An 11-year-old girl from the Czech Republic was born with genes that camealmost entirely from her father, instead of half from each parent.
Only about 25 people in the world — all girls — have been reported withthis genetic syndrome, and the Czech girl appears to be the first to haveinherited it without developing cancer.
“Ten to fifteen years ago, we didn’t think this condition was compatiblefor life,” clinical geneticist Jennifer Kalish of the Children’s Hospitalof Philadelphia, who was not involved in the new case, told BuzzFeed News.
Kalish heads a lab investigating ways to help children with imprinted genedisorders, conditions in which at least one gene is doubled up from mom ordad. “It doesn’t happen every day,” she said. Russell-Silver syndrome,for example, leads to stunted growth when a child inherits two copies ofchromosome 7 from their mother. Although rare, more of these cases areturning up due to improved genetic testing worldwide.
Researchers found the Czech case because the girl’s parents were trying tounderstand why she was deaf, as reported in April in the Journal of HumanGenetics.
When she was 9 years old, a genetic test revealed that she had two identicalcopies of a rare gene. At first, the scientists thought it was extremelybad luck, inheriting the same super-rare gene twice, once from each parent.
But as it turned out, the rare gene was, “surprisingly, not in her mother,” wrote the scientific team, led by Irena Borgulová of the Centre forMedical Genetics and Reproductive Medicine Gennet in Prague. Which meant shehad inherited two copies of her father''s gene.
Subsequent testing showed that it wasn’t just that one gene — she haddoubled up on her father’s genes in almost all of her chromosomes in mostof her cells.
The girl is not quite a twin of her father, but what’s known as a genetic“mosaic,” showing variation in different tissues. Only about 7% of herblood cells, for example, showed any maternal genes. And 74% of the cells inher saliva held only paternal genes.
Now 11, the girl does bear a telltale sign of the syndrome: one leg longerand thicker than the other, according to the study. The bigger leg just gotmore of the dad-dad genes.
How did this happen? The classic biology class story of a sperm fertilizingan egg in a musical crescendo that has them first unzipping their genes andthen swapping them together to create a “zygote” is a much messier processin reality. In the girl’s case, instead of the DNA from her father’ssperm and mother’s egg pairing up this way, two copies of the father’sgenes zipped together to create a dad-dad set of 23 chromosomes, the fullhuman genome.
For this to happen in small stretches of genes is rare, about 1 in 10,000births. It’s rarer still for it to happen across the entire genome, as itdid in this girl’s case. When the zygote split to create more cells, mostended up with the dad-dad genome.
For the 25 other cases, this doubling resulted in cancer, perhaps becausetheir paternal DNA included double helpings of cancer-prone genes. So farthe 11-year-old has avoided that fate.
Her deafness, though, may have been caused by her plethora of dad-dad genes,though not the gene that the doctors had initially suspected: Double copiesof that gene are found in about 1 in 50 Europeans, with no discerniblehealth effects.
“The cause of the deafness remains unknown,” the study found.
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