The aim of our project was to find the relationship of plasma thromboxane B2, brain-derived neurotrophic factor, homocysteine, and serum vitamin D levels with the depression severity, the omega-6/omega-3 FA ratio, serum EPA, and DHA concentrations in depressed children and adolescents (the secondary outcomes), as well as their comparison with healthy controls. The gene discussed is BDNF; the disease is depressive symptom measurement.