Correction to: European Journal of Human Genetics advance online publication, 14 October 2009; doi:10.1038/ejhg.2009.177

Since the publication of the above paper, the authors noticed that there are some errors in the Appendix affecting the sense of this paper.

(1) In the lines just below the first equation in the Appendix (page 5), xi and zi should be xi and zi.

(2) In the paragraph just below Equation (A1) in the Appendix (page 5):

• should be

• should be

• should be

The authors would like to apologise for this mistake.