Several studies have shown that certain girls, particularly African-American girls, experience puberty earlier than others, but there’s an ongoing debate about what that might mean. There are a number of reasons why some girls begin puberty earlier than others. Girls who are heavier tend to enter puberty earlier than thinner girls, while there are also disorders that can trigger “precocious puberty”– or puberty before age eight. Environmental factors, such as nutrition and certain chemicals, also can play a role. Understanding the genetic components that influence when a girl begins menstruating – also known as her age at menarche (“men-AR-kee”) – could also help scientists better understand the genetic factors behind diseases associated with early puberty, including type 2 diabetes and breast cancer. But to date, the scientific community has all but overlooked a core population that is perhaps most at risk. Today, African-American women tend to begin menstruating four to six months earlier than girls of European descent. Later in life African-American women also have a higher risk for obesity, hypertension, and metabolic disorders including diabetes. These two trends could be related and genetic factors could be a common denominator. A new study of African-American women looked specifically at genetic variations contributing to age at menarche. The research, done by a multi-institutional team of scientists, crunched data from 15 different studies, which included information from over 18,000 women. Their findings indicate differences in DNA that could help scientists better understand the genetics of menarche timing in all women, as well as the development of diseases associated with early menarche. We’ve written before about the importance of considering ancestry when analyzing trends in disease. Certain diseases are more prevalent in certain populations. For instance, African-American men are more likely to develop and die from prostate cancer than people of European descent. African Americans also tend to be at higher risk for type 2 diabetes, while people of European descent are at higher risk of the heart rhythm disorder atrial fibrillation. Given the difference in risk it seems imperative that researchers investigate a diversity of populations to better understand the genetic factors behind these diseases. Yet research on populations with non-European ancestry continues to lag. In this case study, the researchers performed a meta-analysis of existing research to search for DNA variants associated with earlier menarche in African-American women and then compared their results to data from women of European descent. The variants, called SNPs (or single-nucleotide polymorphisms), can account for some of the differences in biological traits, in this case early menarche, between two individuals. These variants in turn can help scientists identify the genes and biological mechanisms controlling menarche timing. Out of 42 SNPs associated with age at menarche in European women, 25 were also associated with the trait in African-American women, bolstering the evidence that these genes genetic variants are tied to menarche timing. However, they also found variants in eight regions of the genome that were more strongly associated with age at menarche in African-American women than in European-American women. Many of these regions contain genes that influence obesity, underscoring the link between body fat and early menarche. Other regions include genes associated with breast and other cancers. Although this is the largest and most comprehensive study of its kind, the total number of data samples of African-American women available to the researchers was still fewer than are now available for European-American women. And yet the study demonstrates an important fact: by studying diverse ethnicities, scientists can refine their understanding of the role genes play in all populations.