Author + information
- Received November 21, 2002
- Accepted January 22, 2003
- Published online May 21, 2003.
- Robert W Taylor, PhD*,
- Carla Giordano, MD†,
- Mercy M Davidson, PhD†,
- Giulia d’Amati, MD, PhD‡,
- Hugh Bain, MD§,
- Christine M Hayes, BSc*,
- Helen Leonard, MD§,
- Martin J Barron, PhD*,
- Carlo Casali, MD, PhD∥,
- Filippo M Santorelli, MD¶,
- Michio Hirano, MD†,
- Robert N Lightowlers, PhD*,
- Salvatore DiMauro, MD† and
- Douglass M Turnbull, MD, PhD*,* ()
- ↵*Reprint requests and correspondence:
Prof. Douglass M. Turnbull, Department of Neurology, The Medical School, Framlington Place, University of Newcastle upon Tyne, Newcastle upon Tyne, NE2 4HH, United Kingdom.
Objectives The purpose of this study was to understand the clinical and molecular features of familial hypertrophic cardiomyopathy (HCM) in which a mitochondrial abnormality was strongly suspected.
Background Defects of the mitochondrial genome are responsible for a heterogeneous group of clinical disorders, including cardiomyopathy. The majority of pathogenic mutations are heteroplasmic, with mutated and wild-type mitochondrial deoxyribonucleic acid (mtDNA) coexisting within the same cell. Homoplasmic mutations (present in every copy of the genome within the cell) present a difficult challenge in terms of diagnosis and assigning pathogenicity, as human mtDNA is highly polymorphic.
Methods A detailed clinical, histochemical, biochemical, and molecular genetic analysis was performed on two families with HCM to investigate the underlying mitochondrial defect.
Results Cardiac tissue from an affected child in the presenting family exhibited severe deficiencies of mitochondrial respiratory chain enzymes, whereas histochemical and biochemical studies of the skeletal muscle were normal. Mitochondrial DNA sequencing revealed an A4300G transition in the mitochondrial transfer ribonucleic acid (tRNA)Ilegene, which was shown to be homoplasmic by polymerase chain reaction/restriction fragment length polymorphism analysis in all samples from affected individuals and other maternal relatives. In a second family, previously reported as heteroplasmic for this base substitution, the mutation has subsequently been shown to be homoplasmic. The pathogenic role for this mutation was confirmed by high-resolution Northern blot analysis of heart tissue from both families, revealing very low steady-state levels of the mature mitochondrial tRNAIle.
Conclusions This report documents, for the first time, that a homoplasmic mitochondrial tRNA mutation may cause maternally inherited HCM. It highlights the significant contribution that homoplasmic mitochondrial tRNA substitutions may play in the development of cardiac disease. A restriction of the biochemical defect to the affected tissue has important implications for the screening of patients with cardiomyopathy for mitochondrial disease.
☆ This work was supported by grants provided to Drs. Turnbull and Lightowlers from the Wellcome Trust, U.K., to Dr. Davidson from the American Heart Association, and to Dr. Giordano from Telethon-Italia.
- Received November 21, 2002.
- Accepted January 22, 2003.
- American College of Cardiology Foundation