rheumatoid arthritis
"To make a fire you need wood and something to light it with. Let's think of the wood like it's your genes. You need the right type of wood (nice and dry) to light a ire."
"Having rheumatoid arthritis is like spraining all your joints at once and having someone wrap them all with tiny heating pads while they force you to move."
I think this would be especially helpful to the just diagnosed person who is probably terrified of the disease if for no other reason than all the "big words." I'd say that Rheumatoid Arthritis is like an "overzealous evangelist preacher - He's trying to fix something he can't see and it wasn't broke in the first place!"

METAMIA is a free database of analogy and metaphor. Anyone can contribute or search. The subject matter can be anything. Science is popular, but poetry is encouraged. The goal is to integrate our fluid muses with the stark literalism of a relational database. Metamia is like a girdle for your muses, a cognitive girdle.