New method can detect birth defects from maternal blood sample

Robin Wulffson MD's picture
genetic testing, birth defects, fetal genome, amniocentesis, blood test
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Genetic analysis of fetal DNA is currently available via an amniocentesis or chorionic villus sampling. Both tests are invasive procedures that pose a small - bur definite - risk of fetal harm. Now, Stanford researchers have developed a method that is completely without risk. They were able to sequence the entire fetal genomes using only a sample of the mother’s blood.

The researchers published their findings on July 4 in the journal Nature.

The investigators note that their method is related to research that was reported last month from the University of Washington. That research used a technique previously developed at Stanford to sequence a fetal genome using a blood sample from the mother, plus DNA samples from both the mother and father. In contrast to the aforementioned technique, the genome sequencing procedure developed at Stanford does not require DNA from the father; this represents a significant advantage for instances in which the fetus’s true paternity may not be known. This situation is not uncommon; it occurs in up to 10% of births in the United States.

The new method also allows testing in cases in which the father is unavailable or unwilling to provide a sample. The investigators note that it brings fetal genetic testing one step closer to routine clinical use.

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“We’re interested in identifying conditions that can be treated before birth, or immediately after,” noted Stephen Quake, PhD, the Lee Otterson Professor in the School of Engineering and professor of bioengineering and of applied physics. He added, “Without such diagnoses, newborns with treatable metabolic or immune system disorders suffer until their symptoms become noticeable and the causes determined.” Quake is the senior author of the research. Former graduate student H. Christina Fan, PhD, now a senior scientist at ImmuMetrix, and current graduate student Wei Gu are co-first authors of the article.

Not surprisingly, the new technology comes with a high price tag; however, the researchers note that the cost should continue to drop over the next few years. They predict that the procedure will become an increasingly common method of diagnosing genetic defects within the first trimester (first three months). In addition, they have found that sequencing just the exome (the coding portion of the genome) can provide clinically relevant information.

The investigators reported that they were able to use the whole-genome and exome sequences, which they obtained, to determine that a fetus had DiGeorge syndrome; this syndrome is caused by a short deletion of chromosome 22. The exact symptoms and their severity can vary among affected individuals; however, it is associated with cardiac abnormalities, neuromuscular problems, ands cognitive impairment. Newborns with the condition can have significant feeding difficulties, heart defects and convulsions due to excessively low levels of calcium.

A small amount of fetal blood finds its way into the maternal circulation; thus, locating fetal DNA in a sample of the mother’s blood is the foundation of this procedure. The new test should become commonplace once the cost approaches—or even falls below—that of an amniocentesis or chorionic villus sampling.

Reference: Stanford School of Medicine

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