March 26 (Reuters) - French drugmaker Genfit SA said on Thursday it will begin a late stage trial later this year of its lead treatment for a liver-destroying condition, saying it failed a midstage trial in part due to the prevalence of patients with a mild form of the disease in the study.

The company said had it excluded data from those patients with the mildest form of the disease known as NASH (non-alcoholic steatohepatitis) its drug, called GFT505, would have been deemed effective in reversing the condition. The company said it would likely include only more seriously ill patients in its planned much larger Phase III trials.

GFT505 also demonstrated a favorable effect on metabolic issues, lowering bad LDL cholesterol as well as unhealthy blood fats called triglycerides and levels of blood glucose. NASH has been closely associated with obesity and diabetes.

(Reporting by Ransdell Pierson and Bill Berkrot; Editing by Chris Reese)