THURSDAY, Sept. 4 (HealthDay News) -- Researchers have found the earliest developmental changes in embryonic stem cells that lead to Down syndrome, a new study says.

Down syndrome, which is caused by an extra copy of human chromosome 21, is among the conditions called "aneuploidies," defined by an abnormal loss or gain of genetic material such as chromosomes. Aneuploidies, which are on the rise as more women delay childbirth until later in life, cause anomalies that can result in infant death.

The new findings, published online Sept. 4 in the American Journal of Human Genetics, are based on scientists studying embryonic stem cells from a previously genetically engineered species of mice carrying a copy of human chromosome 21. The extra chromosome, known in its genetic state as trisomy 21, disturbs a key regulating gene called NRSF or REST that starts are domino-like effect in disturbing other genes that control development.

The research team also identified one gene (DYRK1A) on human chromosome 21 whose overdose in trisomy (DS) is responsible for the observed effects.

"We hope that further research might lead to clues for the design of new therapeutic approaches tackling developmental delay, mental retardation, aging and regeneration of brain cells, and Alzheimer's disease. In other words, we hope our work will open new routes to tackle the genetics of these health disorders, approaching them from the 'back entrance,' as dominant component-symptoms of Down syndrome," lead researcher Dean Nizetic, professor of cellular and molecular biology at Barts and The London School of Medicine and Dentistry, said in a university news release.

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