Down syndrome (DS), or trisomy 21, is a common disorder associated with several complex clinical phenotypes. Although several hypotheses have been put forward, it is unclear as to whether particular gene loci on chromosome 21 (HSA21) are sufficient to cause DS and its associated features. Here we present a high-resolution genetic map of DS phenotypes based on an analysis of 30 subjects carrying rare segmental trisomies of various regions of HSA21. By using state-ofthe-art genomics technologies we mapped segmental trisomies at exon-level resolution and identified discrete regions of 1.8 -16.3 Mb likely to be involved in the development of 8 DS phenotypes, 4 of which are congenital malformations, including acute megakaryocytic leukemia, transient myeloproliferative disorder, Hirschsprung disease, duodenal stenosis, imperforate anus, severe mental retardation, DS-Alzheimer Disease, and DS-specific congenital heart disease (DSCHD). Our DS-phenotypic maps located DSCHD to a <2-Mb interval. Furthermore, the map enabled us to present evidence against the necessary involvement of other loci as well as specific hypotheses that have been put forward in relation to the etiology of DS-i.e., the presence of a single DS consensus region and the sufficiency of DSCR1 and DYRK1A, or APP, in causing several severe DS phenotypes. Our study demonstrates the value of combining advanced genomics with cohorts of rare patients for studying DS, a prototype for the role of copy-number variation in complex disease. copy number variants ͉ genomic structural variation ͉ human genome ͉ congenital heart disease ͉ leukemia F or over two decades trisomy 21 has represented a prototype disorder for the study of human aneuploidy and copy-number variation (1, 2), but the genes responsible for most Down syndrome (DS) phenotypes are still unknown. The analysis of several overlapping segmental trisomies 21 has led to the suggestion that dosage alteration through duplication of an extended region on chromosome 21 (HSA21) is associated with DS features (2-5, 42). However, humans with segmental trisomy 21 are rare, and thus humanbased DS-phenotypic maps have been of low resolution, far beyond the level of few or single genes, or even exons. Consequently, gene-disease links have often been based on indirect evidence from cellular or animal models (6, 7). Moreover, current hypotheses argue for the existence of a critical region, the DS consensus region (DSCR), responsible for most severe DS features (6, 8, 9), or presume the causative role of a small set of genes including DSCR1 and DYRK1A, or APP, for these phenotypes (6, 7).By using state-of-the-art genomics together with a large panel of partially trisomic individuals, we present the highest resolution DS phenotype map to date and identify distinct genomic regions that likely contribute to the manifestation of 8 DS features. Four of these phenotypes have never been associated with a particular region of HSA21. The map also enables us to rule out the necessary contribution of other HSA21 regions, thus pr...

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In past decades, most individuals with Down syndrome were usually not afforded adequate medical care. Many children with Down syndrome were institutionalized and they were often deprived of all but the most elementary medical services. Fortunately, there have been major improvements in the health care provision during the past 20 years. Professionals who are providing services to persons with Down syndrome need to be aware of those clinical conditions that are more often observed in this populations. Certain congenital anomalies (congenital cataracts, anomalies of the gastrointestinal tract, and congenital heart disease) often require immediate attention, as some of them may be life threatening. During the subsequent childhood years a number of clinical conditions and disorders such as infectious diseases, increased nutritional intake, periodontitis, seizure disorders, sleep apnea, visual impairment, audiologic deficits, thyroid dysfunction, and skeletal problems usually occur at a higher prevalence. During adolescence specific aspects of maturation and certain health issues (skin infections, thyroid disorders, increased weight gain, and others) as well as mental health concerns need to be taken into consideration. Similar concerns may also be observed during adulthood which in addition is often marked by accelerated aging and the threat of Alzheimer disease in some persons with Down syndrome. Special attention needs to be paid to these disorders and conditions during the lifetime of a person with Down syndrome. Appropriate medical care should be withheld from a person with Down syndrome that would be given unhesitatingly to an individual without this chromosome disorder.