Clinical course and molecular characterization of a compound heterozygote for sickle hemoglobin and hemoglobin Kenya

Hemoglobin variants identified in the Uganda Sickle Surveillance Study

The Uganda Sickle Surveillance Study analyzed dried blood spots that were collected from almost 100 000 infants and young children from all 10 regions and 112 districts in the Republic of Uganda, with the primary objective of determining the prevalence of sickle cell trait and disease. An overall prevalence of 13.3% sickle cell trait and 0.7% sickle cell disease was recently reported. The isoelectric focusing electrophoresis technique coincidentally revealed numerous hemoglobin (Hb) variants (defined as an electrophoresis band that was not Hb A, Hb F, Hb S, or Hb C) with an overall country-wide prevalence of 0.5%, but with considerable geographic variability, being highest in the northwest regions and districts. To elucidate these Hb variants, the original isoelectric focusing (IEF) gels were reviewed to identify and locate the variant samples; corresponding dried blood spots were retrieved for further testing. Subsequent DNA-based investigation of 5 predominant isoelectric focusing patterns identified 2 α-globin variants (Hb Stanleyville II, Asn78Lys; Hb G-Pest, Asp74Asn), 1 β-globin variant (Hb O-Arab, Glu121Lys), and 2 fusion globin variants (Hb P-Nilotic, β31-δ50; Hb Kenya, ^Aγ81Leu-β86Ala). Compound heterozygotes containing an Hb variant plus Hb S were also identified, including both Hb S/O-Arab and HbS/Kenya. Regional differences in the types and prevalence of these hemoglobin variants likely reflect tribal ancestries and migration patterns. Algorithms are proposed to characterize these Hb variants, which will be helpful for emerging neonatal hemoglobinopathy screening programs that are under way in sub-Saharan Africa.

Multiplex-PCR Assay for the Deletions Causing Hereditary Persistence of Fetal Hemoglobin

INTRODUCTION

Hereditary persistence of fetal hemoglobin (HPFH) is a benign condition caused by the failure of normal switching from the fetal to the adult beta-globin gene, resulting in continuous production of fetal hemoglobin beyond the perinatal period. To date, eight deletions of variable size and position have been reported for HPFH. Southern hybridization and PCR are the most common methods used to detect each deletion.

AIM

Our aim was to develop a multiplex-PCR assay to detect these deletions in a single tube in order to facilitate rapid and accurate molecular diagnosis.

METHODS AND RESULTS

This report is the first application of multiplex-gap-PCR to detect all HPFH deletions simultaneously to expedite diagnosis. The deletion breakpoints were precisely identified for each deletion and primers were designed in the unique regions across the breakpoints of HPFH-1 (Black), HPFH-2 (Ghanaian), HPFH-3 (Asian Indian), HPFH-4 (Italian), HPFH-5 (Italian), HPFH-6 (Vietnamese), HPFH-7 (Kenyan), and SEA-HPFH (Southeast Asian). As many as 16 primers were used in a single amplification reaction by adjusting the relative primer concentrations. The multiplex-PCR approach was standardized on known positive control samples. We identified unique deletion-specific products for each deletion. The results were confirmed by sequence analysis.

CONCLUSIONS

We conclude that our multiplex-gap PCR strategy provides the most rapid and accurate diagnosis for the deletions in the beta-globin gene cluster causing HPFH.

Compound heterozygosity for Hb S [β6(A3)Glu→Val] and Hb Kenya (Aγ81Leu-β86Ala) in a Ugandan woman

Hb Kenya is a hemoglobin (Hb) tetramer composed of two normal α- and two non α-globin chains. The latter are the product of a fusion gene in which the 5' end is (A)γ and the 3' end is β. The crossover point is between codon 81 of the (A)γ gene and codon 86 of the β gene. Like the other non α genes, the hybrid protein product ((A)γ81Leu-β86Ala) has 146 amino acids. The purpose of this report is to highlight the laboratory findings of Hb Kenya and to emphasize the pitfalls in misdiagnosis, particularly when associated with another variant such as Hb S [β6(A3)Glu→Val].

Hemoglobin Kenya composed of alpha- and ((A)gammabeta)-fusion-globin chains, associated with hereditary persistence of fetal hemoglobin

Hb Kenya is made up of two normal alpha-globin chains and two (A)gammabeta-fusion globin chains. The latter are the product of an (A)gammabeta-hybrid globin gene formed as a result of misalignment during meiosis and nonhomologous crossing over. It is associated with a deletion of 22.7 kb including the delta-globin gene, between the (A)gamma- and beta-globin genes. Hb Kenya is found in Kenyans and Ugandans. Heterozygotes have moderately increased Hb F, and this mutation has been known as an ((A)gammabeta)(+) hereditary persistence of fetal hemoglobin (HPFH). Compound heterozygotes for Hb Kenya/Hb S are thought to be asymptomatic, but reports of long term follow-up of these patients are lacking. The correct identification of Hb Kenya is sometimes problematic. In cation exchange high performance liquid chromatography, Hb Kenya elutes in similar position as Hb A(2), Hb Lepore, Hb E, and several other variant hemoglobins. Definitive diagnosis that is necessary for proper patient management is best done by DNA-based gap-PCR tests.

Identification of two novel beta zero-thalassemia mutations in a Filipino family: frameshift codon 67 (-TG) and a beta-globin gene deletion

The frequency of beta-thalassemia alleles among Filipinos is estimated to be 0.02, although little is known about the actual mutations represented in this population. Here, we describe a Filipino family in which a child has severe beta-thalassemia major. Molecular studies of the family revealed that the proband is a compound heterozygote for two previously unreported beta zero-thalassemia alleles: a frameshift mutation (-TG) at codon 67 and a deletion of the entire beta-globin gene. The 5' endpoint of this novel deletion is located approximately 3.9 kb to approximately 4.3 kb upstream of beta-globin gene, and the deletion extends 3' beyond the beta-globin gene for an undetermined distance. The occurrence of two novel beta-thalassemia alleles in a single family suggests that the Filipino population may have a unique spectrum of beta-thalassemia alleles.