RESUMEN
Mutations in the SLC26A4 gene at the DFNB4 locus are responsible for Pendred syndrome and non-syndromic hereditary hearing loss (DFNB4). This study included 80 nuclear families with two or more siblings segregating presumed autosomal recessive hearing loss. All deaf persons tested negative for mutations in GJB2 at the DFNB1 locus and were, therefore, screened for autozygosity by descent (ABD) using short tandem repeat polymorphisms (STRPs) that flanked SLC26A4. In 12 families, homozygosity for STRPs suggested possible ABD in this genomic region. Affected individuals in five families had a positive perchlorate discharge test. Sequence analysis of SLC26A4 identified ten mutations in eight families (T420I, 1197delT, G334V, R409H, T721M, R79X, S448L, L597S, 965insA and L445W), of which, four are novel (T420I, G334V, 965insA and R79X). These results imply that Pendred syndrome is the most prevalent form of syndromic hereditary hearing loss in Iran.
Asunto(s)
Pérdida Auditiva/genética , Proteínas de Transporte de Membrana/genética , Transporte Biológico/genética , Conexina 26 , Conexinas , Pérdida Auditiva/congénito , Homocigoto , Humanos , Irán , Repeticiones de Microsatélite , Mutación/genética , Análisis de Secuencia de ADN , Transportadores de Sulfato , Síndrome , Acueducto Vestibular/patologíaRESUMEN
Branchio-oto-renal syndrome (BOR) is a clinically heterogeneous autosomal dominant form of syndromic hearing loss characterized by variable hearing impairment, malformations of the pinnae, the presence of branchial arch remnants, and various renal abnormalities. Both EYA1 and SIX1 are expressed in developing otic, branchial and renal tissue. Consistent with this expression pattern, mutations in both genes cause BOR syndrome. Mutations in EYA1 are found in approximately 40% of patients with the BOR phenotype, however, the role of SIX1 is much lower. To date only three different SIX1 mutations have been described in BOR patients. The current screen of 247 BOR families detected five novel SIX1 mutations (c.50T>A, c.218A>C, c.317T>G, c.329G>A, c.334C>T) and one previously reported mutation (c.328C>T) seen in 5 unrelated families. All mutations are within the protein-binding Six domain. Phenotypic variability was high in these BOR families. Seven of the eight known SIX1 mutations are missense and the one in frame deletion is predicted to be functionally similar. The wide phenotypic variability precludes making genotype-phenotype correlations at this time.
Asunto(s)
Síndrome Branquio Oto Renal/genética , Proteínas de Homeodominio/genética , Mutación Missense , Adolescente , Secuencia de Aminoácidos , Niño , Preescolar , Femenino , Genes Dominantes , Pruebas Genéticas , Proteínas de Homeodominio/química , Humanos , Péptidos y Proteínas de Señalización Intracelular/genética , Intrones , Masculino , Persona de Mediana Edad , Datos de Secuencia Molecular , Proteínas Nucleares/genética , Linaje , Fenotipo , Estructura Terciaria de Proteína , Proteínas Tirosina Fosfatasas/genética , Homología de Secuencia de AminoácidoRESUMEN
Branchio-oto-renal syndrome (BOR) is an autosomal dominant disorder characterized by the association of branchial and external ear malformations, hearing loss, and renal anomalies. The phenotype varies from ear pits to profound hearing loss, branchial fistulae, and kidney agenesis. The most common gene mutated in BOR families is EYA1, a transcriptional activator. Over 80 different disease-causing mutations have been published (www.healthcare.uiowa.edu/labs/pendredandbor/, last accessed 20 November 2007). We analyzed the EYA1 coding region (16 exons) from 435 families (345 at the University of Iowa [UI] and 95 at Boys Town National Research Hospital [BTNRH], including five at both) and found 70 different EYA1 mutations in 89 families. Most of the mutations (56/70) were private. EYA1 mutations were found in 31% of families (76/248) fitting established clinical criteria for BOR and 7% of families with questionable BOR phenotype (13/187). Severity of the phenotype did not correlate with type of mutation nor with the domain involved. These results add considerably to the spectrum of EYA1 mutations associated with BOR and indicate that the BOR phenotype is an indication for molecular studies to diagnose EYA1-associated BOR.
Asunto(s)
Síndrome Branquio Oto Renal/genética , Péptidos y Proteínas de Señalización Intracelular/genética , Mutación , Proteínas Nucleares/genética , Proteínas Tirosina Fosfatasas/genética , Secuencia de Aminoácidos , Estudios de Casos y Controles , Análisis Mutacional de ADN , Exones , Femenino , Mutación del Sistema de Lectura , Genes Dominantes , Humanos , Masculino , Datos de Secuencia Molecular , Mutación Missense , Fenotipo , Polimorfismo de Nucleótido Simple , Empalme del ARN/genética , Homología de Secuencia de AminoácidoRESUMEN
Branchio-oto-renal syndrome, a phenotype consisting of hearing loss, auricular malformations, branchial arch remnants, and renal anomalies is now recognized as one of the more common forms of autosomal dominant syndromic hearing impairment. Three loci known to be associated with the BOR phenotype have been identified and two genes that act in a regulatory network have been cloned, EYA1 and SIX1. EYA1 and SIX1 are homologous to genes involved in Drosophila eye development, eyes absent gene (eya), and sine oculis (so), respectively. EYA1, a transcriptional co-activator has a conserved, 271-amino acid, C-terminal known as the Eya Domain (ED). SIX1 has two highly conserved domains; a homeodomain (HD) and a specific Six-domain (SD) whose products function as transcription factors with specific DNA-binding activity that are crucial for protein-protein interaction. To determine the molecular basis for the organ defects that occur in BOR syndrome, many studies have focused on the effects of mutations to EYA and effects of mutations of the EYA-SIX regulatory system. However, over 60% of BOR syndrome patients do not have known mutations in EYA1 and relatively little is known about mutations to SIX1. Further evaluation of SIX1 and its related target genes may provide a better understanding of the pathophysiology of BOR syndrome and offer greater clues to the disease mechanisms.
Asunto(s)
Síndrome Branquio Oto Renal/genética , Síndrome Branquio Oto Renal/patología , Predisposición Genética a la Enfermedad/genética , Proteínas de Homeodominio/genética , Humanos , Péptidos y Proteínas de Señalización Intracelular/genética , Mutación , Proteínas Nucleares/genética , Proteínas Tirosina Fosfatasas/genéticaRESUMEN
Genetic testing was completed on 1,294 persons with deafness referred to the Molecular Otolaryngology Research Laboratories to establish a diagnosis of DFNB1. Exon 2 of GJB2 was screened for coding sequence allele variants by denaturing high-performance liquid chromatography (DHPLC) complemented by bidirectional sequencing. If two deafness-causing mutations of GJB2 (encoding Connexin 26) were identified, further screening was not performed. If only a single deafness-causing mutation was identified, we screened for the g.1777179_2085947del (hereafter called del(GJB6-D13S1830); GenBank NT_024524.13) and mutations in the noncoding region of GJB2. Phenotype-genotype correlations were evaluated by categorizing mutations as either protein truncating or nontruncating. A total of 205 persons carried two GJB2 exon 2 mutations and were diagnosed as having DFNB1; 100 persons carried only a single deafness-causing allele variant of exon 2. A total of 37 of these persons were c.35delG carriers, and 51 carried other allele variants of GJB2. Persons diagnosed with DFNB1 segregating two truncating/nonsense mutations had a more severe phenotype than persons carrying two missense mutations, with mean hearing impairments being 88 and 37%, respectively (P < 0.05). The number of deaf c.35delG carriers was greater than expected when compared to the c.35delG carrier frequency in normal-hearing controls (P < 0.05), suggesting the existence of at least one other mutation outside the GJB2 coding region that does not complement GJB2 deafness-causing allele variants.