Patients with homozygous sickle-
cell disease may be homozygous for
alpha-thalassemia 2 (O-/O-), may be heterozygous for alpha-thalessemia 2 (O-/OO), or may have a normal
alpha-globin-
gene complement (OO/OO). We compared the clinical and hematologic features of 44
patients who had sickle-
cell disease and homozygous
alpha-thalassemia 2 with those of controls with the two hematologic conditions. The
patients with homozygous
alpha-thalassemia 2 had significantly higher red-
cell counts and levels of
hemoglobin and
hemoglobin Aý, as well as significantly lower
hemoglobin F,
mean corpuscular hemoglobin,
mean corpuscular hemoglobin concentration,
mean corpuscular volume,
reticulocyte counts, irreversibly-sickled-
cell counts, and
serum total billirubin levels, than those with a normal
alpha-globin-
gene complement.
Heterozygotes (O-/OO) had intermediate values. In the group with homozygous
alpha-thalassemia 2, fewer
patients had episodes of
acute chest syndrome and chronic
leg ulceration and more
patients had
splenomegaly, as compared with
patients in the other two subgroups. These data confirmed previous
suggestions that
alpha-thalassemia inhibits in vivo sickling in homozygous sickle-
cell disease and may be an important genetic determinant of its hematologic severity.