KCNK9 imprinting syndrome is characterized by a variety of symptoms including distinctive facial features, varying degrees of intellectual disability, and low muscle tone at birth (hypotonia). The specific symptoms and severity of the disorder can vary from one person to another. Affected children may have a head that is long and narrow (dolichocephaly). Children have an elongated face with a narrow bitemporal diameter, full eyebrows that are arched and flared upward, a short groove or depression that runs from the nose to the upper lip (short philtrum), a tented upper lip, abnormalities of the roof of the mouth (cleft palate in 42% of cases), and a small lower jaw with micrognathia and retrognathia. The bridge of the nose may be narrow and high, and the tip of the nose may be broad. Severe generalized congenital hypotonia may be present at birth, and these infants may have transient neonatal hypoglycemia. Some infants experience severe difficulties with feeding because of a poor ability to suck, with dysphagia, and some children require the placement of a gastrostomy tube to aid with feeding. They may also have difficulty speaking (dysphonia) and a muffled voice into early adulthood. Older children have moderate to severe intellectual disability, delays in reaching developmental milestones, proximal muscle weakness, and severely reduced facial movements. Muscle weakness and hypotonia may eventually progress to cause contractures, and this can be alleviated by physical therapy. Some children will develop seizures.
KCNK9