Introduction. Primary mitochondrial disorders (PMD) are a heterogeneous group of multisystem disorders that mostly involve severe nervous system manifestations. This phenomenon can be explained by the increased need of neurons for energy, a proces that is affected in mitochondrial diseases. Aim of the study. Understanding the neuropathogenesis and recognisint the early symptoms in order to facilitate the diagnosis of patiens with PMD, through a clinical case study. Methods. The study was conducted by reviewing the literature and describing the clinical case of a 3-year-old girl with MELAS syndrome. Results. A 3-year-old girl, presented to the hospital with the following complains: superior paraplegia, balance disorders, aphasia. From the history of the disease: at one year and 8 months on the background of pneumonia, she develops the first convulsive crisis for which anticonvulsivant drugs are administered. Clinically it manifested by right hemiparesis and motor dysphasia. Cerebral MRI showed signs of ischemic stroke with postischemic encephalomalacia, and left cerebrovascular malformation. After about a year, based on the results of next generation sequencing by target panels (pathogenic variants m.3243A>G, m.3271T>C in the MT-TL1 gene and m.13513G>A in the MT-ND5 gene) and the multisystemic affect, the diagnosis of mitochondrial encephalopathy, MELAS syndrome with multisystemic affect is confirmed based on the clinical manifestations as well as the genetic test (m.3243A>G). In the process of following the patient, other diagnoses were evaluated and excluded. Conclusions. The neurogenetic aspects of mitochondrial disorders involve cognitive impairment, neurodevelopmental disorders, especially when the symptoms start early. At the same time, vascular or convulsive episodes can cause brain damage with the subsequent impairment of central and peripheral nervous system functions. Thus, CNS involvement requires a thorough study of symptoms for early detection and effective management.