Prader-Willi syndrome (PWS) is a genetic disorder associated with growth hormone (GH) deficiency, central hypotonia and hyperphagia that leads to life-threatening obesity. Treatment with GH in adult patients is not well stablished in guidelines of Health National System (HNS). The investigators has experience in the study of brain connectivity in these patients in relation to satiety. To date, there is no evidence about the effect of GH on central hypotonia (brain areas related with muscle tone maintenance). So, the main objective is to examine these anatomical areas before and one year after GH treatment.

Methodology: Structural and functional magnetic resonance imaging to 30 PWS patients before and after GH treatment and we will compare them to a control group.

Expected results: PWS group will show abnormal functional and structural connectivity in circuitry of muscle tone maintenance that will improve after GH treatment. These favorable changes and the absence of secondary effects will help to justify the use of this treatment and its inclusion in practical clinical guidelines of HNS for the management of this syndrome in the adulthood.

Inclusion Criteria:

• PWS >=18 years with growth hormone deficit
• Signed informed consent by the patients or their legal guardian

Exclusion Criteria:

• Severe obesity
• No controled diabetes mellitus
• No treated obstructive sleep apnea or severe obstructive sleep apnea
• Active cancer
• Active psychosis