A proposed change to the type of prenatal genetic testing offered to couples in the UK could result in certain chromosome abnormalities being missed, suggests a study published online today (Thursday June 30, 2005) by The Lancet.
In 2004, the UK National Screening Committee (UKNSC) recommended that new screening programmes for Down’s syndrome* do not have to include karyotyping—a process that generates a picture of a person’s 23 chromosome pairs. Karyotyping can detect a range of numerical or structural genetic chromosome abnormalities, but can take up to 14days to produce a result. The UKNSC recommended that instead, prenatal diagnosis of genetic abnormalities should use one of two rapid techniques called FISH (fluorescence in-situ hybridisation) or PCR (polymerase chain reaction) that can give a result in 24–48hours. However, FISH and PCR can only detect the common alterations in copy number, principally trisomies (extra copies), of chromosomes 21, 18, 13, X, and Y.