Depression among Adolescents: Measurement and diagnosis, Environmental factors, and Genetics

Depression is a common disorder and a major cause of disability. The prevalence of depression in adolescents is 12-25%. The use of valid instruments in psychiatric assessment contributes to diagnostic validity and consistency. This thesis is divided into four parts: The first and second parts study the psychometric properties of the MADRS-P and CSDS/CSDSP scales. The scales are adapted to measure symptoms and function in adolescents. In the first part, the psychometric properties of the Montgomery-Åsberg Depression Rating Scale Parent used for the assessment of parent-reported depressive symptoms in adolescents are studied. In the second part, the properties of the Swedish Child Sheehan Disability Scales, in the adolescent and parent versions, are studied. These scales are used to assess levels of function in school, relationships with friends and relationships with family. The properties of the scales were studied in a population of adolescents referred to the child and adolescent psychiatric clinic. The third study analyses the interaction between BDNF rs6265 polymorphism, childhood stress and physical activity in relation to depressive symptoms, showing that the interaction of BDNF rs6265 with childhood stress and physical activity is significant in moderation models. For A allele carriers, physical activity reduces depressive symptoms in youth exposed to childhood stress. In turn, exposure to a higher level of stress increases depressive symptoms in adolescents aged 13 and 15. The minor allele confers plasticity characteristics when interacting with the mentioned environmental factors. The fourth study shows that the interaction of the three factors PER2 rs56013859 , sex and family maltreatment in relation to depressive symptoms is significant in female minor C allele carriers aged 13 and 15 years. The results obtained in this thesis are applicable in the practice of child and adolescent psychiatry, and in the prevention of depressive disorders in the child and adolescent population. La depresión es un trastorno frecuente y una causa importante de discapacidad. La prevalencia de depresión en adolescentes es 12-25% . El uso de instrumentos válidos en la evaluación psiquiátrica contribuye a la validéz y consistencia en el diagnóstico. Esta tesis esta dividida en cuatro partes: En la primera y la segunda se estudian las propiedades psicométricas de las escalas MADRS-P y CSDS/CSDSP. Las escalas estan adaptadas para medir los síntomas y la función en adoles