Introduction
Prader-Willi syndrome (PWS) is a rare genetic disease that affects approximately 1 in 15 000 children [
1]. Its phenotypes are expressed as 65–75% absent paternally expressed imprinted genes at 15q11.2-q13 through paternal deletion of this region, 20–30% maternal uniparental disomy (mUPD) of chromosome 15, and 1–3% an imprinting defect [
1]. Patients with PWS at the infancy stage presented with low birth weight, neonatal hypotonia, difficulty in feeding, and endocrine disorders. While early diagnosis is possible with advancements in science and technology, there is currently no established cure for the disease. However, an integrated multidisciplinary approach, including the use of the synthetic version of the recombinant human growth hormone (rhGH), development therapy, and occupational therapy, is recommended to minimize complications, improve quality of life, and increase life expectancy [
2].
Most children with PWS have growth hormone (GH) deficiency, which can be identified through real-time monitoring of daily spontaneous GH release and associated stimulation tests [
3]. Studies have shown that rhGH therapy can improve linear growth, body composition, physical strength, agility, and mental development in children with PWS [
4,
5]. This treatment should be accompanied by dietary, environmental, and lifestyle interventions for genetically-confirmed PWS patients [
3]. Consensus guidelines suggest initiating rhGH treatment before the age of two [
3]. However, some endocrinologists argue for initiating treatment as soon as PWS is diagnosed, especially during infancy and toddlerhood [
6,
7]. It is worth noting that the initial weeks of rhGH treatment may lead to worsened sleep-related breathing disorders (SRBDs) and adenoid hypertrophy, possibly due to high levels of insulin-like growth factor 1 (IGF-1) after starting rhGH [
8]. SRBDs are common symptoms of PWS, and they can contribute to poor physical health, neurocognitive function, and prognosis due to obesity, narrowed upper airways, reduced saliva excretion, adenoid/tonsillar hypertrophy, hypotonic breathing muscles, or scoliosis [
9].
A study by Pacoricona Alfaro investigated the causes of death in PWS and found that out of 104 deaths, 14 patients had previously used or were currently using rhGH at the time of their death, with respiratory infection, cardiac failure, and sudden death being the main causes [
10]. Moreover, a striking 98% of the patients older than 18 years old were identified as obese. In contrast, among pediatric PWS population under the age of 18, only 25% exhibited obesity [
10]. Another pharmaceutical company reported that 5 out of 675 children treated with GH died suddenly due to respiratory issues [
11]. Extensive research has been conducted over the past two decades to assess the safety of rhGH in PWS, and regular PSG and adenotonsillar examinations are recommended for long-term monitoring of children on rhGH treatment [
12,
13]. Although the mortality rate associated with rhGH treatment in children with PWS is extremely low, there are still concerns among clinicians regarding its safety based on previous studies reporting adverse effects. There is limited research on the safety of rhGH in infants and toddlers with PWS. Therefore, the safety of rhGH therapy in infants and toddlers with PWS requires further investigation. This retrospective cohort study aims to explore the effects of initiating rhGH on SRBDs in toddlers with PWS. The article follows Strengthening the Reporting of Observational studies in Epidemiology (STROBE) checklists [
14].
Discussion
This longitudinal, retrospective cohort rhGH study analyzed a consecutive cohort of 34 children diagnosed with PWS and found that rhGH treatment exerts no negative influence on the indices of PSG evaluation. Moreover, the AHI, OAHI, CAI, ODI, mean SPO2, lowest SpO2, duration of SpO2 when lower than 90%, and proportion of patients with SpO2 lower than 90% were similar across the groups.
Lumeng et al.have shown that the prevalence of pathologically sleep-disordered breathing in patients who were not on treatment was similar to those on treatment. Moreover, the occurrence of sleep-disordered breathing was similar at six months after GH therapy onset [
23,
24]. Consistent with the majority of existing literature, our findings align with these results, indicating that the occurrence of OAHI remains similar across the groups after a one-year follow-up period. These collective findings suggest that rhGH treatment is relatively safe for children under the age of three, in accordance with current research. Conversely, Zimmermann et
al. showed that OSA increased significantly in the rhGH treatment group in the first three months [
25]. Berini et al
. showed a significant increase in the occurrence of OAHI for up to 4 years after rhGH onset, and the proportion of patients with an OAHI > 1 increased from 3 to 22, 36 and 38 at the 6 weeks, 2 years, and 4 years after the rhGH treatment, respectively [
12], but the authors did explore the effect of hypopnea on the OAHI. A recent study has provided evidence indicating that there is a correlation between the aggravation of SRBDs and the progressive rise in insulin resistance among children with simple obesity and patients with PWS treated with rhGH [
26].
To monitor the effect of rhGH treatment on SRBDs, PSG-associated indices were recorded before the treatment initiation, at 26 weeks and 52 weeks following rhGH treatment. At 26 weeks after rhGH treatment, OAHI, OAI, CAI, and ODI exhibited a decrease, indicating a potential reduction in the incidence of SRBDs in children with PWS receiving rhGH treatment, although statistical significance was not observed. Correspondingly, Festen et al
. demonstrated that after 26 weeks of treatment of rhGH treatment in PWS children, the CAI and AHI levels decreased [
27]. However, Miller et al
. reported that 32% of the PWS patients experienced worsening of sleep disturbance in the presence of upper respiratory tract infection and adenotonsillar hypertrophy [
28]. It is important to note that the limited sample sizes and broad age ranges in different studies may introduce potential selection biases.
In this present study, the mean value of SpO
2 and the lowest SpO
2 at 26 weeks and 56 weeks after initiating treatment exhibited no significant differences across different time points. More importantly, a notable finding was the decrease in the duration of SpO2 below 90% and the proportion of SpO2 below 90% at 26 weeks post-treatment initiation. However, compared to the 6-month time point, the duration of SpO2 below 90% increased at 52 weeks, although it remained lower than the onset of treatment. Additionally, the proportion of SpO2 below 90% also increased. At the 1-year time point, the value exceeded that of the rhGH treatment onset, but this increase was not statistically significant. In a study conducted by Zimmermann et
al., they compared different onset age groups for rhGH treatment in PWS patients (younger than 1 year old or older than 1 year old) and found no significant differences in OAHI, CAI, ODI, and SpO2 depending on treatment onset [
25]. While short-term rhGH therapy showed worsening ODI, the group treated with rhGH for a longer duration did not significantly differ from the control group [
29].
IGF-1, a growth hormone with molecular similarity to insulin, plays a crucial role in mediating the anabolic effects of pituitary GH and linear growth through its interaction with insulin-like growth factor binding protein 3 (IGFBP-3) [
30]. Patients with PWS are sensitive to rhGH treatment and usually have high levels of IGF-1 [
31,
32]. IGF-1, as a major downstream target of GH, influences growth, development, and tissue homeostasis [
7]. Nevertheless, elevated levels of IGF-1 have been associated with lymphoid hyperplasia, potentially increasing the risk of OSA and raising concerns of malignancy [
33]. However, our study revealed that despite rhGH therapy leading to a significant increase in IGF-1 and IGFBP-3, this elevation did not contribute to the development of OSA. This finding aligns with the research conducted by Shukur et al., who observed a significant rise in IGF-1 levels among the rhGH-treated group without significant differences in respiration and sleep parameters [
34]. While the association between IGFBP-3 and sleep-related breathing disorders (SRBDs) in PWS remains unexplored, our study indicates that the heightened levels of IGF-1 and IGFBP-3 resulting from rhGH treatment do not adversely affect SRBDs.
Consensus guidelines for rhGH treatment in children with PWS recommend conducting a baseline PSG evaluation before initiating treatment, followed by repeat assessments within the first 3–6 months. In cases where there is a deterioration of sleep-disordered breathing, snoring, or enlargement of tonsils and adenoids, additional evaluations such as ear, nose, and throat assessments, PSG, and IGF-1 measurements are deemed necessary [
3].
Even though rhGH treatment did not exert any negative impact on SRBDs, several limitations were encountered in this study. Firstly, it is important to acknowledge that this analysis is a retrospective, non-randomized, single-institution study with a limited sample size. For further high-level investigations, we recommend a prospective, randomized, and multi-centre collaborative study to confirm the safety of rhGH treatment in toddlers. Secondly, this dataset only consisted of PWS patients with rhGH treatment and was limited to a 1-year follow-up period. To obtain a more comprehensive understanding of patient prognosis, a longer follow-up duration would be necessary. Lastly, it is noteworthy that adenotonsillar evaluation plays a pivotal role in the pathophysiological of SRBDs. However, regrettably, this aspect was not incorporated into our evaluations. Future studies should consider incorporating thorough adenotonsillar assessments to provide a more comprehensive analysis of SRBDs in relation to rhGH treatment.
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.