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Become familiar with the spectrum of cardiac involvement in mitochondrial diseases (MDs).
Recognise the clinical features of cardiac involvement in MDs.
Understand the current strategy for management of MDs.
Mitochondrial diseases (MDs) include a wide range of clinical entities involving tissues that have high energy requirements such as heart, muscle, kidney and the endocrine system1 (figure 1). Defects in mitochondrial DNA (mtDNA) mutations are the most common cause of MDs in adults.2 ,3 However, the nuclear gene defects are increasingly recognised as a cause of disease.4 Although the true prevalence of cardiac involvement in MD is unknown, cardiovascular involvement presents specific clinical issues that require systematic evaluation. In addition, in some MD-related mutations (eg, m.3243A.G) cardiac disease is the most common cause of early death.5 Hence, cardiologists are likely to become increasingly involved in the multidisciplinary care of patients with MD.
Genetics of mitochondria and MD
A detailed description of the genetics of the mitochondria is beyond the scope of this review, but the general principles are summarised in box 1.
Biology and genetics of mitochondria
Structure and function
Mitochondria have two genomes: the mitochondrial (mtDNA) and the nuclear genome (nDNA).
mtDNA contains 37 genes, 28 on the H-strand and 9 on the L-strand. Thirteen of the genes encode one polypeptide component of the mitochondrial respiratory chain (RC).
nDNA encodes components of oxidative phosphorylation system, and over 35 proteins required for the RC assembly (complex I=11 nDNA assembly factors, complex III=2 assembly factors, complex IV=18 assembly factors and complex V=4 assembly factors).
mtDNA is maternally inherited
nDNA inheritance pattern is Mendelian (dominant and recessive)
Homoplasmy (copies of mtDNA are all identical)
Cells contain thousands of molecules of mtDNA.
In the majority of cases their sequence is identical
Heteroplasmy (multiple mtDNA variants …
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