Hemoglobin San Martin: A New Unstable Variant Associated with Hemoglobin S in an Argentinean Boy.

A new unstable hemoglobin (Hb) detected in a 10 year-old boy from San Martin, Buenos Aires, Argentina, is hereby described. The patient (pt) was born at term, after a normal pregnancy, by cesarean section. He had a history of multiple episodes of pallor, jaundice and dark urine related to infections, since 6 months of age. The physical examination only revealed pallor and icterus, with no hepatosplenomegaly. The pt and his mother showed the presence of an anomalous band on both alkaline and acid pH electrophoresis. Isopropanol and sickling tests were positive. In order to identify the abnormal Hb variant the β globin gene was analysed. Three exons were amplified and automatically sequenced with direct and reverse probes. Two mutations were identified in the same β globin gene. One in Exon 1, corresponding to Hb S [Ex1 β6 Glu→Val (GAG→GTG)]; and the second one in Exon 2 [Ex2 β85 (F1) Phe→Leu (TTT→CTT)]. This second mutation is responsible for a new unstable Hb that has not been described so far, in association with Hb S. The substitution occurs in an external position between two hydrophobic residues of different size.