The Venezuelan Type of Nondeletional Hereditary Persistence of Fetal Hemoglobin Is Due C →T Mutation at Nucleotide -211 of the ^Aγ Globin Gene.

Hereditary Persistence of Fetal Hemoglobin (HPFH) is a clinically benign condition characterized by continuous synthesis of fetal hemoglobin (Hb F) in adult life without major related hematological changes. The nondeletional HPFH is characterized by hemoglobin F level between 5% and 30%, in heterozygotes state. This condition has been observed among Blacks, Italians, Greeks, English and Chinese. Two different forms are known, characterized by the type of chain involve, either ^Gγ or ^Aγ. Several point mutations in the promoter region of the ^Aγ globin gene have been identified in ndHPFH: −202, −198, −196, −195, −117, −114, deletion 4pb (−222 −225) and −158.

The propositus is a 36 year old black female with a moderate increased level of Hb F, also her sister and her sibling had the same condition. She was discovered during studies due to the presence of splenomegaly and gastroesophageal reflux. The Hbs A, A₂ and F were eluted and quantified by cation exchange high-performance liquid chromatography (HPLC-CE), using Beta Tal short program, Variant BioRad (Hercules, California, USA). DNA was isolated from peripheral blood leukocytes by a salting-out extraction procedure. The ^Aγ and ^Gγ promoters globins gene were amplified independently by PCR and the presence of the HPFH mutation was determined by denaturing gradient gel electrophoresis technique (DGGE) as previously described Gottardi et al., (1992). The ^Aγ promoter globin gene was sequenced in three members of the family using the BigDye^TM Terminator Cycler Sequencing Kit and the ABI PRISM^TM 310 Genetic Analyzer (PE Applied Biosystems, Foster City, CQ, USA).

Her hematological studies revealed Hb: 14.2 g/dl, Hcto: 41.1 %, MCV: 94.4 fl, MCHC: 34.5 fl, Hb A: 81.9 %, Hb A2: 2.1 % and Hb F: 6.3 %. The sibling hematological finding was Hb: 13.1 g/dl, Hcto: 41.8 %, MCV: 83.7 fl, MCHC: 31.3 fl, Hb A: 83.2 %, Hb A2: 3.2 % and Hb F: 5.1. The sister was Hb: 14.3 g/dl, Hcto: 46.4 %, MCV: 105.9 fl, MCHC: 30.8 fl, Hb A: 83.7 %, Hb A2: 3.3 % and Hb F: 2.7 %. No spleen enlargement was seen in the other two affected members of the family. The DGGE results in the ^Aγ promoter, suggested the presence of a non-deletion form of HPFH in heterozygotes state. The ^Aγ promoter region revealed the presence of a substitution C→T at position −211. This mutation does not modify any restriction site.

To our knowledge the −211 (C→T) mutation in the ^Aγ promoter have not been reported previously. Since modulation of g-globin gene expression in adults could provide a therapeutic intervention in hemoglobinopathy, the study of the molecular mechanisms generating HPFH is medically relevant.