Growth Hormone Therapy
A level of growth hormone deficiency is present in nearly all individuals with PWS so growth hormone therapy has been widely used internationally as a treatment for PWS since 2000. The primary benefit of treatment is not the normalisation of height which occurs, but the significant changes to body composition (increased lean body mass and reduced fat mass), with parents observing dramatic changes in strength and activity levels. In conjunction with an appropriate diet and exercise, “GHT is a potent force for counteracting the clinical course of obesity in Prader-Willi syndrome.” (Bakker et al 2013.) Studies have also shown improvements in bone mineral density, motor development, cognitive skills and speech, plus improvements in mental health and quality of life for adults. Research has also observed that these benefits increase with earlier treatment. In 2012, consensus guidelines for GH therapy in PWS were produced by 43 international experts concluding that GH treatment should be considered for all patients with genetically confirmed PWS.
Analysis of data shows GHT is a safe treatment for PWS with minimal reported side effects. There has been concern of a possible association between GHT, sleep abnormalities and sudden death, however, recent studies show that with the development of respiratory muscle, GH therapy actually improves oxygenation and cardiovascular function during sleep in patients with PWS. (Sleep abnormalities are common and well documented in PWS, including central sleep apnoea which is common in infancy). Lymphoid hyperplasia (increase in lymph node cells) may obstruct breathing and is related to high levels of IGF-I (Insulin-like Growth Factor-1 which the body produces in response to GHT), but research has shown that GH treatment does not change the prevalence or severity of obstructive sleep apnoea. As a result of this possible concern, the GH consensus guidelines recommend that for the paediatric age range, IGF-I levels should be maintained within the upper part of normal range. Prerequisites of GH treatment in New Zealand include there being no evidence of type II diabetes or uncontrolled obesity and tests for obstructive sleep disorder are performed prior to and during treatment. If obstructive sleep apnoea is observed, treatment is necessary before starting GHT, which means an adeno-tonsillectomy is usually required. During GH treatment, IGF-1 levels are closely monitored by endocrinologists. Studies have found that upper respiratory infections during the initiation phase of GH therapy can cause breathing problems in young children with PWS and whilst there is still some uncertainty about whether GH was responsible for worsening respiratory symptoms, some doctors advocate monitoring with several nights of pulse oximetry during upper respiratory infections or briefly pausing treatment. In conclusion, close monitoring of IGF-1 levels, breathing and sleep abnormalities is recommended throughout GH treatment and especially during respiratory illness.
Since January 2017, funded Somatropin (human growth hormone) can be prescribed from 6 months old without a need for the collection of growth data. As benefits increase with earlier treatment, we recommend parents discuss growth hormone treatment with their endocrinologist as soon as possible because of the time needed for the various referrals that need to take place prior to starting treatment. As a safety precaution, a sleep study should be undertaken and if OSA is observed, a referral needs to be made to a respiratory physician or ENT for assessment and possible removal of tonsils and adenoids before starting GHT. (PHARMAC require a sleep study or overnight oximetry, but a sleep study is more thorough.) For children under 2 years, PHARMAC also require an upper airway assessment prior to starting treatment and at 6-12 weeks following treatment initiation. We would recommend a follow up sleep study for all patients after starting GH treatment.
The brand of Somatropin currently used in New Zealand is Omnitrope. GHT is given daily before bedtime using an injection pen which is child and parent friendly and parents are shown how to use it during an appointment with a specialist nurse. Endocrinologists continue to see children at three monthly intervals and will monitor growth, weight and regular blood test results. At the time of writing, special authority for funded GH treatment in New Zealand is renewed 12 monthly until a bone age of 14 years girls / 16 years boys is reached, providing growth criteria are met. The PWSA(NZ) continues to appeal to PHARMAC asking that changes are made to extend treatment time further and to remove the remaining growth criteria.
If you require more information about GHT for PWS, we recommend reading this clear and comprehensive book ‘Growth Hormone and Prader-Willi Syndrome’, published by PWSA USA.
Growth Hormone Treatment for Adolescents and Adults
As yet, GHT for PWS is not funded in NZ beyond end of growth, but some adults may qualify for funded treatment for Growth Hormone Deficiency. A level of deficiency which increases with age is thought to be present in all individuals with PWS, but emerging data on the prevalence of severe GHD in adults with PWS currently varies. To qualify for funded treatment, adults need to be tested and meet PHARMAC’s criteria for severe GHD. If the criteria are not met, some families choose to continue self-funding GH treatment if they are financially able. As the GH dose reduces to an adult maintenance dose, the monthly cost of treatment also becomes less. If you would like to find out more about self-funding GHT, we would be happy to provide further information and put you in touch with other families with experience of this.