title: Selection bias in genetic-epidemiological studies of cleft lip and palate.
abstract: The possible impact of selection bias in genetic and epidemiological studies of cleft lip and palate was studied, using three nationwide ascertainment sources and an autopsy study in a 10% sample of the Danish population. A total of 670 cases were identified. Two national record systems, when used together, were found suitable for ascertaining facial cleft in live births. More than 95% ascertainment was obtained by means of surgical files for cleft lip (with or without cleft palate) without associated malformations/syndromes. However, surgical files could be a poor source for studying isolated cleft palate (CP) (only a 60% and biased ascertainment), and they cannot be used to study the prevalence of associated malformations or syndromes in facial cleft cases. The male:female ratio was 0.88 in surgically treated cases of CP and was 1.5 in nonoperated CP cases, making the overall sex ratio for CP 1.1 (95% confidence limits 0.86-1.4) The sex ratio for CP without associated malformation was 1.1 (95% confidence limits 0.84-1.6). One of the major test criteria in CP multifactorial threshold models (higher CP liability among male CP relatives) must be reconsidered, if other investigations confirm that a CP sex-ratio reversal to male predominance occurs when high ascertainment is achieved.
authors.affiliation: Institute of Community Health, University Clinic, Odense University, Denmark.
authors.forename: K
authors.initials: K
authors.lastname: Christensen
authors.forename: N V
authors.initials: NV
authors.lastname: Holm
authors.forename: J
authors.initials: J
authors.lastname: Olsen
authors.forename: K
authors.initials: K
authors.lastname: Kock
authors.forename: P
authors.initials: P
authors.lastname: Fogh-Andersen
mesh_terms: D002971:Cleft Lip / Q000453:epidemiology* / Q000235:genetics; D002972:Cleft Palate / Q000453:epidemiology* / Q000235:genetics; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006801:Humans; D008297:Male; D008957:Models, Genetic; D015983:Selection Bias; D012744:Sex Ratio