Tissue Disease

 Scurvy
Caused by a lack of vitamin C, this disease affects the connective tissue, leading to abnormal collagen synthesis. This in turns causes people to have bleeding from the gums and other mucus membranes, as well as lethargy and malaise.

Sources:
Picture:
   http://en.wikipedia.org/wiki/File:Scorbutic_gums.jpg
Info:
   http://emedicine.medscape.com/article/125350-overview