title: A synonymous codon variant in two patients with autosomal recessive bestrophinopathy alters in vitro splicing of BEST1.
abstract: OBJECTIVE
  Autosomal recessive bestrophinopathy (ARB) is a newly defined retinal dystrophy caused by biallelic mutations in bestrophin-1 (BEST1) and is hypothesized to represent the null bestrophin-1 phenotype in humans. The aim was to determine whether a synonymous BEST1 variant, c.102C>T, identified in two unrelated ARB patients, alters pre-mRNA splicing of the gene. Additionally a detailed phenotypic characterization of this distinctive condition is presented for both patients.
  
  
  METHODS
  BEST1 was analyzed by direct sequencing. Patients underwent standard ophthalmic assessment. In silico and in vitro analysis using a minigene system was performed to assess whether a synonymous variant identified, c.102C>T p.Gly34Gly, alters pre-mRNA splicing of BEST1.
  
  
  RESULTS
  Both ARB patients harbored either proven (patient 1; c.102C>T p.Gly34Gly and c.572T>C p.Leu191Pro) or presumed (patient 2; c.102C>T p.Gly34Gly and c.1470_1471delCA, p.His490GlnfsX24) biallelic mutations in BEST1 and were found to have phenotypes consistent with ARB. In vitro analysis of the synonymous variant, c.102C>T p.Gly34Gly, demonstrated it to introduce a cryptic splice donor site 52 nucleotides upstream of the actual splice donor site.
  
  
  CONCLUSIONS
  The novel BEST1 variant identified, c.102C>T p.Gly34Gly, alters pre-mRNA splicing in vitro and is potentially pathogenic. In vivo this splicing variant is predicted to lead to the production of an mRNA transcript with a premature termination codon (p.Glu35TrpfsX11) that is predicted to be degraded by NMD.
authors.affiliation: School of Biomedicine, The University of Manchester, Manchester Academic Health Science Centre, Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK.
authors.forename: Alice E
authors.initials: AE
authors.lastname: Davidson
authors.forename: Panagiotis I
authors.initials: PI
authors.lastname: Sergouniotis
authors.forename: Rosemary
authors.initials: R
authors.lastname: Burgess-Mullan
authors.forename: Nichola
authors.initials: N
authors.lastname: Hart-Holden
authors.forename: Sancy
authors.initials: S
authors.lastname: Low
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Foster
authors.forename: Forbes D C
authors.initials: FD
authors.lastname: Manson
authors.forename: Graeme C M
authors.initials: GC
authors.lastname: Black
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Webster
mesh_terms: D000328:Adult; D000075002:Bestrophins; D002648:Child; D018118:Chloride Channels / Q000235:genetics*; D003062:Codon / Q000235:genetics*; D019295:Computational Biology; D005136:Eye Proteins / Q000235:genetics*; D005260:Female; D005353:Fibronectins / Q000737:chemistry / Q000235:genetics; D005453:Fluorescence; D005654:Fundus Oculi; D005808:Genes, Recessive / Q000235:genetics*; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation / Q000235:genetics*; D017434:Protein Structure, Tertiary; D012326:RNA Splicing / Q000235:genetics*; D058499:Retinal Dystrophies / Q000235:genetics*; D055815:Young Adult; D055542:alpha-Globins / Q000235:genetics
chemical_list: C113133:BEST1 protein, human; D000075002:Bestrophins; D018118:Chloride Channels; D003062:Codon; D005136:Eye Proteins; D005353:Fibronectins; D055542:alpha-Globins