- Severe hypotonia at birth
- Feeding difficulties at first
- Hypogonadism (undescended testicles in males, reduced or lacking menstruation in females)
- Mild to moderate intellectual disabilities (see entry Learning Disability)
- Obesity (in the absence of food restrictions this appears to be universal).
The syndrome often includes:
- short stature
- developmental delay in walking and speech
- obsessive behaviour
- strabismus (squint)
- small hands and feet
- skin picking
- scoliosis (spinal curvature)
- diabetes (see entry Diabetes Mellitus)
- challenging behaviour
- psychiatric illnesses (usually starting in late adolescence and adulthood).
The two main genetic subtypes (deletion and maternal disomy; see 'What are the causes') differ in many respects, including: average maternal age at birth, 'fair for family' pigmentation, cognitive strengths and weaknesses, and risk of depressive (greater in deletion subtype) and psychotic (greater in maternal disomy subtype) illnesses.
The above characteristics, although typical of people with Prader-Willi syndrome in general, are not all universal and vary in severity.