ABSTRACT
Hemoglobin (Hb) Vancleave (NM_000518.5:c.431 A > T; dbSNP: rs33918338) is an extremely rare structural hemoglobin variant worldwide, and studies are limited. This report describes the case of a 16-year-old male patient who presented with secondary erythrocytosis. The diagnosis of Hb Vancleave, in combination with codon 41/42 (-TTCT) (NM_000518.5:c.126_129del; dbSNP: rs80356821), was confirmed by direct sequencing. This report highlights the importance of sequencing in the differential diagnosis of beta-thalassemia syndrome in Malaysia.
ABSTRACT
Haemoglobin (Hb) G-Makassar is a rare Hb variant. It presents a diagnostic challenge as it imitates sickle Hb (Hb S) in standard electrophoresis and high-performance liquid chromatography assays requiring DNA analysis to confirm diagnosis. Both have point mutations in codon 6, exon 1 in the ß-globin (HBB) gene with different pathogenicities. This study describes the clinical phenotype, haematology and genotype of Hb G-Makassar. Clinical and laboratory data of 38 cases of Hb G-Makassar over 8 years were analysed. Hb G-Makassar was confirmed by a direct sequencing of HBB gene and co-inheritance of α-thalassaemia determined through multiplex gap-PCR and multiplex Amplification Refractory Mutation System polymerase chain reaction. All cases were Malays, predominantly from Terengganu (n = 20, 52.6%). There were 14 (36.8%) males and 24 (63.2%) females with median age of 25 years. Majority (n = 33, 86.8%) had features of thalassaemia trait with mean ± SD for Hb, mean cell volume (MCV) and mean cell haemoglobin (MCH) as 13.21 g/dL ± 1.69, 73.06 ± 4.48 fL and 24.71 ± 1.82 pg, respectively. None had evidence of haemolysis or thromboembolic complications. Six genotypes were identified; ßG-Makassar/ß,αα/αα (n = 19, 50.0%), ßG-Makassar/ßE,αα/αα (n = 4, 10.5%), ßG-Makassar/ßNewYork,αα/αα (n = 1, 2.6%), ßG-Makassar/ß,αα/-α (n = 11, 28.9%), ßG-Makassar/ß,αα/αAdanaα (n = 2, 5.3%) and ßG-Makassar/ß,αα/-SEA (n = 1, 2.6%). The ßG-Makassar/ß,αα/αα showed that features of thalassaemia trait with mean ± SD for Hb, MCV and MCH were 13.74 g/dL ± 2.40, 76.18 ± 6.02 fL and 25.79 ± 2.41 pg, respectively. This is the largest study reporting a significant number of Hb G-Makassar in Malaysia. Although the mutation is similar to Hb S, the phenotype is benign.
ABSTRACT
This study sought to determine the potential role of HBB haplotypes to predict beta-thalassemia in the Malaysian population. A total of 543 archived samples were selected for this study. Five tagging SNPs in the beta-globin gene (HBB; NG_000007.3) were analyzed for SNP-based and haplotype association using SHEsis online software. Single-SNP-based association analysis showed three SNPs have a statistically significant association with beta-thalassemia. When Bonferroni correction was applied, four SNPs were found statistically significant with beta-thalassemia; IVS2-74T>G (padj = 0.047), IVS2-16G>C (padj = 0.017), IVS2-666C>T (padj = 0.017) and 3'UTR + 314G>A (padj = 0.002). However, 3'UTR + 233G>C did not yield a significant association with padj value = 0.076. Further investigation using combined five SNPs for haplotype association analysis revealed three susceptible haplotypes with significant p values of which, haplotypes 1-2-2-1-1 (p = 6.49 × 10-7, OR = 10.371 [3.345-32.148]), 1-2-1-1-1 (p = 0.009, OR = 1.423 [1.095-1.850] and 1-1-1-1-1 (p = 1.39 × 10-4, OR = 10.221 [2.345-44.555]). Three haplotypes showed protective effect with significant p value of which, 2-2-1-1-1 (p = 0.006, OR = 0.668 [0.500-0.893]), 1-1-2-2-1 (p = 0.013, OR = 0.357 [0.153-0.830]) and 1-1-2-1-1 (p = 0.033, OR = 0.745 [0.567-0.977]). This study has identified the potential use of intragenic polymorphic markers in the HBB gene, which were significantly associated with beta-thalassemia. Combining these five SNPs defined a new haplotype model for beta-thalassemia and further evaluation for predicting severity in beta-thalassemia.
