The main research question this protocol aims to answer is whether treatment with growth hormone will impact body composition, quality of life, and energy balance in PWS adults, and if there is a loss of effects after cessation of treatment for at least 12 months.

The main research question this protocol aims to answer is whether treatment with growth hormone will impact body composition, quality of life, and energy balance in PWS adults, and if there is a loss of effects after cessation of treatment for at least 12 months. Specific outcomes to be evaluated are as follows:

• Increased IGF-1 as a function of human growth hormone dosage compared with baseline.

1. Improvement of indicators or risk factors for co-morbid diseases [diabetes (by measuring insulin and glucose levels), cardiovascular disease (by measuring lipids and fatty acids), and pulmonary function] in participants.
2. Improvement in quality of life measures as indicated by ratings on established behavior checklists in participants.
3. Changes in body composition (decreased fat, increased lean body mass and bone density) as determined by DEXA in participants.
4. Increased energy expenditure as determined by whole-room calorimeter measures (8 hour energy expenditure, RMR, TEF, mechanical work); diet records, physical activity monitors and strength measures.

Inclusion Criteria:

• 16 to 60 years old
• Male or female with diagnosed Prader-Willi syndrome confirmed by genetic testing (e.g., mPCR)
• Low IGF-1 level (e.g.,≤25%) at baseline
• Ability to provide informed consent or availability of a suitable legally authorized representative

Exclusion Criteria:

• Pregnancy
• Previous treatment with growth hormone
• Uncontrolled endocrine disease, (i.e. diabetes or thyroid)
• History of severe scoliosis
• Heart disease
• Uncontrolled high blood pressure or history of stroke
• Morbid obesity (using PWS growth charts)
• Severe sleep apnea or known breathing difficulties/obstruction (as per history or diagnostic testing results

24 months