Deletions in the GATA-1 gene encompassing exon 2 and IVS boundary sequences in TMD and DS-AMKL. Sequence analysis of genomic DNA revealed 3 patients with the GATA-1 mutation encompassing exon 2 and the surrounding IVS. TMD 20 had a large deletion of 1415 nucleotides extending from IVS1 to IVS2, which resulted in the expression of GATA-1 mRNA without the sequences corresponding to the entire exon 2. AMKL 7 and AMKL 10 had deletions of 59 and 465 nucleotides, respectively, and the expected sequences of GATA-1 mRNA are identical to that of TMD 20.