Definition: a congenital facial abnormality of the lip (usually of the upper lip) resulting from failure of union of the medial and nasal prominences with maxillary prominence; may be unilateral, bilateral, or median; frequently but not necessarily associated with cleft alveolus and cleft palate. In many families and in various forms [MIM*119300, *119500, *119530, *119540, and *119550], there seems to be autosomal dominant inheritance; likewise for X-linked inheritance [MIM*303400]. But generally, as with the supposed autosomal recessive forms, the genetics is more confusing, and this abnormality may represent a variable feature of a syndrome.
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Examples: glitazone, GI cocktail, etc.