Profile as a Phenotype Impacted by Functional Genetic Polymorphism


Carlo Colantuoni, National Institute of Mental Health, Bethesda, MD


We have

conducted a hypothesis-driven genomics investigation of mRNA expression profiles

in postmortem human brain. Expression profiles were treated as a molecular

phenotype dependent on functional genetic polymorphisms. In a recent study, we

have demonstrated the functional impact of a single nucleotide polymorphism (SNP)

in the catechol-O-methyl transferase (COMT) gene on frontal cortical brain

function and working memory (Egan et al. PNAS 2001). The Val/Met amino acid

substitution in the COMT protein which results from this SNP causes a 4-fold

change in the enzyme’s dopamine metabolizing activity and may also increase risk

for schizophrenia. In the present study, frontal cortical mRNA expression

profiles were measured in two distinct cohorts of 24 normal individuals

segregated by COMT genotype. cDNA microarrays from the National Institute of

Aging in Baltimore were used to assess the expression of thousands of genes in

each postmortem frontal cortex sample. PCR assays were used to determine COMT

genotype in blood or cerebellar tissue from each subject. In addition to the

largest individual gene expression changes, we have focused on the detection of

more subtle expression changes occurring in groups of functionally related genes

that are consistently differentially expressed across COMT genotype. The use of

functional genetic data in combination with both clinical and basic

investigation of functional SNPs provides a link to hypothesis-driven

experimentation in gene expression analysis, and a method to elucidate the

impact of normal genetic variation on gene expression in the brain. We plan to

investigate the Stanley tissue collection in a similar fashion, by analyzing

gene expression patterns across several functional genetic polymorphisms.