My DS used to love playing with magnetic letters and was obsessed with spelling around 2y6m - he'd be forever asking how particular words were spelt and could spell many words, and consistently work out what letter words started with (modulo vagueries of English!). He'd also make very long sequences of letters and ask what they said (he knew very well they weren't real words, but he thought it was hilarious when people agreed to attempt to pronounce them for him). I'm pretty sure everything he did was closely connected with the use of letters to communicate, not "just" sequencing. I don't remember him copying written words, but that might just be because as an only child he didn't have too much difficulty in capturing an adult to tell him how to spell words he wanted to spell!
Don't know whether that helps at all. FWIW I think classifying traits as ASD or GT can be very tricky, and may not always be useful!
