What causes marionette lines

[Klasik616]

I have a bit of nasolabial folds but my mouth which is slighty turned down creates a fine line below the mouth that continues the nasolabial line. What bone is lacking here? It's a lack of facial fat, muscles or bones? My mouth area seems to lack support compared to other users I know.

 

[Spookybah]

It's either an aging issue or has to do with receding mandible/SFS.