ANTENATAL DIAGNOSIS OF BETA-THALASSEMIA BY ISOELECTRIC-FOCUSING IN IMMOBILIZED PH GRADIENTS

A new method for antenatal diagnosis of thalassemias is reported based on the analysis of the major Hb components of fetal cord blood, sampled at week 18 of pregnancy under ultrasonic guidance, by isoelectric focusing in immobilized pH gradients (IPG). In an IPG gel encompassing a pH 6.7-7.6 span, HbA and HbF(ac) are separated by a distance nine times greater than in a conventional carrier ampholyte pH 6-8 gel and three times greater than in an ampholine gel with separators (an equimolar mixture of β-alanine and 6-amino caproic acid). Band evenness (in sterms of uniform protein concentration within a zone) and straightness (in terms of parallel alignment of the bands to the electrodes), because of insensitivity of IPG gels to salt distortions, allows for accurate and reproducible quantitation of HbF, -A, and -F(ac) levels. The possibility of greatly overloading IPG matrices in total Hbs increases the sensitivity of the technique to the detection of only 0.5% HbA in the total Hb mixture, the lower limit of conventional IEF being only 2.5% HbA. Of 15 fetuses from couples at risk analyzed in the region of Ozieri, three were found to be homozygous β-thalassemic, eight heterozygous, and four normal with no false-positives or -negatives.