Why me? The question I was dreading

Last week, I was prepping my son for his quarterly eye-exam (the doc told us on Jan 19, "I'll see him in 3 or 4 months.") and he finally asked the question I've been dreading ever since he was diagnosed with Coats in July 2007.
He was fussing about the stinging he has to bear because of the eye dilation drops they put into both his eyes when he suddenly blurted: "Why did this happen to me, Mamma?"
I had anticipated this question, but I still didn't have an answer that was convincing.
"Well..." I hesitated, but then decided it was best to simply state the facts. "We don't know, baby. A man called George Coats discovered this condition, but the doctors still haven't figured why it happens."
"Does anybody in our family have it?"
"No, and it doesn't run in families. It just...happens."
"How can something just happen?"
My mind flashed back to the innumberable times when he'd dropped milk/juice/other stubborn liquids on the sofa or left his toy cars on the floor, almost causing a serious skid accident...and I smiled, grateful that I could manage a smile.
"Well, sometimes they just do. Take me...all the joints in the left hand side of my body are kinda loose."
"Loose? How did they get that way?"
"No idea. My left arm broke when the doctors were taking me out of your Grandma's tummy. And I can do some neat tricks with my left thumb. And you already know the doctors put in a screw below my left knee to prevent it from getting dislocated over and over."
He was quiet a bit, then said: "But the eye drops really sting." I was just grateful he's never complained about the cryo-related pain (mostly managed with painkillers and he doesn't remember the psot-op thrashing around).
"I know, baby. And I'm really, really sorry you have to go through that. But you see, the eye drops help the doctor look right into your eyes and see if everything's fine." He needs regular eye exams for the rest of his life, but I didn't feel like saying that out loud just then.
"Did it pain when they put the screw into your knee?"
I gulped - I still freak out a bit when I recall the pain of the dislocation. "No, they put me to sleep when they did that..."
"You had anaesthesia too!"
"Yes, I did. And then they put a cast on my leg with a little window at the knee to check on the stitches."
"Did you have to use a stick to walk?"
"Well, I had to use crutches first. And the first time I lowered my leg from the bed after the surgery, it was so painful that I had tears flowing down my face although I didn't mean to cry."
And then I told him about how I had stood there, at the foot of my bed, refusing to budge for God knows how long, hanging on to the railing for dear life. How I had finally taken three steps and was ready to collapse, too exhausted to climb back into bed. How I had learnt to walk, first with two crutches, then with one and then with a walking stick, and how my knee wouldn't bend much in the first few months so I would upturn a waste basket to rest my leg on at my very first job. And how I had one day phoned my doctor, without letting my mother know, and asked him if I would ever be able to fully bend my left knee again. "It will take time. Have faith," said my surgeon.
With Coats, time is not part of the equation.
Faith is all we have.
That's what I told my son: We may not know why, but we do have faith in the Almighty.
He nodded his head and cuddled up to me to go to sleep.

Munchkin's eye exam has been delayed to mid-May because his specialist is away attending a conference in Florida.