The beta-thalassemia syndromes are a heterogeneous group of genetic disorders 
characterized by reduced or absent expression of the beta-globin gene. To date, 
over 300 beta-thalassemia alleles have been characterized in or around the 
beta-globin region. Thalassemia major is severe anemia necessitating chronic 
blood transfusions, splenectomy, iron chelation therapy, and bone marrow 
transplantation. Usually thalassemia major results from homozygosity or compound 
heterozygosity for severe betaO- and/or beta+-thalassemia mutations. Thalassemia 
intermedia is a clinical diagnosis that describes a symptomatic but less severe 
condition than beta-thalassemia major. beta-thalassemia intermedia may arise 
from several different combinations of alpha- and/or beta-thalassemia mutations. 
Heterozygous beta-thalassemia is typically characterized by a mild microcytic 
hypochromic anemia without any significant clinical implications. In this 
report, we describe a 63-year-old Africian American woman with asymptomatic 
homozygous beta-thalassemia, who seems to carry 2 copies of the -29 mutation in 
the promoter region of the beta-globin gene. Her elevated hemoglobin F level of 
83% was associated with heterozygosity for the Xmn I polymorphism upstream of 
the Ggamma-globin gene. Southern blot analysis at the alpha-globin locus did not 
show any deletion that would account for the mildness of her phenotype. 
Therefore, homozygosity for the -29 mutation along with the Xmn I polymorphism 
appears to confer an extremely mild beta-thalassemia phenotype. This observation 
has important implications in the prenatal diagnosis and genetic counseling of 
families segregating this type of genetic defect.