The following description of the clinical manifestations is based on a comprehensive review of the literature and personal observations of the moderators (unpublished data).
Neurological features
Individuals with Snyder-Robinson syndrome present with global developmental delay and ID. The level of ID is variable, and can range from mild to severe. Speech delay is always present, and hypernasal voice is very common. A minority never walks independently; those who ambulate are unsteady. Neonatal hypotonia is seen in the majority of patients, and may result in delayed motor development. Most patients have a friendly personality. Autistic features have been described in a subset of patients. Seizures have been identified in over a third of affected males. Structural anomalies of the central nervous system can be occasionally present, including enlarged ventricles or hypoplasia of the corpus callosum.
Growth parameters
Although prenatal growth parameters are usually within the normal range, low birth weight has been reported in several individuals. Post-natal height and weight are usually normal, and head circumference is in the upper centiles. All affected individuals develop hypotonia in the first months of life and have a characteristic thin habitus with diminished muscle mass.
Craniofacial features
Males with Snyder-Robinson syndrome have common facial features, although a distinctive facial gestalt has not been described yet. Asymmetric face, long palpebral fissures, and prominence of the lower lip vermillion are frequently seen. The palate is usually highly arched, determining a characteristic nasal and dysarthric voice.
Orthopedic manifestations
Kyphoscoliosis is present in almost all affected individuals starting from the first decade of life, and is thought to be progressive. Pectus carinatum or excavatum is occasionally seen. A key manifestation of Snyder-Robinson syndrome is early-onset osteoporosis, often leading to bone fractures that occur spontaneously or after minor trauma. Most patients have and unsteady and wide-based gait.
Other physical characteristics
Genitourinary abnormalities have been described. Some affected males have hearing impairment and recurrent respiratory infections, especially in childhood.