Two UMass Medical School researchers used a naturally occurring off switch to shut down the chromosomes that cause Down syndrome during laboratory experiments that used human stem cells, according to a press release from the school.

This discovery could lead to treatment and therapy based on the chromosome that causes the condition, rather than treatment based on its symptoms, the researchers said.

Our hope is that for individuals living with Down syndrome, this proof-of-principal opens up multiple exciting new avenues for studying the disorder now, and brings into the realm of consideration research on the concept of chromosome therapy in the future, said lead researcher Jeanne B. Lawrence, professor of cell and developmental biology.

The news was met with guarded applause by a Bay State advocacy group which praised the research, but warned of ethical concerns for parents of children with Down syndrome.

This appears to be one of the most important scientific advancements in the field since French physician Jerome Lejeune identified Down syndrome as a chromosomal condition in 1959, Maureen Gallagher, executive director of the Massachusetts Down Syndrome Congress said in a statement. Its important for us to understand that any direct therapeutic implications as a result of this new research is many years away and that although it is an exciting discovery, it will bring with it many ethical and emotional issues for the Down syndrome community.

People without Down syndrome are born with 23 pairs of chromosomes in each cell. Down syndrome occurs when one pair of those chromosomes, No. 21, appears three times rather than in a pair. To stop this from happening in their stem cell samples, the researchers used a gene that silences the X chromosome in females, and moved it to a spot on the chromosome where it repressed the growth of that third No. 21 chromosome.

Dr. Lawrence has harnessed the power of a natural process to target abnormal gene expression in cells that have an aberrant number of chromosomes, said Anthony Carter, of the National Institutes of Health, which partly supported the study. Her work provides a new tool that could yield novel insights into how genes are silenced on a chromosomal scale, and into the pathological processes associated with chromosome disorders such as Down syndrome.

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Stem cell research yields Down syndrome breakthrough