To further characterize this boy's COMT genotype, we generated a lymphocyte cell line. DNA nucleotide sequence analysis indicated that the patient was heterozygous for the G675A COMT haplotype (Figure 2(a)i) and that the chromatogram peak height for the 675G variant was consistently two times higher than that of the 675A variant (Figure 2(a)i). This suggests that the 675G (higher-expressing) allele [11] was duplicated. We then compared mRNA/cDNA sequence for the patient and a normal individual. The G : A ratio for the normal control heterozygote was slightly >1 (Figure 2(a)iii) consistent with the instability of the 675A mRNA transcript [11]. In contrast, the G : A ratio for the patient was >2 (Figure 2(a)ii) which again suggested that the patient has a higher than normal level of expression of the COMT gene.
