Sidedness in unilateral orofacial clefts: A systematic scoping review

ABSTRACT Objectives An overview of the literature relating to the sidedness of unilateral cleft lip with or without cleft palate to map current knowledge on the cause and impact of directional asymmetry in the unilateral cleft lip phenotype. Data Sources Medline and Embase from inception to May 2023 Study selection Studies including left and right unilateral cleft lip subgroups as a co-occurrence, an outcome or an exposure. Data analysis Narrative synthesis. Results Forty-one studies were eligible for inclusion; 12 studies reported cleft sidedness co-occurring with another phenotype, 12 studies report sidedness as an outcome and 17 studies as an exposure. Phenotypes which were reported to co-occur with either left or right sided clefts included congenital dental anomalies, handedness and additional congenital anomalies. Variables investigated as a potential cause of left or right sided clefts as an outcome included chromosomal anomalies, genetic variants and environmental factors. Outcomes investigated in relation to cleft sidedness as an exposure included facial anatomical features, facial growth, educational attainment, functional and psychological characteristics. More studies showed worse outcomes in right sided clefts versus left sided clefts than vice versa, although studies were inconsistent, and a quality assessment was not performed. Conclusions The field of cleft sidedness research is expanding and there are promising early findings to differentiate cause and outcome by sidedness of the cleft.