Most extensive analysis of genes unlocks secrets

Reproductive discoveries come from DNA of 140,000 pregnant women

WASHINGTON — Scientists from China and the United States have sequenced and analyzed a portion of the genomes of more than 140,000 pregnant women in China, the largest-scale genetic analysis of Chinese people to date. The work revealed associations between genes and reproduction, including the birth of twins and a woman’s age at first pregnancy.

The study published on Thursday in the journal Cell also allowed researchers to reconstruct the intermarriage of different ethnic groups in China, and promised to help identify genes that make people susceptible to infectious diseases.

Researchers from BGIShenzhen used data from noninvasive prenatal testing to sequence randomly 6 to 10 percent of each mother’s genome. BGI stands for Beijing Genomics Institute — the nonprofit research institute was started in Beijing and its headquarters later was moved to Shenzhen.

While this is partial rather than whole genome sequencing, “there’s still a chance that using this data with a large population size will help us to have a much broader vision of what the Chinese genetic population looks like”, according to the study’s co-senior author Xu Xun, from BGI-Shenzhen.

The noninvasive testing, which sequences small amounts of a mother’s DNA, has grown in popularity in China. It has been administered to 6 million to 7 million women.

They found that the variation in a gene called NRG1 was linked to a greater or lesser incidence of twins. One variant of the gene is more common in mothers with twins and is associated with hyperthyroidism.

A variant of another gene, EMB, was associated with older first-time mothers, according to the study.

DNA sequencing of maternal blood also revealed links between viruses and genes that determine susceptibility to disease. A variation in one gene was linked to a higher concentration of herpesvirus 6 in a mother’s blood.

Herpesvirus 6 is the most common cause of the relatively benign baby rash called roseola, but a high “viral load” correlates with more severe symptoms. People with Alzheimer’s disease also have higher levels of herpesvirus 6 in their brains.

“It’s amazing that this is even possible, that you can take these massive samples and do association mapping to see what the genetic variants are that explain human traits,” said co-author Rasmus Nielsen, a professor of integrative biology at the University of California, Berkeley, who oversaw the computational analysis performed by researchers at BGI in Shenzhen.

The study looked at 141,431 participants, including 36 of China’s 55 ethnic minority groups.

“We’re excited about the volume. Our participants represent 1/10,000 of the Chinese population, so it really is large sampling and a good reflection of the entire population,” said co-senior author Jin Xin with BGI-Shenzhen and the South China University of Technology.

The analyses allowed scientists to identify patterns in the evolutionary history of China’s ethnic groups, pinpoint novel genetic centers linked to characteristics like height and body mass index, and to identify viral DNA distributions specific to the Chinese genome, the authors said.

The researchers found many Chinese had genetic variants common among Indians, Southeast Asians and, along the ancient Silk Road, Europeans.