Chromosome 21

About: Chromosome 21 is a research topic. Over the lifetime, 4736 publications have been published within this topic receiving 206655 citations. The topic is also known as: chr21 & Homo sapiens chromosome 21.

Genes contributing to Alzheimer's disease.

Abstract: We propose that Alzheimer's disease (AD) is a single disease with a common metabolic APP-beta A4-amyloid pathway. The multiple genetic and other factors already identified to induce this pathway are reviewed. The molecular genetics of AD has been successfully studied within the last years, and we now can account for the genetic and molecular alterations underlying the majority of familial AD cases inherited with an autosomal dominant pattern of complete penetrance. AD in these pedigrees can be caused by missense mutations within the recently identified PS1 (S182) gene on chromosome 14 (AD3 locus) and the PS2 (STM2/E5-1) gene on chromosome 1, in addition to previously described point mutations of the beta A4-amyloid protein precursor (APP) gene on chromosome 21 (AD1 locus). The majority of AD cases, however, appears to be sporadic or 'familial' in terms of an increased family-associated AD-probability. Genetic risk factors contributing to AD in these cases have also been identified. On chromosome 19, allelic segregation of the APOE gene with both late onset 'familial' (AD2) and sporadic AD has been demonstrated, with the APOE epsilon 4 allele conferring a relatively higher risk of developing AD at an earlier age. Several other risk factors have also been proposed, including the alpha 1-antichymotrypsin allele A (ACT-A), the 5-repeat allele of the VLDL-receptor (VLDL-R) gene, the A2 allele of the HLA-A locus, and possibly yet unknown mitochondrial mutations. All these findings are discussed against the background of what is known about APP metabolism leading to beta A4 amyloid formation, a process that is also modified by APP expression level, alternative splicing of APP exon 15, extracellular signalling and intracellular sorting.

Mouse chromosome 17.

Abstract: Although less than a year separates the first report of the Committee for Mouse Chromosome (Chr) 17 from this second report, the number of loci that have been assigned to Chr 17 has increased dramatically with a current count, as of June 5, 1991, of 324. A complete list of these loci in alphabetical order is presented in Table 1. Table 2 lists the same set of loci according to their subchromosomal location. The first group of loci in this table include 241 that have been mapped to a specific site along the 37 cM linkage group associated with the chromosome; these are listed according to their distance from the centromere. The remaining 83 loci have either not been further localized or are mapped broadly to the proximal, distal or central regions of the chromosome. Thirty-two loci described by phenotype alone have been mapped within the major histocompatibility complex (H-2) in the center of the chromosome, and some of these may actually be equivalent to well-characterized H-2 class I or class II genes. Table 3 lists other symbols that have been used to represent some of the loci present in the master databases shown in Tables 1 and 2. Further details pertaining to the representation of the data presented in each table are provided in the corresponding legends. A total of 226 Chr 17 loci have been characterized at the DNA level, and at least portions of each are available as clones. Of these, 102 represent expressed genes, 26 represent pseudogenes, and 98 are anonymous sequences. The products of an additional 38 loci have been characterized biochemically or immunologically, but the genes themselves have yet to be cloned. Finally, 60 loci are defined by phenotypic expression alone, with unknown gene products. The average saturation of the chromosome in terms of just cloned markers is six per cM. With a total chromosome distance of 37 cM and a 2000 kb per cM conversion factor, the average inter-marker distance be-