Characterization of a disease-associated mutation affecting a putative splicing regulatory element in intron 6b of the cystic fibrosis transmembrane conductance regulator (CFTR) gene

Cystic fibrosis (CF) is a common recessive disorder caused by >1600 mutations in the CF transmembrane conductance regulator (CFTR) gene. About 13% of CFTR mutations are classified as “splicing mutations,” but for almost 40% of these, their role in affecting the pre-mRNA splicing of the gene is not yet defined. In this work, we describe a new splicing mutation detected in three unrelated Italian CF patients. By DNA analyses and mRNA studies, we identified the c.1002–1110_1113delTAAG mutation localized in intron 6b of the CFTR gene. At the mRNA level, this mutation creates an aberrant inclusion of a sequence of 101 nucleotides between exons 6b and 7. This sequence corresponds to a portion of intron 6b and resembles a cryptic exon because it is characterized by an upstream ag and a downstream gt sequence, which are most probably recognized as 5′- and 3′-splice sites by the spliceosome. Through functional analysis of this splicing defect, we show that this mutation abolishes the interaction of the splicing regulatory protein heterogeneous nuclear ribonucleoprotein A2/B1 with an intronic splicing regulatory element and creates a new recognition motif for the SRp75 splicing factor, causing activation of the cryptic exon. Our results show that the c.1002–1110_1113delTAAG mutation creates a new intronic splicing regulatory element in intron 6b of the CFTR gene exclusively recognized by SRp75

Skeletal dysplasia with bowing long bones: Proposed flowchart for prenatal diagnosis with case demonstration

Abstract Objective Skeletal dysplasia with bowing long bones is a rare group of multiple characterized congenital anomalies. Materials and Methods We introduce a simple, practical diagnostic flowchart that may be helpful in identifying the appropriate pathway of obstetrical management. Results Herein, we describe four fetal cases of bent bony dysplasia that focus on ultrasound findings, phenotype, molecular tests, distinctive X-ray features, and chondral growth plate histology. The first case was a typical campomelic dysplasia resulting from a de novo mutation in the SOX9 gene. The second fetus was affected by osteogenesis imperfecta Type II carrying a mutation in the COLA1 gene. The third case was a rare presentation of campomelic dysplasia, Cumming type, in which SOX9 examination was normal. Subsequently, a femoral hypoplasia unusual facies syndrome is also discussed. Conclusion Targeted molecular tests and genetic counseling are required for supplementing ultrasound imaging in order to diagnose the correct skeletal disorders

Duplications upstream and downstream of SHOX identified as novel causes of Leri-Weill dyschondrosteosis or idiopathic short stature

Leri–Weill dyschondrosteosis is a pseudoautosomal dominantly-inherited skeletal dysplasia ascribed to haploinsufficiency of the SHOX gene caused by deletions, point mutations, or partial duplications of the gene, or to heterozygous deletions upstream or downstream of the intact SHOX gene involving conserved non-coding cis-regulatory DNA elements that show enhancer activity. Recently, two SHOX conserved non-coding element duplications, one upstream and one downstream, were reported in patients referred with idiopathic short stature. To further evaluate the role of these duplications in SHOX-related disorders, we describe seven patients (five with Leri-Weill dyschondrosteosis and two with short stature) all of whom have duplications of part of the upstream or downstream conserved non-coding element regions, identified by multiplex ligation-dependent probe amplification. In addition, we show data from 32 patients with an apparently identical downstream duplication that includes a proposed putative regulatory element (identified by multiplex ligation-dependent probe amplification or array comparative genome hybridization), which results in a variable phenotype from normal to mild Leri–Weill dyschondrosteosis. These additional data provide further evidence that duplications of upstream and downstream long range cis-regulatory DNA elements can result in a SHOX-related phenotype. © 2015 Wiley Periodicals, Inc

Craniosynostosis, hydrocephalus, Chiari I malformation and radioulnar synostosis: Probably a new syndrome

We report on clinical and molecular findings of two brothers that both presented with sagittal craniosynostosis, hydrocephalus, Chiari I malformation, blepharophimosis, small low-set ears, hypoplastic philtrum, radioulnar synostosis, kidney malformation, and hypogenitalism. Their father presented mild brachydactyly. Conventional cytogenetic and array CGH screening did not show any chromosomal gains or losses. Furthermore, molecular genetic screening of genes involved in different craniosynostosis syndromes, namely FGFR1, FGFR2, FGFR3, TWIST, RECQL4, and POR genes failed to detect any mutations in genomic DNA. The unique range of clinical manifestations in these two patients and the negative findings of the molecular genetic screening suggest the hypothesis of a previously unrecognized syndrome

The L467F-F508del Complex Allele Hampers Pharmacological Rescue of Mutant CFTR by Elexacaftor/Tezacaftor/Ivacaftor in Cystic Fibrosis Patients: The Value of the Ex Vivo Nasal Epithelial Model to Address Non-Responders to CFTR-Modulating Drugs

Loss-of-function mutations of the CFTR gene cause cystic fibrosis (CF) through a variety of molecular mechanisms involving altered expression, trafficking, and/or activity of the CFTR chloride channel. The most frequent mutation among CF patients, F508del, causes multiple defects that can be, however, overcome by a combination of three pharmacological agents that improve CFTR channel trafficking and gating, namely, elexacaftor, tezacaftor, and ivacaftor. This study was prompted by the evidence of two CF patients, compound heterozygous for F508del and a minimal function variant, who failed to obtain any beneficial effects following treatment with the triple drug combination. Functional studies on nasal epithelia generated in vitro from these patients confirmed the lack of response to pharmacological treatment. Molecular characterization highlighted the presence of an additional amino acid substitution, L467F, in cis with the F508del variant, demonstrating that both patients were carriers of a complex allele. Functional and biochemical assays in heterologous expression systems demonstrated that the double mutant L467F-F508del has a severely reduced activity, with negligible rescue by CFTR modulators. While further studies are needed to investigate the actual prevalence of the L467F-F508del allele, our results suggest that this complex allele should be taken into consideration as plausible cause in CF patients not responding to CFTR modulators

Skeletal dysplasia with bowing long bones: Proposed flowchart for prenatal diagnosis with case demonstration

Objective: Skeletal dysplasia with bowing long bones is a rare group of multiple characterized congenital anomalies. Materials and Methods: We introduce a simple, practical diagnostic flowchart that may be helpful in identifying the appropriate pathway of obstetrical management. Results: Herein, we describe four fetal cases of bent bony dysplasia that focus on ultrasound findings, phenotype, molecular tests, distinctive X-ray features, and chondral growth plate histology. The first case was a typical campomelic dysplasia resulting from a de novo mutation in the SOX9 gene. The second fetus was affected by osteogenesis imperfecta Type II carrying a mutation in the COLA1 gene. The third case was a rare presentation of campomelic dysplasia, Cumming type, in which SOX9 examination was normal. Subsequently, a femoral hypoplasia unusual facies syndrome is also discussed. Conclusion: Targeted molecular tests and genetic counseling are required for supplementing ultrasound imaging in order to diagnose the correct skeletal disorders