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 neurotr ansmission in the human brain. Genetic association studies have used a vari able number of tandem repeat (VNTR) polymorphism in the 3'-flanking region of the dopamine transporter gene (DAT1) to implicate the DAT in the develop ment of various neuropsychiatric disorders, In this study, we have examined the possibility that a mutation exists in the coding region of the DAT1 ge ne which through linkage disequilibrium accounts for the observed associati ons. The complete coding region, as well as exon-intron boundaries, was scr eened in 91 unrelated individuals including 45 patients with bipolar affect ive disorder and 46 healthy control individuals by the means of single stra nd conformation analysis. Our findings suggest that the DAT1 gene is highly conserved since we detected only two rare missense substitutions (Ala559Va l, Glu602Gly) and three silent mutations (242C/T, 1342A/G, and 1859C/T) in the whole coding region. Five sequence variants were observed in intronic s equences but none affects known splice sites. The lack of frequent variants of possible functional relevance indicates that genetic variation in the c oding region of the DAT1 gene is not responsible for the previously observe d associations with neuropsychiatric disorders. The two rare missense subst itutions were found in single bipolar patients but not in controls. Investi gation of the patients' families revealed independent segregation between t he Ala559Val variant and affective disorder, The Glu602Gly variant was inhe rited by the proband from an affected father. It therefore remains possible that Glu602Gly may be a rare cause of bipolar affective disorder.