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Mapping the Williams syndrome region in humans and mice
  
By
Edward R. Winstead


 

Scientists have mapped a medically important region of human chromosome 7 by sequencing the corresponding region in mice and comparing it to the draft human sequence. The region has been extremely difficult to sequence using conventional tools. The comparison revealed nine previously unreported human genes. Six of these reside in the region that is often missing in persons with Williams syndrome, a genetic disorder with distinct facial and physiological features.


Detail of Williams syndrome regions in humans and mice. View larger

"This study illustrates why sequencing the mouse genome is so important for gaining insights into problems of human genetics," says Eric D. Green, of the US National Human Genome Research Institute in Bethesda, Maryland, who led the project. His team sequenced more than three million base pairs along mouse chromosome 5 and compared them to the draft sequence of human chromosome 7.

"Laying the mouse sequence on top of the human sequence is like putting a yellow highlighter on the human sequence," says Green. "It reveals the sequences that are common to both, and evolutionarily conserved sequences are likely to be functionally important."

A breakthrough in the study of Williams syndrome (WS) occurred in 1993, when researchers demonstrated that the disorder is caused by a chromosome 7 deletion. The deletion occurs when two large blocks of DNA at either end of the Williams syndrome region come together and eliminate the stretch in between. The large blocks have made the region difficult to sequence.

In 1999, Green led a team that surveyed the mouse WS region. They found that the human and mouse WS regions were strikingly different—the duplicated blocks of DNA were not present in mice. The current study is part of a larger cross-species comparative analysis of the region. "We are sequencing eleven non-human vertebrates, and doing comparisons to primates and lower organisms such as birds and fish," says Green.

For information on Williams syndrome visit Williams Syndrome Foundation (UK)

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DeSilva, U. et al. Generation and comparative analysis of ~3.3 Mb of mouse genomic sequence orthologous to the region of human chromosome 7q11.23 implicated in Williams syndrome. Genome Res 12, 3-15 (January 2002).
 

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