Common clinical features encompass developmental delay, neurological features including structural brain abnormalities, seizures and hypotonia, growth abnormalities, feeding difficulties, musculoskeletal abnormalities, facial dysmorphism, vision and/or auditory problems, craniosynostosis, and a variety of congenital malformations. Many children have feeding difficulties during the neonatal period due to muscle weakness (hypotonia). Also, epilepsy is rather prevalent in this period.
Concerning the appearance, people with disease-causing mutations in SON often have a short stature and notable facial features such as an asymmetrical face, low-set ears, horizontal eyebrows and a broad and/or flat nose.