How common are duplications of chromosome 15?
Several types of studies have been done to address this question. First, population studies have been done to examine the frequency of extra chromosomes, often called marker chromosomes, in newborns. Based on those studies, 1 in 8000 people carry an extra chromosome that came from chromosome 15. The most common type of marker chromosome 15 is tiny and contains few active genes, thus they do not usually cause any problems and are only identified incidentally when chromosome testing is done for other reasons1. In rare cases, the presence of this extra chromosome can cause errors in sorting of the chromosomes into the egg or sperm cells, and thus leading to either Prader Willi or Angelman syndromes. Studies have also been done to specifically examine the role of chromosome 15q duplications in several neurologic and developmental disorders. Moeschler and colleagues (2002) looked for duplications in 400 children with developmental delay and found evidence for duplications in two children (a
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