The 2 ATM truncation mutations identified for low expresser patient 13 are non-allelic. (A) RT-PCR nucleotide sequence chromatogram showing a novel premature termination mutation c.1918A>T: Lys640Stop (arrowed top panel) compared to the normal sequence (lower panel). Note: the upper chromatogram shows no evidence of expression of the normal 'A' nucleotide from the alternate allele. (B) RT-PCR amplification of the ATM cDNA for patient 13 using 8 sets of overlapping primers (supplementary table 1) returned single amplicons (lanes 2-8) with the exception of Fragment 1 (lane 1) which returned a dual amplicon suggestive of a deletion in one allele. (C) RT-PCR nucleotide sequence chromatograms for these two amplicons; sequence from the normal allele (upper panel) and the shorter allele (lower panel). Note: the shorter allele is missing sequence from exon 11. (D) Genomic sequencing revealed a heterozygous variation IVS10-6T-->G (1065del164) within the extended 5' splice site of intron 10 (ATM Ref Seq. NM_000051). Extended RT-PCR sequencing across both mutations confirmed these two mutations were non-allelic (result not shown).