De novo mutation within the intron-exon junction in the PiZ allele of the alpha-1-antitrypsin gene.

A proband homozygous for the PiZ allele of the alpha-1-antitrypsin gene was found to be a heterozygous carrier of the additional nucleotide substitution (C-T) within the intron IV-exon V junction (position 9955 in intron IV, 3 bp upstream of its 3'-splice site). This mutation was not found in DNA from either the PiZ heterozygous parents or the PiZ homozygous brother of proband.