alpha Thalassemia and the expression of hemoglobin G-Philadelphia.

The findings presented for these two families help to explain the inheritance of alpha thalassemia, alpha-chain variants, and the relative expression of alpha genes. An 18.0-kb EcoRI fragment contains only one functional alpha gene, whereas a 20.5-kb fragment contains two. Individuals homozygous for the 18.0-kb EcoRI fragment also lack the 4.1-kb HindIII fragment that normally connects the centers of the duplicated alpha genes. These findings are consistent with a deletion involving the 5' alpha-gene locus. Presence of alpha G-Philadelphia in both families was found in association with the 18.0-kb EcoRI fragment; this short fragment was also found in an individual with alpha A. Inheritance of alpha G-Philadelphia at one alpha-gene locus was therefore also linked to the inheritance of alpha thalassemia due to a deletion involving the second alpha gene. The high percentage (46% to 48%) of alpha G found in some family members was due to alpha-thalassemia trait, or deletion of two alpha genes (-alpha G/-alpha); others with levels of variant of 32% to 34% were shown to have three functional alpha genes (-alpha G/alpha alpha). The genetic expression of the four normal alpha genes therefore appears to be equal and furthermore implies the existence of separate independently functioning transcriptional units for each of these genes in humans. It would be interesting to analyze the alpha genes in Afro-Americans reported to have alpha G-Philadelphia in the 20% to 25% range to determine whether the inheritance of alpha G can be linked to a normal alpha gene.