Association of a novel high oxygen affinity haemoglobin variant with delta beta thalassaemia

A New Case of Hb Headington (HBB: c.217A>C) Due to a New DNA Transversion, Found in a Patient with Type 2 Diabetes Mellitus

We here report a novel case of Hb Headington [β72(E16)Ser→Arg, HBB: c.217A>C, p.Ser73Arg], in a 68-year-old woman with type 2 diabetes mellitus (T2DM). Glycosylated hemoglobin (Hb) was measured by capillary electrophoresis (CE). The spectrum showed abnormal peaks between the A₀ and A₂ peaks. DNA sequencing demonstrated a mutation on the HBB gene, which predicted a substitution of serine to arginine at position 73 in the β-globin chain. Moreover, this amino acid substitution occurs at the same position as Hb Headington [β72(E16)Ser→Arg, HBB: c.219T>A, p.Ser73Arg], which showed increased oxygen affinity.

Hemoglobin variant analysis of whole blood and dried blood spots by MS

MS allows for the unequivocal diagnosis of hemoglobin variants, or hemoglobinopathies. Hemoglobinopathies are the most common inherited disorder and there is a need for rapid detection of clinically significant variants, such as sickle hemoglobin, which is responsible for sickle cell disease. In this review, we describe the development of MS approaches for the determination of hemoglobin variants from both whole blood samples and dried blood spots. MS approaches that are suitable for population screening are discussed, as are recent advances in direct surface analysis of dried blood spots.

Erythrocytosis in a child due to Hb Andrew-Minneapolis [β144(HC1)Lys→Asn (AAG>AAT or AAC)] associated with a Spanish (δβ)(0)-thalassemia

We report a rare association of δβ-thalassemia (δβ-thal) and a hemoglobin (Hb) variant with high oxygen affinity in a Spanish newborn. The proband had no Hb A and showed microcytosis and hypochromia; the peripheral blood smear was compatible with a thalassemia trait. Molecular studies revealed that the proband had a Spanish (δβ)(0)-thal (inherited from his father) and also carried a de novo variant (Hb Andrew-Minneapolis) because from the point of hematology, his mother was quite normal. The hemoglobinopathies with high affinity for oxygen constitute an infrequent cause of secondary congenital erythrocytosis. The degree of erythrocytosis and the resulting clinical manifestations are highly variable, depending on the degree of altered oxygen affinity and the presence of thalassemic genes. Thus, when these variants are associated with β(0)- or δβ-thal, as in our case, the proportion of abnormal Hb is ∼100.0%, which may cause polycythemia, hyperviscosity, and iron deficiency. This type of association is very rare and few have been described, especially in children, as they would normally be detected in adults as the increased packed cell volume (PCV) also increases blood viscosity and causes the typical symptoms (cephalalgia, drowsiness, dizziness). The association of a high oxygen affinity Hb and a δβ-thal presents a greater degree of erythrocytosis than when this same variant is associated with a β(0)-thal, mainly because the Hb F percentage is usually greater in the δβ-thal, and Hb F normally shows a greater affinity for oxygen and a reduced P(50), although one must always take into account the degree of oxygen affinity of the Hb variant. Familial erythrocytosis and an abnormal electrophoresis finding are indicative of a high affinity Hb. However, the absence of these findings does not reject the possibility of hemoglobinopathies, and in these cases, functional and molecular studies would be justified and should be mandatory for the differential diagnosis of erythrocytosis.

Top-down proteomics and direct surface sampling of neonatal dried blood spots: diagnosis of unknown hemoglobin variants

We have previously shown that liquid microjunction surface sampling of dried blood spots coupled with high resolution top-down mass spectrometry may be used for screening of common hemoglobin variants HbS, HbC, and HbD. In order to test the robustness of the approach, we have applied the approach to unknown hemoglobin variants. Six neonatal dried blood spot samples that had been identified as variants, but which could not be diagnosed by current screening methods, were analyzed by direct surface sampling top-down mass spectrometry. Both collision-induced dissociation and electron transfer dissociation mass spectrometry were employed. Four of the samples were identified as β-chain variants: two were heterozygous Hb D-Iran, one was heterozygous Hb Headington, and one was heterozygous Hb J-Baltimore. The fifth sample was identified as the α-chain variant heterozygous Hb Phnom Penh. Analysis of the sixth sample suggested that it did not in fact contain a variant. Adoption of the approach in the clinic would require speed in both data collection and interpretation. To address that issue, we have compared manual data analysis with freely available data analysis software (ProsightPTM). The results demonstrate the power of top-down proteomics for hemoglobin variant analysis in newborn samples.

Hyperhomocysteinaemia and protein S deficiency in complicated pregnancies

OBJECTIVE

The aim of our study was to investigate whether women with placental abruption, intrauterine fetal death or small for gestational age infants have metabolic and/or haemostatic abnormalities which are known to be risk factors for intravascular thrombosis.

DESIGN

For two years blood tests were performed at > 10 weeks after delivery on all women without hypertensive disorders either before or during pregnancy, who had been consecutively admitted to our hospital with placental abruption, intrauterine fetal death and small for gestational age.

SAMPLE

A total of 62 women who had placental abruption (n = 31), intrauterine fetal death (n = 18) and a small for gestational age infant (n = 13).

SETTING

Obstetric outpatient clinic in a university hospital (Free University Hospital, Amsterdam).

METHODS

Presence of hyperhomocysteinaemia, various coagulation abnormalities and anticardiolipins was investigated.

RESULTS

Abnormalities were found in 20 women in the placental abruption group (20/31, 65%), in 10 women in the intrauterine fetal death group (10/18, 56%) and in 11 women in the small for gestational age group (11/13, 85%). Eight out of these 31 women had more than one abnormality. In the group of 62 women protein S deficiency was demonstrated in 26%, hyperhomocysteinaemia in 24%, Protein C deficiency in 6%, anticardiolipin IgG in 11%, anticardiolipin IgM in 5%, Lupus anticoagulant in 2%. An antithrombin III deficiency was not found. Thirty-three women were tested for activated protein C resistance (9% positive) and factor V Leiden mutation (6% positive). Hyperhomocysteinaemia was treated with a daily oral dose of 250 mg pyridoxine and 5 mg folic acid. After six weeks of vitamin supplementation homocysteine levels were tested again. At that time a mean reduction of fasting homocysteine value of 68% (95% CI 57-79) was found and of post-load value of 65% (95% CI 55-76).

CONCLUSIONS

Based on the results of our study, it can be concluded that women whose pregnancies are complicated by either placental abruption, intrauterine fetal death or small for gestational age, even if there is no history of thrombo-embolic disorders or hypertension during pregnancy, should be advised to undergo an examination for metabolic and/or haemostatic abnormalities.

Hb Arta [beta 45 (CD4) Phe-->Cys]: a new unstable haemoglobin with reduced oxygen affinity in trans with beta-thalassaemia

The interaction of rare Hb variants with beta(0)-thalassaemia results in a quasihomozygous state where the erythrocytes contain the variant as the only major adult Hb component. Such a situation is a unique model that enables functional studies even in the case of a neutral variant that could not be isolated from Hb A. We report here an unusual patient carrying Hb Arta, a novel Hb variant [beta 45 (CD4) Phe-->Cys], in trans with beta(0)-thalassaemia gene (beta(0) 39). The aminoacid substitution at the critical CD corner of this Hb molecular renders the molecule unstable. In addition, haem is displaced in a position that favours the deoxy (T) conformation of the variant, but less than in Hb Cheverly [beta 45 (CD4) Phe-->Ser], and results in a p50 of 43 mmHg (pH 7.4, 37 degrees C) in the red cells with preservation of cooperativity. Solution studies of the almost pure Hb Arta show a 50% decrease in oxygen affinity and normal cooperativity; the Bohr effect and the interaction with organic phosphates are similar to those of Hb A. Hb Arta retains both normal homo- and heterotropic effects allowing a well-preserved oxygen transport in vivo despite a mild anaemia.