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Online mutation report
Characterisation of repeat and palindrome elements in patients harbouring single deletions of mitochondrial DNA
  1. A Solano1,
  2. J Gámez2,
  3. F J Carod3,
  4. M Pineda4,
  5. A Playán1,
  6. E López-Gallardo1,
  7. A L Andreu2,
  8. J Montoya1
  1. 1Departamento de Bioquímica y Biología Molecular y Celular, Universidad de Zaragoza, Zaragoza, Spain
  2. 2Centre d’Investigació en Bioquimica i Biologia Molecular, Hospital Universitari Vall d’Hebron, Barcelona, Spain
  3. 3Servicio de Neurología, Hospital Sarah, Brasilia, Brasil
  4. 4Servei de Neuropediatria, Hospital Sant Joan de Déu, Barcelona, Spain
  1. Correspondence to:
 Dr A L Andreu, Centre d’Investigació en Bioquimica i Biologia Molecular, University Hospital Vall d’Hebron, P Vall d’Hebron 119–129, 08035 Barcelona, Spain; 
 tandreu{at}hg.vhebron.es

https://doi.org/10.1136/jmg.40.7.e86

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    Single deletions of mitochondrial DNA (mtDNA) were the first pathogenic mutations to be identified in human mtDNA. In a seminal paper, Holt et al1 reported the presence of single deletions of the mitochondrial genome in patients presenting with mitochondrial myopathies, and since then, the field has experienced enormous progress. To date, 97 different deletions have been reported in MITOMAP, the main international database for mtDNA related disorders (www.mitomap.org), and most of these deletions are associated with two clinical presentations: chronic progressive external ophthalmoplegia (CPEO) and Kearns-Sayre syndrome (KSS). Here, we report the molecular characterisation of a series of 18 patients in whom we have identified single deletions of mtDNA. These patients were, as expected, diagnosed with CPEO and KSS. Deletions were identified and measured by Southern blot analysis and were mapped by long polymerase chain reaction (PCR) to locate the deletion breakpoint. We report nine novel deletions and defined their characteristics in terms of sequence of the tandem repeat, presence of palindrome sequences, length of the deleted molecule, and heteroplasmy level in muscle.

    METHODS

    Patients

    The 18 patients included in this study were clinically diagnosed with CPEO (10 patients) and KSS (eight patients), and there was no evidence of maternal inheritance. CPEO was defined by the presence of ophthalmoplegia, ptosis, and proximal limb weakness. Patients with KSS presented with the invariant triad of: (1) onset before 20 years, (2) progressive external ophthalmoplegia; and (3) pigmentary retinopathy, plus at least one of heart block, cerebellar syndrome, or a protein concentration in cerebrospinal fluid above 100 mg/ml. Muscle biopsies were performed after informed consent.

    Molecular genetic studies

    Blood DNA was extracted from peripheral blood cells by conventional methods, and muscle DNA was obtained from 10 mg of muscle after treatment with proteinase K and extraction with phenol/chloroform/isoamyl alcohol. Southern blot analysis was performed using 5 μg …

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