Molecular geneticists studying an autoradiograph of DNA results which shows the presence of Duchenne muscular dystrophy (DMD), Great Ormond Street Hospital, London, May 2000. DMD is a quite rare genetic condition, so people are not routinely tested to see if they carry it. But when a boy is disgnosed with DMD, his family may seek genetic counselling to find out whether other relatives carry the altered gene. Doctors can work out who is at risk by studying the family tree. A genetic test can usually establish which female relatives are DMD carriers.
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