Respiratory disorder (6)
I believe the answer is:
asthma
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">respiratory disorder</span>' is the definition.<br/ ><span class="explanation-format__explanation">(asthma is a kind of respiratory disorder)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for asthma that I've seen before include "Respiratory disease" , "Mat has a breathing disorder" , "Breathing problem" , "Chest disorder" , "Distressing ailment affecting breathing" .)