Table 2.

The history of disease-related loci currently mapped to chromosomes 21 and 22

	Chromosome 21 (26 disorders)			Chromosome 22 (62 disorders)
	To December 1999	From January 2000	Pending	To December 1999	From January 2000	Pending
Mapped to chromosome	23 (88%)	3 (12%)	0 (0%)	50 (81%)	12 (19%)	0 (0%)
Mutation identified	15 (58%)	5 (19%)	6 (23%)	23 (37%)	9 (15%)	30 (48%)
First gene sequence published	22 (85%)	0 (0%)	4 (15%)	42 (68%)	6 (10%)	14 (23%)
Full-length cDNA published	20 (77%)	2 (8%)	4 (15%)	39 (63%)	7 (11%)	16 (26%)

There are currently 26 disorders mapped to chromosome 21, and 62 disorders mapped to chromosome 22. Numbers indicate the date by which the loci were first mapped to the chromosomes, when the first phenotype-related mutations were identified, when the first gene sequences were published, and when the first full-length cDNAs were published. Since exact date information was not available, a cutoff of January 2000 was used. Data were obtained from the NCBI resources OMIM [17], GenBank [18] and LocusLink [19].