Growth hormone therapy should be universally available, given to adults as well as children with Prader–Willi syndrome (PWS) and based solely on a genetic PWS diagnosis.
This is the position of the Clinical and Scientific Advisory Board of the International Prader-Willi Syndrome Organisation (IPWSO). Its reasoning was detailed in a letter, “Time for a general approval of growth hormone treatment in adults with Prader–Willi syndrome,” written to the editor of the Orphanet Journal of Rare Diseases.
“In adults with PWS, GH’s [growth hormone’s] main effects are to maintain normal body structure and metabolism,” scientists in Sweden, the U.K. and the U.S. wrote, on behalf of the board. “The positive effects of GH treatment on body composition, physical fitness and beneficial effects on cardiovascular risk markers, behaviour and quality of life in adults with PWS are also well established from several studies.”
PWS is characterized by low muscle tone in infants, and short stature, intellectual disability, behavioral or psychiatric problems, and abnormal body composition with increased body fat throughout life.
Deficient growth hormone (GH) is common in PWS and is caused by a malfunctioning hypothalamus, a small region of the brain that controls the pituitary gland and regulates body functions that include GH secretion.
GH treatment in children with PWS began in the 1990s, with improvements in height and body composition as well as greater muscle strength and exercise endurance. Consequently, GH therapy was approved for use in children in the U.S. and Europe.
However, its use with adults has only been approved in a few countries, leaving many older PWS patients with limited treatment options such as a strict lifelong diet, regular physical activity, and therapies for other hormone deficiencies.
GH treatment for adults is of considerable interest to the PWS community, being the “single most commonly asked question at the awareness booth hosted by the [IPWSO] at the European Society of Paediatric Endocrinology meeting in 2019,” the team wrote.
Support for adult GH treatment in PWS was traced back to the treatment of children with growth hormone deficiency (GHD) in the 1950s — a rare disorder characterized by the inadequate secretion of GH from the pituitary gland. Regarding body composition and increased fat mass, adults with PWS share similarities with GHD.
Since the 1990s, adults with severe GHD have been treated with growth hormone, leading to better body composition, heart disease risk factors, and quality of life with few side effects. While GH no longer triggers growth in adults, it helps maintain normal body structure, metabolism, and set blood glucose levels.
According to the GHD diagnostic criteria, up to 55% of PWS adults have profound growth hormone deficiency. However, tests to measure GH levels to diagnose deficiency (GH stimulation) detect GH secretions from the pituitary gland, leading to false normal results in those whose deficiency is caused by the hypothalamus, as in PWS. Greater PWS-related fat tissue can also affect test results.
As a result, “GH stimulation tests are of questionable value and are not of clinical relevance in this group of patients,” the researchers wrote.
Several studies have investigated the impact of growth hormones in PWS adults. A meta-analysis of eight studies, including 134 adults treated with GH, showed better body composition with lesser body fat and increased lean body mass. This positive impact on body composition was reported in all studies, and later confirmed in long-term research.
A three-year study evaluating GH therapy in young adults with PWS demonstrated that, after reaching a final height and body composition from childhood treatment, continued therapy maintained these improvements.
As a result of better body composition, improvements in physical activity have been observed. Exercise intensity in GH-treated PWS adults improved 16% after six months and 19% after one year, with long-term GH therapy increasing muscle strength by 13% and exercise endurance by 17%, researchers reported. GH treatment also improved cognitive function, and other studies have reported a better quality of life.
These findings were confirmed indirectly after GH use was discontinued. One study reported that one year without this therapy led to a 22% increase in body fat in young adults. Consistently, another study demonstrated impaired motor skills within six months of stopping GH. Significant difficulties with social activities in adults was also found after stopping treatment.
While the team described clear benefits of GH treatment in PWS adults, however, the therapy is administered daily with subcutaneous (under-the-skin) injections, which PWS adults may not well manage. Supervision may be needed, increasing the burden on caregivers.
The incidence of psychoses (problems with thinking and perception) is also high in adults with PWS. GH therapy may impact psychiatric medications by altering their metabolism. As such, regular psychiatric evaluations may be required after GH is started.
“GH has an important role in optimisation of care in people with PWS, and we advocate for approval for continuing GH treatment in young adults with PWS based on the genetic diagnosis of PWS without testing of GH secretion,” the team concluded.
“We also propose GH replacement should be offered to older adults with genetically confirmed PWS who did receive GH during childhood, but it was stopped when they reached adulthood, as well as those adults who never received GH during childhood,” they added.
“Hopefully, we will see that soon.”
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