What happens to the protein to cause this effect (mutation, over- or under-expression, etc.)?

Pathological effect of montelukast sodium and How is the protein related to disease? What is a disease? What happens to the protein to cause this effect (mutation, over- or under-expression, etc.)? Montelukast sodium is a drug which if it is used incorrectly it causes pathological effects, I want a 100-word effect of it and answer the question above. Please use primary sources as much as possible. Please cite the sources in AMA format. If you have any questions or concerns do not hesitate to contact me. Thank you