The major features of MWS are:
- moderate-to-severe learning disability
- seizures (see entry Epilepsy)
- constipation (Hirschsprung's disease is only present in a minority of patients).
Typical facial features that include:
- deep-set, widely-spaced eyes
- thick eyebrows
- characteristic ear shape with a turned-up ear lobe
- broad nasal tip and short philtrum (the vertical central groove from the nose to the upper lip)
- small open mouth with a highly arched palate
- prominent chin.
Other features that have been observed in individuals with MWS include:
- growth, and developmental delay - speech can be delayed or absent
- failure to thrive in early life
- congenital heart disease (see entry Heart Defects)
- genitourinary anomalies
- eye anomalies
- white patches on the skin
- agenesis of the corpus callosum, which is visible on a magnetic resonance imaging (MRI) scan.
A number of behavioural features have been seen in MWS, these include:
- sociable, happy disposition
- disrupted sleep pattern
- tooth grinding and repetitive movements.