Functional genomics of Down syndrome: a multidisciplinary approach

The availability of the DNA sequence of human chromosome 21 (HSA21) is a la ndmark contribution that will have an immediate impact on the study of the role of specific genes to Down syndrome (DS). Trisomy 21, full or partial, is a major cause of mental retardation and other phenotypic abnormalities, collectively known as Down syndrome (DS), a disorder affecting 1 in 700 bir ths. The identification of genes on HSA21 and the elucidation of the functi on of the proteins encoded by these genes have been a major challenge for t he human genome project and for research in DS. Over 100 of the estimated 3 00-500 genes of HSA21 have been identified, but the function of most remain s largely unknown. It is believed that the overexpression of an unknown num ber of HSA21 genes is directly or indirectly responsible for the mental ret ardation and the other clinical features of DS. For this reason, HSA21 gene s that are expressed in tissues affected in DS patients are of special inte rest.