A rare case of compound Hemoglobin Lansing/Hemoglobin S coinherited with alpha thalassemia trait (-alpha3.7) presented with spurious hypoxemia and moderate hemolytic anemia

Abstract

Abstract We present a case of a 27-year-old female at 27 weeks of gestation, who presented at the emergency department for vaginal spotting. She was also found to have low oxygenation on pulse oximetry of approximately 82% at room air. Her SpO2 did not improve with O2 supplement. She had a similar presentation a month before, with mild light-headedness and low oxygenation. However, two repeated air blood gas (ABG) findings were normal for oxygen saturation. Hemoglobinopathy was suspected due to the disparity. She was anemic during her presentation, with hemoglobin 8.3 g/dl, RBC count 3.36 million/ul, MCV 81 fl and MCH 24.7 pg. Additional workup showed increased reticulocyte count, decreased haptoglobin, negative direct Coombs test, negative G6PD test, and no evidence of a PNH clone. Capillary hemoglobin electrophoresis showed HbA 59.8%, HbS 34.5%, HbA2 3.6% and a small peak (2.1%) in the Z8 zone with a trailing edge at HbF window. HPLC revealed an “unknown peak” of 8.2% with a retention time of 1.93 minutes as well as the HbS peak. There was also a tiny additional A2 peak unresolved from the main A2 peak. Alpha globin gene sequencing revealed one copy of the -alpha3.7 alpha-globin deletion and one copy of Hb Lansing variant in the alpha2-globin gene. This is consistent with the compound Hemoglobin Lansing/Hemoglobin S coinherited with alpha thalassemia trait. Hemoglobin Lansing is a rare unstable alpha hemoglobin variant with mutation of c.264C>G resulting with a substitution of His by Gln at codon 87. The mutation was first discovered in the alpha 2 gene. Then the same mutation was found in alpha 1 gene later and named as Hemoglobin Lansing-Ramathibodi. To the best of our knowledge, this is the first reported case of Hemoglobin Lansing with alpha thalassemia trait (-alpha3.7) and HbS. Spuriously low pulse oximetry measurements have previously been reported in Hb Lansing variants. It was speculated to be due to different absorption spectra of Hb Lansing which is under study now. The patient also presented with hemolytic anemia. The exact cause was undetermined yet although it might be related to her hemoglobinopathy. Mild hemolytic anemia was reported in two cases of co-inheritance of Lansing-Ramathibodi and Hb Pakse (a non-deletional alpha thalassemia) but not in the members of the same family with Hb Lansing alone. It was also reported that some unstable alpha chain variants, when associated with another alpha thalassemia defect, present with a more severe phenotype including hemolytic anemia even though essentially asymptomatic in a heterozygous state.