Cleft lip and handedness: a study of laterality

Research on the malformation cleft lip with or without cleft of the palate is complex and may involve studies of etiology, pathogenesis, natural history, and other disease associations. One of the more intriguing areas of study is developmental lateralization. The 3 extant reports of the relationship between laterality of cleft lip and handedness are in conflict. The purpose of the present study is an attempt to resolve the confusion and to explore possible hypotheses that could explain the data. A random sample of 149 probands with unilateral cleft lip +/- palate was ascertained from 2 Los Angeles area hospitals. Laterality of clefting and handedness was determined for each, the former by inspection and the latter by the method of Oldfield [1971]. Information was also obtained on the nuclear family about the number of sibs, presence of clefting, and handedness of the probands' parents. The probability of non-right-handedness (NRH) was much greater for probands with left-sided cleft lip than those with right-sided cleft lips; this was independent of the proband's sex. The cleft lip laterality in probands was independent of parental handedness, suggesting that the significantly increased frequency of left-sided clefting and NRH is embryologic in origin and may have a common etiology and/or pathogenesis. Several explanations are proposed and discussed.