Puerto Rican Child with Combined Heterozygocity for Hemoglobin S and Porto Alegre.

Abstract

Hemoglobin S is the most common abnormal hemoglobin detected in newborn screening in Puerto Rico. The purpose of this report is to present laboratory and clinical data from a newborn proven to have combined heterozygocity for hemoglobin S and a very rare hemoglobin. Abnormal newborn screening results using isoelectric focusing prompted us to further study an infant with an unknown hemoglobin. Testing with cellulose acetate and citrate agar electrophoresis revealed that this patient had, besides hemoglobin S, a rare fast moving band. We consulted the Haemoglobinopathy Screening Service at St. James’s University Hospital in Leeds, UK where our patient’s hemoglobin was identified as hemoglobin Porto Alegre by means of mass spectrometry. DNA sequencing at the molecular genetics laboratory in the Medical Sciences Campus, University of Puerto Rico confirmed our patient’s hemoglobin to be Hb Porto Alegre. The patient’s father was found to be heterozygous for hemoglobin S and her mother a carrier of hemoglobin Porto Alegre. Our patient has been followed-up for the last two years. She has remained asymptomatic, except for usual mild childhood diseases. Laboratory results up to 18 months of age have revealed Hgb 11.4–11.6 g/dl, MCV 87.5 fl, MCH 28.7 pg, reticulocyte count 2%, normal total bilirubin and LDH levels. Hemoglobin Porto Alegre involves a mutation in ß9(A6)Ser→Cys which promotes hemoglobin polymerization via disulfide bonds (Baudin-Creuza 2002). This mutation does not seem to alter hemoglobin function and apparently does not increase tendency for sickling. Tondo (1963) has reported that in vivo hemoglobin Porto Alegre exists in its normal tetrameric form, with no associated hemolysis. Martinez (1977) has suggested that hemoglobin Porto Alegre can exist in its tetrameric functional form by means of high levels of glutathione in red blood cells. Therefore, patients with combined hemoglobin S and Porto Alegre would be expected to be asymptomatic. Hemoglobin Porto Alegre has been documented in a few patients from Brazil, Portugal, Argentina, Cuba, and the Canary Islands. To our knowledge this is the first reported double heterozygote for hemoglobin S and Porto Alegre. We are following our patient closely for the development of any significant hematologic or clinical symptoms.