So far, more than 20 babies have been born using the screening programme, which checks for chromosomeabnormalities.
到目前为止，通过筛选方法出生的婴儿已有超过20个，这种方法可以检验出染色体异常。
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Chromosomal abnormalities are thought to account for 10 to 20 percent of cases and duplication of chromosome 15q11-13 is the only recurrent aberration so far linked to the disease.
The team is working on the disease's chromosome structure and has just identified the karyotype. (Karyotypes are pictures of cellular chromosomes that are used to check for abnormalities.)