Researchers have developed a DNA test that might allow doctors to detect Down's syndrome in embryos during infertility treatment.
Currently, the genetic disorder is diagnosed about 16 weeks into pregnancy by using amniotic fluid taken from the mother. The new test, presented at a European infertility conference, uses a single cell to detect Down's syndrome during in vitro fertilisation (IVF) treatment before the embryo is implanted in the womb.
Down's syndrome occurs when a baby inherits three copies of chromosome 21 instead of two. In this study the researchers identified six areas on chromosome 21 that could be used as markers to detect how many copies of chromosome 21 are in a single cell. They used the test to compare cells taken from healthy people with those taken from people with Down's syndrome, as well as with individual cells from embryos.
“The third chromosome was successfully detected in 94% of single cells,” said Dr Mandy Katz, one of the scientists at the Monash Institute of Reproduction and Development in Melbourne, Australia, who developed the test.
Scientists believe that the new test could allow couples undergoing preimplantation genetic diagnosis for other genetic disorders to determine whether the embryo has Down's syndrome. “We want to be able to offer women over 36 years old the possibility to eliminate Down's syndrome,” Dr Katz said at the European Society for Human Reproduction and Embryology's conference in Lausanne, Switzerland.
A senior researcher at the institute, Dr David Cram, said that the new DNA test was more reliable than existing methods and would avoid situations where people had elective abortions because the condition was not detected until later in development.
“More than 30% of women who attend [in vitro fertilisation clinics at the Monash Institute] are at high risk of genetic defects, so we need a test that can best eliminate children being born with these conditions or the defects causing miscarriages,” Dr Cram said.
The incidence of Down's syndrome increases with advancing maternal age—from 1 in 1000 births at age 29 to 1 in 100 at age 40. The new test is available only to women in high risk groups, such as those aged over 35 or with a family history of the condition. Dr Cram said if results proved successful it could replace the current test for Down's syndrome in these high risk groups of women who are undergoing in vitro fertilisation.
The researchers said the Down's syndrome test could also be combined with preimplantation genetic diagnosis screening for other single cell genetic disorders.