Novel De Novo Splice Site Mutation İn EFNB1 Gene Cause Craniofrontonasal Syndrome

Abstract

Craniofrontonasal syndrome (CFNS [MIM#304110]) is an Xlinkeddisorder paradoxically presenting with greater severityin heterozygous females than in hemizygous males. Eighty percentof CFNS cases are caused by mutations in EFNB1 (ephrinB1) gene located at Xq13.1. Molecular approach to CFNSpatients may be initiated with a screening of the EFNB1 genefor mutations followed by multiplex ligation-dependent probeamplification (MLPA) analysis to exclude possible deletionand duplications in several other genes involved in craniofacialdevelopment – including EFNB1. We report here the molecularfindings of a female patient presenting mild clinical featuresof CFNS. Sequence analysis of the EFNB1 gene covering allthe exons, exon–intron boundaries and the previouslydescribed mutation sites presented heterozygous A to Gchange in the fourth nucleotide from the five prime site of thesecond intron (IVS2+4A>G). There were no other alterations.Testing of the parents revealed normal sequence, disclosingde novo occurrence without excluding gonadal mosaicismin either parent. The change was not observed in any of the 50control chromosomes. MLPA analysis confirmed the absenceof any duplication or deletions in the genes; FGFR1, FGFR2,FGFR3, TWIST, MSX2, ALX4, RUNX2. According to SpliceSite Prediction Analysis, IVS2+4A>G abolishes the donorsite. Furthermore, observations of the genomic alignmentswith the sequences of the other mammalians shows that thenucleotide is highly conserved, as comprehensively agreed thatthose nucleotides immediately adjacent to splicing donor andacceptor sites present considerable conservation. Based uponthese findings, we propose that IVS2+4A>G to be a diseasecausing mutation in our isolated CFNS case.