My lab has done lipoprotein Mendelian randomization. It is certainly a useful technique. The article linked here doesn't really address any of the technique's shortcomings, and those are important to know. For example, population stratification can affect your conclusions, and pleiotropy can lead to biased enrollment. For more info, see (free article) <a href="http://aje.oxfordjournals.org/cgi/content/full/163/5/397" rel="nofollow">http://aje.oxfordjournals.org/cgi/content/full/163/5/397</a>