There have also been attempts to investigate other substances in the treatment of COPD, including inhibitors of enzymes in sphingolipid pathways such as sphingosine kinase, S1P lyase, acid sphingomyelinase, and sphingosine-1-p receptor agonists, but the results are not conclusive [30,31,32]. The gene discussed is SMPD1; the disease is chronic obstructive pulmonary disease.