A study using zebrafish sheds new light on the causes of the congenital heart defects associated with a rare developmental disorder, claim researchers from the University of Otago in New Zealand.

The disorder, Cornelia de Lange Syndrome (CdLS), is estimated to occur in up to one in 10,000 births worldwide, according to the team. Approximately 70 percent of people with CdLS have congenital heart defects, and the disorder leads to a range of developmental physical and cognitive anomalies.

According to the new study published in the international journal Human Molecular Genetics, the mechanisms leading to heart defects in CdLS have been poorly understood to date. CdLS is reportedly caused by mutations in sub-units or regulators of cohesin, a group of linked proteins necessary for cell division and other cell processes.

The team used zebrafish, a tropical freshwater fish popularly sold for display in aquariums, which is found to have a genetic structure close to humans. About 70 percent of human genes turn out to have a zebrafish counterpart, and 84 percent of genes that cause disease in humans have zebrafish analogues, according to an article in The Guardian. As a result, scientists are using the fish for various medical studies, such as determining the functions of human genes.

“Through our new study, we show that lowering levels of a particular cohesin protein called Rad21 in embryonic zebrafish produces similar types of heart defects to those found in people with CdLS,” said Otago Department of Pathology researcher Associate Professor Julia Horsfield.

The research team found that depleting the protein causes a key downstream effect, wherein particular cells fail to migrate to the heart where they would usually have played key roles in developing heart structures. They were surprised to find that zebrafish embryos partially depleted of Rad21 developed almost normally, except for the presence of the structural abnormalities of the heart, Horsfield noted.

Horsfield further said that their findings suggest that heart development is exquisitely sensitive to the available amount of Rad21 and cohesion, which means it can be compromised even when there is sufficient cohesin present to support relatively normal growth. This also raises the possibility that mild mutations in cohesin genes may be the cause of some fraction of congenital heart defects in the general population, Horsfield added.

In addition to being used in developmental biology, studies on zebrafish have led to the identification of diseases similar to humans, such as cancer. About 50 articles were said to have been published since 2000 in which zebrafish was used as a cancer model, since the species have been found to develop almost any tumor type known from human.

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