Is the Poly A (T>C) Mutation a Causative Factor For Misdiagnosis in Second Trimester Prenatal Diagnosis of β-Thalassemia by Fetal Blood Analysis on High Performance Liquid Chromatography?

Abstract

We report the problems in diagnosis faced by two families referred for prenatal diagnosis of thalassemia where cordocentesis and fetal blood analysis by high performance liquid chromatography (HPLC) had to be done. The Hb A levels of the fetal blood measured by HPLC on the VARIANT™ Hemoglobin Testing System were 1.2 and 6.7%, respectively, suggestive of a heterozygous β-thalassemia (β-thal) fetus in the first case and a normal fetus in the second case. In one family, one of the parents had a borderline Hb A₂ level and in the other, one parent had normal RBC indices. However, DNA sequencing, done later, showed that in the first case the fetus was a compound heterozygote for the IVS-I-5 (G>C) and the polyadenylation signal site [poly A (T>C)] mutation, while in the second case, the fetus was homozygous for the poly A mutation. This emphasizes that characterization of β-thal mutations must be done whenever one of the parents has a borderline Hb A₂ level or normal RBC indices, and one should not rely on fetal blood analysis by HPLC for prenatal diagnosis of β-thal so as to avoid misdiagnosis.

• β-Thalassemia (β-thal)
• Prenatal diagnosis
• High performance liquid chromatography (HPLC)
• Fetal blood analysis
• Polyadenylation signal site (poly A)