**11. Kearns-Sayre syndrome**

The Kearns-Sayre syndrome (KSS) is characterized by the triad: onset of the disorder before the age of 20, progressive external ophthalmoplegia and pigmentary retinopathy. A cerebro‐ spinal fluid protein concentration greater than 100 mg/d, and a commonly elevated lactate and pyruvate concentrations in blood and cerebrospinal fluid are found.

The KSS has cardiac involvement with conduction defects such as right bundle branch block, left anterior hemiblock or complete A-V block. These patients can develop a cardiomyopathy usually dilated (Roberts, 1979; Anan, 1995; Carrasco, 2005).

#### **11.1. MELAS**

It is a multisystem disorder with onset in childhood with mitochondrial encephalomyopathy, lactic acidosis, and recurrent stroke-like episodes. The variability of symptoms and the severity of the syndrome make it difficult to confirm the diagnosis. MELAS is transmitted by maternal inheritance.

The cardiac involvement is considered to be 18–100% (Hirano, 1994; Vydt, 2007; Wortmann, 2007). The first symptom the affected children have is the cardiomyopathy. The most common feature is a hypertrophic cardiomyopathy, although dilation has also been reported (Okajima, 1998).

Mutations in the nuclear genes that also encode mitochondrial proteins can cause cardiomyo‐ pathies. These disorders are sometimes not considered among the group of mitochondrial primary disorders. Two of the most well known disorders are Friedreich´s ataxia and Barth syndrome (de Jonge, 2011).

Friedreich´s ataxia is an autosomal recessive disorder. Frataxin, the protein encoded by *FXN,* is involved in the mitochondrial transport and is needed for the synthesis of the enzymes of the respiratory chain complexes I – III and aconitase. When the protein is mutated in Friederich ´s ataxia, it does not allow the correct respiratory function.

Barth syndrome is a recessive X-linked inherited disease chacterized by cardiomyopathy and neutropenia. The cardiac disease presents a dilated cardiomyopathy, often with a degree of left myocardial thickening and, sometimes, endocardial fibroelastosis. The cardiac disease appears at birth or in the first few months of life

Mutations in the tafazzin gene are to be held responsible for this disorder because of the inhibition of this pathway leads to changes in mitochondrial architecture and function (Spencer, 2006, Schamme, 2006).
