Following on from the mapping of a fetal genome from blood and saliva samples from both parents, researchers have sequenced the fetal genome from an unborn baby from a blood sample from the mother alone, opening up the potential for tests for genetic biomarkers without risky fetal tissue sampling, even when the father's DNA is unavailable.
The difficulty faced by the researchers, from Stanford University, was the issue of separating fetal and maternal DNA, made especially hard if both share the same genetic abnormality. The researchers compared the relative levels of the maternal DNA (found in both the mother's and the baby's DNA) and the paternal DNA (found in the baby's DNA only). By doing this, they could identify the DNA from the baby and isolate it for sequencing.
The team sequenced the fetal DNA circulating in the blood of two women, one with an inherited disorder, DiGeorge syndrome, the other without. In this condition, caused by a short deletion of chromosome 22, newborn babies have heart and immune system problems, feeding and learning difficulties and issues caused by low calcium levels, but early treatment can help with many of the symptoms. The sequencing process showed that the child of the woman with DiGeorge syndrome also had the condition, which was confirmed by umbilical cord blood sequencing after birth.
Study co-author Yair Blumenfeld said: "This important study confirms our ability to detect individual fetal gene defects simply by testing mom's blood." The next step is to develop the technology for use in the clinic.
One of the advantages of this technique is that it uses only samples from the mother--in some cases, the father is not willing to give a DNA sample, and in as many as around 1 in 10 pregnancies, paternity is not known. While there will always be ethical concerns that more fetal genetic tests could lead to abortions of children with treatable conditions, or children that could lead happy and productive lives despite disabilities. The flip side is, early diagnosis of many genetic disorders can support immediate treatment, improving the outcomes for many children.
"We're interested in identifying conditions that can be treated before birth, or immediately after," said Stephen Quake of the School of Engineering. "Without such diagnoses, newborns with treatable metabolic or immune system disorders suffer until their symptoms become noticeable and the causes determined."
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