Male individuals with Christianson syndrome have moderate to severe developmental delay / intellectual disability. The disorder often starts with delayed early motor development, followed by generalised and complex seizures patterns in early childhood. Motor skills may be significantly delayed and associated with unsteady balance and gait. Patients exhibit persistent restlessness and extremely active behaviour. There is poor or absent speech and delayed or reduced brain growth. Behaviourally, a majority exhibit a happy demeanour and unprovoked laughter. Secondary symptoms include autistic behaviour, abnormal eye movements, gastroesophageal reflux disease, decreased muscle tone, low weight for age group, difficulty sleeping, and reduced sensitivity to painful stimuli.
Females who carry a defective variant of SLC9A6are generally asymptomatic but in exceptional cases can exhibit moderate intellectual disability, delays in speech and language acquisition, and psychiatric illnesses, including separation anxiety disorder, difficulty forming emotional attachments to others, uncooperative behaviour and attention deficit/hyperactivity disorder (ADHD).
SLC9A6