A second case of Hb Fontainebleau [alpha21(B2)Ala-->Pro] in an individual with microcytosis.

The identification of a second case of Hb Fontainbleau [alpha21(B2)Ala-->Pro] allowed us to re-examine its association with microcytosis, explore the effects of the mutation on protein stability and define the mutation at a DNA level. Although slightly unstable, the variant was expressed at 28-29% of the total and was caused by a heterozygous mutation in the alpha2 gene. There was no evidence for concomitant alpha-thalassemia (alpha-thal); both alpha-globin gene deletion analysis and sequencing of the alpha-globin locus failed to detect any additional mutations that might explain the relatively high expression level.