This X-linked form of mental retardation is characterized by typical facial features (progressive development of coarse facies with prominent chin and ears and heavy brow; down-slanting palpebral fissures and epicanthal folds, broad nose with thick alae nasi, septum and anteverted nares; large open mouth with full lips, hypodontia and other dental and bite anomalies, narrow high palate). A consistent feature is the large, puffy, soft hands with tapering fingers distally, small fingernails and full forearms. Skeletal anomalies include kyphoscoliosis, lordosis, and pectus carinatum or excavatum. Patients are usually short with delayed bone age; joints are hyperextensible. The cognitive function of affected males is usually severely impaired. Patients are hypotonic and may have “drop attacks”. Sensorineural hearing loss has been described.
Complications resulting in early death include spinal stenosis leading to neurologic symptoms, and progressive kyphoscoliosis leading to impaired cardiorespiratory function. Heterozygous females may exhibit mild to severe features of the disorder.