Congenital absence of depressor anguli oris: rare cause of f
The following case has been reported in BMJ.

A 2-year-old developmentally normal girl presented to with a history of deviation of angle of mouth to right only during crying, persisting from neonatal period. She was born at term by normal vaginal delivery to a primigravida mother with a birth weight of 2.2 kg and smooth perinatal transition.

Parents noticed asymmetry of face from neonatal period visible only during crying, which disappeared when she was consoled, without any drooling, regurgitation of feeds or poor sucking.

Local examination revealed thinning of lower lip near left angle of mouth on palpation. There was no facial asymmetry while the child was calm, however, on crying there was deviation of the angle of mouth downwards and towards right side. There was no evidence of hypoplasia or weakness of any other facial or extraocular muscle.

There was no dysmorphism, facial or ocular deformity and any overt evidence of systemic disease. Neurological examination of this alert, conscious and cooperative child revealed normal power, tone and deep tendon reflexes. There was no evidence of any cranial nerve palsy, cerebellar signs or synkinesis.

A diagnosis of congenital hypoplasia of depressor anguli oris muscle (CHDAOM) of left side was made and parents were counselled about the benign nature of the condition.

Learning points
• Congenital absence of depressor anguli oris is a rare cause of facial deviation in infancy and childhood.

• History and clinical examination are crucial for diagnosis and avoid unnecessary investigations.

• It usually becomes unnoticeable by adulthood and parental counselling is of paramount importance.