Hb I-Toulouse in Association with Homozygosity for the α3.7 Deletion in a Pacific Island Woman

Abstract

Only four cases of Hb I-Toulouse have been reported to date. Current literature associates Hb I-Toulouse in the heterozygote with a mild chronic hemolytic anemia. The variant is mildly unstable with a tendency to form metHb. The quantity of the variant in heterozygotes has been reported as varying between 33 to 40%. This report confirms the finding from a single case, that a reduced percentage of Hb IToulouse along with microcytosis can be attributed to the co-inheritance of an abnormal α globin genotype. This current case was found in a woman of Pacific People ethnicity residing in New Zealand. There is a high prevalence of α thalassemia in this ethnic group and New Zealand has the highest Pacific population in the world. Therefore, if a reduced percentage of Hb I-Toulouse is found with microcytosis and normal iron studies, co-inheritance with α thalassemia should be considered.

Hemoglobin I‐Toulouse: A rare hemoglobinopathy presenting with low oxygen saturations

“…4,5 Interestingly, two of the previously reported cases 5,6 were also from Solomon Islands, possibly suggesting clustering of this Hb variant in people of Solomon Island descent. Hb I-Toulouse has been previously reported to cause methemoglobinemia, 2,6 which is consistent with findings in our case. Although the association between Hb I-Toulouse and alpha thalassemia has been seen in the previous case, 5 one case of compound heterozygosity of Hb S-and Hb I-Toulouse presenting with possible vaso-occlusive episodes has been reported, 4 there is insufficient evidence to define the clinical implications of interactions between Hb I-Toulouse and other beta-globin variants such as Hb S or beta thalassemia.…”

“…Interestingly, two of the previously reported cases 5,6 were also from Solomon Islands, possibly suggesting clustering of this Hb variant in people of Solomon Island descent. Hb I‐Toulouse has been previously reported to cause methemoglobinemia, 2,6 which is consistent with findings in our case.…”

“…Hb I‐Toulouse has been described to be unstable and sensitive to spontaneous oxidation 2 . The presentations of the previously reported cases include anemia, 3 joint pain, 4 and symptoms of thalassemia 5 and thrombocytosis, 6 though it is likely that some of these features were due to compound heterozygosity with Hb S and possibly alpha thalassemia in some of these cases 4,5 …”

“…Pullon 6 A 50-year-old Solomon Island woman, who presented to the hospital with thrombocytosis Hemoglobin electrophoresis on cellulose acetate revealed the presence of two major bands; one with mobility of Hb A and the other fast band running in the Hb I position. DNA mapping result supported the mass spectrometry findings with the variant previously reported as Hb I-Toulouse.…”