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The annual incidence is 1/4,000 to 1/10,000 births with major variation occurring between geographic locations and ethnic groups. Cleft lip is twice as common in boys as girls and is seen more frequently on the left side.

The cleft is paramedian and located at the level of the philtrum. It presents as a cutaneous, muscular and mucosal interruption from the lip to the nasal base, associated with nostril and nasal septum deformations. Clinical forms range from a simple notch in the upper lip to a complete cleft lip with an opening at the base of the nostril without reaching as far as the gum (alveolar ridge).

This embryopathy appears between the 5th and 12th week of pregnancy due to a failure in the fusion of the frontal processes (fronto-nasal process, medial and lateral nasal processes, maxillary process). Cleft lip is an isolated, non-syndromic anomaly in 70% of cases. The remaining 30% of cases are seen in at least 300 syndromes where cleft lip is just one of the featured anomalies. Non-syndromic clefts are possibly caused by a combination of genetic and environmental factors. Factors such as the exposure to teratogenic substances during pregnancy (alcohol, tobacco or drugs) can have an influence on genetic susceptibility.

The diagnosis is clinical.

The presence of associated malformations allows for differentiation between isolated and syndromic forms.

Antenatal diagnosis is often possible with a prenatal ultrasound. The case is submitted to a multidisciplinary center for prenatal diagnosis in order to establish if it is an isolated anomaly.

Management requires multidisciplinary medical and surgical intervention from birth until the end of development. It involves primary surgery sometimes followed by secondary maxillo-facial and plastic surgery. An initial treatment timeline is established during the neonatal period. Secondary management is adapted to the child's age and based on morphological and functional problems that may arise during growth and development. Breathing difficulties can occur due to the nostril anomaly and the deviation of the vomer, of the nasal septum and to the turbinate hypertrophy. Secondary surgery of the nose can be performed to improve appearance and function.

Prognosis is dependent on the quality of initial management and the regular follow-up by an experienced interdisciplinary team until the child is fully grown. Cleft lip can have functional (morphological, respiratory), esthetic and psychological consequences that require management in a specialized health center.