Chromosome imbalance (aneusomy) is the leading known cause of both spontaneous abortion and mental retardation in human beings. The primary abnormality is thought to result from quantitative changes of transcription products from the unbalanced genetic material. To document this point, I compared chromosome 21-specific transcription in skin fibroblasts from subjects with monosomy 21, disomy 21 (normal), and trisomy 21 (Down syndrome (aneusomy) are shown by the lethality in human beings of monosomy for more than 2-3% and trisomy for more than 5-6% of the haploid autosomal genome (1).Smaller deficiencies and duplications of autosomal material are associated with altered phenotypes which can be recognized by specific patterns of malformation and are usually associated with mental retardation (2-4). Chromosome imbalance represents, in sum, the major known cause of both abortion (5) and mental retardation (6) in human beings. Down syndrome (trisomy 21) is the most common viable human aneusomy and comprises the majority of individuals who are retarded because of chromosomal imbalance (7).The actual mechanism whereby chromosomal imbalance results in major phenotypic effects remains poorly understood. However, several points are clear: (i) The defect is due to quantitative alteration of normal genetic material. This point is best illustrated by a case report of monozygotic twins who are discordant for Down syndrome (8 Given this background, elucidation of the mechanism(s) whereby aneusomy results in metabolic and phenotypic aberrations will require analyses at the primary level of gene action-i.e., transcription. This report describes some first steps toward such an analysis: RNA sequences transcribed from human chromosome 21 are quantitated in skin fibroblasts with one, two, and three copies per genome of chromosome 21.
MATERIALS AND METHODSSynthesis of cDNAs. Human skin fibroblasts were grown to confluency in Dulbecco-Vogt medium containing 16% heat-inactivated fetal calf serum, fed, and harvested 4 days later. They were scraped off with a rubber policeman into ice-cold phosphate-buffered saline containing 1:200 (vol/vol) diethylpyrocarbonate (Sigma). The cells were pelleted and resuspended in 5 vol of 5 M guanidine thiocyanate (Tridom), 50 mM Tris-HCl (pH 7.6), 10 mM EDTA, and 5% (vol/vol) 2-mercaptoethanol. Sarkosyl was added to 4% (wt/vol), and 0.5 g of CsCl was added per ml of solution. The solution was layered over a 1-ml cushion of 5.7 M CsCl in 100 mM EDTA and centrifuged in a Spinco SW 50.1 rotor at 35,000 rpm for 12 hr at 20°C (16
2372The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact.