Major gene determination of liability to cleft lip with or without cleft palate: a multiracial view.

Despite nearly half a century of intensive investigation, the etiology of non-syndromic cleft lip with or without cleft palate (CL +/- P) remains unknown because most studies have been descriptive rather than analytic. This study summarizes rigorous analyses of CL +/- P in the families of non-syndromic, CL +/- P surgical probands from three populations: Denmark, London, England, and Shanghai, China. Three main conclusions could be drawn from the results. The data provide no support for the multifactorial threshold model summarized by Carter (1976) and most often proposed to explain the etiology of CL +/- P. Each dataset provides evidence that there may be a major gene for liability to CL +/- P in at least a portion of cases. The data are consistent with possible genetic heterogeneity in CL +/- P.