A study published yesterday in the New England Journal of Medicine has found a higher-than-expected lack of diversity in the human embryonic stem cell lines most in use by researchers.

Researchers at the University of Michigan Center for Stem Cell Biology analyzed 47 stem cell lines, including 22 of the 40 lines approved for federal funding this month by the National Institutes of Health. While up to 700 stem cell lines are thought to exist, those the researchers looked at have been used in most published stem cell papers to date.

The researchers, stem cell scientists Sean Morrison and Jack Mosher and population geneticist Noah Rosenberg, genotyped the genome-wide single nucleotide polymorphisms (SNPs) in each of the 47 lines, and then compared them with the genomes of a reference set of subjects of known ancestry from the HapMap Project and the Human Genome Diversity Project.

“We found that most lines clustered primarily with subjects of northern and western European ancestry. The remaining lines clustered with Middle Eastern and southern European populations,” the researchers write, adding that “none of these lines derive from populations with recent African ancestry.”

They argue that efforts from here on out to derive new lines should focus on under-represented populations. The lack of diversity to date, says Morrison in this press release from the University of Michigan, “highlights an important social justice issue.”

If you have NEJM access, you can view details about the 47 lines in the paper’s supplementary appendix here.

A look at the lines reveals that 35 are from the United States and that, among these, nine have elements of South European and/or Middle Eastern ancestry, while the rest derive from Northern and Western Europe. The two East Asian lines are from Singapore.

To compare this list against lines approved this month for federal funding under President Barack Obama’s newly liberalized policy, see NIH’s registry of eligible lines here.