The first Japanese case of Hb Santa Ana, an unstable abnormal hemoglobin, identified rapidly by electrospray ionization mass spectrometry

The First Iranian Case of Unstable Hemoglobin Santa Ana

In this report, we describe a 6-year-old girl with a medical history of pallor, mild icterus, anemia, blood transfusion and abnormal hemoglobin variant analysis on capillary electrophoresis. She was referred for further analysis. DNA sequencing of the proband revealed a de novo mutation in Codon 88 (CTG > CCG) of the β-globin gene (HBB: c.266T > C) in a heterozygous state compatible with hemoglobin Santa Ana, an unstable hemoglobin. This is the first case of Hb Santa Ana from Iran associated with moderate to severe anemia who underwent splenectomy with clinical improvement.

The first Chinese case of unstable Hemoglobin Santa Ana detected by capillary electrophoresis: a case report and literature review

Hemoglobin Santa Ana [β88(F4)Leu→Pro (CTG > CCG) HBB: c.266T > C] is an unstable hemoglobin variant characterized by a substitution of the amino acid leucine by proline at the 88th position of the β-globin chain. We for the first time identified this hemoglobin variant in a Chinese patient by capillary electrophoresis (CE). The proband was an 8-year-old boy with chronic anemia, brown urine and splenomegaly. He had been affected by moderate anemia, twice approaching a severe degree, that was attributed to infection. The CE result revealed an abnormal hemoglobin peak at electrophoretic zone 4 that correspond to the hemoglobin Santa Ana peak, and a CTG > CCG mutation at codon 88 of the β-globin gene was confirmed by DNA sequencing. To avoid misdiagnosis and genetic risks, a literature review of other unstable hemoglobins that migrate similarly to the hemoglobin Santa Ana was performed. Our findings indicate that hemoglobin Santa Ana can be clearly separated by CE, with accurate diagnosis depending on molecular analysis. This information will be useful for providing appropriate genetic counselling and for prenatal diagnosis.

Pulse oximetry error in a patient with a Santa Ana haemoglobinopathy

A young man with a rare unstable haemoglobinopathy presented with a high fever, worsening shortness of breath and abdominal pain. At triage his pulse oximetry (SpO2) suggested that his blood oxygen saturation was 84% at room air. However, an arterial blood gas (ABG) oxygen saturation reading (SaO2) was 100%. The significant disparity between the two measurements demonstrates that using pulse oximetry in some unstable haemoglobinopathies may significantly underestimate the actual reading. This error is most probably due to the structural differences in the variant haemoglobin causing light to be absorbed at a different wavelength beyond the normal range of the oximeter. Haemoglobinopathies affect about 7% of the world's population and is often asymptomatic; so, there may be many more undiagnosed cases. Therefore, clinicians may confirm low SpO2 readings with an ABG and, where there is significant disparity with no obvious extrinsic cause, they should consider haemoglobinopathies.

Detection and characterization of variant and modified structures of proteins in blood and tissues by mass spectrometry

Some variant proteins cause diseases, and some diseases result in increases of proteins with abnormally modified structures. The detection, characterization, and estimation of the relative amounts of protein variants and abnormally modified proteins are important for clinical diagnosis and for elucidation of the mechanisms of the pathogenesis of diseases. Analysis of the covalent structures of proteins using matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-TOF-MS) and liquid chromatography-electrospray ionization MS (LC-ESI-MS), which had been developed by the early 1990s, have largely replaced analyses by conventional protein chemistry. Here, we review the detection and characterization of hemoglobin variants, HbA1c measurement, detection of carbohydrate-deficient transferrin, and identification of variants of transthyretin (TTR) and Cu/Zn-superoxide dismutase (SOD-1) using soft ionization MS. We also propose the diagnostic application of the signals of modified forms of TTR, that is, S-sulfonated TTR and S-homocysteinyl TTR. The relative peak height ratio of the abnormal/normal components gives valuable information about the instability of variants and enables the detection of unstable Hb subunits or thalassemia heterozygotes. We found unique modified structures of TTR that suggested changes in amyloid fibrils.

Detection and identification of protein variants and adducts in blood and tissues: an application of soft ionization mass spectrometry to clinical diagnosis

The detection and identification of protein variants and abnormally increased modified proteins are important for clinical diagnosis. We applied soft ionization mass spectrometry (MS) to analyze proteins in blood and tissues from various patients. Over the past 8 years, we diagnosed 132 cases (55 kinds) of variant proteins including hemoglobin (Hb), transthyretin (TTR), and Cu/Zn-superoxide dismutase (SOD-1), using MS as the leading technology. Of these variants, eight were new, and nine were the first cases in Japan. Some abnormal Hb cause diseases, and most of them cause erroneous levels of glycated Hb, HbA1c, i.e., a popular index of diabetes. Most of the variant TTR causes amyloidotic polyneuropathy. Variant SOD-1 causes amyotrophic lateral sclerosis. We first showed that immunoprecipitation by a specific antiserum is a reliable and simple method to prepare protein from sera and tissues for analysis by matrix-assisted laser desorption time-of-flight MS, and liquid chromatography-electrospray ionization MS (LC-ESI-MS). The use of this technology has become widespread. Using an immunoprecipitated target protein and LC-ESI-MS, we showed that the ratios of tetra-, di- and a-sialo-transferrin from two cases of congenital glycoprotein deficient syndrome were clearly distinguishable from those of control samples. We first reported a unique modified form of TTR, that is, S-sulfonated TTR, which increased markedly and specifically in three cases with molibdenum cofactor deficiency. We proposed that S-sulfonated TTR is a useful marker for screening this disease. ESI-MS was successfully used for the accurate determination of HbA1c, and we clarified the extent of discrepancies between the HbA1c value measured by conventional methods and the accurate values for samples containing various Hb variants determined by the MS method.

Toward a simple, expedient, and complete analysis of human hemoglobin by MALDI-TOFMS

MALDI mass spectrometry is explored as a method for hemoglobin characterization. To simplify and expedite the analysis, hemoglobin is obtained without purification directly from whole human blood. The use of trypsinactivated bioreactive MALDI probes is evaluated as a means to further reduce the analysis time from hours to minutes. Moreover, variations of the MALDI matrix preparation facilitate detection of the problematic tryptic peptides alpha T12, alpha T13, and beta T12. The results reveal that MALDI-based methods are easily implemented, are rapid, and allow detection of traditionally elusive tryptic peptides.

A simple and reliable method of detecting variant transthyretins by multidimensional liquid chromatography coupled to electrospray ionization mass spectrometry

Transthyretin (TTR) variants cause amyloidosis. A method, originally reported by us, of detecting the variants by high performance liquid chromatography/electrospray ionization mass spectrometry (ESIMS) using materials precipitated with anti-TTR antiserum, has been successfully applied by several institutions. The method is simple and reliable, but some variants may not precipitate with the antiserum or may precipitate in different yields compared to normal TTR. Moreover, unidentified minor peaks were observed, which may have been derived from cross reactive materials. We have now devised a new procedure to overcome these problems. An anion exchange and reversed phase liquid chromatography system and ESI mass spectrometer were connected in a tandem fashion using a 6 port valve and a protein trap cartridge. The profile of ion peaks by the method was the same as that by MS with immunoprecipitates. The minor peaks were proved not to be derived from cross reactive materials, and the molecular species of these peaks were characterized. This method is faster than immunoprecipitation method and using no antibody is a great benefit. The method can be applied widely to the study various proteins, when antibodies are not available.