A closer look at a particular recommendation:

Gene: PEMT ( phosphatidylethanolamine N-methyltransferase )

Function: Converts phosphatidylethanolamine to phosphatidylcholine by methylation in the liver.

Here is a diagram of choline metabolism:




Disrupted PEMT function can block the creation of phosphatidylcholine.
http://www.ncbi.nlm.nih.gov/pubmed/1...?dopt=Abstract

23andMe assesses 57 snps on the gene PEMT. Of these, the ones that have been researched to have an impact on choline metabolism are:

rs12325817 http://www.ncbi.nlm.nih.gov/pubmed/1...?dopt=Abstract
rs7946 http://www.ncbi.nlm.nih.gov/pubmed/19167960 (disputed)

PEMT is induced by estrogen, so postmenopausal women have an increased need for choline as their estrogen is low. http://www.ncbi.nlm.nih.gov/pubmed/20861172 In addition, the need is further increased by the rs12325817 polymorphism and ameliorated by choline supplementation. http://www.ncbi.nlm.nih.gov/pubmed/21059658/

The consequences from choline deficiency (and observed with these mutations) are fatty liver and multiple organ dysfunction.

http://www.ncbi.nlm.nih.gov/pubmed/21270363
http://www.ncbi.nlm.nih.gov/pubmed/16002808
http://www.ncbi.nlm.nih.gov/pubmed/22877991

The great news is that supplementation with choline or phosphatidylcholine bypasses this genetic issue.