Early dynamics of the genome in Down syndrome.

Down syndrome (or trisomy 21) is a disorder caused by the triplication of human chromosome 21 (HSA21) and is the most common genetic cause of intellectual disability (1). The brain is substantially altered by trisomy 21 beginning prenatally, leading to profound changes in brain size and function. Down syndrome is an exceedingly complex multigenic disorder with phenotypes that unfold across the lifespan. This complexity has hampered understanding of how the brain is affected by trisomy 21, negatively impacting clinical management and quality of life for people with Down syndrome. On pages 385 and 386 of this issue, Risgaard et al. (2) and Vuong et al. (3), respectively, report findings from cutting-edge molecular approaches that identify the earliest genomic changes occurring in the brains of individuals with Down syndrome. The studies establish a clear foundation of how trisomy 21 affects the brain's cells from before birth to 3 years of age. [ABSTRACT FROM AUTHOR]