Hb Extremadura [β64(E8)Gly→Ser;β133(H11)Val→Leu]: a new molecular analysis.

Unstable hemoglobin (Hb) variants account for 9.5% of structural hemoglobinopathies. The majority of these unstable variants are the result of gene point mutations resulting in the substitution of a single amino acid by another. The presence of two mutations in the same allele is infrequent: of the 781 variants of the β-globin cluster described, only 32 are due to two point mutations (4.1%). Hb Extremadura is a structural variant that is included within the so-called unstable Hb anomalies. It was first described in 1989, employing the most up-to-date techniques available at that time, reversed phase high performance liquid chromatography (HPLC) to separate the abnormal chain (β(X)) digesting it with trypsin and analysis of the fragments with an automatic analyzer.