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Generally, nonsense codons 50 bp or more upstream of the 3′-most intron of the human β-globin gene reduce mRNA abundance. In contrast, dominantly inherited β-thalassemia is frequently associated with nonsense mutations in the last exon. In this work, murine erythroleukemia (MEL) cells were stably transfected with human β-globin genes mutated within each of the 3 exons, namely at codons 15 (TGG→TGA), 39 (C→T), or 127 (C→T). Primer extension analysis after erythroid differentiation induction showed codon 127 (C→T) mRNA accumulated in the cytoplasm at approximately 20% of the normal mRNA level. Codon 39 (C→T) mutation did not result in significant mRNA accumulation. Unexpectedly, codon 15 (TGG→TGA) mRNA accumulated at approximately 90%. Concordant results were obtained when reticulocyte mRNA from 2 carriers for this mutation was studied. High mRNA accumulation of codon 15 nonsense-mutated gene was revealed to be independent of the type of nonsense mutation and the genomic background in which this mutation occurs. To investigate the effects of other nonsense mutations located in the first exon on the mRNA level, nonsense mutations at codons 5, 17, and 26 were also cloned and stably transfected into MEL cells. After erythroid differentiation induction, mRNAs with a mutation at codon 5 or 17 were detected at high levels, whereas the mutation at codon 26 led to low mRNA levels. These findings suggest that nonsense-mediated mRNA decay is not exclusively dependent on the localization of mutations relative to the 3′-most intron. Other factors may also contribute to determine the cytoplasmic nonsense-mutated mRNA level in erythroid cells.

X-linked chronic granulomatous disease (CGD) is due to mutations in the gp91phox gene on Xp21.1. Studies in white and Japanese X-linked CGD patients have shown mutations in nearly every exon. We studied the molecular defect of seven Chinese patients with X-linked CGD from six unrelated families. Mutations were located by single-strand conformation polymorphism and then defined by sequence analysis. The mutations were two different amino acid substitutions, a nonsense mutation, an in-frame trinucleotide deletion, a single A insertion causing a frameshift, and a premature stop. Lastly, a rare splice site mutation caused by G to A transition at the terminal nucleotide of exon 3, resulting in the skipping of exon 3, was found. The possible effects of these mutations on protein structure-function or splicing were discussed. Together with previous reports, the A insertion in the run of six As from nucleotide 749 to 754 and the G to A transition at the terminal position of exon 3 may be mutation hotspots of the gp91phox gene. The extreme heterogeneous mutations found in our patients suggest the absence of ethnic group-specific mutation.