Spontaneous mutation in beta-thalassaemia producing the same nucleotide substitution as that in a common hereditary form.

The molecular basis of a spontaneous mutation causing beta-thalassaemia in a boy of north European descent was characterised. The codon at the beta 39 position had mutated from CAG (glutamine) to the stop codon TAG. This nonsense mutation occurs commonly in a hereditary form of beta-thalassaemia in the Mediterranean area; its production by a spontaneous mutation suggests that this region of the beta-globin gene is a mutational hot spot.