Hi WD
Try not to worry about this. It sounds as if you have already done the sensible thing and told them that your disability limits your communication abilities, both oral and written. If you have a friend or relative who can write a letter which could be included with your form, saying they have witnessed your difficulties with communication, that can be useful (but don't worry if you don't).
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems