Linkage of a gene regulating dopamine-beta-hydroxylase activity and the ABO blood group locus

Previous studies have presented evidence suggesting that levels of dopamine-beta-hydroxylase (DBH) activity are controlled by a gene linked to the ABO blood group locus. In this study, linkage analyses in four large families of whites and one family of blacks were performed on the untransformed and on the square root--and natural log--transformed DBH activity. In the families of white individuals, the results of both the sib-pair and lod-score linkage analyses strongly indicate that a gene regulating DBH activity is linked to the ABO blood group locus on chromosome 9q (i.e., lod score 5.88 at a recombination fraction of .0). However, the transformation used has a large effect on the maximum lod score and estimated recombination fraction. This putative gene does not appear to be polymorphic in the family of blacks.