When Does A Difference Become A Diagnosis?

Hanif Kureishi's son, who had trouble with reading and writing, has been diagnosed as dyslexic and dyspraxic. Kureishi asks:

[C]an the inability to do a particular thing be described as a "condition" at all? Would the fact that I can’t do the tango, read music or speak Russian be considered a "condition"? Is it a failure of my development? Am I ill?

Will Wilkinson sympathizes:

I've been diagnosed with a fairly serious case of "adult ADHD," but I am convinced that this is mostly a hand-waving, pseudo-scientific way of saying that my constitution leaves me ill-suited to perform certain tasks under certain conditions. And it turns out that many of the opportunities available to people with my interests and education require performing those tasks under those conditions. This mismatch between these opportunities and my–what's the gee-whiz word?–my neurotype is the problem, not my neurotype per se. There is nothing really wrong with me.