Main objective: To determine serum GDF-15 and FGF-21 as the potential diagnostic biomarkers for Mitochondrial Respiratory Chain (MRC) disorders through the assessment of their levels due to the metabolic errors associated within association with neurological. Specific objectives: (1) To measure serum GDF-15 and FGF-21 concentration in the high risk patients of MRC disorders (criteria 1) (2) To measure serum GDF-15 and FGF-21 concentration in patients of myopathic but non-mitochondrial (criteria 2) Study design: This is a descriptive study with 3 groups of subjects to be studied, and at least 10 serum samples from newborn to young adults, less than 18 years old from each group. The first group (criteria 1) consists of either diagnosed patients or patients with strong clinical suspicion and fit the inclusion criteria of high risk subjects of mitochondrial disorders.