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Asymmetric crying facies (ACF), also known as congenital unilateral lower lip palsy (CULLP) , is a defect present at birth characterized by facial weakness on one side of a child's face. ACF is only noticeable when the child is frowning, crying or smiling and not when the child is at rest. ACF only affects the lower lip, while the rest of the face is unaffected. ACF occurs in about 1 out of 160 live births. The defect is either due to the angenesis or hypoplasia of the depressor anguli oris muscle, the muscle that joins the lower jaw to the corners of the mouth, or compression of the facial nerve. The left side of the face is affected in 80% of cases. It is important to establish the origin of ACF to determine whether or not there are associated anomalies.

Symptoms
ACF is characterized by the following traits :
 * One side of the mouth is pulled downward while the other side of the mouth is unaffected when the baby cries, frowns or smiles
 * Thinning of lip on affected side
 * There is no other indication of asymmetry and the face appears symmetrical at rest

Causes
There are two common causes of ACF. One is due to a birth trauma and the other is a developmental issue in the womb.

Trauma During Delivery
During vaginal delivery, pressure from the mother's pelvis bone to one of the branches of the facial nerves can cause ACF. Other traumas could be due to incorrect or improper birth delivery methods. This can include trauma inflicted by forceps blades or intracranial hemorrhage during birth.

Developmental Issues in the Womb
During development, the depressor anguli oris muscle either fails to develop or develops incompletely. The most common cause of underdevelopment of the depressor anguli oris muscle is due to deletion of the of a piece of chromosome 22, known as Cayler syndrome or 22q11.2 deletion syndrome.

Diagnosis
ACF is solely a malformation of one side of the lower lip. If there are other noticeable asymmetries or abnormalities of the face, it is likely not ACF.

A child born with signs of asymmetrical crying facies must be examined to determine whether the defect is genetic or acquired due to trauma. If the cause is found to be acquired during delivery, there is no further search needed for other major anomalies. If it is suspected to be genetic then electromyography and ultrasound techniques may be used to confirm underdevelopment or absence of the depressor anguli oris.

If it is confirmed to be of genetic origin, a search for other major anomalies should be conducted. ACF can be an indication of cardiovascular, head and neck, musculoskeletal, respiratory, gastrointestinal, central nervous system and genitourinary anomalies. One major anomaly usually associated with ACF is Cayler syndrome.

Treatment
The symptoms of acquired ACF normally improve within a month and eventually disappear naturally within a year. If ACF is due to birth trauma, it becomes less noticeable as the child grows up. If it is a genetic defect or symptoms do not become less noticeable, surgery is usually the main option. However, if surgery is unfavourable or the muscle pull is mild, botulinum toxin injections can balance the muscles along the lower lip.

Cayler Syndrome
Although ACF is usually a standalone effect, there is a 10% risk of major anomalies including Cayler syndrome. When the hypoplasia of the depressor anguli oris muscle is associated with cardiac defects, it is known as Cayler syndrome. Cayler syndrome is also known as the cardiofacial syndrome. Cayler syndrome is associated with a deletion of a small piece of chromosome 22 and is part of the 22q11.2 deletion syndrome.

Defects associated with Cayler syndrome may include ventricular septal defects, atrial septal defects and tetralogy of Fallot. Common defects include microcephaly, mental retardation, micrognathia, micropthalmia.