KCNK9 imprinting syndrome is a rare condition characterized by weak muscle tone (hypotonia) from birth. As a result, affected infants have a lack of energy (lethargy), a weak cry, and they move less than normal. Facial weakness and a poor ability to suck cause feeding difficulties, which can lead to an inability to grow and gain weight (failure to thrive). Difficulty swallowing (dysphagia) often lasts into adolescence. While muscle tone may improve over time, affected individuals usually have some weakness into adulthood. The weakness can lead to permanently bent joints (contractures) and abnormal curvature of the spine ().
KCNK9 imprinting syndrome is also characterized by intellectual disability and delayed development of speech and motor skills, such as sitting and walking. Many affected individuals have limited speech throughout life.
This condition is associated with unusual facial features, including an elongated face that narrows at the temples; an upper lip that points outward (called a tented lip); a short, broad space between the lip and the nose (); a small lower jaw (micrognathia); and abnormally shaped eyebrows. Some affected individuals have an opening in the roof of the mouth (). In addition to unusual facial features, some people with KCNK9 imprinting syndrome have a long neck, a narrow chest, and tapered fingers.