Breathing deficits of the Prader-Willi syndrome

Hypoventilation in patients with Prader-Willi syndrome across the pediatric age

OBJECTIVES

Few data on alveolar hypoventilation in Prader-Willi syndrome (PWS) are available and the respiratory follow-up of these patients is not standardized. The objectives of this study were to evaluate the prevalence of alveolar hypoventilation in children with PWS and identify potential risk factors.

STUDY DESIGN

This retrospective study included children with PWS recorded by polysomnography (PSG) with transcutaneous carbon dioxide pressure (PtcCO2) or end-tidal CO2 (ETCO2) measurements, between 2007 and 2021, in a tertiary hospital center. The primary outcome was the presence of alveolar hypoventilation defined as partial pressure of carbon dioxide (pCO2) ≥ 50 mmHg during ≥2% of total sleep time (TST) or more than five consecutive minutes.

RESULTS

Among the 57 included children (38 boys, median age 4.8 years, range 0.1-15.6, 60% treated with growth hormone [GH], 37% obese), 19 (33%) had moderate-to-severe obstructive sleep apnea syndrome (defined as obstructive apnea-hypopnea index ≥5/h) and 20 (35%) had hypoventilation. The median (range) pCO2 max was 49 mmHg (38-69). Among the children with hypoventilation, 25% were asymptomatic. Median age and GH treatment were significantly higher in children with hypoventilation compared to those without. There was no significant difference in terms of sex, BMI, obstructive or central apnea-hypopnea index between both groups.

CONCLUSION

The frequency of alveolar hypoventilation in children and adolescents with PWS is of concern and may increase with age and GH treatment. A regular screening by oximetry-capnography appears to be indicated whatever the sex, BMI, and rate of obstructive or central apneas.

Control of Breathing and Central Hypoventilation Syndromes

Control of breathing in children varies with age and sleep state. There is overlap between central hypoventilation, autonomic dysfunction, and hypothalamic dysfunction in the rare disorders (congenital central hypoventilation syndrome and rapid-onset obesity, hypoventilation, hypothalamic dysfunction, and autonomic dysregulation). Other, more common disorders that typically present in childhood also include central hypoventilation and disordered ventilatory responses.

Phenotypic variance in pediatric obstructive sleep apnea

It is crucial that clinicians understand what underpins the considerable phenotypic variance in pediatric obstructive sleep apnea syndrome (OSAS), if they are to implement individually tailored phenotype-based approaches to diagnosis and management. This review summarizes the current literature on how disease severity, comorbidities, genetic and environmental/lifestyle factors interact to determine the overall OSAS phenotype. The first part discusses the impact of these factors on OSAS-related morbidity in the context of otherwise healthy children, whilst the second half details children with complex conditions, particularly focusing on the anatomical and functional abnormalities predisposing to upper airway obstruction unique to each condition. One can then understand the need for a multidimensional assessment strategy for pediatric OSAS; one that incorporates the history, physical examination, sleep study results, and biomarkers to enable precise stratification, so vital for effective determination of the timing and the nature of the therapeutic interventions required.

Measures of nocturnal oxyhemoglobin desaturation in children with neuromuscular disease or Prader-Willi syndrome

OBJECTIVES

Evidence for nocturnal oximetry interpretation in patients with abnormal neuromuscular function is limited. We aimed to compare children with neuromuscular disease (NMD) or Prader-Willi syndrome (PWS) to otherwise healthy subjects with obstructive sleep-disordered breathing (SDB) or without respiratory disorder (controls) regarding nocturnal oximetry parameters.

METHODS

We analyzed recordings from children with: (a) NMD; (b) PWS; (c) snoring and adenotonsillar hypertrophy and/or obesity (SDB); and (d) controls. Outcomes included: (a) basal SpO₂ ; (b) proportions of subjects with McGill oximetry score (MOS) >1 (clusters of desaturations); and (c) desaturation index (SpO₂ drops ≥3%/h-ODI3).

RESULTS

Data of 12 subjects with NMD (median age, 5.2 years; IQR, 2.7, 8.2), 14 children with PWS (5 years; 2.3, 6.9), 21 children with SDB (5.8 years; 4.6, 9.6), and 20 controls (6.2 years; 5.4, 11.2) were analyzed. Children with NMD, PWS, and SDB had lower basal SpO₂ than controls (95.6% [94.5%, 96.9%], 96.2% [95.1%, 97.4%], 96.1% [95.8%, 97.5%] vs 97.8% [97.2%, 97.9%], respectively; (P < .01). NMD and PWS showed the greatest negative effect on basal SpO₂ (P < .05). Children with SDB or PWS had a higher risk of MOS >1 than patients with NMD (OR, 25.9 [95% CI, 3.4-200.4] and 9.5 [1.5-62.6]). NMD, PWS, and SDB were similar regarding ODI3, which was elevated compared to ODI3 in controls (P < .05). Frequent desaturations predominated in NMD, while periods of sustained desaturation were noted in NMD and PWS.

CONCLUSION

PWS and NMD have a negative effect on basal SpO₂ , while clusters of desaturations are prevalent in patients with PWS or obstructive SDB.

Quipazine Elicits Swallowing in the Arterially Perfused Rat Preparation: A Role for Medullary Raphe Nuclei?

Pharmacological neuromodulation of swallowing may represent a promising therapeutic option to treat dysphagia. Previous studies suggested a serotonergic control of swallowing, but mechanisms remain poorly understood. Here, we investigated the effects of the serotonergic agonist quipazine on swallowing, using the arterially perfused working heart-brainstem (in situ) preparation in rats. Systemic injection of quipazine produced single swallows with motor patterns and swallow-breathing coordination similar to spontaneous swallows, and increased swallow rate with moderate changes in cardiorespiratory functions. Methysergide, a 5-HT2 receptor antagonist, blocked the excitatory effect of quipazine on swallowing, but had no effect on spontaneous swallow rate. Microinjections of quipazine in the nucleus of the solitary tract were without effect. In contrast, similar injections in caudal medullary raphe nuclei increased swallow rate without changes in cardiorespiratory parameters. Thus, quipazine may exert an excitatory effect on raphe neurons via stimulation of 5-HT2A receptors, leading to increased excitability of the swallowing network. In conclusion, we suggest that pharmacological stimulation of swallowing by quipazine in situ represents a valuable model for experimental studies. This work paves the way for future investigations on brainstem serotonergic modulation, and further identification of neural populations and mechanisms involved in swallowing and/or swallow-breathing interaction.

d-serine regulation of the timing and architecture of the inspiratory burst in neonatal mice

d-serine, released from mouse medullary astrocytes in response to increased CO₂ levels, boosts the respiratory frequency to adapt breathing to physiological demands. We analyzed in mouse neonates, the influence of d-serine upon inspiratory/expiratory durations and the architecture of the inspiratory burst, assessed by pwelch's power spectrum density (PSD) and continuous wavelet transform (CWT) analyses. Suction electrode recordings were performed in slices from the ventral respiratory column (VRC), site of generation of the respiratory rhythm, and in brainstem-spinal cord (en bloc) preparations, from the C5 ventral roots, containing phrenic fibers that in vivo innervate and drive the diaphragm, the main inspiratory muscle. In en bloc and slice preparations, d-serine (100 μM) reduced the expiratory, but not the inspiratory duration, and increased the frequency and the regularity of the respiratory rhythm. In en bloc preparations, d-serine (100 μM) also increased slightly the amplitude of the integrated inspiratory burst and the area under the curve of the integrated inspiratory burst, suggesting a change in the recruitment or the firing pattern of neurons within the burst. Time-frequency analyses revealed that d-serine changed the burst architecture of phrenic roots, widening their frequency spectrum and shifting the position of the core of firing frequencies towards the onset of the inspiratory burst. At the VRC, no clear d-serine induced changes in the frequency-time domain could be established. Our results show that d-serine not only regulates the timing of the respiratory cycle, but also the recruitment strategy of phrenic motoneurons within the inspiratory burst.

Causes of death in Prader-Willi syndrome: lessons from 11 years' experience of a national reference center

Background

In the last 20 years, substantial improvements have been made in the diagnosis, treatment and management of patients with Prader-Willi syndrome (PWS). Few data on causes of death are available since those improvements were made. Our study assessed the causes of death among French patients with PWS over the first 11 years of experience of the nationwide French Reference Center for PWS (FRC-PWS).

Methods

Our study relied on two sources of mortality information at national level between 2004 and 2014: The French Epidemiological Centre for the Medical Causes of Death (CépiDc) Registry and the FRC-PWS database. Causes of death were classified into seven categories: respiratory, cardiovascular, gastrointestinal, severe infection, sudden death, other causes, and unknown. Descriptive statistics were calculated separately for children (< 18 years-old) and adults (≥18 years-old).

Results

One hundred and four deaths were identified in France from 2004 to 2014. The median age at death was 30 years, ranging from less than 1 month to 58 years. Seventeen deaths occurred in patients under 18 years, with 70% of them in children under 2 years. Respiratory causes accounted for more than 50% of the deaths in patients with PWS in both children and adults. Both cause and age of death did not significantly differ according to gender or genetic subtype.

Conclusions

Patients with PWS die prematurely due to a respiratory cause in most cases at all ages. In those adult patients with data on obesity, 98% were reported to be obese.

Preclinical Testing in Translational Animal Models of Prader-Willi Syndrome: Overview and Gap Analysis

Prader-Willi syndrome (PWS) is a rare neurodevelopmental disorder causing endocrine, musculoskeletal, and neurological dysfunction. PWS is caused by the inactivation of contiguous genes, complicating the development of targeted therapeutics. Clinical trials are now underway in PWS, with more trials to be implemented in the next few years. PWS-like endophenotypes are recapitulated in gene-targeted mice in which the function of one or more PWS genes is disrupted. These animal models can guide priorities for clinical trials or provide information about efficacy of a compound within the context of the specific disease. We now review the current status of preclinical studies that measure the effect of therapeutics on PWS-like endophenotypes. Seven categories of therapeutics (oxytocin and related compounds, K⁺-ATP channel agonists, melanocortin 4 receptor agonists, incretin mimetics and/or GLP-1 receptor agonists, cannabinoids, ghrelin agents, and Caralluma fimbriata [cactus] extract) have been tested for their effect on endophenotypes in both PWS animal models and clinical trials. Many other therapeutics have been tested in clinical trials, but not preclinical models of PWS or vice versa. Fostering dialogs among investigators performing preclinical validation of animal models and those implementing clinical studies will accelerate the discovery and translation of therapies into clinical practice in PWS.

Hypoventilation disproportionate to OSAS severity in children with Prader-Willi syndrome

OBJECTIVE

To test the hypothesis that children with Prader-Willi syndrome (PWS) and obstructive sleep apnoea syndrome (OSAS) have hypercapnia for higher proportion of total sleep time (TST) than non-syndromic children with similar obstructive apnoea-hypopnoea index (OAHI).

DESIGN

Cross-sectional study.

SETTING

Two tertiary care hospitals.

PATIENTS

Patients with PWS and non-syndromic children with snoring who underwent polygraphy and were of similar age, body mass index (BMI) z-score and OAHI.

MAIN OUTCOME MEASURE

The two groups were compared regarding %TST with transcutaneous CO₂ (PtcCO₂) >50 mm Hg. The interaction between PWS diagnosis and OSAS severity (OAHI <1 episode/h vs 1-5 episodes/h vs >5 episodes/h) regarding %TST with PtcCO₂ >50 mm Hg was tested using multiple linear regression.

RESULTS

48 children with PWS and 92 controls were included (median age 2.3 (range 0.2-14.1) years vs 2.2 (0.3-15.1) years; BMI z-score 0.7±1.9 vs 0.8±1.7; median OAHI 0.5 (0-29.5) episodes/h vs 0.5 (0-33.9) episodes/h; p>0.05). The two groups did not differ in %TST with PtcCO₂ >50 mm Hg (median 0% (0-100%) vs 0% (0-81.3%), respectively; p>0.05). However, the interaction between PWS and OSAS severity with respect to duration of hypoventilation was significant (p<0.01); the estimated mean differences of %TST with PtcCO₂ >50 mm Hg between children with PWS and controls for OAHI <1 episode/h, 1-5 episodes/h and >5 episodes/h were +0.2%, +1% and +33%, respectively.

CONCLUSION

Increasing severity of upper airway obstruction during sleep in children with PWS is accompanied by disproportionately longer periods of hypoventilation when compared with non-syndromic children with similar frequency of obstructive events.

Ventilatory Responses During Submaximal Exercise in Children With Prader-Willi Syndrome

PURPOSE

Prader-Willi syndrome (PWS) is a genetic neurobehavioral disorder presenting hypothalamic dysfunction and adiposity. At rest, PWS exhibits hypoventilation with hypercapnia. We characterized ventilatory responses in children with PWS during exercise.

METHODS

Participants were children aged 7-12 years with PWS (n = 8) and without PWS with normal weight (NW; n = 9, body mass index ≤ 85th percentile) or obesity (n = 9, body mass index ≥ 95th percentile). Participants completed three 5-minute ambulatory bouts at 3.2, 4.0, and 4.8 km/h. Oxygen uptake, carbon dioxide output, ventilation, breathing frequency, and tidal volume were recorded.

RESULTS

PWS had slightly higher oxygen uptake (L/min) at 3.2 km/h [0.65 (0.46-1.01) vs 0.49 (0.34-0.83)] and at 4.8 km/h [0.89 (0.62-1.20) vs 0.63 (0.45-0.97)] than NW. PWS had higher ventilation (L/min) at 3.2 km/h [16.2 (13.0-26.5) vs 11.5 (8.4-17.5)], at 4.0 km/h [16.4 (13.9-27.9) vs 12.7 (10.3-19.5)], and at 4.8 km/h [19.7 (17.4-31.8) vs 15.2 (9.5-21.6)] than NW. PWS had greater breathing frequency (breaths/min) at 3.2 km/h [38 (29-53) vs 29 (22-35)], at 4.0 km/h [39 (29-58) vs 29 (23-39)], and at 4.8 km/h [39 (33-58) vs 32 (23-42)], but similar tidal volume and ventilation/carbon dioxide output to NW.

CONCLUSION

PWS did not show impaired ventilatory responses to exercise. Hyperventilation in PWS may relate to excessive neural stimulation and metabolic cost.

Subclinical dysphagia in persons with Prader-Willi syndrome

Prader-Willi Syndrome (PWS) is caused by a genetic imprinting abnormality resulting from the lack of expression of the paternal genes at 15q11-q13. Intellectual disability, low muscle tone, and life-threatening hyperphagia are hallmarks of the phenotype. The need for the Heimlich maneuver, death from choking, and pulmonary infection occur in a disproportionally high number of persons with PWS. The widely held belief is that eating behaviors are responsible for choking and aspiration; yet, no investigation had sought to determine if swallowing impairments were present in persons with PWS. To address this research and clinical gap, simultaneous videofluoroscopy and nasal respiratory signals were used to record swallowing function and breathing/swallowing coordination in 30 participants with PWS. Subjects consumed thin liquid and barium cookies under two randomized conditions as follows: (i) controlled (cues to swallow and standardized bolus sizes); (ii) spontaneous (no cues or bolus size control). Under videofluoroscopy, the cohort showed disordered pharyngeal and esophageal swallowing in both conditions with disturbances in timing, clearance, and coordination of swallowing with the respiratory cycle. No participant showed a sensory response such as attempting to clear residue or coughing; thereby supporting the lack of overt symptoms. We conclude that the high death rate from choking and pulmonary infection in children and adults with PWS may be related, in part, to underlying, asymptomatic dysphagia. The combination of rapid eating and dysphagia would increase the risk of aspiration-related morbidity and mortality. © 2016 Wiley Periodicals, Inc.

Imprinting analysis of the mouse chromosome 7C region in DNMT1-null embryos

The mouse chromosome 7C, orthologous to the human 15q11-q13 has an imprinted domain, where most of the genes are expressed only from the paternal allele. The imprinted domain contains paternally expressed genes, Snurf/Snrpn, Ndn, Magel2, Mkrn3, and Frat3, C/D-box small nucleolar RNAs (snoRNAs), and the maternally expressed gene, Ube3a. Imprinted expression in this large (approximately 3-4 Mb) domain is coordinated by a bipartite cis-acting imprinting center (IC), located upstream of the Snurf/Snrpn gene. The molecular mechanism how IC regulates gene expression of the whole domain remains partially understood. Here we analyzed the relationship between imprinted gene expression and DNA methylation in the mouse chromosome 7C using DNA methyltransferase 1 (DNMT1)-null mutant embryos carrying Dnmt1(ps) alleles, which show global loss of DNA methylation and embryonic lethality. In the DNMT1-null embryos at embryonic day 9.5, the paternally expressed genes were biallelically expressed. Bisulfite DNA methylation analysis revealed loss of methylation on the maternal allele in the promoter regions of the genes. These results demonstrate that DNMT1 is necessary for monoallelic expression of the imprinted genes in the chromosome 7C domain, suggesting that DNA methylation in the secondary differentially methylated regions (DMRs), which are acquired during development serves primarily to control the imprinted expression from the maternal allele in the mouse chromosome 7C.

Prader Willi syndrome and obstructive sleep apnea: co-occurrence in the pediatric population

BACKGROUND

A high prevalence of obstructive sleep apnea (OSA) occurs in children with Prader-Willi syndrome (PWS). Yet, due in part to the relatively small samples previously used, the prevalence of OSA has varied greatly across studies. It is also unclear if factors such as age, gender, body mass index (BMI), or type of genetic imprinting are associated with increased risk for OSA among children with PWS.

OBJECTIVES

To evaluate the (a) prevalence of OSA, as well as narcolepsy, in pediatric populations diagnosed with PWS; (b) effects of age, gender, body mass index, and genetic imprinting on OSA severity; and (c) efficacy of adenotonsillectomy (AT) for decreasing OSA severity in this population.

METHODS

All studies assessing OSA among children with PWS through August 2013 were identified using the PubMed/Medline, Psych Info, Cochrane library, and Google Scholar data bases.

RESULTS

Fourteen studies of children diagnosed with PWS and who were assessed for OSA using polysomnography (PSG) met inclusion criteria (n = 224 children). The prevalence of OSA across studies was 79.91% (n = 179/224). Among youths with OSA, 53.07% had mild OSA, 22.35% moderate OSA, and 24.58% severe OSA. Narcolepsy was found to occur in 35.71% of children with PWS. Adenotonsillectomy was associated with improvement in OSA for most children with PWS. However, residual OSA was present in the majority of cases post-surgery.

CONCLUSION

This study confirms the high prevalence of OSA and narcolepsy among children with PWS. Screening for OSA and narcolepsy among children with PWS is recommended. In addition, while adenotonsillectomy was effective in reducing OSA for some children, alternative treatments may need to be considered, given the only moderate response rate.

Genetic diseases: congenital central hypoventilation, Rett, and Prader-Willi syndromes

The present review summarizes current knowledge on three rare genetic disorders of respiratory control, congenital central hypoventilation syndrome (CCHS), Rett syndrome (RTT), and Prader-Willi syndrome (PWS). CCHS is characterized by lack of ventilatory chemosensitivity caused by PHOX2B gene abnormalities consisting mainly of alanine expansions. RTT is associated with episodes of tachypneic and irregular breathing intermixed with breathholds and apneas and is caused by mutations in the X-linked MECP2 gene encoding methyl-CpG-binding protein. PWS manifests as sleep-disordered breathing with apneas and episodes of hypoventilation and is caused by the loss of a group of paternally inherited genes on chromosome 15. CCHS is the most specific disorder of respiratory control, whereas the breathing disorders in RTT and PWS are components of a more general developmental disorder. The main clinical features of these three disorders are reviewed with special emphasis on the associated brain abnormalities. In all three syndromes, disease-causing genetic defects have been identified, allowing the development of genetically engineered mouse models. New directions for future therapies based on these models or, in some cases, on clinical experience are delineated. Studies of CCHS, RTT, and PWS extend our knowledge of the molecular and cellular aspects of respiratory rhythm generation and suggest possible pharmacological approaches to respiratory control disorders. This knowledge is relevant for the clinical management of many respiratory disorders that are far more prevalent than the rare diseases discussed here.

Recommendations for the investigation of animal models of Prader-Willi syndrome

Prader-Willi syndrome (PWS) occurs in about 1 in 15,000 individuals and is a contiguous gene disorder causing developmental disability, hyperphagia usually with obesity, and behavioral problems, including an increased incidence of psychiatric illness. The genomic imprinting that regulates allele-specific expression of PWS candidate genes, the fact that multiple genes are typically inactivated, and the presence of many genes that produce functional RNAs rather than proteins has complicated the identification of the underlying genetic pathophysiology of PWS. Over 30 genetically modified mouse strains that have been developed and characterized have been instrumental in elucidating the genetic and epigenetic mechanisms for the regulation of PWS genes and in discovering their physiological functions. In 2011, a PWS Animal Models Working Group (AMWG) was established to generate discussions and facilitate exchange of ideas regarding the best use of PWS animal models. Here, we summarize the goals of the AMWG, describe current animal models of PWS, and make recommendations for strategies to maximize the utility of animal models and for the development and use of new animal models of PWS.

Apnea of prematurity: pathogenesis and management strategies

Apnea of prematurity (AOP) is a significant clinical problem manifested by an unstable respiratory rhythm reflecting the immaturity of respiratory control systems. This review will address the pathogenesis of and treatment strategies for AOP. Although the neuronal mechanisms leading to apnea are still not well understood, recent decades have provided better insight into the generation of the respiratory rhythm and its modulation in the neonate. Ventilatory responses to hypoxia and hypercarbia are impaired and inhibitory reflexes are exaggerated in the neonate. These unique vulnerabilities predispose the neonate to the development of apnea. Treatment strategies attempt to stabilize the respiratory rhythm. Caffeine remains the primary pharmacological treatment modality and is presumed to work through blockade of adenosine receptors A(1) and A(2). Recent evidences suggest that A(2A) receptors may have a greater role than previously thought. AOP typically resolves with maturation suggesting increased myelination of the brainstem.

Differences in serotoninergic metabolism possibly contribute to differences in breathing phenotype of FVB/N and C57BL/6J mice

Mouse readiness for gene manipulation allowed the production of mutants with breathing defects reminiscent of breathing syndromes. As C57BL/6J and FVB/N inbred strains were often used as background strains for producing mutants, we compared their breathing pattern from birth onwards. At birth, in vivo and in vitro approaches revealed robust respiratory rhythm in FVB/N, but not C57BL/6J, neonates. With aging, rhythm robustness difference persisted, and interstrain differences in tidal volume, minute ventilation, breathing regulations, and blood-gas parameters were observed. As serotonin affected maturation and function of the medullary respiratory network, we examined the serotoninergic metabolism in the medulla of C57BL/6J and FVB/N neonates and aged mice. Interstrain differences in serotoninergic metabolism were observed at both ages. We conclude that differences in serotoninergic metabolism possibly contribute to differences in breathing phenotype of FVB/N and C57BL/6J mice.

The role of serotonin in respiratory function and dysfunction

Serotonin (5-HT) is a neuromodulator-transmitter influencing global brain function. Past and present findings illustrate a prominent role for 5-HT in the modulation of ponto-medullary autonomic circuits. 5-HT is also involved in the control of neurotrophic processes during pre- and postnatal development of neural circuits. The functional implications of 5-HT are particularly illustrated in the alterations to the serotonergic system, as seen in a wide range of neurological disorders. This article reviews the role of 5-HT in the development and control of respiratory networks in the ponto-medullary brainstem. The review further examines the role of 5-HT in breathing disorders occurring at different stages of life, in particular, the neonatal neurodevelopmental diseases such as Rett, sudden infant death and Prader-Willi syndromes, adult diseases such as sleep apnoea and mental illness linked to neurodegeneration.

Foreword: Respiratory rhythmogenesis

This special issue of Respiratory Physiology & Neurobiology summarizes the current standing of research concerned with synaptic mechanisms, membrane properties, plasticity, pre- and postnatal development and evolutionary origin of neurones involved in respiratory rhythm generation and central chemosensitivity. Moreover, a variety of articles link pathophysiological alterations of synaptic function in rhythmogenesis and chemosensitivity with breathing disorders in neurodevelopmental diseases.