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Prader–Willi syndrome (PWS) is a rare orphan disease and complex genetic neurodevelopmental disorder, with a birth incidence of approximately 1 in 10,000–30,000. Management of people with PWS requires a multi-disciplinary approach, ideally through a multi-disciplinary team (MDT) clinic with community support. Hypotonia, poor feeding and faltering growth are characteristic features in the neonatal period, followed by hyperphagia and risk of rapid weight gain later in childhood. Children and adolescents (CA) with PWS usually display developmental delay and mild learning disability and can develop endocrinopathies, scoliosis, respiratory difficulties (both central and obstructive sleep apnoea), challenging behaviours, skin picking, and mental health issues, especially into adulthood. This consensus statement is intended to be a reference document for clinicians managing children and adolescents (up to 18 years of age) with PWS. It considers the bio-psycho-social domains of diagnosis, clinical assessment, and management in the paediatric setting as well as during and after transition to adult services. The guidance has been developed from information gathered from peer-reviewed scientific reports and from the expertise of a range of experienced clinicians in the United Kingdom and Ireland involved in the care of patients with PWS.

Background: Hypogonadism is a key feature of Prader–Willi syndrome (PWS) but clear strategies for hormone replacement are lacking. Objective: To evaluate the gonadal status and outcome in patients attending a Scottish PWS clinic from 1991 to 2019. Methods: In 93 (35F:56M) patients, median follow-up 11.2 years, gonadal and pubertal status were assessed clinically. Pelvic ultrasound findings and basal/stimulated gonadotrophins were compared with age-matched controls. Results: Females: of 22 patients aged > 11, 9 had reached B4–5, while 5 were still at B2–3, and 6 remained prepubertal. Eight patients experienced menarche aged 9.8–21.4 years, none with a normal cycle. Uterine length and ovarian volumes were normal but uterine configuration remained immature, with low follicular cou nts. Gonadotrophins were unremarkable, serum oestradiol 129 (70–520) pmol/L. Only 5 patients received oestrogen replacement. Males: fifty-four (96%) patients were cryptorchid (9 unilateral). Weekly hCG injections resulted in unilateral/bilateral descent in 2/1 of 25 patients. Of 37 boys aged > 11, 14 (9 with failed/untreated bilateral cryptorch idism) failed to progress beyond G1, 15 arrested at G2–3 (testes 3–10 mL), and 8 reached G4–5. Gonadotrophins were unremarkable except in boys at G2–5 in whom FSH was elevat ed: 12.3/27.3 vs 3.25/6.26 U/L in controls (P < 0.001). In males aged > 13, testosterone was 3.1 (0.5–8.4) nmol/L. Androgen therapy, given from 13.5 to 29.2 years, was st opped in 4/24 patients owing to behavioural problems. Conclusion: Despite invariable hypogonadism, few females and only half the males with PWS in this study received hormone replacement. Double-blind placebo-controlled crossover trials of sex steroids are required to address unproven behavioural concerns.