Blood, Vol. 89 No. 10 (May 15), 1997:
pp. 3888-3888
CORRESPONDENCE
A Novel 
+-Thalassemia Mutation (Codon 10 GCC 
GCA) and a Rare Transcriptional Mutation (-28A G) in Indians
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LETTER |
To the Editor:
Characterization of 
-thalassemia mutations in different populations has shown 180 mutant alleles.1 So far, 25 mutations have been reported among Indians, 5 of which comprise more than 80% of the mutant alleles.2-4
We report two interesting Indian families showing a novel +-thalassemia mutation and a rare transcriptional mutation. They had come to us for second trimester prenatal diagnosis by globin biosynthesis.
The -thalassemia mutations were characterized by denaturing gradient gel electrophoresis (DGGE) analysis.5 Both mutations were detected in fragment B of the -globin gene spanning from the upstream -64 nucleotide to IVS-I-nt61 containing the promoter boxes and exon-1. DNA Sequencing was performed by the dideoxy method using Sequenase version 2.0 to identify the mutation.6
Family I was from Madhya Pradesh in central India. Both parents (I-1) and (I-2) had classical -thalassemia trait (Fig 1). Their 3-year-old son (II-1) with severe homozygous -thalassemia had been diagnosed at 8 months of age and had been transfused every month. This child was not available for investigation. Fetal diagnosis at 18 weeks of gestation in the next pregnancy showed that the /
biosynthetic ratio was 0.021, indicating that the fetus had homozygous +-thalassemia (normal / ratio, >0.03).
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| Fig 1.
Family I. The hematologic profile and the -thalassemia mutations characterized in the parents (I-1 and I-2).
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DGGE analysis showed that the mother (I-2) had the IVS I-5 G 
C mutation, whereas the father (I-1) had an anomalous DGGE pattern in fragment B.
Sequencing of this region using the forward primer showed a novel mutation at codon 10 GCC GCA on the coding strand. Both the normal codon (GCC) and the mutant codon (GCA) code for alanine. This C A substitution creates the sequence CAGTTA in the mutated region. A catalogue of the sequences found at functional splice sites has identified the 5' consensus sequence C/A AGG TG/AA. The C A change in codon 10 produces a sequence that has homology to 5 of 6 nucleotides of the normal splice site at the exon 1-intron-I boundary. It has been reported earlier that this homologous sequence in the exon causes alternative splicing at the site giving a +-phenotype.2,7
Family II was from Karnataka in south India. Both parents (I-1 and I-2) had classical -thalassemia trait (Fig 2A). Their 6-year-old daughter had a homozygous -thalassemic picture but had never been transfused. Globin biosynthesis in the next pregnancy showed that the 18-week-old fetus was normal.
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| Fig 2.
Family II. (A) The hematologic profile and the -thalassemia mutations characterized in the parents (I-1 and I-2) and their 6-year-old daughter (II-1). (B) Part of a sequencing gel showing the rare T C mutation on the noncoding strand at position (-28) of the upstream ATA box in the father (I-1).
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DGGE analysis showed the IVS I-5 G C mutation in the mother (I-2), whereas the father (I-1) had another anomalous DGGE pattern in fragment B. The DGGE pattern in the homozygous child (II-1) was different from that seen in the parents.
Sequencing of this -globin gene region using the forward primer did not show any mutation. Sequencing with the reverse primer showed a T C change on the noncoding strand (Fig 2B). This mutation was found in the daughter (II-1) as well, who also showed the presence of the IVS-I-5 G C mutation. This A G change in the upstream ATA box at position (-28) is a transcriptional mutant reported among Chinese.8 Nevertheless, it has not been reported among Indians.
These two new rare mutations could be added to the 25 different -thalassemic mutations that have been reported among Indians so far.
A.R. Pawar
R.B. Colah
D. Mohanty
Institute of Immunohaematology (ICMR) KEM Hospital Mumbai, India
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ACKNOWLEDGEMENT |
We thank S.R. Shirsat for preparation of the manuscript.
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