Blood, 15 February 2002, Vol. 99, No. 4, pp. 1498-1499
CORRESPONDENCE
To the editor:
A single mutation 202G>A in the human glucose-6-phosphate
dehydrogenase gene (G6PD) can cause acute hemolysis by
itself
Glucose-6-phosphate dehydrogenase (G6PD) A-
is a common G6PD variant among Africans that may cause acute
hemolysis triggered by infections and certain drugs, as well as by fava
beans. This class-3 phenotype can be caused by a combination of the
common 376A>G (Asn126Asp) mutation and either of 3 additional
mutations: 202G>A (Val68Met), 680G>T (Arg227Leu), or 968T>C
(Leu323Pro).1,2 The structure and function relationship of
the most common type with 376A>G + 202G>A has been studied in
detail.3,4 The missense mutation 376A>G by itself causes
an asymptomatic class-4 variant G6PD A with normal enzyme
activity,5 whereas the other mutation 202G>A has never
been found in humans by itself. Some investigators insisted that both
mutations in G6PD A- are necessary to produce the
G6PD-deficient phenotype.6 Here we report a symptomatic
G6PD deficiency case associated with the missense mutation 202G>A but
not the 376A>G.
A 3-year-old Japanese boy was noted to have jaundice and anemia, and
was referred to the Department of Pediatrics, Asahi General Hospital
(K.K. and A.Ho.), for evaluation. At the time of admission, he showed
clinical and laboratory findings compatible with acute hemolysis,
including hemoglobin concentration, 9.6 g/dL; reticulocyte count,
2.9%; and serum total bilirubin, 4.7 mg/dL (83% of which was
indirect reacting). His anemia and jaundice improved
spontaneously within 5 days. At the time of follow-up visits, no signs
of chronic hemolysis were observed. He had a history of prolonged
neonatal jaundice.
The patient's red cell G6PD activity was decreased (2.9 IU/gHb;
referential range (mean ± SD): 7.12 ± 0.79 IU/gHb). The enzyme activity of the mother was also decreased (2.8 IU/gHb). Using PCR-SSCP (polymerase chain reaction-single strand conformation polymorphism) analysis combined with direct
sequencing,7 we identified a missense mutation 202G>A,
which predicts the amino acid substitution Val68Met in the proband's
G6PD gene, but surprisingly failed to find the counterpart
376A>G (Figure 1). Because it was quite
unusual for 202G>A to be found alone, we further sequenced the whole
coding exons and flanking regions of adjacent introns to search the
second mutation. But we did not find any additional mutation except for
a single base deletion in intron 5 (636delT or 637delT), which has been
identified in various Mongoloid populations, including
Japanese.7 Thus we concluded that the patient's
reduced enzyme activity was caused entirely by the 202G>A mutation
alone. Produced unique variant designated G6PD Asahi falls into class 3 in the World Health Organization criteria.8 The mother was found to be heterozygous for this mutation.
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| Figure 1.
Partial nucleotide sequence of G6PD Asahi.
The proband's G6PD gene has the mutation 202G>A (left) but
not the 376A>G (right).
|
|
It is evident that the 202G>A mutation found in our patient has arisen
separately from those common in Africans, because the patient had none
of the silent mutations closely linked with the African
mutation,9 while he had an intronic single base deletion common in Mongoloid.7
An in vitro study6 using recombinant human G6PD
mutants expressed in Escherichia coli suggested that
202G>A, as well as 376A>G, does not cause enzyme deficiency by
itself, and the synergistic action of these 2 mutations is necessary to
produce the class-3 phenotype of G6PD A-. This synergistic
interaction was also supported by the fact that Val68 and Asn126 are
closely located in a 3-dimensional model of human
G6PD.3 Our results are inconsistent with those previous observations. Although there still remains a rare possibility that we
have overlooked a second mutation in introns or in 5'- and 3'-noncoding
regions, the inconsistency suggests that the function and the fate of a
mutant enzyme in vivo might be very different from those deduced from
experiments using the recombinant enzyme.
Akira Hirono, Kazuhiro Kawate, Akihito Honda, Hisaichi Fujii, and Shiro Miwa
Correspondence: Akira Hirono, Okinaka Memorial Institute for
Medical Research, 1-4-11-405, Seishin-cho, Edogawa-ku, Tokyo 134-0087, Japan; e-mail: ncc01353{at}nifty.ne.jp
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