Compound heterozygotes and beta-thalassemia: top-down mass spectrometry for detection of hemoglobinopathies.

We have shown previously that liquid extraction surface analysis of dried blood spots coupled to high resolution top-down MS may be applied for the diagnosis of hemoglobin (Hb) variants FS, FAS, FC, FAC, FAD in newborn samples. The objective of the current work was to determine whether the structural variant HbE, compound heterozygote variants FSC and FSD, and β-thalassemia were amenable to diagnosis by this approach. Anonymized residual neonatal dried blood spot samples, taken as part of the routine newborn screening program, were analyzed by liquid extraction surface analysis coupled to high resolution MS/MS. The samples had been previously screened and were known to be FAE, FSC, FSD, or β-thalassemia. Manual analysis of the mass spectra revealed that, in all cases, the variants may be confirmed. Direct surface sampling MS should be considered as an alternative to current screening techniques for the diagnosis of Hb variants.