由于控制α-链合成的4个基因均缺失，故无α-链合成，因此不能合成含α-链的HbA、HbA2</sub>和HbF，在胎儿后期γ、β链各自形成大量的γ4</sub>（HbBart）和β4</sub>（HbH），同时胚胎早期ζ链合成代偿性增加并持续至整个胎儿期，并与α链组成HbPortland。
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