Lejeune et al. (1959) first described the presence of an extra G chromosome in Down’s syndrome patients. Up to now, it has not been possible to distinguish with certainty between chromosomes 21 and 22. In the case of patients with clinical Down’s syndrome the chromosome is usually numbered 21. A number of patients have been described with an extra G chromosome without the clinical stigmata of Down’s syndrome, in which cases it has been suggested that this might be a chromosome 22. A review of these patients has been given by Chaudhuri et al. (1968).
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