title: Contribution of mutation load to the intrafamilial genetic heterogeneity in a large cohort of Spanish retinal dystrophies families.
abstract: OBJECTIVE
  The aim of this study was to deepen our knowledge on the basis of intrafamilial genetic heterogeneity of inherited retinal dystrophies (RD) to further discern the contribution of individual alleles to the pathology.
  
  
  METHODS
  Families with intrafamilial locus and/or allelic heterogeneity were selected from a cohort of 873 characterized of 2468 unrelated RD families. Clinical examination included visual field assessments, electrophysiology, fundus examination, and audiogram. Molecular characterization was performed using a combination of different methods: genotyping microarray, single strand conformational polymorphism (SSCP), denaturing high pressure liquid chromatography (dHPLC), high resolution melt (HRM), multiplex ligation-dependent probe amplification (MLPA), Sanger sequencing, whole-genome homozygosity mapping, and next-generation sequencing (NGS).
  
  
  RESULTS
  Overall, intrafamilial genetic heterogeneity was encountered in a total of 8 pedigrees. There were 5 of 873 families (~0.6%) with causative mutations in more than one gene (locus heterogeneity), involving the genes: (1) USH2A, RDH12, and TULP1; (2) PDE6B and a new candidate gene; (3) CERKL and CRB1; (4) BBS1 and C2orf71; and (5) ABCA4 and CRB1. Typically, in these cases, each mutated gene was associated with different phenotypes. In the 3 other families (~0.35%), different mutations in the same gene (allelic heterogeneity) were found, including the frequent RD genes ABCA4 and CRB1.
  
  
  CONCLUSIONS
  This systematic research estimates that the frequency of overall mutation load promoting RD intrafamilial heterogeneity in our cohort of Spanish families is almost 1%. The identification of the genetic mechanisms underlying RD locus and allelic heterogeneity is essential to discriminate the real contribution of the monoallelic mutations to the disease, especially in the NGS era. Moreover, it is decisive to provide an accurate genetic counseling and in disease treatment.
authors.affiliation: Department of Genetics, Fundacion Jimenez Diaz University Hospital (IIS - FJD, UAM), Madrid, Spain Centre for Biomedical Network Research on Rare Diseases, ISCIII, Valencia, Spain.
authors.forename: Rocío
authors.initials: R
authors.lastname: Sánchez-Alcudia
authors.affiliation: Department of Genetics, Fundacion Jimenez Diaz University Hospital (IIS - FJD, UAM), Madrid, Spain Centre for Biomedical Network Research on Rare Diseases, ISCIII, Valencia, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Cortón
authors.affiliation: Department of Genetics, Fundacion Jimenez Diaz University Hospital (IIS - FJD, UAM), Madrid, Spain Centre for Biomedical Network Research on Rare Diseases, ISCIII, Valencia, Spain.
authors.forename: Almudena
authors.initials: A
authors.lastname: Ávila-Fernández
authors.affiliation: Department of Genetics, Fundacion Jimenez Diaz University Hospital (IIS - FJD, UAM), Madrid, Spain Centre for Biomedical Network Research on Rare Diseases, ISCIII, Valencia, Spain.
authors.forename: Olga
authors.initials: O
authors.lastname: Zurita
authors.affiliation: Department of Genetics, Fundacion Jimenez Diaz University Hospital (IIS - FJD, UAM), Madrid, Spain Centre for Biomedical Network Research on Rare Diseases, ISCIII, Valencia, Spain.
authors.forename: Sorina D
authors.initials: SD
authors.lastname: Tatu
authors.affiliation: Department of Genetics, Fundacion Jimenez Diaz University Hospital (IIS - FJD, UAM), Madrid, Spain Centre for Biomedical Network Research on Rare Diseases, ISCIII, Valencia, Spain.
authors.forename: Raquel
authors.initials: R
authors.lastname: Pérez-Carro
authors.affiliation: Department of Genetics, Fundacion Jimenez Diaz University Hospital (IIS - FJD, UAM), Madrid, Spain Centre for Biomedical Network Research on Rare Diseases, ISCIII, Valencia, Spain.
authors.forename: Patricia
authors.initials: P
authors.lastname: Fernandez-San Jose
authors.affiliation: Department of Genetics, Fundacion Jimenez Diaz University Hospital (IIS - FJD, UAM), Madrid, Spain Centre for Biomedical Network Research on Rare Diseases, ISCIII, Valencia, Spain.
authors.forename: Miguel Ángel
authors.initials: MÁ
authors.lastname: Lopez-Martinez
authors.affiliation: Centre for Biomedical Network Research on Rare Diseases, ISCIII, Valencia, Spain Unidad de Genética Molecular, Hospital Universitario Ramón y Cajal, Instituto Ramón y Cajal de Investigación Sanitaria (IRYCIS), Madrid, Spain.
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: del Castillo
authors.affiliation: Centre for Biomedical Network Research on Rare Diseases, ISCIII, Valencia, Spain Grupo de Investigación en Enfermedades Neurosensoriales, Instituto de Investigación Sanitaria IIS-La Fe, Valencia, Spain.
authors.forename: Jose M
authors.initials: JM
authors.lastname: Millan
authors.affiliation: Department of Genetics, Fundacion Jimenez Diaz University Hospital (IIS - FJD, UAM), Madrid, Spain Centre for Biomedical Network Research on Rare Diseases, ISCIII, Valencia, Spain.
authors.forename: Fiona
authors.initials: F
authors.lastname: Blanco-Kelly
authors.affiliation: Centre for Biomedical Network Research on Rare Diseases, ISCIII, Valencia, Spain Department of Ophthalmology, Fundacion Jimenez Diaz University Hospital (IIS - FJD, UAM), Madrid, Spain.
authors.forename: Blanca
authors.initials: B
authors.lastname: García-Sandoval
authors.affiliation: Centre for Biomedical Network Research on Rare Diseases, ISCIII, Valencia, Spain Department of Ophthalmology, Fundacion Jimenez Diaz University Hospital (IIS - FJD, UAM), Madrid, Spain.
authors.forename: Maria Isabel
authors.initials: MI
authors.lastname: Lopez-Molina
authors.affiliation: Department of Genetics, Fundacion Jimenez Diaz University Hospital (IIS - FJD, UAM), Madrid, Spain Centre for Biomedical Network Research on Rare Diseases, ISCIII, Valencia, Spain.
authors.forename: Rosa
authors.initials: R
authors.lastname: Riveiro-Alvarez
authors.affiliation: Department of Genetics, Fundacion Jimenez Diaz University Hospital (IIS - FJD, UAM), Madrid, Spain Centre for Biomedical Network Research on Rare Diseases, ISCIII, Valencia, Spain.
authors.forename: Carmen
authors.initials: C
authors.lastname: Ayuso
mesh_terms: D000368:Aged; D000483:Alleles; D004252:DNA Mutational Analysis; D004596:Electroretinography; D005136:Eye Proteins / Q000235:genetics* / Q000378:metabolism; D005260:Female; D018740:Genetic Heterogeneity; D005838:Genotype; D006801:Humans; D008297:Male; D060885:Multiplex Polymerase Chain Reaction; D009154:Mutation; D010375:Pedigree; D010641:Phenotype; D015995:Prevalence; D058499:Retinal Dystrophies / Q000208:ethnology / Q000235:genetics* / Q000378:metabolism; D013030:Spain / Q000453:epidemiology
chemical_list: D005136:Eye Proteins
keywords: intrafamilial heterogeneity; mutation load; retinal dystrophies