PRENATAL DIAGNOSIS OF β-THALASSEMIA IN EGYPT: Implementing Accurate High-Tech Methods Did not Reflect Much on the Outcome

Abstract

The clinical severity of thalassemia major makes it a priority genetic disease for prevention programs through prenatal diagnosis for carrier couples. Incorporation of automated DNA sequencing that enables the characterization of mutations not detected by other mutation specific detection procedures was a prime goal of this work. Automated DNA sequencing was offered on fetal tissues in 30 pregnancies during the year 2005. The pregnancies were at high risk for homozygosity or compound heterozygosity for β-thalassemia based on mutation analysis of both parents before prenatal diagnosis. Both parents have β-thalassemia trait. Fetal samples were collected by chorionic villus sampling (CVS) in the first trimester and by amniocentesis in the second trimester. The point mutations were characterized by PCR (ARMS). The absence of the expected fragment with all the mutant ARMS primers insinuated an uncharacterized DNA segment that was further subjected to direct automated fluorescent DNA sequencing in an attempt to know if the fetus was affected by parents’ mutations. If no mutation was detected using the PCR ARMS, the sample was further analyzed using direct automated fluorescent DNA sequencing. The mean gestation when carrying out the invasive procedure was 14 (10 –18) weeks. All mothers had a previous affected pregnancy, and 13 had two or more previous affected pregnancies. Pregnancies were: 8 carrier fetuses (trait) and 22 affected fetuses in which 2 were homozygous and 20 double heterozygous. Fourteen parents of affected fetuses preferred to continue pregnancy and the babies were born as diagnosed. The other 8 parents decided on termination and DNA of the abortuses proved to be as previously diagnosed by DNA sequencing. The use of PCR amplification and direct sequencing have permitted the accurate characterization of unidentified alleles and successfully solved 100% of the examined samples. However, it has resulted in minor changes of the outcome as the majority of couples preferred continuation of pregnancy.