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  • Heteroplasmy for the 1555A>G mutation in the mitochondrial 12S rRNA gene in six Spanish families with non-syndromic hearing loss

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Heteroplasmy for the 1555A>G mutation in the mitochondrial 12S rRNA gene in six Spanish families with non-syndromic hearing loss
  1. F J del Castillo1,
  2. M Rodríguez-Ballesteros1,
  3. Y Martín1,
  4. B Arellano2,
  5. J Gallo-Terán3,
  6. C Morales-Angulo3,
  7. R Ramírez-Camacho2,
  8. M Cruz Tapia4,
  9. J Solanellas5,
  10. A Martínez-Conde6,
  11. M Villamar,
  12. M A Moreno-Pelayo1,
  13. F Moreno1,
  14. I del Castillo1
  1. 1Unidad de Genética Molecular, Hospital Ramón y Cajal, Madrid, Spain
  2. 2Servicio de ORL, Hospital Puerta de Hierro, Madrid, Spain
  3. 3Servicio de ORL, Hospital Sierrallana, Torrelavega, Cantabria, Spain
  4. 4Servicio de ORL, Hospital Clínico San Carlos - Pabellón 8, Madrid, Spain
  5. 5Servicio de ORL, Hospital Universitario Nuestra Señora de Valme, Sevilla, Spain
  6. 6Servicio de ORL, Hospital Ramón y Cajal, Madrid, Spain
  1. Correspondence to:
 Dr I del Castillo, Unidad de Genética Molecular, Hospital Ramón y Cajal, Carretera de Colmenar, Km 9, 28034 Madrid, Spain; 
 idelcastillo.hrc{at}salud.madrid.org

https://doi.org/10.1136/jmg.40.8.632

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    Hearing impairment is the most prevalent sensory disorder and genetic causes are thought to be responsible for over 60% of the cases in developed countries.1 Inherited hearing impairment is highly heterogeneous from both the clinical and genetic points of view.1,2 It varies in age of onset, severity, and audiological characteristics, and it can be associated or not with other clinical features (syndromic or non-syndromic hearing impairment). Genetic transmission includes autosomal (dominant and recessive), X linked, and maternal inheritance patterns. This unparalleled heterogeneity is well illustrated by the fact that over 70 loci in the nuclear genome have been reported to be involved in non-syndromic hearing impairment, and about 30 genes have been isolated from their critical intervals.3 Furthermore, a number of different mutations in several genes of the mitochondrial genome are responsible for syndromic and non-syndromic forms of hearing loss.4,5

    Mutations responsible for maternally inherited non-syndromic hearing loss are so far confined to only two genes in the mitochondrial genome. These include mutations 7510T>C6 and 7511T>C7 in the tRNASer(UCN) gene, and 1095T>C8 and 1555A>G9 in the gene for the 12S rRNA. This last mutation is responsible for a dual phenotype, since it also confers increased susceptibility to the ototoxic action of aminoglycoside antibiotics.9 Most of these mutations have been reported in a small number of families from several countries, with the exception of 1555A>G, which seems to be more frequent than the others,10–13 although its real prevalence remains to be determined in most populations. Remarkably, in Spain it accounts for about 15–20% of all familial cases of non-syndromic hearing loss, irrespective of their mode of inheritance and age of onset14,15 (our unpublished results). In a majority of these patients, the hearing loss is not …

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