20 independent family groups with no traceable consanguinity. Lastly, analysis of clinical data showed, in our patients, that the p.Ser740* nonsense variant was often associated with a late-onset and relatively mild phenotype. Conclusions. The high prevalence of the p.Ser740* variant in ADRP patients from Western Sicily suggests the presence of a founder effect, which has useful implications for the molecular diagnosis of RCD in patients coming from this Italian region. This variant can be primarily searched for in RP-affected subjects displaying compatible modes of transmission and phenotypes, with an advantage in terms of the required costs and time for analysis. Moreover, given its high prevalence, the RP1 p.Ser740* variant could represent a potential candidate for the development of therapeutic strategies based on gene editing or translational read-through therapy for suppression of nonsense variants.

MiR-27a downregulates 14-3-3θ, RUNX1, AF4, and MLL-AF4, crucial drivers of blast transformation in t(4;11) leukemia cells.

The chromosomal translocation t(4;11)(q21;q23), a hallmark of an aggressive form of acute lymphoblastic leukemia (ALL), encodes mixed-lineage leukemia (MLL)-AF4 oncogenic chimera that triggers aberrant transcription of genes involved in lymphocyte differentiation, including HOXA9 and MEIS1. The scaffold protein 14-3-3θ, which promotes the binding of MLL-AF4 to the HOXA9 promoter, is a target of MiR-27a, a tumor suppressor in different human leukemia cell types. We herein study the role of MiR-27a in the pathogenesis of t(4;11) ALL. Reverse transcription quantitative PCR (qPCR) reveals that MiR-27a and 14-3-3θ expression is inversely correlated in t(4;11) ALL cell lines; interestingly, MiR-27a relative expression is significantly lower in patients affected by t(4;11) ALL than in patients affected by the less severe t(12;21) leukemia. In t(4;11) leukemia cells, ectopic expression of MiR-27a decreases protein level of 14-3-3θ and of the key transcription factor RUNX1. We show for the first time that MiR-27a also targets AF4 and MLL-AF4; in agreement, MiR-27a overexpression strongly reduces AF4 and MLL-AF4 protein levels in RS4;11 cells. Consequent to AF4 and MLL-AF4 downregulation, MiR-27a overexpression negatively affects transcription of HOXA9 and MEIS1 in different t(4;11) leukemia cell lines. In agreement, we show through chromatin immunoprecipitation experiments that MiR-27a overexpression impairs the binding of MLL-AF4 to the HOXA9 promoter. Lastly, we found that MiR-27a overexpression decreases viability, proliferation, and clonogenicity of t(4;11) cells, whereas it enhances their apoptotic rate. Overall, our study identifies the first microRNAthat strikes in one hit four crucial drivers of blast transformation in t(4;11) leukemia. Therefore, MiR-27a emerges as a new promising therapeutic target for this aggressive and poorly curable form of leukemia.

Nuclear FGFR2 Interacts with the MLL-AF4 Oncogenic Chimera and Positively Regulates HOXA9 Gene Expression in t(4;11) Leukemia Cells.

The chromosomal translocation t(4;11) marks an infant acute lymphoblastic leukemia associated with dismal prognosis. This rearrangement leads to the synthesis of the MLL-AF4 chimera, which exerts its oncogenic activity by upregulating transcription of genes involved in hematopoietic differentiation. Crucial for chimera's aberrant activity is the recruitment of the AF4/ENL/P-TEFb protein complex. Interestingly, a molecular interactor of AF4 is fibroblast growth factor receptor 2 (FGFR2). We herein analyze the role of FGFR2 in the context of leukemia using t(4;11) leukemia cell lines. We revealed the interaction between MLL-AF4 and FGFR2 by immunoprecipitation, western blot, and immunofluorescence experiments; we also tested the effects of FGFR2 knockdown, FGFR2 inhibition, and FGFR2 stimulation on the expression of the main MLL-AF4 target genes, i.e., HOXA9 and MEIS1. Our results show that FGFR2 and MLL-AF4 interact in the nucleus of leukemia cells and that FGFR2 knockdown, which is associated with decreased expression of HOXA9 and MEIS1, impairs the binding of MLL-AF4 to the HOXA9 promoter. We also show that stimulation of leukemia cells with FGF2 increases nuclear level of FGFR2 in its phosphorylated form, as well as HOXA9 and MEIS1 expression. In contrast, preincubation with the ATP-mimetic inhibitor PD173074, before FGF2 stimulation, reduced FGFR2 nuclear amount and HOXA9 and MEIS1 transcript level, thereby indicating that MLL-AF4 aberrant activity depends on the nuclear availability of FGFR2. Overall, our study identifies FGFR2 as a new and promising therapeutic target in t(4;11) leukemia.

Genetic characterization of Italian patients with Bardet-Biedl syndrome and correlation to ocular, renal and audio-vestibular phenotype: identification of eleven novel pathogenic sequence variants.

BACKGROUND: Bardet-Biedl syndrome (BBS) is a rare genetic disorder that features retinal degeneration, obesity, polydactyly, learning disabilities and renal abnormalities. The diagnosis is often missed at birth, the median age at diagnosis being 9 years. In the attempt to shed light on BBS and improve its diagnosis and treatment, we evaluated the genotype-phenotype relationship in patients with a molecular diagnosis of BBS. METHODS: We analyzed three common BBS genes, BBS1, BBS10 and BBS2, in 25 Italian patients fulfilling the clinical criteria of BBS. In 12 patients, we identified gene-specific biallelic variants and thus correlated genotype to the ophthalmic, renal and audio-vestibular phenotypes. RESULTS: At least one sequence variant was found in 60% of patients. The most common mutated gene was BBS1 followed by BBS10. Of the 17 sequence variants we found, 11 have not previously been associated with BBS. In 12 patients, we identified biallelic pathogenic variants; they had retinitis pigmentosa with early onset of visual impairment. However, retinal dystrophy was less severe in patients with BBS1 than in those with BBS10 variants. Overall, we found a high prevalence of renal dysmorphism and dysfunction. Notably, patients with BBS10 variants had the most severe renal impairment, which resulted in a critical decline in renal function. All the patients who underwent audio-vestibular evaluation had dysfunction of the cochlear outer hair cells, thus confirming the presence of hearing defects. CONCLUSION: BBS1, BBS2 and BBS10 are major causative genes in Italian BBS patients. BBS10 was associated with the worse outcome in terms of the renal, ocular and audiovestibular phenotypes. Cochlear dysfunction should be included among the hallmarks of BBS.

Precise mapping of 17 deletion breakpoints within the central hotspot deletion region (introns 50 and 51) of the DMD gene.

Exon deletions in the human DMD gene, which encodes the dystrophin protein, are the molecular defect in 50-70% of cases of Duchenne/Becker muscular dystrophies. Deletions are preferentially clustered in the 5' (exons 2-20) and the central (exons 45-53) region of DMD, likely because local DNA structure predisposes to specific breakage or recombination events. Notably, innovative therapeutic strategies may rescue dystrophin function by homology-based specific targeting of sequences within the central DMD hot spot deletion region. To further study molecular mechanisms that generate such frequent genome variations and to identify residual intronic sequences, we sequenced 17 deletion breakpoints within introns 50 and 51 of DMD and analyzed the surrounding genomic architecture. There was no breakpoint clustering within the introns nor extensive homology between sequences adjacent to each junction. However, at or near the breakpoint, we found microhomology, short tandem repeats, interspersed repeat elements and short sequence stretches that predispose to DNA deletion or bending. Identification of such structural elements contributes to elucidate general mechanisms generating deletion within the DMD gene. Moreover, precise mapping of deletion breakpoints and localization of repeated elements are of interest, because residual intronic sequences may be targeted by therapeutic strategies based on genome editing correction.

Nuclear localization of Formyl-Peptide Receptor 2 in human cancer cells.

Current models of G protein-coupled receptors (GPCRs) signaling describe binding of external agonists to cell surface receptors which, in turn, trigger several biological responses. New paradigms indicate that GPCRs localize to and signal at the nucleus, thus regulating distinct signaling cascades. The formyl-peptide receptor FPR2 belongs to the GPCR super-family and is coupled to PTX-sensitive Gi proteins. We show by western blot analysis, immunofluorescence experiments and radioligand binding assays that FPR2 is expressed at nuclear level in CaLu-6 and AGS cells. Nuclear FPR2 is a functional receptor, since it participates in intra-nuclear signaling, as assessed by decreased G protein-FPR2 association and enhanced ERK2, c-Jun and c-Myc phosphorylation upon stimulation of intact nuclei with the FPR2 agonist, WKYMVm. We analyzed FPR2 sequence for the search of a nuclear localization sequence (NLS) and we found a stretch of basic aminoacids (227-KIHKK-231) in the third cytoplasmic loop of the receptor. We performed single (K230A) and multiple (H229A/K230A/K231A) mutagenesis of NLS. The constructs were individually overexpressed in HEK293 cells and immunofluorescence and western blot analysis showed that nuclear localization or translocation of FPR2 depends on the integrity of the H(229) and K(231) residues within the NLS.

Comprehensive Molecular Analysis of Disease-Related Genes as First-Tier Test for Early Diagnosis, Classification, and Management of Patients Affected by Nonsyndromic Ichthyosis.

Inherited ichthyoses are a group of clinically and genetically heterogeneous rare disorders of skin keratinization with overlapping phenotypes. The clinical picture and family history are crucial to formulating the diagnostic hypothesis, but only the identification of the genetic defect allows the correct classification. In the attempt to molecularly classify 17 unrelated Italian patients referred with congenital nonsyndromic ichthyosis, we performed massively parallel sequencing of over 50 ichthyosis-related genes. Genetic data of 300 Italian unaffected subjects were also analyzed to evaluate frequencies of putative disease-causing alleles in our population. For all patients, we identified the molecular cause of the disease. Eight patients were affected by autosomal recessive congenital ichthyosis associated with ALOX12B, NIPAL4, and TGM1 mutations. Three patients had biallelic loss-of-function variants in FLG, whereas 6/11 males were affected by X-linked ichthyosis. Among the 24 different disease-causing alleles we identified, 8 carried novel variants, including a synonymous TGM1 variant that resulted in a splicing defect. Moreover, we generated a priority list of the ichthyosis-related genes that showed a significant number of rare and novel variants in our population. In conclusion, our comprehensive molecular analysis resulted in an effective first-tier test for the early classification of ichthyosis patients. It also expands the genetic, mutational, and phenotypic spectra of inherited ichthyosis and provides new insight into the current understanding of etiologies and epidemiology of this group of rare disorders.

De Novo Large Deletions in the PHEX Gene Caused X-Linked Hypophosphataemic Rickets in Two Italian Female Infants Successfully Treated with Burosumab.

Pathogenic variants in the PHEX gene cause rare and severe X-linked dominant hypophosphataemia (XLH), a form of heritable hypophosphatemic rickets (HR) characterized by renal phosphate wasting and elevated fibroblast growth factor 23 (FGF23) levels. Burosumab, the approved human monoclonal anti-FGF23 antibody, is the treatment of choice for XLH. The genetic and phenotypic heterogeneity of HR often delays XLH diagnoses, with critical effects on disease course and therapy. We herein report the clinical and genetic features of two Italian female infants with sporadic HR who successfully responded to burosumab. Their diagnoses were based on clinical and laboratory findings and physical examinations. Next-generation sequencing (NGS) of the genes associated with inherited HR and multiple ligation probe amplification (MLPA) analysis of the PHEX and FGF23 genes were performed. While a conventional analysis of the NGS data did not reveal pathogenic or likely pathogenic small nucleotide variants (SNVs) in the known HR-related genes, a quantitative analysis identified two different heterozygous de novo large intragenic deletions in PHEX, and this was confirmed by MLPA. Our molecular data indicated that deletions in the PHEX gene can be the cause of a significant fraction of XLH; hence, their presence should be evaluated in SNV-negative female patients. Our patients successfully responded to burosumab, demonstrating the efficacy of this drug in the treatment of XLH. In conclusion, the execution of a phenotype-oriented genetic test, guided by known types of variants, including the rarest ones, was crucial to reach the definitive diagnoses and ensure our patients of long-term therapy administration.

SET-PP2A complex as a new therapeutic target in KMT2A (MLL) rearranged AML.

KMT2A-rearranged (KMT2A-R) is an aggressive and chemo-refractory acute leukemia which mostly affects children. Transcriptomics-based characterization and chemical interrogation identified kinases as key drivers of survival and drug resistance in KMT2A-R leukemia. In contrast, the contribution and regulation of phosphatases is unknown. In this study we uncover the essential role and underlying mechanisms of SET, the endogenous inhibitor of Ser/Thr phosphatase PP2A, in KMT2A-R-leukemia. Investigation of SET expression in acute myeloid leukemia (AML) samples demonstrated that SET is overexpressed, and elevated expression of SET is correlated with poor prognosis and with the expression of MEIS and HOXA genes in AML patients. Silencing SET specifically abolished the clonogenic ability of KMT2A-R leukemic cells and the transcription of KMT2A targets genes HOXA9 and HOXA10. Subsequent mechanistic investigations showed that SET interacts with both KMT2A wild type and fusion proteins, and it is recruited to the HOXA10 promoter. Pharmacological inhibition of SET by FTY720 disrupted SET-PP2A interaction leading to cell cycle arrest and increased sensitivity to chemotherapy in KMT2A-R-leukemic models. Phospho-proteomic analyses revealed that FTY720 reduced the activity of kinases regulated by PP2A, including ERK1, GSK3ß, AURB and PLK1 and led to suppression of MYC, supporting the hypothesis of a feedback loop among PP2A, AURB, PLK1, MYC, and SET. Our findings illustrate that SET is a novel player in KMT2A-R leukemia and they provide evidence that SET antagonism could serve as a novel strategy to treat this aggressive leukemia.

Molecular Characterization of Choroideremia-Associated Deletions Reveals an Unexpected Regulation of CHM Gene Transcription.

Choroideremia (CHM) is a X-linked recessive chorioretinal dystrophy due to deficiency of the CHM gene product, i.e., Rab escort protein isoform 1 (REP1). To date, gene therapy for CHM has shown variable effectiveness, likely because the underlying pathogenic mechanisms as well as genotype-phenotype correlation are not yet fully known. Small nucleotide variants leading to premature termination codons (PTCs) are a major cause of CHM, but about 20% of patients has CHM gene deletions. To improve understanding of the disease mechanisms, we analyzed molecular features of seven deletions involving the CHM gene sequence. We mapped the deletion breakpoints by using polymerase chain reaction, sequencing and array comparative genomic hybridization; to identify rearrangement-promoting DNA sequences, we analyzed genomic architecture surrounding the breakpoint regions. Moreover, in some CHM patients with different mutation types, we measured transcript level of CHM and of CHML, encoding the REP2 isoform. Scattered along the whole CHM gene and in close proximity to the deletion breakpoints we found numerous repeat elements that generate a locus-specific rearrangement hot spot. Unexpectedly, patients with non-PTC variants had increased expression of the aberrant CHM mRNA; CHML expression was higher than normal in a patient lacking CHM and its putative regulatory sequences. This latest evidence suggests that mechanisms regulating CHM and CHML gene expression are worthy of further study, because their full knowledge could be also useful for developing effective therapies for this hitherto untreatable inherited retinal degeneration.

A putative frameshift variant in the CHM gene is associated with an unexpected splicing alteration in a choroideremia patient.

BACKGROUND: Due to the limited availability of mRNA analysis data, the number of exonic variants resulting in splicing impairment is underestimated although aberrant splicing correction is a promising therapeutic option to treat monogenic diseases, including choroideremia (CHM), a rare X-linked eye disorder arising from sequence alteration of the CHM gene. Herein we report an exonic frameshift variant associated with an mRNA splicing alteration that leads to a CHM hypomorphic allele. METHODS: Total RNA and genomic DNA were extracted from peripheral blood of a patient affected by a mild form of CHM. The CHM gene was analyzed by PCR-based methods and Sanger sequencing. RESULTS: Besides the known c.1335dup frameshift variant, mRNA analysis revealed a splicing alteration that restored the reading frame of the mutant transcript, likely leading to an aberrant protein with residual activity. Bioinformatic analyses identified novel putative exonic splicing enhancer elements and provided clues that also pre-mRNA secondary structure should be taken into account when exploring splicing mechanisms. CONCLUSION: A careful molecular characterization of the c.1335dup variant's effect explains the relationship between genotype and phenotype severity in a CHM patient and provides new perspectives for the study of therapeutic strategies based on splicing correction in human diseases.

Multi-Gene Next-Generation Sequencing for Molecular Diagnosis of Autosomal Recessive Congenital Ichthyosis: A Genotype-Phenotype Study of Four Italian Patients.

Autosomal recessive congenital ichthyoses (ARCI) are rare genodermatosis disorders characterized by phenotypic and genetic heterogeneity. At least fourteen genes so far have been related to ARCI; however, despite genetic heterogeneity, phenotypes associated with mutation of different ARCI genes may overlap, thereby making difficult their clinical and molecular classification. In addition, molecular tests for diagnosis of such an extremely rare heterogeneous inherited disease are not easily available in clinical settings. In the attempt of identifying the genetic cause of the disease in four Italian patients with ARCI, we performed next-generation sequencing (NGS) analysis targeting 4811 genes that have been previously linked to human genetic diseases; we focused our analysis on the 13 known ARCI genes comprised in the panel. Nine different variants including three novel small nucleotide changes and two novel large deletions have been identified and validated in the ABCA12, ALOX12B, CYP4F22, and SULT2B1 genes. Notably, two patients had variants in more than one gene. The identification and validation of new pathogenic ABCA12, ALOX12B, CYP4F22, and SULT2B1 variants through multi-gene NGS in four cases of ARCI further highlight the importance of these genes in proper skin function and development.

Crosstalk between 14-3-3θ and AF4 enhances MLL-AF4 activity and promotes leukemia cell proliferation.

PURPOSE: The t(4;11)(q21;q23) translocation characterizes a form of acute lymphoblastic leukemia with a poor prognosis. It results in a fusion gene encoding a chimeric transcription factor, MLL-AF4, that deregulates gene expression through a variety of still controversial mechanisms. To provide new insights into these mechanisms, we examined the interaction between AF4, the most common MLL fusion partner, and the scaffold protein 14-3-3θ, in the context of t(4;11)-positive leukemia. METHODS: Protein-protein interactions were analyzed using immunoprecipitation and in vitro binding assays, and by fluorescence microscopy in t(4;11)-positive RS4;11 and MV4-11 leukemia cells and in HEK293 cells. Protein and mRNA expression levels were determined by Western blotting and RT-qPCR, respectively. A 5-bromo-2'-deoxyuridine assay and an annexin V/propidium iodide assay were used to assess proliferation and apoptosis rates, respectively, in t(4;11)-positive and control cells. Chromatin immunoprecipitation was performed to assess binding of 14-3-3θ and AF4 to a specific promoter element. RESULTS: We found that AF4 and 14-3-3θ are nuclear interactors, that 14-3-3θ binds Ser588 of AF4 and that 14-3-3θ forms a complex with MLL-AF4. In addition, we found that in t(4;11)-positive cells, 14-3-3θ knockdown decreased the expression of MLL-AF4 target genes, induced apoptosis and hampered cell proliferation. Moreover, we found that 14-3-3θ knockdown impaired the recruitment of AF4, but not of MLL-AF4, to target chromatin. Overall, our data indicate that the activity of the chimeric transcription factor MLL-AF4 depends on the cellular availability of 14-3-3θ, which triggers the transactivating function and subsequent degradation of AF4. CONCLUSIONS: From our data we conclude that the scaffold protein 14-3-3θ enhances the aberrant activity of the chimeric transcription factor MLL-AF4 and, therefore, represents a new player in the molecular pathogenesis of t(4;11)-positive leukemia and a new promising therapeutic target.

CHM/REP1 Transcript Expression and Loss of Visual Function in Patients Affected by Choroideremia.

Purpose: To evaluate the disease progression in patients with clinical and genetic diagnoses of choroideremia during a long-term follow-up and to investigate the relationship between pathogenic variants in the CHM/REP1 gene and disease phenotypes. Methods: We performed a retrospective longitudinal study on 51 affected men by reviewing medical charts at baseline and follow-up visits to extract the following ocular findings: best-corrected visual acuity, Goldmann visual field, optical coherence tomography, microperimetry. Data obtained from the analysis of DNA and mRNA were reevaluated for genetic classification of patients. Results: The longitudinal analysis showed a significant (P < 0.001) worsening of best-corrected visual acuity with a mean rate of 0.011 logMar per year before 50 years and 0.025 logMar per year after 50 years. Similarly, V4e Goldmann visual field area significantly (P ≤ 0.01) decreased at a mean rate of 2.7% per year before 40 years and 5.7% after 40 years. Moreover, we observed a significant (P < 0.05) decrease of macular sensitivity with a mean rate of 5.0% per year and a decrease of mean macular thickness with a mean rate of 0.8% per year. We classified our patients into two groups according to the expression of the CHM/REP1 gene transcript and observed that mutations leading to mRNA absence are associated with an earlier best-corrected visual acuity and Goldmann visual field loss. Conclusions: Our analysis of morphological and functional parameters in choroideremia patients showed a slow disease progression, particularly in the first decades of life. Overall, reevaluation of clinical and molecular data suggests exploring the genotype-phenotype relationship based on CHM/REP1 transcript expression.

Photoletter to the editor: Lamellar ichthyosis and arthrogryposis in a premature neonate.

Lamellar ichthyosis is a rare congenital disorder characterized by collodion membrane at birth and facial anomalies (eclabium and ectropion). The major underlying genetic defect is in TGM1, with mutations of this gene found in 50% of patients. An early diagnosis is fundamental in view of establishing a specific treatment due to the severity of the disease. We report a case of severe lamellar ichthyosis and arthrogryposis, without the typical facial presentation, negative for TGM1 mutations. The clinical improvement was achieved only after treatment with oral retinoids, highlighting the importance of early diagnosis and prompt administration of a specific therapy.