Properly speaking, it's "An high IQ can harm communication with lower IQs."
If you can understand that.
[Grin!]
Funny how the English laugh at our ‘English’ Grammar rules.
Utter disdain.
No wait — ‘udder disdain’.
That’s better, isn’t it?
I thought the an went with the vowel sound, and the h in high is a hard h. I was taught that was an A situation. Gonna have to go read my Strunk.
Use a before words that start with a consonant sound and an before words that start with a vowel sound. Other letters can also be pronounced either way. Just remember it is the sound that governs whether you use a or an, not the actual first letter of the word.
From GrammarGirl.com