RESUMEN
ß-Thalassemia is the most common autosomal recessive single-gene disorder in Sardinia, where approximately 10.3% of the population is a carrier. Prenatal diagnosis is carried out at 12 weeks of gestation via villocentesis and is commonly aimed at ascertaining the presence or absence of the HBB variant c.118C>T, which is the most common in Sardinia. In this study, we describe for the first time the application of semiconductor sequencing to the non-invasive prenatal diagnosis of ß-thalassemia in 37 couples at risk for this variant. In particular, by using a haplotyping-based approach with a hidden Markov model (HMM) and a dedicated pipeline, the two parental haplotypes most likely inherited by the foetus could be established in 30 out of 37 cffDNA samples. Specifically, the paternally inherited haplotype was correctly determined in all 30 of the samples, while the maternal haplotype was incorrectly predicted in six of the 30 genotyped samples. The lack of informative SNPs hampered the inference of both parental haplotypes in the remaining seven samples. As shown in previous studies, we have confirmed that the haplotyping-based approach represents a valuable resource, as it improves the detection of both parental haplotypes inherited by the foetus. In general, our results are encouraging, as we have proven that NIPD is also feasible in couples who are at risk for a monogenic disorder and share the same variant.
Asunto(s)
Pruebas Genéticas/métodos , Hemoglobinas Anormales/genética , Diagnóstico Prenatal/métodos , Análisis de Secuencia de ADN/métodos , Talasemia beta/genética , Estudios de Factibilidad , Femenino , Haplotipos , Humanos , Italia , Polimorfismo de Nucleótido Simple , Embarazo , Semiconductores , Análisis de Secuencia de ADN/instrumentación , Talasemia beta/diagnósticoRESUMEN
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.