Interim head coach Rob Howley will go into next week's opening round game against Ireland at the Millennium Stadium without the services of specialist locks Alun Wyn Jones, Luke Charteris and Bradley Jones, as well as second row cover
Ryan Jones. In addition, he is awaiting a fitness report on Ian Evans to see if he will be fit for 2 February.
His only other lock options are the uncapped Dragons forward Andrew Coombs, former Wales Under 20 back row man James King or two other back row men, Aaron Shingler and Josh Turnbull.
With more than 100 appearances for the reigning English Premiership champions, who recently ended the Heineken Cup Pool stages as No 1 seeds with an unbeaten run of six games, Kohn has a lot of top-class experience
"We looked at Olly when we initially selected the Six Nations squad and we have brought him in now as we believe he will be an experienced addition. He has been performing very well for Quins and has been a feature in their pack," said Howley.
"He's a strong ball carrier and dominant at the set piece and it will be good to see him in the international environment."
Kohn wil join the Welsh camp on Sunday and could win a first cap six days later as Wales seek to make it four wins in a row over the Irish.
"Receiving the call up was surreal and I can't wait to join up with the squad this weekend. It's a really proud moment for me and a great opportunity to show what I can do," said Kohn.
"It will be good to meet the squad, get training and hopefully be part of a successful Six Nations campaign with Wales. My grandfather was a massive Welsh rugby fan.
"I remember sitting in the house and there was my dad cheering for England and my grandfather going nuts for Wales. That's my Welsh connection.
"I've been at Harlequins for seven years now and I'm enjoying my rugby playing well in a good team and I'd be honoured to play for Wales.
"I'm playing week-in, week-out in a top Premiership team who play a good style of rugby all across the park and we've just qualified for the quarter-finals of the Heineken Cup. I'm pleased about my form and where my rugby's at and I think I've definitely got something to offer.
"I don't know if people were aware of my Welsh connection because with a name like Kohn, a lot of people can mistake for German or South African. In fact the name's Czech, from the other half of the family."