We report a new unstable variant identified in three carriers of a family from East Sicily; it was named
Hb Bronte after the place from which the family originated.
DNA sequencing from
nucleotides -181 to +894 (alpha1) and to +884 (alpha2) revealed a GTG-->GGG substitution at
codon 93 of the alpha2-globin gene. The MCV and MCH values were at the lower end of the normal range in the carriers. On
cation exchange high performance liquid chromatography (HPLC), the
Hb A2 level was apparently increased to around 6%, and a small abnormal peak (0.3-0.4%) was detected after
Hb A2. Two abnormal bands were detected by
cellulose acetate electrophoresis: a major band (about 3-4%) migrated between Hb A and Hb F; a minor band (<1%) migrated between
Hb A2 and
carbonic anhydrase. Normal values of
Hb A2 were detected by
DEAE microchromatography. On reversed phase HPLC the variant chain was not detected, and most likely it was eluted with the alpha chain peak. The
isopropanol stability test was very slightly positive in the carriers. Hemolytic symptoms were absent with the exception of indirect
bilirubin, which was at high borderline in 2/3 carriers. In biosynthesis in vitro, the specific activity of the alpha chains was much higher than that of the
beta-globin chains, and the alpha/beta biosynthetic ratio in the mother and proband was of the
beta-thalassemia (thal) type (2.24 and 2.54, respectively). Time course experiments showed that the increase of the 3H-specific activity of the peak containing normal and variant alpha chains was not linear and was much higher than that of beta chains; moreover, the alpha/beta biosynthetic ratio varied during the 2 hours incubation.