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denotes that this is a ticketed session.Program: Oral and Poster Abstracts
Session: 901. Health Services and Outcomes Research – Non-Malignant Conditions: Poster I
Background: Hemoglobin (Hb) analysis sometimes yields unidentified Hb variants. However, there have been no validated phenotypic characteristics differentiating between a- and b-variants. Furthermore, amplification of α-globin genes are problematic due to almost identical α1-and α2-gene sequences.
Methods: Cases showing unidentified variants on isoelectric focusing (IEF) or high performance liquid chromatography (HPLC) during 2012-2013 were subjected to direct sequencing of α1-, α2- and b-globin genes. The appropriate cutoff Hb variant percentages were determined using receiver operator characteristic (ROC) analysis. The distinctive phenotypes of a-globin mutations were used to construct an algorithm which was subsequently validated in the other cohort of unknown variants.
Results: The characteristics that can differentiate between subjects with rare a-globin variants (N = 39) and b-variants (N = 24) were the presence of unknown variants of HbA2 (23.1% sensitivity and 100% specificity) and/or Hb variant levels of < 37% on IEF and < 31% on HPLC (100% sensitivity and 100% specificity). Applying these phenotypes (Figure 1) to another validation cohort (N = 67), a-globin variants could be correctly identified with 100% sensitivity and 97.1% specificity. Among the total of 72 subjects with rare a-globin variants, Hb Hekinan (69.4%) was the most common followed by Hb Q-Thailand (8.3%). Other mutations were very rare. This was the first report of Hb Lansing, Hb Owari, Hb G-Georgia, Hb Port Phillip, Hb I and Hb J-Singapore in Thai population. When iron deficiency anemia was excluded, these α-globin variants demonstrated normal or α+-thalassemia phenotypes. The percentages of Hb variants and their phenotypes were determined by the presence of mutations on either α1-globin or α2-globin gene and co-inherited α-globin gene deletions. Notably, some a-globin variants such as Hb Hekinan and Hb G-Georgia showed more severe phenotypes similar to thalassemia intermedia when they were co-inherited with other a- and/or β-globin gene mutations. We hereby reported the Hb Lansing mutation on the α1-globin gene coexisting with a+-thalassemia resulting in increased Hb Lansing percentage and hence falsely low oxygen saturation.
Conclusions: This is the largest series of rare α-globin mutations. An unknown Hb variant level is the most effective criteria to suggest α-globin variants. Our proposed simple algorithm and DNA sequencing protocol are effective for characterization of α-globin variants.
Table 1 Hematological parameters and hemoglobin analysis data of rare α-globin variants in Thailand
Genotypes (N) |
Mutation |
Hb (g/dL) |
MCV (fL) |
HbX-IEF/HPLC (%) |
HbXA2-IEF/HPLC (%) |
Coexistence with other mutations |
Hb Hekinan (39) |
α1 27(B8) Glu>Asp |
13.0+1.4 |
85.7 + 5.7 |
22.9±6.5/ ND |
5.4±0.6 (4)/ND |
|
Hb Hekinan (3) |
α1 27(B8) Glu>Asp |
11.8+1.2 |
68.7 + 3.5 |
34.8±3.6/ 24.5 ± 3.4 |
6.9±4.8/3 ± 2.7 |
SEA deletion |
Hb Hekinan(6) |
α1 27(B8) Glu>Asp |
12.8+1.3 |
79.8 + 6.6 |
16.7±11.1/ 25.4 (1 case) |
5.5±2.0/ 4.5 (1 case) |
Heterozygous HbE |
Hb Hekinan (1) |
α1 27(B8) Glu>Asp |
8.4 |
66.0 |
6.0/ ND |
ND/ ND |
Homozygous HbE |
Hb Hekinan (1) |
α1 27(B8) Glu>Asp |
9.6 |
88.0 |
17.0 (Hekinan)/46.8 (Hope) |
10.0 (Hekinan)/ 60.0 (Hope) |
HbHope/HbE |
Hb Q-Thailand (6) |
α1 74(EF3) Asp>His |
12.1+0.6 |
77.7 +2.9 |
35.0 ± 1.0/ 28.7 ±1.0 |
1.6 (1)/ND |
|
Hb Owari (3) |
α1 121(H4) Val>Met |
11.3±0.6 |
89.7 +5.9 |
19.7 ± 6.8/ ND |
ND/ND |
|
Hb G-Georgia (1) |
α2 95(G2) Pro>Leu |
12.0 |
92.0 |
25.6/ ND |
2.0/ND |
|
Hb G-Georgia (1) |
α2 95(G2) Pro>Leu |
9.9 |
75.0 |
22.4/ ND |
3.3/ND |
Homozygous HbE |
Hb G-Georgia (1) |
α2 95(G2) Pro>Leu |
7.5 |
67.0 |
4.4/ ND |
1.2/ ND |
Codon 17 A>T (Lys>Stop) |
Hb Westmead (2) |
α2 122(H5) His>Gln |
11.8, 12.7(CB) |
71.0, 117.0 (CB) |
23.6, 4.7(CB)/ ND |
ND/ ND |
|
Hb Port Phillip (2) |
α1 91(FG3) Leu>Pro |
12.3, 10.6 |
84.0, 73.0 |
17.4/ 5.9, 21.3/10.7 |
1.7/ ND, ND/ND |
|
Hb Lansing (1) |
α1 87(F8) His>Gln |
11.9 |
78.0 |
7.2/ 2.5 |
ND/ ND |
|
Hb Lansing (1) |
α1 87(F8) His>Gln |
12.6 |
88.0 |
14.2/ 5.5 |
ND/ ND |
-3.7 kb deletion |
Hb I (1) |
α2 16(A14) Lys>Glu |
13.1 |
95.0 |
28.9/ 28.4 |
ND/ ND |
|
Hb J-Singapore (1) |
α2 79(EF8) Ala>Gly |
15.9 |
94.0 |
30.0/ 25.1 |
ND/ ND |
|
Hb J-Buda (1) |
a1 61(E10) Lys>Asn |
15.1 |
89.0 |
25.4/ 15.8 |
ND/ ND |
|
Hb Phnom Penh (1) |
α1 117(GH5)-Ile-α118(H1) |
16.0 |
82.0 |
30.7/ ND |
ND/ ND |
|
Data were shown as mean + standard deviation when sample sizes were of ³ 3.
HbX-IEF/HPLC: unknown variant on IEF and HPLC, HbXA2-IEF/HPLC: unknown variant of HbA2 on IEF and HPLC, ND: not detected, SEA: Southeast Asia deletion
Disclosures: No relevant conflicts of interest to declare.
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