title: Recessive mutations in TSPAN12 cause retinal dysplasia and severe familial exudative vitreoretinopathy (FEVR).
abstract: OBJECTIVE
  Familial exudative vitreoretinopathy (FEVR) is an inherited disorder that disrupts the development of the retinal vasculature and can result in blindness. FEVR is genetically heterogeneous and mutations in four genes, NDP, FZD4, LRP5, and TSPAN12, encoding components of a novel ligand-receptor complex that activates the Norrin-β-catenin signaling pathway, account for approximately 50% of cases. We recently identified mutations in TSPAN12 as a cause of dominant FEVR. The purpose of this study was to identify recessive TSPAN12 mutations in FEVR patients.
  
  
  METHODS
  Mutation screening was performed by directly sequencing PCR products generated from genomic DNA with primers designed to amplify the coding sequence of TSPAN12. Splicing defects were verified by reverse transcriptase PCR of leukocyte cDNA.
  
  
  RESULTS
  TSPAN12 screening in a large dominant FEVR family unexpectedly led to the identification of homozygous mutations in severely affected family members, whereas mildly affected family members were heterozygous. Further screening in a cohort of 10 retinal dysplasia/severe FEVR patients identified an additional three cases with recessive TSPAN12 mutations. In all examined cases, single mutation carriers were mildly affected compared to patients harboring two TSPAN12 mutations.
  
  
  CONCLUSIONS
  We report for the first time recessive mutations in TSPAN12 and describe the first genetic cause for the clinical variation seen in FEVR families. Our data raise the possibility that patients with severe FEVR actually may harbor two mutant alleles, derived either from the same gene or potentially from other genes encoding components of the Norrin-β-catenin signaling pathway.
authors.affiliation: Leeds Institute of Molecular Medicine, St. James's University Hospital, Leeds, United Kingdom.
authors.forename: James A
authors.initials: JA
authors.lastname: Poulter
authors.forename: Alice E
authors.initials: AE
authors.lastname: Davidson
authors.forename: Manir
authors.initials: M
authors.lastname: Ali
authors.forename: David F
authors.initials: DF
authors.lastname: Gilmour
authors.forename: David A
authors.initials: DA
authors.lastname: Parry
authors.forename: Helen A
authors.initials: HA
authors.lastname: Mintz-Hittner
authors.forename: Ian M
authors.initials: IM
authors.lastname: Carr
authors.forename: Helen M
authors.initials: HM
authors.lastname: Bottomley
authors.forename: Vernon W
authors.initials: VW
authors.lastname: Long
authors.forename: Louise M
authors.initials: LM
authors.lastname: Downey
authors.forename: Panagiotis I
authors.initials: PI
authors.lastname: Sergouniotis
authors.forename: Genevieve A
authors.initials: GA
authors.lastname: Wright
authors.forename: Robert E
authors.initials: RE
authors.lastname: MacLaren
authors.forename: Anthony T
authors.initials: AT
authors.lastname: Moore
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Webster
authors.forename: Chris F
authors.initials: CF
authors.lastname: Inglehearn
authors.forename: Carmel
authors.initials: C
authors.lastname: Toomes
mesh_terms: D004252:DNA Mutational Analysis; D005260:Female; D005808:Genes, Recessive / Q000235:genetics*; D006801:Humans; D008297:Male; D020125:Mutation, Missense; D010375:Pedigree; D012333:RNA, Messenger; D015792:Retinal Dysplasia / Q000235:genetics*; D059470:Tetraspanins / Q000235:genetics*; D018630:Vitreoretinopathy, Proliferative / Q000235:genetics*
chemical_list: D012333:RNA, Messenger; C545100:TSPAN12 protein, human; D059470:Tetraspanins