Rare diseases in neurometabolic pathologies

Abstract

Metabolic myopathies are genetic disorders that decrease the capacity of skeletal muscle to use energy substrates and ATP. These disturbances can be classified into three categories: i) disorders of carbohydrate metabolism (glycogen and glucose), ii) defects in lipid metabolism, and iii) dysfunctions of oxidative phosphorylation-OXPHOS-. The first two are caused by enzyme deficiencies involved in the metabolic pathways of degradation and synthesis of carbohydrates and lipids, and although they show distinct clinical manifestations, exercise intolerance is a predominant symptom present in most of them. Although a good number of patients with these muscle disorders display symptoms in childhood, the diagnosis is often delayed until the second and third decades of life. Therefore, recognizing the clinical features of these deficiencies can lead to an earlier diagnosis and better treatment. Mitochondrial diseases are a group of disorders caused by an alteration of the oxidative phosphorylation system, that leads to a deficient synthesis of ATP. This system is composed of proteins codified in the two genetic systems of the cell, the nuclear and mitochondrial genomes, and, therefore, the mode of inheritance could be either Mendelian or maternal. This review will describe the special characteristics of the mitochondrial genetic system and the main mutations in mtDNA that cause human diseases.