Research has been carried out with respect to chromosome 21 analysis. New polymorphic markers were developed for one centromeric marker D21S258, and for a marker located within intron 1 of the APP gene. The linkage map of these markers was realized. 12 restriction fragment length polymorphisms and 18 microsatellites were placed on the chromosome 21 map. A map of 43 polymerase chain reaction (PCR) markers was constructed with an average heterozygocity of 61%.
A slot blot method has been developed to assess the copy number of 30 markers in the deoxyribonucleic acid (DNA) of 11 patients with rearranged chromosome 21 in order to determine their physical order. Genomic maps have been constructed around the oncogene ETS2 and around the t(8;21) breakpoint. A 135 to 500 kilobase (kb) region of homology on the long arm of chromosome 21 has been identified as have 4 physical linkage groups in the regions CRYA1 to BCEI (1200 kb), ETS2 to D21S65 (5000 kb), APP to D21S12 (1450 kb), D21S52 to D21Z1 (6500 kb). These macrorestriction maps cover a third of the 21q arm.
A chromosome 21 specific enriched YAC library of 4 genome equivalents has been generated and a collection of 1.5 genome equivalent of YAC clones has been added to this library. These collections have been used to construct a YAC overlap spanning 90% of the chromosome. A set of YACs spanning ETS2 to ERG (1200 kb) and D21S55 to D21S65 (3600 kb) have been selected.
Mapping and analysis of diseases related to chromosome 21 have enabled critical regions to be identified for down syndrome, monosomy 21, acute myelogenous leukemia, presenile dimentia and cerebral amyloid angiopathy. Known genes have been localized accurately on chromosome 21. The human glutamate receptor gene GLuR5 has been assigned to 21q22 and the conservation of the SON gene which maps on 21q22 has been observed.
The consortium intends to generate an integrated overlap, physical, genetic and transcriptional map of human chromosome 21.
New technologies already developed among the participating organizations will be used: overlap map of cosmids created by successive hybridizations of oligonucleotides on a chromosome 21 cosmid library; physical map obtained by combining gene dosage data, in situ hybridization data and pulsed field gel electrophoresis data; genetic map by using existing and new markers (classic and PCR polymorphisms); YAC contigs from total human genome libraries (this consortium and others), and a chromosome 21 specific YAC library ; transcriptional map by combining classical and new methods of gene identification such as Alu PCR on mRNAs. The overlap, physical, genetic and transcriptional data will be integrated in the same database. By combining the skills of the participating laboratories the proposed work provides a new approach towards the analysis of human chromosome 21. This effort, which combines unique resources and capabilities, might benefit the identification of genes associated with diseases as common as Downs yndrome or Alzheimer's disease ; this can be applied to the integrated study of other large regions of the human genome.
Funding SchemeCSC - Cost-sharing contracts
WC2A 3PX London
CB2 2QH Cambridge