Hemoglobin chain synthesis in two children with trisomy 13. Evidence for temporary imbalance during switch from gamma to beta chain synthesis.

Hemoglobin chain synthesis was studied in 2 infants with trisomy 13, one in the newborn period, the other at 5 months of age. The relative rate of beta globin synthesis was much below normal in the newborn, resulting in an overall imbalance of nonalpha/alpha globin synthesis. In the 5-month-old child, globin synthesis was balanced, although gamma globin synthesis accounted for a larger than normal percentage of nonalpha globin synthesis. Thus, the presence of a third 13 chromosome causes sever disturbances in the gamma to beta switch mechanism primarily affecting the onset of beta globin synthesis. The appearance of two previously unobserved bands in isoelectric focusing gels of the newborn's Hb is suggestive of the presence of embryonic hemoglobins.