I am so sorry to hear this, it's hard finding out you have any illness at any age, but it seems like it's worse hearing the age of someone so young.
I have a son who was born with a Primary Immune Deficiency and one of the side effects from it is Juvenal Rheumatoid Arthritis, He developed it at age 2 years with it effecting his knees, hips, fingers and shoulders. At first we could only treat him with prescription liquid Naperson. Now that he is 13 he voices when he he is having trouble and pain better then when he was a baby so they are able to treat him with other meds and they seem to help him be comfortable. Its sad to see a kid not able to pick up a fork or pencle because his fingers are so swollen they look like a Ball Park Frank cooked up!
You are lucky that allot of research has been done and their is allot of options in treatments out their. It sucks when one is young and has to face living the rest of your life with some illness
