Human Chromosome 21 Sequenced

May 9, 2000; Westport, CT (Reuters Health) -- An international team of researchers has determined almost all of the DNA sequence of human Chromosome 21. The data were published electronically on Monday and will appear in the May 18th issue of Nature. The team, which was led by Dr. Y. Sakaki of RIKEN, in Sagamihara, Japan, announced that it has achieved 99.7 percent coverage of the long arm of the chromosome and has sequenced 281,116 Base Pairs (BP) from the short arm.

On the long arm, Dr. Sakaki and colleagues say that they have sequenced "33,546,361 bp of DNA with very high accuracy, the largest contig being 25,491,867 bp." They note that "only three small clone gaps and seven sequencing gaps remain, comprising about 100 kilobases."

"Analysis of the chromosome revealed 127 known genes, 98 predicted genes, and 59 pseudogenes," the investigators say. They also identified structural features that include "duplications that are probably involved in chromosomal abnormalities and repeat structures in the telomeric and pericentromeric regions."

Dr. Sakaki and co-authors say that "the chromosome 21 gene catalogue will open new avenues for deciphering the molecular bases of Down syndrome and of aneuploidies in general." The findings also may have implications for several cancers, including cancers of the head and neck, breast, pancreas, mouth, stomach, esophagus, and lung. Dr. Sakaki's group points out that "the observed loss of heterozygosity [with these cancers] indicates that there may be at least one tumor suppressor gene" on Chromosome 21.

In addition, the research team notes, Chromosome 21 is thought to play a role in the development of several monogenic disorders, such as one form of Alzheimer's disease and a predisposition to leukemia, so the study findings may have implications for these conditions as well.

Nature, Vol. 405, pp. 311-319 (May 18, 2000).