Friday April 15 2011
The study aimed to identify genes involved in the timing of birth
Scientists have discovered “a gene linked to premature birth”, BBC News reported.
This research investigated the genetic factors that may underlie the duration of human pregnancy and time of birth. The researchers’ theory was that human premature birth is associated with the evolution of the species. They looked at which genes show more variation in their DNA sequence in humans than in other primates. Of these genes with “accelerated evolution”, they selected 150 that could be associated with pregnancy and birth. These genes were then examined in a sample of 328 Finnish mothers. Certain DNA sequence variants in one gene, known to be involved in the release of an egg from the ovary, were found more often in women who had had a premature birth.
The research is an important step in understanding how genetic and environmental factors contribute to disease risk. The researchers hope this may lead to ways of predicting women’s risk of preterm birth. However, this is very early research and this association has only been examined in a very small sample of women. Other genes may be involved and there are many other medical, health and lifestyle factors associated with preterm births. These include smoking, having multiple pregnancies (for example twins), infection and conditions of the uterus or cervix.
Where did the story come from?
The study was carried out by researchers from Vanderbilt University School of Medicine, Tennessee, and many other institutions in the USA and Finland. Funding was provided by several sources including grants from the Children’s Discovery Institute at Washington University School of Medicine and St. Louis Children’s Hospital. The study was published in the peer-reviewed scientific journal Plos Genetics.
The BBC has accurately reflected the findings of this study.
What kind of research was this?
This research investigated the theory that genes that control the regulation of pregnancy, labour and birth are among those that are most evolved in humans, compared with other primates. The researchers surmise that these genes also affect the risk of premature birth. The human brain and head are large relative to the size of the body, including the size of the pelvis. Because the increase in human head size happened relatively quickly in evolutionary terms, the genes that control timing of birth must have evolved rapidly to allow babies to be born sooner, ensuring they would be born safely. It is for this reason, the researchers suggest, that human babies are less well developed when they are born than other primates.
The study involved several stages. First, the researchers attempted to demonstrate that, compared with other primates and mammals, the length of human pregnancy is shorter than expected. They theorise that this is because it has been subject to evolutionary change. Second, the researchers aimed to identify candidate genes that could be involved in the timing of birth.
What did the research involve?
The researchers began by examining various data sources that discussed the adaptations and changes that have occurred in humans compared with other primates (including earlier closely related species, such as Neanderthals). They were particularly interested in research looking at the large size of the human brain relative to body size, and the fact that the length of pregnancy is shorter in humans.
The researchers then used a genetic database that contained genetic information for humans and various other primates and mammals. They looked at which human genes showed the most variation in their DNA sequence compared with similar genes in other species. They looked at regions of the DNA that produce (code for) proteins and also at non-coding sections of DNA.
From this data, they selected a subset of 150 candidate genes that were likely to be involved in pregnancy and birth. They then looked at the genetic make-up of 328 Finnish mothers (165 who had had a premature birth), to look at single letter sequence changes (known as single nucleotide polymorphisms or SNPs) in their DNA at 8,490 sites within these 150 candidate genes.
What were the basic results?
The researchers found 10 SNPs showed the most association with prematurity, and eight of these were located in the FSHR (follicle stimulating hormone receptor) gene, which is involved in the release of an egg from the ovary. They say that other studies have made associations between variations in this gene and subfertility.
Further assessment in a sample of 250 African American women (79 who had premature babies, 171 controls) found significant associations between three of these SNPs in the FSHR gene and premature birth. They found the trend was not significant in other populations, for example European Americans or Hispanic Americans, but highlighted that this may have been due to the small sample size that was tested.
How did the researchers interpret the results?
The researchers concluded that the variations they have identified in the FSHR gene could influence the risk of premature birth. They say that, currently, the “understanding of pathways for birth timing in humans is limited, yet its elucidation remains one of the most important issues in biology and medicine”.
They consider that their “evolutionary genetic approach” could assist further investigation into premature birth, and may be applied to the study of other diseases.
The current study was small and largely concerned with testing the researchers’ theories. The evolutionary genetics technique used in this study identified a gene that may be involved in the timing of birth, which had not previously been implicated.
As the authors say, genome-wide association studies that are used to find genes associated with health conditions need to be carried out in large numbers of subjects, allowing several statistical comparisons to be made. They say that their method can also be used to identify candidate genes.
However, so far, this genetic association has only been examined in a very small sample of women and requires further follow-up. Other genes and gene sequences may be involved and, even then, genetics is very unlikely to provide the whole answer to prematurity. There are many other medical, health and lifestyle factors known to be associated with the risk of having a preterm baby, such as smoking, having multiple pregnancies (for example twins), infection and conditions of the uterus or cervix.
The study is an important step forward in “evolutionary genetics” and understanding how genetic and environmental factors may contribute to disease risk. The researchers hope this may pave the way for tests that could predict which women are at higher risk of preterm birth. However, this is very early research, and if it is possible to test for the risk of having a premature baby, much further study will need to take place first. This research will also need to take into account all of the other risks and benefits that have to be considered with any genetic testing.