Midline cleft of lower lip is a rare anomaly defined as Cleft No. 30 in the Tessier classification. Less than 70 cases have been described worldwide. These cases show a broad variation in severity, ranging from a simple notch in the vermillion to a complete cleft of the lip involving the tongue, the chin, the mandible, the supporting structures of the median of the neck and the manubrium sterni. The tongue is often attached to the cleft alveolar margin (ankyloglossia). Other associated anomalies were described in a number of cases such as absence or underdevelopment of the hyoid bone and/or thyroid cartilage. The only known familial cases were reported in 1936 with 18 affected individuals spanning four generations. [from
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