- A human serotonin 1D receptor variant (5HT1D beta) encoded by an intronless gene on chromosome 6. Demchyshyn, L., Sunahara, R.K., Miller, K., Teitler, M., Hoffman, B.J., Kennedy, J.L., Seeman, P., Van Tol, H.H., Niznik, H.B. Proc. Natl. Acad. Sci. U.S.A. (1992)