- Polymorphisms and linkage disequilibrium in the COL6A1 and COL6A2 gene cluster: novel DNA polymorphisms in the region of a candidate gene for congenital heart defects in Down's syndrome. Davies, G.E., Howard, C.M., Gorman, L.M., Farrer, M.J., Holland, A.J., Williamson, R., Kessling, A.M. Hum. Genet. (1993)