McGrath, J J
Wray, N R
Pedersen, C B
Mortensen, P B
Greve, A N
Petersen, L
Article History
Received: 27 February 2014
Revised: 28 May 2014
Accepted: 2 June 2014
First Online: 22 July 2014
Competing interests
: The authors declare no conflict of interest.