Interaction of the ααα globin gene haplotype and sickle haemoglobin

Novel alpha haemoglobin haplotypes in horses

Four minor haplotypes that produce abnormal haemoglobin phenotypes in horses have been characterized. Two of them, AIIb and V, are copy number variants with, respectively, one and three alpha genes instead of the normal complement of two. The AIIa and C haplotypes, on the other hand, each have two alpha genes but, as a result of probable gene conversions, they now encode identical, though haplotype specific, globins. Two out of 60 unrelated and phenotypically normal horses studied had an unusual triplicated rearrangement in the embryonic zeta-gene locus. Each of these variants appears to have been produced by aberrant recombination events.

Outcome in hemoglobin SC disease: a four-decade observational study of clinical, hematologic, and genetic factors

Over the past 40 years, we observed 284 subjects with hemoglobin SC disease (Hb SC) for 2,837 person-years. We examined the association of the course of clinical events with hematologic and genetic factors. The mean entry age was 21 years, although 15% entered before one year of age. The mean Hb concentration was 11.3 g/dL, the mean fetal hemoglobin was 2.5%, and the mean MCV was 84.4 fL. Twenty-five subjects died at a median age of 37 years. Chronic organ-specific complications occurred in 112 subjects (39.4%), with advanced retinopathy in 65 subjects (22.9%) and osteonecrosis (avascular necrosis) in 42 subjects (14.8%). We identified the beta-globin haplotypes in 82 subjects and the alpha-gene status in 79. Twenty-nine percent had alpha-thalassemia-2. The beta(CI) haplotype was present in 85.4%. We found a decreased incidence of retinopathy in the beta(CI) subjects compared to the non-beta(CI) subjects (33% vs. 67%; P = 0.049) with a later mean onset age (29 years vs. 21 years; log-rank test, P= 0.026). We also found a consistent pattern of decreased morbidity in subjects who had alpha-thalassemia-2 in comparison to those who did not. We found a reduced risk of chronic organ-specific complications (log-rank test, P= 0.003), lower incidence of sickle crisis (48% vs. 80%, P= 0.001), later onset of gallbladder disease (age of onset: 55 years vs. 34 years; P= 0.055), and lower risk of osteonecrosis (log-rank test, P= 0.024). Our findings suggest that Hb SC subjects who have not inherited alpha-thalassemia-2 might benefit from erythrocyte rehydration therapy.

Expression of triplicated and quadruplicated alpha globin genes in sheep

In the sheep alpha alpha alpha globin gene haplotype, the three genes display from the 5' to the 3' end the percentage efficiencies of about 30:14:6, as indicated by the amounts of the three types of alpha chain produced in the alpha alpha alpha/alpha alpha alpha homozygotes. The 3' gene in the alpha alpha alpha alpha haplotype appears to have an efficiency around 1%, as suggested by analysis of one quadruple alpha homozygote. Moreover, the total outputs of the alpha alpha alpha as well as of the alpha alpha alpha alpha haplotypes do not substantially differ from that of the common alpha alpha haplotype.

Sickle cell trait in a white Jewish family presenting as splenic infarction at high altitude

We report the presence of sickle cell trait in several members of a white Jewish family. The trait was discovered when the propositus developed massive splenic infarction at high altitude. No erythrocyte markers characteristic of African ancestry were detected in any of the family members. This is the first bona fide documentation of sickle trait among white Jews.

A benign form of thalassaemia intermedia may be determined by the interaction of triplicated alpha locus and heterozygous beta-thalassaemia

In this paper we report that the combination of a triplicated alpha globin locus with heterozygous beta-thalassaemia produces a clinical phenotype of thalassaemia intermedia in five Italian subjects from four unrelated families, while in two other cases the phenotype was thalassaemia minor. The haematological findings of the five patients were uniform, producing a benign form of thalassaemia intermedia, transfusion independent, with a long life expectancy. The pattern of inheritance of the two genetic determinants and the more pronounced beta/alpha globin chain imbalance, demonstrates that the genetic combination is indeed the cause of the phenotype. The pattern of restriction enzyme site polymorphisms suggests the presence of the beta IVS I 110 G----A mutation at least in three of these cases.

Thalassaemia intermedia: interaction of the triple alpha-globin gene arrangement and heterozygous beta-thalassaemia

Five patients with heterozygous beta-thalassaemia with an unusually severe clinical picture, low haemoglobin levels occasionally requiring blood transfusion, splenomegaly and unusually prominent basophilic stippling were found to have co-inherited a triple alpha-globin gene arrangement on one chromosome (alpha alpha alpha/alpha alpha). It seems probable that the expression of a single extra alpha-globin gene is sufficient in some patients with heterozygous beta-thalassaemia to give rise to a clinically significant degree of dyserythropoietic anaemia.

Influence of HbS levels upon the hematological and clinical characteristics of sickle cell trait

The variable concentration of HbS in individuals with sickle cell trait led us to study the relationship between HbS level and selected vascular events in 355 hospitalized black men with sickle cell trait. There were significant differences in hemoglobin concentration and mean corpuscular volume found in four groups divided by their HbS level, the lowest proportion of HbS (less than 30%) being associated with the lowest hemoglobin concentration (12.6 g/dl) and MCV (77 fl). The percent HbS did not influence the incidence of pulmonary embolism, thrombophlebitis, myocardial infarction, cerebrovascular accident, or idiopathic hematuria. Our results suggest that HbS level does not influence vascular disease, and while certain hematological alterations occur, they are very unlikely to have any clinical significance. Regardless of the proportion of HbS, sickle cell trait in black men is benign.

Functional activity of the triplicated alpha alpha alpha 4.2/gene rearrangement

Function of the triplicated alpha alpha alpha 4.2/gene rearrangement was assessed by measurement of Hb Bart's and hematological phenotype including alpha/beta biosynthesis ratio. Increased output of alpha globin chains in alpha alpha alpha 4.2/-- compared to alpha alpha/-- was found in a cord blood. In contrast, hematological phenotypes in two family members with the alpha alpha alpha 4.2/-- genotype were consistent with that expected in alpha alpha/--. This would suggest that the additional alpha gene in the alpha alpha alpha 4.2/rearrangement has variable expression.