Compound heterozygosity for Hb S and the hybrid HbS Lepore, P-Nilotic, and Kenya; comparison of hematological and hemoglobin composition data

Rare occurrence of hemoglobin Lepore variant in a Palestinian patient: a case report and brief literature review

Introduction

In hemoglobinopathies, a basic lesion alters the rate of globin synthesis or the structure of the globin in healthy hemoglobin (Hb). Genetic instructions are used to synthesize the polypeptide chains that make up globin chains. The kind and extent of the structural aberration of the Hb molecule are closely related to the clinical features. Hematologically, the heterozygous form of the Lepore syndrome has a pattern resembling minor thalassemia, and electrophoretically, it is characterized by aberrant Hb Lepore fractions at a rate of 5-15% and a decreased percentage of HbA and mildly increased HbF. Clinically speaking, Hb Lepore heterozygotes patients are asymptomatic and resemble the clinical picture of patients with mild thalassemia.

Case Presentation

A 28-year-old female came to our attention for assessment of generalized weakness and fatigue for a 4-month duration. Laboratory evaluation, including complete blood count, showed mild microcytic hypochromic anemia with parameters resembling the thalassemia trait. Iron profile studies were normal. Abdominal ultrasound showed mild splenomegaly. Hb electrophoresis was performed and showed an abnormal high-performance liquid chromatography pattern with an abnormal Hb band, mild elevated HbF, and mild reduction in HbA. The interpretation of the Hb electrophoresis curve suggested heterozygosity for beta chain variant Hb Lepore.

Discussion and Conclusion

Hb Lepore is one of the structural Hb variants with a characteristic fusion gene between the delta and beta chains. Hematologically, the heterozygous form of the Lepore syndrome has a pattern resembling the thalassemia trait. In Palestine, the prevalence of Hb Lepore, either homozygous or homozygous state, is unknown.

Biochemical and Molecular Analysis of the Hb Lepore Boston Washington in a Syrian Homozygous Child

Hemoglobin (Hb) Lepore is composed of two normal α chains and two δβ fusion globins that arise from unequal crossover events between the δ- and β-globin genes. The Hb Lepore is widespread all over the world and in many ethnic groups. It includes some of the few clinically significant Hb variants that are associated with a β-thalassemia phenotype. Here, we describe the first occurrence of Hb Lepore Boston Washington in a Syrian individual. The patient, a 10-year-old child, shows severe anemia with a Hb level of 6.85 g/dL and typical thalassemic red cell indices. The diagnostic procedure implies hematological, biochemical, and molecular analysis, including multiplex ligation-dependent probe amplification (MLPA) assay, GAP-PCR, and DNA sequencing. This latter allowed us to define the correct structure of the hybrid δβ-globin gene. The knowledge of the spectrum of mutations associated with different geographical areas is the prerequisite to set up large-scale screening programs and be able to offer genetic counseling to couples at risk.

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.

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.

Fetal hemoglobin elevation in Hb Lepore heterozygotes and its correlation with beta globin cluster linked determinants

We have analysed, at the hematological and molecular level, 51 Hb lepore heterozygotes and three compound heterozygotes for Hb Lepore and HbS (HbLep/HbS) in 26 unselected Portuguese families. The Lepore Boston variant was present in one family, in association with classical haplotype V. All of the other Lepore alleles present haplotype III in association with XmnI (+)5' of (G)gamma gene, in tight linkage disequilibrium to the major mutation found in the Portuguese population, the Lepore Baltimore variant ( delta(68Leu)-beta(84Thr)). The three compound heterozygotes are the first HbLep/HbS individuals reported in the literature, with the Lepore Baltimore mutation linked to haplotype III. In agreement with other studies, these Lepore Baltimore heterozygotes have higher HbF (1.4-14.1% of total hemoglobin) than published cases of Lepore Boston (0.8-5.4%), which is associated with XmnI(-). Among the Lepore Baltimore heterozygotes, the (AT)xTy repeat region at -540 bp of the beta globin gene in trans to the Lepore chromosome, can account for much of the variability in HbF level. The allele (AT)7T7 is associated with lower HbF, and (AT)9T5 is associated with higher HbF. As we previously reported for beta thalassemic carriers, we observe in Lepore Baltimore carriers an effector in trans, linked to the (AT)xTy sequence, acting as an HPFH (Hereditary Persistence of Fetal Hemoglobin) determinant.

Complex interactions of deltabeta hybrid haemoglobin (Hb Lepore-Hollandia) Hb E (beta(26G-->A)) and alpha+ thalassaemia in a Thai family

Haemoglobin Lepore-Hollandia is an extremely rare condition in which a small deletion gives rise to a deltabeta hybrid, beta-like globin. There are two single reports of patients from South Pacific Islands and Bangladesh. We describe a family from central Thailand, in which this Hb Lepore-Hollandia interacts with a common beta globin variant (beta(E) resulting from the codon 26, G-->A mutation) and alpha(+) thalassaemia (alpha(3.7)). This intriguing interaction caused a troublesome diagnosis, as the two proband brothers were diagnosed as having Hb E/beta thalassaemia. Molecular analysis of genomic DNA performed in this study allowed the definitive diagnosis of this complicated interaction. Such studies are required in the diagnosis of thalassaemia and haemoglobinopathies for particular regions like South-east Asia, where many different genotypes may give rise to haemoglobin disorders.