The discovery of a large population of long, cell-free DNA (cfDNA) molecules in maternal plasma, along with a method to identify the molecules' tissues of origin, is reported in this week Proceedings of the National Academy of Sciences. To date, studies of circulating cfDNA have focused on short molecules of less than 500 basepairs, leaving cfDNA molecules poorly explored. To investigate, scientists from the Chinese University of Hong Kong applied single-molecule real-time sequencing to maternal plasma samples, revealing a substantial proportion of long DNA molecules from both fetal and maternal sources. The molecules, the team notes, were beyond the size detection limits of short-read sequencing technologies, with the longest fetal-derived plasma DNA molecule being 23,635 basepairs. The scientists also developed an approach that uses the analysis of methylation patterns of the series of CpG sites on a long DNA molecule to determine its tissue origin. This allows the differentiation between fetal and maternal plasma DNA molecules and enables the determination of maternal inheritance and recombination events in the fetal genome. The work, they write, points to the clinical potential of long cfDNA analysis for detecting and monitoring pregnancy-associated disorders.
A polygenic score related to an individual's genetic propensity to acquire education can also be used to help predict who will vote in elections, according to a new study appearing in this week's Proceedings of the National Academy of Sciences. While twin and adoption studies have pointed to a role for genetics in political participation, this research cannot identify the specific genes or pathways involved. To explore this, a team led by New York University's Christopher Dawes examined three genetically informative samples from the US and Sweden, which, combined, include more than 50,000 individuals, to test whether a polygenic score could predict voter turnout. They find that an educational attainment polygenic score is significantly related to self-reported and validated measures of voting, with the strongest associations related to second-order midterm elections in the US and European Parliament elections in Sweden. Such elections tend to be viewed as less important by voters and the media and are more information-poor than first-order elections, they note. A within-family analysis, meanwhile, suggests education-linked genes exert direct effects on voter turnout and reveals evidence of genetic nurture in second-order elections. "Scholars have argued that parental education is the main driver of the reproduction of political inequality across generations," the investigators write. "By separating the effect of genes from parental nurturing, our findings suggest that the roots of individual-level political inequality run deeper than family background."