Systematic screening for DNA sequence variation in the coding region of the human dopamine transporter gene (DAT1)

The dopamine transporter (DAT) plays a central role in dopaminergic neurotransmission in the human brain. Genetic association studies have used a variable number of tandem repeat (VNTR) polymorphism in the 3'-flanking region of the dopamine transporter gene (DAT1) to implicate the DAT in the development of various neuropsychiatric disorders. In this study, we have examined the possibility that a mutation exists in the coding region of the DAT1 gene which through linkage disequilibrium accounts for the observed associations. The complete coding region, as well as exon-intron boundaries, was screened in 91 unrelated individuals including 45 patients with bipolar affective disorder and 46 healthy control individuals by the means of single strand conformation analysis. Our findings suggest that the DAT1 gene is highly conserved since we detected only two rare missense substitutions (Ala559Val, Glu602Gly) and three silent mutations (242C/T, 1342A/G, and 1859C/T) in the whole coding region. Five sequence variants were observed in intronic sequences but none affects known splice sites. The lack of frequent variants of possible functional relevance indicates that genetic variation in the coding region of the DAT1 gene is not responsible for the previously observed associations with neuropsychiatric disorders. The two rare missense substitutions were found in single bipolar patients but not in controls. Investigation of the patients' families revealed independent segregation between the Ala559Val variant and affective disorder. The Glu602Gly variant was inherited by the proband from an affected father. It therefore remains possible that Glu602Gly may be a rare cause of bipolar affective disorder.