The most common mutation in RPS6KA3 is an early stop codon that fails to produce a functional protein, indicating that disease etiology most likely arises from loss-of-function effects. Substitution mutations (which alter a single amino acid) have also been shown to give rise to the disease. RSK2 is highly expressed in the brain, specifically in the neocortex, hippocampus, and Purkinje cells, all of which are involved in cognitive function and behavior. There is some experimental evidence that RSK2 regulates synaptic transmission and plasticity in neuronal cell types. Diagnosis Affected individuals are often short in stature. Behavioral symptoms include aggression and depression, but these may be secondary to the emotional consequences of significant physical disabilities associated with the disorder. Coffin–Lowry patients may be affected by chewing and swallowing difficulties, for which there are diagnostic assessments. Among these are the Videofluoroscopic Swallowing Evaluation (VFSE), the Karaduman Chewing Performance Scale, and the Penetration Aspiration Scale (PAS) which is used to evaluate accidental aspiration of food particles. The Pediatric Assessment Tool (PEDI-EAT-10) also includes measurement of severity of dysphagia (difficulty in swallowing). Molecular genetic testing can be used to confirm the genetic diagnosis of Coffin–Lowry syndrome or to assess pregnancy risk in affected families. Symptoms table: Generally symptoms listed as "rare" are common in more severe cases. Imaging studies X-ray and neuroimaging studies may be helpful in confirming a diagnosis of Coffin–Lowry syndrome. Decreased ribosomal S6 kinase activity in cultured fibroblast or transformed lymphoblast cells from a male indicates Coffin–Lowry syndrome. Studies of enzyme activity can not be used to diagnose an affected female. Molecular genetic testing on a blood specimen or cells from a cheek swab is available to identify mutations in the RSK2 gene. This testing can be used to confirm but not rule out the diagnosis of Coffin–Lowry syndrome because not all affected individuals have a detectable mutation. Treatment There is no cure for Coffin–Lowry syndrome. Clinical objectives are centered on symptom management. Because stimulus-induced drop attacks (SIDAs) can result in physical harm to patients with the disorder, the use of medication to prevent or reduce the number of SIDA episodes is a safety priority. Physical precautionary measures have also been used to protect patients from injury, including the use of a helmet or a wheelchair. Because sudden excitement or fright can trigger a SIDA episode it is important to minimize exposure to startling stimuli. Medications prescribed include benzodiazepines (tranquilizers used