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Down Syndrome: The Super Genome

Actualizado: 29 dic 2020


Université de Genève

Down syndrome, also known as trisomy 21, is a genetic disorder caused by a third chromosome 21. Although this genetic abnormality is found in one in every 700 births, only 20% of fetuses with trisomy 21 reach term. But how do they manage to survive the first trimester of pregnancy despite this serious handicap? Researchers have found that children born with Down syndrome have an excellent genome in many ways, better than the average genome of people without the genetic abnormality.

Researchers from the Universities of Geneva (UNIGE) and Lausanne (UNIL) have found that children born with Down syndrome have an excellent genome in many ways, in fact better than the average genome of people without the genetic abnormality. It is possible that this genome compensates for the disabilities caused by the extra chromosome, helping the fetus to survive and the child to grow and develop. You can find more information about these discoveries in the journal Genome Research.

.Trisomy 21 is a serious genetic disorder, with four out of five pregnancies not reaching full term naturally if the fetus is affected. However, 20% of babies with Down syndrome are born alive, grow up and can reach 65 years of age. How is this possible? Researchers from UNIGE and UNIL hypothesized that people born with Down syndrome possess a high-quality genome that has the ability to compensate for the effects of the third chromosome 21

Variation, regulation and expression all proven

"El genoma se compone de todo el material genético que forma un individuo", explica Stylianos Antonarakis, el profesor honorario de la Facultad de Medicina de UNIGE que dirigió la investigación. "Es el genoma el que determina qué se convierte en una persona y lo hace crecer y envejecer, con o sin enfermedad. Algunos genomas son de mejor calidad que otros y también pueden ser menos propensos a enfermedades como el cáncer". Basando su trabajo en la hipótesis de la calidad del genoma, los genetistas probaron la variación, regulación y expresión génica de 380 individuos con síndrome de Down y los compararon con personas sin el trastorno genético.

The first test consisted in observing the presence of rare variants, that this, is potentially harmful genetic mutations, in people with Down Syndrome. It is known that chromosome can have different rare variants in this two copies.In a person with Down syndrome, however, rare mutations that are identical for all three copies of chromosome 21 and are limited in number, thus reducing the total of potentially harmful variants.

In a next step, geneticists have studied the regulation of genes on chromosome 21. Each gene has switches that regulate its expression, either positively or negatively. Since people with Down have three chromosomes 21, most of these genes are overexpressed. "But we found that people with Down syndrome have more regulators that decrease the expression of all 21 genes, which makes it possible to compensate for the surplus induced by the third copy," says Konstantin Popadin, a researcher at the UNIL Center for Integrative Genomics.

Finally, the researchers focused on the expression of the variant gene for the chromosomes of the entire genome. Each gene expression on a scale of 0 to 100 is part of a global spread curve, with the median - 50 - considered the ideal expression. "For a normal genome, the expressions range between 30 and 70, while for a person with Down syndrome, the curve is narrower around the peak which is very close to 50 for genes on all chromosomes", continues the professor. Antonarakis. "In other words, this means that someone with Down's genome leans toward average and optimal functioning." In fact, the smaller the gene expression variations, the better the genome.

A superior genome that compensates for disability.

Geneticists from UNIGE and UNIL were able to evaluate the three functions of the genomes of people with Down syndrome. "Research has shown that for a child with Down to survive pregnancy and then grow up, its genome must be of higher quality so that it can compensate for the disabilities caused by the extra copy of chromosome 21," Popadin concludes. These conclusions can also be applied to other serious genetic disorders in which pregnancies reach their full term. Story Source: Materials provided by the Université de Genève. Note: Content can be edited for style and length.

Journal reference: Konstantin Popadin, Stephan Peischl, Marco Garieri, M. Reza Sailani, Audrey Letourneau, Federico Santoni, Samuel W. Lukowski, Georgii A. Bazykin, Sergey Nikolaev, Diogo Meyer, Laurent Excoffier, Alexandre Reymond, Stylianos E. Antonarakis. Mildly damaging genomic variants and transcriptomic disturbances in embryonic selection for Down syndrome. Genome Research, 2018; 28 (1): 1 DOI: 10.1101 / gr.228411.117

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