Sickle-cell anemia results from an A leads to T transversion in the second 
nucleotide of codon 6 of the beta-globin gene. We now report an uncommon 
beta-thalassemia gene that contains a deletion of this nucleotide. Thus, one 
mutation (GAG leads to GTG) produces sickle-cell anemia, while the other (GAG 
leads to GG) eliminates beta-globin production. These data establish that 
different alterations affecting one specific nucleotide can produce either an 
abnormal hemoglobin or beta-thalassemia. Moreover, the nucleotide sequence 
comprising codons 6-8 of the beta-globin gene appears to be particularly 
susceptible to mutations affecting nucleotide number.