Occurring in about one per eight hundred births, Down syndrome - or trisomy 21 - is the most frequent genetic cause of intellectual disability. It results from a chromosomal abnormality where cells of affected individuals contain a third copy of chromosome 21 (1% of the human genome). A study conducted by Stylianos Antonarakis and his team in the Department of Genetic Medicine and Development at the University of Geneva (UNIGE) Faculty of Medicine, published in Nature, shed light on how the extra chromosome 21 upsets the equilibrium of the entire genome, causing a wide variety of pathologies.
Despite much research, the exact mechanisms causing the various symptoms associated with Down syndrome remain a mystery. According to a hypothesis called gene dosage disequilibrium, the presence of a third chromosome 21 could influence the expression of all the other genes in the genome. That is, this extra genetic material could disrupt the process through which information carried in the genes is decoded, therefore modifying the cellular function.
Based on this hypothesis, several research groups have tried, so far without success, to identify changes in gene expression within trisomic cells and link them with symptoms seen in patients. However, as the level of most gene expression varies from one person to another, it is extremely difficult to discriminate between changes exclusively linked to trisomy 21 and those due to natural variation between individuals.
Comparing Identical Twins
At UNIGE, Stylianos Antonarakis's team has the unique opportunity to examine the genomes of two identical twins with the exact same genetic makeup, except for an extra chromosome 21 present in one of them. Indeed, the chromosome 21 distribution error can take place during an early cellular division, after the original fertilized egg splits in two.
To compare gene expression levels between the twins, UNIGE researchers used recent, high-throu
|Contact: Stylianos Antonarakis|
Universit de Genve