GATA1 mutation in an adult patient with AMKL not accompanying DS. Direct sequence analysis of cDNA and genomic DNA from AMKL blast cells of the adult patient who did not have accompanying DS showed that 20 nucleotides of the duplicated sequence were inserted in exon 2 of the GATA1 gene. The mutation resulted in the introduction of a premature stop codon in the gene sequence encoding the N-terminal activation domain. The predicted protein from a downstream initiation site, GATA-1s, lacks the transactivation domain.