The present invention relates to a method for treating pulmonary alveolar proteinosis related to MARS gene mutations in a subject in need thereof comprising a step of administering said subject with a therapeutically effective amount of supplementation of methionine and/or its derivatives. Pulmonary alveolar proteinosis related to mutations in the gene encoding the methionine tRNA synthetase is a severe, early-onset lung disease that also associates liver involvement, failure to thrive, and systemic inflammation. Inventors describe an infant affected by this disease who was successfully treated by oral methionine supplementation. After three months of treatment she was free of respiratory symptoms, inflammation and cholestasis resolved, and there was a catchup in growth. Her bronchoalveolar lavage fluid was free of extracellular lipoproteinaceous material. Functional assays on peripheral monocytes, initially altered, normalized. This study paves the way for similar strategies in other tRNA synthetase deficiencies.