An official ATS clinical policy statement: Congenital central hypoventilation syndrome: genetic basis, diagnosis, and management

Intrinsic Molecular Proton Sensitivity Underlies GPR4 Effects on Retrotrapezoid Nucleus Neuronal Activation and CO2-Stimulated Breathing

An interoceptive homeostatic reflex monitors levels of CO2/H+ to maintain blood gas homeostasis and rapidly regulate tissue acid-base balance by driving lung ventilation and CO2 excretion-this CO2-evoked increase in respiration is the hypercapnic ventilatory reflex (HCVR). Retrotrapezoid nucleus (RTN) neurons provide crucial excitatory drive to downstream respiratory rhythm/pattern-generating circuits, and their activity is directly modulated by changes in CO2/H+ RTN neurons express GPR4 and TASK-2, global deletion of which abrogates CO2/H+ activation of RTN neurons and the HCVR. It has not been determined if the intrinsic pH sensitivity of these proton detectors is required for these effects. We used CRISPR/Cas9 genome editing to generate mice with mutations in either of two pH-sensing histidine residues in GPR4 to determine effects on RTN neuronal CO2/H+ sensitivity and the HCVR. In global GPR4(H81F) and GPR4(H167F) mice, CO2-stimulated breathing and CO2-induced RTN neuronal activation were strongly blunted, with no effect on hypoxia-stimulated breathing. In brainstem slices from GPR4(H81F) mice, peak firing of RTN neurons during bath acidification was significantly reduced compared with GPR4 wild-type mice, and a subpopulation of RTN neurons was rendered pH-insensitive, phenocopying previous results from GPR4-deleted mice. These effects were independent of changes in RTN number/distribution, neuronal excitability or transcript levels for GPR4 and TASK-2. CO2-stimulated breathing was reduced to a similar extent in GPR4(H81F) and TASK-2-deleted mice, with combined mutation yielding no additional deficit in the HCVR. Together, these data demonstrate that the intrinsic pH sensitivity of GPR4 is necessary for full elaboration of the HCVR.

Assessment of Chronic Hypercapnic Respiratory Failure

Undiagnosed chronic hypercapnic respiratory failure may be encountered during the evaluation of sleep-related breathing disorders at the sleep clinic. This article reviews the mechanism of chronic hypercapnic respiratory failure and the systematic approach to the assessment of specific sleep disorders associated with nocturnal hypoventilation encountered in clinical practice.

Congenital Central Hypoventilation Syndrome and Disorders of Control of Ventilation

Congenital disorders of ventilatory control typically manifest as central apneas, periodic breathing, and hypoventilation in the neonatal period, but some may present at a later age. Obstructive apneas may be the initial presentation, and some may have associated autonomic nervous system dysfunction. Individuals with these disorders can have absent or impaired ventilatory and arousal responses to hypoxemia and hypercapnia. This article discusses the presentation, pathophysiology, evaluation, and management of congenital central hypoventilation syndrome, rapid-onset obesity with hypothalamic dysfunction, hypoventilation, and autonomic dysregulation (ROHHAD) syndrome, Prader-Willi syndrome, and myelomeningocele.

An Implantable Self-Driven Diaphragm Pacing System Based on a Microvibration Triboelectric Nanogenerator for Phrenic Nerve Stimulation

Spinal cord injury poses considerable challenges, particularly in diaphragm paralysis. To address limitations in existing diaphragm pacing technologies, we report an implantable, self-driven diaphragm pacing system based on a microvibration triboelectric nanogenerator (MV-TENG). Leveraging the efficient MV-TENG, the system harvests micromechanical energy and converts this energy into pulses for phrenic nerve stimulation. In vitro tests confirm a stable MV-TENG output, while subcutaneous implantation of the device in rats results in a constant amplitude over 4 weeks with remarkable energy-harvesting efficacy. The system effectively induces diaphragmatic motor-evoked potentials, triggering contractions of the diaphragm. This proof-of-concept system has potential clinical applications in implantable phrenic nerve stimulation, presenting a novel strategy for advancing next-generation diaphragm pacing devices.

Congenital central hypoventilation syndrome in korea: 20 years of clinical observation and evaluation of the ventilation strategy in a single center

Congenital central hypoventilation syndrome (CCHS) is a rare genetic disorder characterized by hypoventilation due to impaired breathing control by the central nervous system and other symptoms of autonomic dysfunction. Mutations in paired-like homeobox 2 B (PHOX2B) are responsible for most cases of CCHS. Patients with CCHS have various phenotypes and severities, making the diagnosis difficult. This study aimed to present a comprehensive single-center experience of patients with CCHS, including key clinical features, treatment strategies, and outcomes. A retrospective chart review was performed for patients diagnosed with CCHS between January 2001 and July 2023 at Seoul National University Children's Hospital. Finally, we selected 24 patients and collected their demographic data, genotypes, ventilation methods, and clinical features related to autonomic dysfunction. The relationship between the clinical manifestations and genotypes was also examined. All patients used home ventilators, and tracheostomy was performed in 87.5% of patients. Fifteen (62.5%) patients had constipation and nine (37.5%) were diagnosed with Hirschsprung disease. Arrhythmia, endocrine dysfunction, and subclinical hypothyroidism were present in nine (37.5%), six patients (25.0%), and two patients (16.7%), respectively. A significant number of patients exhibited neurodevelopmental delays (19 patients, 79.2%). There was a correlation between the phenotype and genotype of PHOX2B in patients with CCHS. (r = 0.71, p < 0.001).   Conclusion: There was a positive correlation between paired-like homeobox 2 B mutations (especially the number of GCN repeats in the polyalanine repeat mutations sequence) and clinical manifestations. This study also demonstrated how initial treatment for hypoventilation affects neurodevelopmental outcomes in patients with CCHS. What is Known: • Congenital central hypoventilation syndrome is a rare genetic disorder characterized by hypoventilation and dysfunction of autonomic nervous system. • The disease-defining gene of CCHS is PHOX2B gene - most of the cases have heterozygous PARMs and the number of GCN triplets varies among the patients(20/24 - 20/33). What is New: • We have noted in the Korean patients with CCHS that there is a correlation between genotype (number of GCN repeats) and severity of phenotype. • National support for rare diseases allowed for a prompter diagnosis of patients with CCHS in Korean population.

Congenital Central Hypoventilation Syndrome: A Case Report

Congenital central hypoventilation syndrome (CCHS) is a rare cause of apnea and hypoventilation requiring long-term multidisciplinary care. In this article, we report the case of a two-month-old female child who presented with recurrent apnea and cyanosis, requiring long-term ventilation. After ruling out other common causes of apnea like sepsis, metabolic disorders, and neuromuscular disorders, a genetic study was done, which confirmed the diagnosis of CCHS. The child was discharged on home oxygen therapy, and the parents were counseled about genetic testing and informed about the prognosis and requirement for home ventilation therapy, as well as parental testing.

Tracheostomy and inpatient outcomes among children with congenital central hypoventilation syndrome: A kids' inpatient database study

STUDY OBJECTIVES

Congenital central hypoventilation syndrome (CCHS) is a rare disease predisposing children to respiratory failure due to abnormal ventilatory drive. Variability in hypoventilation and respiratory support need have been reported. We aim to identify clinical variables associated with incident tracheostomy and common etiologies of hospitalization among children with CCHS.

METHODS

Hospital discharge records were obtained for children (<21 years) with CCHS hospitalized between 2006 and 2019 from the Kid's Inpatient Database. Primary diagnostic categories for hospitalizations with CCHS were summarized. Multivariable logistic regression models were used to explore risk factors associated with incident tracheostomy.

RESULTS

Among 2404 hospitalizations with CCHS, 133 (5.5%) had incident tracheostomy, 1230 (51.2%) had established tracheostomy, and 1041 (43.3%) had no tracheostomy. Compared with children without tracheostomy, those with incident tracheostomy were younger, had a history of prematurity, congenital heart disease, laryngeal, glottic, and subglottic stenosis (LGSS), congenital airway anomalies, neuromuscular weakness, gastroesophageal reflux disease. Children without tracheostomy had higher mortality than those with tracheostomy status (2.19% vs. 0.66%). Multivariable-adjusted analyses showed that incident tracheostomy was associated with infancy (0-1 years), neuromuscular weakness, and congenital heart disease. Most common diagnostic categories include (1) diseases of the respiratory system (30.23%), (2) injury and poisoning (9.35%), and (3) diseases of the nervous system and sense organs (6.71%).

CONCLUSIONS

Children with CCHS who received incident tracheostomy are more likely to be younger and with LGSS, neuromuscular weakness and congenital heart disease. Clinicians should be aware of these risk factors representing more severe CCHS with earlier manifestation needing tracheostomy. Higher mortality among nontracheostomy group highlights the need for considering tracheostomy in caring for children with CCHS.

Genetic identification of medullary neurons underlying congenital hypoventilation

Mutations in the transcription factors encoded by PHOX2B or LBX1 correlate with congenital central hypoventilation disorders. These conditions are typically characterized by pronounced hypoventilation, central apnea, and diminished chemoreflexes, particularly to abnormally high levels of arterial PCO2. The dysfunctional neurons causing these respiratory disorders are largely unknown. Here, we show that distinct, and previously undescribed, sets of medullary neurons coexpressing both transcription factors (dB2 neurons) account for specific respiratory functions and phenotypes seen in congenital hypoventilation. By combining intersectional chemogenetics, intersectional labeling, lineage tracing, and conditional mutagenesis, we uncovered subgroups of dB2 neurons with key functions in (i) respiratory tidal volumes, (ii) the hypercarbic reflex, (iii) neonatal respiratory stability, and (iv) neonatal survival. These data provide functional evidence for the critical role of distinct medullary dB2 neurons in neonatal respiratory physiology. In summary, our work identifies distinct subgroups of dB2 neurons regulating breathing homeostasis, dysfunction of which causes respiratory phenotypes associated with congenital hypoventilation.

Computer-aided diagnostic screen for Congenital Central Hypoventilation Syndrome with facial phenotype

BACKGROUND

Congenital Central Hypoventilation Syndrome (CCHS) has devastating consequences if not diagnosed promptly. Despite identification of the disease-defining gene PHOX2B and a facial phenotype, CCHS remains underdiagnosed. This study aimed to incorporate automated techniques on facial photos to screen for CCHS in a diverse pediatric cohort to improve early case identification and assess a facial phenotype-PHOX2B genotype relationship.

METHODS

Facial photos of children and young adults with CCHS were control-matched by age, sex, race/ethnicity. After validating landmarks, principal component analysis (PCA) was applied with logistic regression (LR) for feature attribution and machine learning models for subject classification and assessment by PHOX2B pathovariant.

RESULTS

Gradient-based feature attribution confirmed a subtle facial phenotype and models were successful in classifying CCHS: neural network performed best (median sensitivity 90% (IQR 84%, 95%)) on 179 clinical photos (versus LR and XGBoost, both 85% (IQR 75-76%, 90%)). Outcomes were comparable stratified by PHOX2B genotype and with the addition of publicly available CCHS photos (n = 104) using PCA and LR (sensitivity 83-89% (IQR 67-76%, 92-100%).

CONCLUSIONS

Utilizing facial features, findings suggest an automated, accessible classifier may be used to screen for CCHS in children with the phenotype and support providers to seek PHOX2B testing to improve the diagnostics.

IMPACT

Facial landmarking and principal component analysis on a diverse pediatric and young adult cohort with PHOX2B pathovariants delineated a distinct, subtle CCHS facial phenotype. Automated, low-cost machine learning models can detect a CCHS facial phenotype with a high sensitivity in screening to ultimately refer for disease-defining PHOX2B testing, potentially addressing gaps in disease underdiagnosis and allow for critical, timely intervention.

ATS core curriculum 2023. Pediatric pulmonary medicine: Respiratory disorders in infants

The American Thoracic Society Core Curriculum updates clinicians annually in pediatric pulmonary disease. This is a summary of the Pediatric Pulmonary Medicine Core Curriculum presented at the 2023 American Thoracic Society International Conference. The respiratory disorders of infancy discussed in this year's review include: the care of the patient with bronchopulmonary dysplasia in the neonatal intensive care unit, clinical phenotypes and comorbidities; diffuse lung disease; pulmonary hypertension; central and obstructive sleep apnea. The care of infants with respiratory disorders often poses significant challenges to the general pediatric pulmonologist, sleep clinician, and neonatologist. This review aims to highlight the most clinically relevant aspects of the evaluation, management, and outcomes of infants with these key respiratory disorders, while emphasizing the importance of multidisciplinary care. Furthermore, this document summarizes essential aspects of genetic testing, novel imaging and treatment modalities, and includes multiple resources for clinical practice.

Loss-of-function of chemoreceptor neurons in the retrotrapezoid nucleus: What have we learned from it?

Central respiratory chemoreceptors are cells in the brain that regulate breathing in relation to arterial pH and PCO2. Neurons located at the retrotrapezoid nucleus (RTN) have been hypothesized to be central chemoreceptors and/or to be part of the neural network that drives the central respiratory chemoreflex. The inhibition or ablation of RTN chemoreceptor neurons has offered important insights into the role of these cells on central respiratory chemoreception and the neural control of breathing over almost 60 years since the original identification of acid-sensitive properties of this ventral medullary site. Here, we discuss the current definition of chemoreceptor neurons in the RTN and describe how this definition has evolved over time. We then summarize the results of studies that use loss-of-function approaches to evaluate the effects of disrupting the function of RTN neurons on respiration. These studies offer evidence that RTN neurons are indispensable for the central respiratory chemoreflex in mammals and exert a tonic drive to breathe at rest. Moreover, RTN has an interdependent relationship with oxygen sensing mechanisms for the maintenance of the neural drive to breathe and blood gas homeostasis. Collectively, RTN neurons are a genetically-defined group of putative central respiratory chemoreceptors that generate CO2-dependent drive that supports eupneic breathing and stimulates the hypercapnic ventilatory reflex.

Congenital Central Hypoventilation Syndrome: The Singularity of A Successful Case

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Images: Atypical presentation of congenital central hypoventilation syndrome in an infant with central and obstructive sleep apnea

Congenital central hypoventilation syndrome (CCHS), a rare disease caused by paired-like homeobox 2B variants, affects control of breathing. We report on a 21-month-old boy with CCHS caused by a novel nonpolyalanine repeat mutation, neuroblastoma, severe obstructive and central sleep apnea, and sleep-related hypoxemia without hypoventilation. At 10 months, due to persistent central sleep apnea during serial polysomnography, bilevel positive airway pressure therapy was initiated despite the absence of hypoventilation. Nonpolyalanine repeat mutations are associated with severe phenotypes requiring continuous assisted ventilation, Hirschsprung's disease, and neural crest tumors; however, our patient had a relatively milder respiratory phenotype requiring sleep-only assisted ventilation without tracheostomy. Although alveolar hypoventilation is the hallmark of CCHS, our patient lacked hypoventilation. Bilevel positive airway pressure could be considered in some infants with CCHS requiring sleep-only assisted ventilation for tracheostomy avoidance. Our case demonstrates the expanding phenotypic spectrum in CCHS and the importance of formulating an individualized care plan.

CITATION

Fain ME, Raghunandan S, Pencheva B, Leu RM, Kasi AS. Images: atypical presentation of congenital central hypoventilation syndrome in an infant with central and obstructive sleep apnea. J Clin Sleep Med. 2024;20(3):478-481.

Pulmonary hypertension in an adult patient with congenital central hypoventilation syndrome: a case report

Background

Congenital central hypoventilation syndrome (CCHS) is a life-threatening disorder of autonomic respiratory control. Mutations in the paired-like homeobox 2B (PHOX2B) gene impair respiratory drive, causing hypercarbia and hypoxaemia. Most patients with CCHS are diagnosed in the neonatal period; however, a few are diagnosed in adulthood.

Case summary

We report a 32-year-old man with a history of unexplained cyanosis 14 days after birth. He presented to our hospital with breathlessness and abnormal electrocardiogram findings discovered in a health check-up. Pulmonary hypertension (PH) was suspected based on electrocardiographic and echocardiographic evidence of right ventricular (RV) overload. Results of pulmonary function tests and chest computed tomography were normal. Arterial blood gas analysis revealed type 2 respiratory failure without a significant alveolar-arterial oxygen gradient, indicating alveolar hypoventilation. Right heart catheterization (RHC) showed pre-capillary PH [pulmonary artery pressure 47/24 (35) mmHg], and a hyperventilation challenge test and a non-invasive positive pressure ventilation (NPPV) treatment during RHC provided drastic improvement in PH [pulmonary artery pressure 28/12 (18) mmHg]. Congenital central hypoventilation syndrome was diagnosed based on genetic testing (20/25 polyalanine repeat expansion mutations in PHOX2B). After NPPV therapy initiation, the RV overload was slightly improved.

Discussion

Some patients with CCHS develop mild hypoventilation without overt clinical signs, and PH can be the first clinical manifestation. In our case, the hyperventilation challenge test improved PH. Although CCHS causes chronic alveolar hypoxia and hypoxic pulmonary vasoconstriction with subsequent PH, optimal ventilation therapy can improve pulmonary circulation even in affected adults.

Defective exercise-related expiratory muscle recruitment in patients with PHOX2B mutations: A clue to neural determinants of the congenital central hypoventilation syndrome

INTRODUCTION AND OBJECTIVES

The human congenital central hypoventilation syndrome (CCHS) is caused by mutations in the PHOX2B (paired-like homeobox 2B) gene. Genetically engineered PHOX2B rodents exhibit defective development of the brainstem retrotrapezoid nucleus (RTN), a carbon dioxide sensitive structure that critically controls expiratory muscle recruitment. This has been linked to a blunted exercise ventilatory response. Whether this can be extrapolated to human CCHS is unknown and represents the objective of this study.

MATERIALS AND METHODS

Thirteen adult CCHS patients and 13 healthy participants performed an incremental symptom-limited cycle cardiopulmonary exercise test. Responses were analyzed using guideline approaches (ventilation V'E, tidal volume VT, breathing frequency, oxygen consumption, carbon dioxide production) complemented by a breathing pattern analysis (i.e. expiratory and inspiratory reserve volume, ERV and IRV).

RESULTS

A ventilatory response occurred in both study groups, as follows: V'E and VT increased in CCHS patients until 40 W and then decreased, which was not observed in the healthy participants (p<0.001). In the latter, exercise-related ERV and IRV decreases attested to concomitant expiratory and inspiratory recruitment. In the CCHS patients, inspiratory recruitment occurred but there was no evidence of expiratory recruitment (absence of any ERV decrease, p<0.001).

CONCLUSIONS

Assuming a similar organization of respiratory rhythmogenesis in humans and rodents, the lack of exercise-related expiratory recruitment observed in our CCHS patients is compatible with a PHOX2B-related defect of a neural structure that would be analogous to the rodents' RTN. Provided corroboration, ERV recruitment could serve as a physiological outcome in studies aiming at correcting breathing control in CCHS.

Characteristics and outcomes in children with congenital central hypoventilation syndrome on long-term mechanical ventilation in the Netherlands

Congenital central hypoventilation syndrome (CCHS) is a rare condition characterized by central hypoventilation, leading to the majority of patients being dependent on ventilatory support during sleep. This condition is often accompanied by various associated symptoms, due to a PHOX2B gene variant involved in neuronal crest cell migration. This study is the first to review the characteristics and outcomes in children with CCHS on long-term mechanical ventilation in the Netherlands. We performed a retrospective study of all CCHS patients treated in the 4 Centers of Home Mechanical Ventilation of the University Medical Centers in the Netherlands from 2000 till 2022 by collecting information from the electronic medical records, documented during follow-up. We included 31 patients, out of which 27 exhibited a known genetic profile associated with CCHS, while no PHOX2B variant was identified in the remaining patients. Among the 27 patients with known genetic profiles, 10 patients had a non-polyalanine repeat expansion mutation (NPARM), followed by 20/27, 20/25, and 20/26 polyalanine repeat expansion mutations (PARMs) in descending order. The most common presentation involved respiratory failure or apneas during the neonatal period with an inability to wean off ventilation. The majority of patients required ventilatory support during sleep, with four patients experiencing life-threatening events related to this dependency. Daily use of ventilatory support varied among different genetic profiles. All genotypes reported comorbidities, with Hirschsprung's disease and cardiac arrhythmias being the most reported comorbidities. Notably, Hirschprung's disease was exclusively observed in patients with a 20/27 PHOX2B variant.

CONCLUSION

Our study results suggest that in our cohort, the genotype is not easily associated to the phenotype in CCHS. Consistent with these findings and international literature, we recommend a thorough annual evaluation for all patients with CCHS to ensure optimal management and follow-up.

WHAT IS KNOWN

• The majority of CCHS patients are dependent on ventilatory support. • Variants in the PHOX2B gene are responsible for the characteristics of CCHS.

WHAT IS NEW

• This study provides insight into the clinical course and long-term outcomes of CCHS patients in the Netherlands. • In CCHS, the genotype is not easily associated with the phenotype, requiring a thorough life-long follow-up for all patients.

ROHHAD syndrome spectrum in an adult: a possible new variant

This case report describes for the first time the evolution of a mature patient with all the diagnostic criteria for ROHHAD syndrome. It shows a rare case of central alveolar hypoventilation with hypothalamic impairment, dysautonomia and rapid weight gain. https://bit.ly/49AN3Vv.

Later Onset Congenital Central Hypoventilation Syndrome

Congenital central hypoventilation syndrome (CCHS) is a rare disorder of the autonomic nervous system involving multiple organ systems, with the hallmark symptom of respiratory failure due to aberrant central control of breathing resulting in hypoxemia and hypercapnia. Later onset CCHS (LOCCHS) is defined as the diagnosis of CCHS in children older than 1 month. Molecular genetic testing for PHOX2B variants has led not only to increased diagnosis of neonates with CCHS but also the increased identification of older children, adolescents, and adults with LOCCHS who may have a milder clinical presentation of this multisystem disease.

Elevated transaminases in congenital central hypoventilation syndrome

Patients with CCHS who also have Hirschsprung disease, elevated or low BMI, or pulmonary hypertension may be predisposed to elevated transaminases and may need periodic follow-up of their hepatic function https://bit.ly/3uW7AUG.

A Case of Nemaline Myopathy With Sleep-Related Hypoventilation Diagnosed Using Polysomnography During Daytime Napping

This is the case of a 49-year-old woman who was admitted to the hospital for a close examination of pulmonary hypertension; however, the next morning, she developed carbon dioxide (CO2) narcosis and was started on artificial ventilation. As pulmonary arterial hypertension was ruled out, the patient was extubated, and 24-hour transcutaneous partial pressure of carbon dioxide (PCO2)(transcutaneous carbon dioxide (TcPCO2)) monitoring was performed to diagnose sleep-related hypoventilation. Polysomnography (PSG) during daytime napping revealed markedly decreased chest motion and a "pseudo-central event," which was neither central nor obstructive hypopnea. Based on the PSG results and physical examination findings, a neuromuscular disorder was suspected, and a muscle biopsy was performed to diagnose nemaline myopathy. Neuromuscular diseases are widely recognized for their association with sleep-disordered breathing; thus, sleep-related hypoventilation should also be considered. Monitoring of TcPCO2 and PSG are useful tools in identifying the cause of hypoventilation; however, overnight PSG may cause CO2 narcosis in some diseases. In such cases, PSG may be beneficial during daytime napping.

Multidisciplinary approach to congenital central hypoventilation syndrome during pregnancy: case report

Congenital central hypoventilation syndrome is a rare genetic disorder that affects control of breathing caused by variants in the paired-like homeobox 2B (PHOX2B) gene. During pregnancy, women with congenital central hypoventilation syndrome are at risk for hypoventilation and require frequent assessments of oxygenation and ventilation during wakefulness and sleep on their ventilator. This could potentially lead to adjustments in the ventilator settings or a change in the assisted ventilation modality. We report the case of a 31-year-old pregnant woman with congenital central hypoventilation syndrome and an implanted cardiac pacemaker who underwent prenatal genetic testing for congenital central hypoventilation syndrome and who delivered a healthy newborn by cesarean delivery. She received collaborative multidisciplinary care from a team that included specialists in obstetrics, maternal and fetal medicine, medical genetics, sleep and pulmonary medicine, cardiology, and anesthesiology. She used bilevel positive airway pressure therapy throughout pregnancy and after cesarean delivery without requiring adjustments in the bilevel positive airway pressure settings. Our case highlights the importance of multidisciplinary care in women with congenital central hypoventilation syndrome during pregnancy to optimize pregnancy and fetal outcomes.

Obstructive sleep apnea as a presentation of congenital central hypoventilation syndrome

Congenital central hypoventilation syndrome is a rare disorder due to a mutation in the PHOX2B gene, characterized by a failure in autonomic control of breathing with diminished or absent response to hypoxia and hypercapnia, which is most pronounced during sleep. Most patients present from birth with central apneas and hypoventilation, or later in the setting of a physiologic stress. Recent literature in mice with a Phox2b27Ala/+ mutation suggests a predisposition to obstructive apneas likely due to hypoglossal dysgenesis. We report on three patients with obstructive sleep apneas with absent or mild hypoventilation. Our cases propose that obstructive apneas can be the primary presentation in patients who subsequently develop the classic phenotype of congenital central hypoventilation syndrome and emphasize their close monitoring and surveillance.

CITATION

Kagan O, Zhang C, McElyea C, Keens TG, Davidson Ward SL, Perez IA. Obstructive sleep apnea as a presentation of congenital central hypoventilation syndrome. J Clin Sleep Med. 2023;19(9):1697-1700.

Sleep Disorders in Childhood

OBJECTIVE

This article provides a comprehensive review of pediatric sleep disorders including the clinical features, diagnosis, and treatment of sleep-disordered breathing, insomnia, parasomnias, restless sleep disorder, restless legs syndrome, narcolepsy in childhood, and Kleine-Levin syndrome.

LATEST DEVELOPMENTS

Our understanding of pediatric sleep pathophysiology continues to evolve, and diagnostic and treatment modalities have expanded. A low-sodium oxybate formulation was approved in July 2020 in the United States to treat cataplexy and excessive daytime sleepiness in patients 7 years old and older with narcolepsy. A validated pediatric hypersomnolence survey for pediatric narcolepsy and idiopathic hypersomnia with high sensitivity, specificity, and interrater reliability is now available.

ESSENTIAL POINTS

The clinical presentation, diagnostics, and treatment of children with sleep disorders differ from those of adults. Untreated sleep disorders in childhood can lead to adverse physical and psychological consequences in adults. Correctly diagnosing and treating sleep disorders in youth can prevent a significant burden of disease in adulthood.

Neuromedin B-Expressing Neurons in the Retrotrapezoid Nucleus Regulate Respiratory Homeostasis and Promote Stable Breathing in Adult Mice

Respiratory chemoreceptor activity encoding arterial Pco2 and Po2 is a critical determinant of ventilation. Currently, the relative importance of several putative chemoreceptor mechanisms for maintaining eupneic breathing and respiratory homeostasis is debated. Transcriptomic and anatomic evidence suggests that bombesin-related peptide Neuromedin-B (Nmb) expression identifies chemoreceptor neurons in the retrotrapezoid nucleus (RTN) that mediate the hypercapnic ventilatory response, but functional support is missing. In this study, we generated a transgenic Nmb-Cre mouse and used Cre-dependent cell ablation and optogenetics to test the hypothesis that RTN Nmb neurons are necessary for the CO2-dependent drive to breathe in adult male and female mice. Selective ablation of ∼95% of RTN Nmb neurons causes compensated respiratory acidosis because of alveolar hypoventilation, as well as profound breathing instability and respiratory-related sleep disruption. Following RTN Nmb lesion, mice were hypoxemic at rest and were prone to severe apneas during hyperoxia, suggesting that oxygen-sensitive mechanisms, presumably the peripheral chemoreceptors, compensate for the loss of RTN Nmb neurons. Interestingly, ventilation following RTN Nmb -lesion was unresponsive to hypercapnia, but behavioral responses to CO2 (freezing and avoidance) and the hypoxia ventilatory response were preserved. Neuroanatomical mapping shows that RTN Nmb neurons are highly collateralized and innervate the respiratory-related centers in the pons and medulla with a strong ipsilateral preference. Together, this evidence suggests that RTN Nmb neurons are dedicated to the respiratory effects of arterial Pco2/pH and maintain respiratory homeostasis in intact conditions and suggest that malfunction of these neurons could underlie the etiology of certain forms of sleep-disordered breathing in humans.SIGNIFICANCE STATEMENT Respiratory chemoreceptors stimulate neural respiratory motor output to regulate arterial Pco2 and Po2, thereby maintaining optimal gas exchange. Neurons in the retrotrapezoid nucleus (RTN) that express the bombesin-related peptide Neuromedin-B are proposed to be important in this process, but functional evidence has not been established. Here, we developed a transgenic mouse model and demonstrated that RTN neurons are fundamental for respiratory homeostasis and mediate the stimulatory effects of CO2 on breathing. Our functional and anatomic data indicate that Nmb-expressing RTN neurons are an integral component of the neural mechanisms that mediate CO2-dependent drive to breathe and maintain alveolar ventilation. This work highlights the importance of the interdependent and dynamic integration of CO2- and O2-sensing mechanisms in respiratory homeostasis of mammals.

Congenital Central Hypoventilation Syndrome in Israel-Novel Findings from a New National Center

BACKGROUND

Congenital central hypoventilation syndrome (CCHS) is a rare autosomal-dominant disorder of the autonomic nervous system that results from mutations in the PHOX2B gene. A national CCHS center was founded in Israel in 2018. Unique new findings were observed.

METHODS

All 27 CCHS patients in Israel were contacted and followed. Novel findings were observed.

RESULTS

The prevalence of new CCHS cases was almost twice higher compared to other countries. The most common mutations in our cohort were polyalanine repeat mutations (PARM) 20/25, 20/26, 20/27 (combined = 85% of cases). Two patients showed unique recessive inheritance while their heterozygotes family members were asymptomatic. A right-sided cardio-neuromodulation was performed on an eight-year-old boy for recurrent asystoles by ablating the parasympathetic ganglionated plexi using radiofrequency (RF) energy. Over 36 months' follow-up with an implantable loop-recorder, no bradycardias/pauses events were observed. A cardiac pacemaker was avoided.

CONCLUSIONS

A significant benefit and new information arise from a nationwide expert CCHS center for both clinical and basic purposes. The incidence of CCHS in some populations may be increased. Asymptomatic NPARM mutations may be much more common in the general population, leading to an autosomal recessive presentation of CCHS. RF cardio-neuromodulation offers a novel approach to children avoiding the need for permanent pacemaker implantation.

Neurocognition as a biomarker in the rare autonomic disorders of CCHS and ROHHAD

PURPOSE

Congenital central hypoventilation syndrome (CCHS) and rapid-onset obesity with hypothalamic dysfunction, hypoventilation, and autonomic dysregulation (ROHHAD) are rare disorders of autonomic regulation with risk for disrupted neurocognitive development. Our aim is to summarize research on neurocognitive outcomes in these conditions, advance understanding of how to best support these individuals throughout development, and facilitate future research.

METHODS

We conducted a narrative review of literature on neurocognitive outcomes in CCHS and ROHHAD, supplemented with previously unpublished data from patients with CCHS and ROHHAD at our Center for Autonomic Medicine in Pediatrics (CAMP).

RESULTS

Individuals with CCHS and ROHHAD experience a wide range of neurocognitive functioning ranging from above average to below average, but are at particular risk for difficulties with working memory, processing speed, perceptual reasoning, and visuographic skills. An assessment framework emphasizing fluid cognition seems especially appropriate for these conditions. Owing to small cohorts and varied methods of data collection, it has been difficult to identify associations between disease factors (including CCHS PHOX2B genotypes) and cognitive outcomes. However, results suggest that early childhood is a period of particular vulnerability, perhaps due to the disruptive impact of recurrent intermittent hypoxic episodes on brain and cognitive development.

CONCLUSION

Neurocognitive monitoring is recommended as a component of routine clinical care in CCHS and ROHHAD as a marker of disease status and to ensure that educational support and disability accommodations are provided as early as possible. Collaborative efforts will be essential to obtain samples needed to enhance our understanding of neurocognitive outcomes in CCHS and ROHHAD.

Transitional care and clinical management of adolescents, young adults, and suspected new adult patients with congenital central hypoventilation syndrome

PURPOSE

With contemporaneous advances in congenital central hypoventilation syndrome (CCHS), recognition, confirmatory diagnostics with PHOX2B genetic testing, and conservative management to reduce the risk of early morbidity and mortality, the prevalence of identified adolescents and young adults with CCHS and later-onset (LO-) CCHS has increased. Accordingly, there is heightened awareness and need for transitional care of these patients from pediatric medicine into a multidisciplinary adult medical team. Hence, this review summarizes key clinical and management considerations for patients with CCHS and LO-CCHS and emphasizes topics of particular importance for this demographic.

METHODS

We performed a systematic review of literature on diagnostics, pathophysiology, and clinical management in CCHS and LO-CCHS, and supplemented the review with anecdotal but extensive experiences from large academic pediatric centers with expertise in CCHS.

RESULTS

We summarized our findings topically for an overview of the medical care in CCHS and LO-CCHS specifically applicable to adolescents and adults. Care topics include genetic and embryologic basis of the disease, clinical presentation, management, variability in autonomic nervous system dysfunction, and clarity regarding transitional care with unique considerations such as living independently, family planning, exposure to anesthesia, and alcohol and drug use.

CONCLUSIONS

While a lack of experience and evidence exists in the care of adults with CCHS and LO-CCHS, a review of the relevant literature and expert consensus provides guidance for transitional care areas.

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.

Congenital central hypoventilation syndrome without hypoventilation: is it congenital central hypoventilation syndrome?

Congenital central hypoventilation syndrome (CCHS) is a rare condition caused by pathogenic variants of the PHOX2B gene. There have been case reports describing variable phenotypes and mutations of the PHOX2B gene, not commonly tested for, that may challenge the classic definition of CCHS. We report on 3 family members with a rare heterozygous deletion encompassing the entire PHOX2B gene with variable phenotypes, including sleep-disordered breathing and autonomic nervous system involvement, but an unexpected lack of alveolar hypoventilation, which is usually a defining feature of CCHS. Our cases highlight the dilemmas in making a diagnosis of CCHS and emphasize the need for expanded genetic testing, including for PHOX2B gene deletion. More patients with variable phenotypes of CCHS may be identified through comprehensive genetic testing and warrant surveillance as they are still at risk for high-risk complications of CCHS.

CITATION

Wo LL, Itani R, Keens TG, Marachelian A, Ji J, Perez IA. Congenital central hypoventilation syndrome without hypoventilation: is it congenital central hypoventilation syndrome? J Clin Sleep Med. 2023;19(6):1161-1164.

Congenital Central Hypoventilation Syndrome: Diagnosis and Long-Term Ventilatory Outcomes

Background

Congenital central hypoventilation syndrome (CCHS), a rare disease caused by variants in the paired-like homeobox 2B (PHOX2B) gene, affects regulation of respiration necessitating lifelong assisted ventilation (AV). Most patients require full-time AV during infancy and some patients may sustain adequate spontaneous ventilation during wakefulness and change AV modalities at a later age. The aims of this study were to assess the changes in duration and modalities of AV, long-term respiratory outcomes, and to correlate them with PHOX2B genotypes.

Methods

We conducted a retrospective study of patients with CCHS treated at our institution between January 1997 and May 2022. Results analyzed included: clinical presentation, PHOX2B genotype, modality and duration of AV at diagnosis and follow-up, survival, and transition to adult care.

Results

We identified 30 patients with CCHS-8 with PHOX2B nonpolyalanine repeat mutations (NPARMs), 21 with polyalanine repeat mutations (PARMs), and 1 with unknown PHOX2B genotype. The median age at presentation was 0.25 months (IQR 0.1-0.7 months). At diagnosis of CCHS, 24 (80%) patients required continuous AV and 28 (93%) received AV via tracheostomy. Twenty-six patients required sleep-only AV at a median age of 9 months (IQR 6-14 months). Nine patients requiring sleep-only AV underwent tracheostomy decannulation at a median age of 11.2 years (IQR 5.9-15.7 years) and used noninvasive positive pressure ventilation or diaphragm pacing. There was insufficient evidence to conclude that patients with PARMs and NPARMs differed by age at presentation (P = .39), tracheostomy (P = .06), and transition to sleep-only AV (P = .9). Six patients transitioned to adult care, 23 continued receiving pediatric care, and 1 patient died due to complications from Hirschsprung's disease.

Conclusion

Our study demonstrates prolonged survival and good long-term respiratory outcomes possibly related to the early diagnosis of CCHS, optimizing AV strategies, and multidisciplinary care. The increasing number of patients attaining adulthood highlights the necessity for multidisciplinary care for adults with CCHS.

phox2ba: The Potential Genetic Link behind the Overlap in the Symptomatology between CHARGE and Central Congenital Hypoventilation Syndromes

CHARGE syndrome typically results from mutations in the gene encoding chromodomain helicase DNA-binding protein 7 (CHD7). CHD7 is involved in regulating neural crest development, which gives rise to tissues of the skull/face and the autonomic nervous system (ANS). Individuals with CHARGE syndrome are frequently born with anomalies requiring multiple surgeries and often experience adverse events post-anesthesia, including oxygen desaturations, decreased respiratory rates, and heart rate abnormalities. Central congenital hypoventilation syndrome (CCHS) affects ANS components that regulate breathing. Its hallmark feature is hypoventilation during sleep, clinically resembling observations in anesthetized CHARGE patients. Loss of PHOX2B (paired-like homeobox 2b) underlies CCHS. Employing a chd7-null zebrafish model, we investigated physiologic responses to anesthesia and compared these to loss of phox2b. Heart rates were lower in chd7 mutants compared to the wild-type. Exposure to tricaine, a zebrafish anesthetic/muscle relaxant, revealed that chd7 mutants took longer to become anesthetized, with higher respiratory rates during recovery. chd7 mutant larvae demonstrated unique phox2ba expression patterns. The knockdown of phox2ba reduced larval heart rates similar to chd7 mutants. chd7 mutant fish are a valuable preclinical model to investigate anesthesia in CHARGE syndrome and reveal a novel functional link between CHARGE syndrome and CCHS.

Analysis and comparisons of gene expression changes in patient- derived neurons from ROHHAD, CCHS, and PWS

Background

Rapid-onset obesity with hypothalamic dysfunction, hypoventilation, and autonomic dysregulation (ROHHAD) syndrome is an ultra-rare neurocristopathy with no known genetic or environmental etiology. Rapid-onset obesity over a 3-12 month period with onset between ages 1.5-7 years of age is followed by an unfolding constellation of symptoms including severe hypoventilation that can lead to cardiorespiratory arrest in previously healthy children if not identified early and intervention provided. Congenital Central Hypoventilation syndrome (CCHS) and Prader-Willi syndrome (PWS) have overlapping clinical features with ROHHAD and known genetic etiologies. Here we compare patient neurons from three pediatric syndromes (ROHHAD, CCHS, and PWS) and neurotypical control subjects to identify molecular overlap that may explain the clinical similarities.

Methods

Dental pulp stem cells (DPSC) from neurotypical control, ROHHAD, and CCHS subjects were differentiated into neuronal cultures for RNA sequencing (RNAseq). Differential expression analysis identified transcripts variably regulated in ROHHAD and CCHS vs. neurotypical control neurons. In addition, we used previously published PWS transcript data to compare both groups to PWS patient-derived DPSC neurons. Enrichment analysis was performed on RNAseq data and downstream protein expression analysis was performed using immunoblotting.

Results

We identified three transcripts differentially regulated in all three syndromes vs. neurotypical control subjects. Gene ontology analysis on the ROHHAD dataset revealed enrichments in several molecular pathways that may contribute to disease pathology. Importantly, we found 58 transcripts differentially expressed in both ROHHAD and CCHS patient neurons vs. control neurons. Finally, we validated transcript level changes in expression of ADORA2A, a gene encoding for an adenosine receptor, at the protein level in CCHS neurons and found variable, although significant, changes in ROHHAD neurons.

Conclusions

The molecular overlap between CCHS and ROHHAD neurons suggests that the clinical phenotypes in these syndromes likely arise from or affect similar transcriptional pathways. Further, gene ontology analysis identified enrichments in ATPase transmembrane transporters, acetylglucosaminyltransferases, and phagocytic vesicle membrane proteins that may contribute to the ROHHAD phenotype. Finally, our data imply that the rapid-onset obesity seen in both ROHHAD and PWS likely arise from different molecular mechanisms. The data presented here describes important preliminary findings that warrant further validation.

Central sleep apnea: pathophysiologic classification

Central sleep apnea is not a single disorder; it can present as an isolated disorder or as a part of other clinical syndromes. In some conditions, such as heart failure, central apneic events are due to transient inhibition of ventilatory motor output during sleep, owing to the overlapping influences of sleep and hypocapnia. Specifically, the sleep state is associated with removal of wakefulness drive to breathe; thus, rendering ventilatory motor output dependent on the metabolic ventilatory control system, principally PaCO2. Accordingly, central apnea occurs when PaCO2 is reduced below the "apneic threshold". Our understanding of the pathophysiology of central sleep apnea has evolved appreciably over the past decade; accordingly, in disorders such as heart failure, central apnea is viewed as a form of breathing instability, manifesting as recurrent cycles of apnea/hypopnea, alternating with hyperpnea. In other words, ventilatory control operates as a negative-feedback closed-loop system to maintain homeostasis of blood gas tensions within a relatively narrow physiologic range, principally PaCO2. Therefore, many authors have adopted the engineering concept of "loop gain" (LG) as a measure of ventilatory instability and susceptibility to central apnea. Increased LG promotes breathing instabilities in a number of medical disorders. In some other conditions, such as with use of opioids, central apnea occurs due to inhibition of rhythm generation within the brainstem. This review will address the pathogenesis, pathophysiologic classification, and the multitude of clinical conditions that are associated with central apnea, and highlight areas of uncertainty.

Sleep disturbances in parental caregivers and patients with congenital central hypoventilation syndrome

STUDY OBJECTIVES

Congenital central hypoventilation syndrome (CCHS) is a rare disease characterized by impaired control of breathing caused by paired-like homeobox 2B (PHOX2B) gene variants, necessitating lifelong assisted ventilation (AV). This study aimed to assess sleep quality in patients with CCHS and their parents using sleep questionnaires.

METHODS

Parents of patients with CCHS completed the Pittsburgh Sleep Quality Index (PSQI) regarding their sleep and the Sleep Disturbance Scale for Children (SDSC) regarding their child's sleep.

RESULTS

Twenty participants completed the questionnaires. The median (interquartile range) ages of the parents and patients were 41.5 (38.5-51.5) and 11.5 (7.4-16.7) years, respectively. The median (interquartile range) PSQI and SDSC scores were elevated at 6.5 (4-10) and 41.5 (34-51.5), respectively, suggesting that parents and patients with CCHS can experience sleep disturbances and poor sleep quality. There were no significant differences in SDSC (P = 1.0) and PSQI (P = .76) scores for AV with or without tracheostomy. Similarly, there were no significant differences in SDSC (P = .22) and PSQI (P = .34) scores based on PHOX2B genotypes. There was a moderately strong, significant, and positive correlation between the CCHS SDSC scores and parental PSQI scores (r = .48, P = .03), suggesting that sleep disturbances in patients with CCHS were associated with poor parental sleep quality. There was no difference in the median parental sleep duration between those with and without nighttime home nursing (P = .09).

CONCLUSIONS

Patients with CCHS and their parents are at risk for sleep disturbances regardless of their AV modality and PHOX2B genotype. In addition to AV management, patients with CCHS and their parents should be assessed for sleep disturbances.

CITATION

Finch CE, Leu RM, Harford K-L, Westbrook AL, Kasi AS. Sleep disturbances in parental caregivers and patients with congenital central hypoventilation syndrome. J Clin Sleep Med. 2023;19(3):549-554.

Serotonin and the ventilatory effects of etonogestrel, a gonane progestin, in a murine model of congenital central hypoventilation syndrome

INTRODUCTION

Congenital Central Hypoventilation Syndrome, a rare disease caused by PHOX2B mutation, is associated with absent or blunted CO₂/H⁺ chemosensitivity due to the dysfunction of PHOX2B neurons of the retrotrapezoid nucleus. No pharmacological treatment is available. Clinical observations have reported non-systematic CO₂/H⁺ chemosensitivity recovery under desogestrel.

METHODS

Here, we used a preclinical model of Congenital Central Hypoventilation Syndrome, the retrotrapezoid nucleus conditional Phox2b mutant mouse, to investigate whether etonogestrel, the active metabolite of desogestrel, led to a restoration of chemosensitivity by acting on serotonin neurons known to be sensitive to etonogestrel, or retrotrapezoid nucleus PHOX2B residual cells that persist despite the mutation. The influence of etonogestrel on respiratory variables under hypercapnia was investigated using whole-body plethysmographic recording. The effect of etonogestrel, alone or combined with serotonin drugs, on the respiratory rhythm of medullary-spinal cord preparations from Phox2b mutants and wildtype mice was analyzed under metabolic acidosis. c-FOS, serotonin and PHOX2B were immunodetected. Serotonin metabolic pathways were characterized in the medulla oblongata by ultra-high-performance liquid chromatography.

RESULTS

We observed etonogestrel restored chemosensitivity in Phox2b mutants in a non-systematic way. Histological differences between Phox2b mutants with restored chemosensitivity and Phox2b mutant without restored chemosensitivity indicated greater activation of serotonin neurons of the raphe obscurus nucleus but no effect on retrotrapezoid nucleus PHOX2B residual cells. Finally, the increase in serotonergic signaling by the fluoxetine application modulated the respiratory effect of etonogestrel differently between Phox2b mutant mice and their WT littermates or WT OF1 mice, a result which parallels with differences in the functional state of serotonergic metabolic pathways between these different mice.

DISCUSSION

Our work thus highlights that serotonin systems were critically important for the occurrence of an etonogestrel-restoration, an element to consider in potential therapeutic intervention in Congenital Central Hypoventilation Syndrome patients.

A Deeper Curse: A Hirschsprung Patient's Evaluation Unmasks a Rare Association with Congenital Central Hypoventilation Syndrome and Neuroblastoma

We present a rare case of a 2-year-old male patient referred for primary evaluation of constipation and ultimately treatment of Hirschsprung disease (HSCR) whose preoperative workup incidentally revealed a posterior paraspinal mass. Following the biopsy of the mass, the patient exhibited hypoventilation and hypoxia requiring a delayed extubation, raising suspicion for congenital central hypoventilation syndrome (CCHS). We focus on the known history of associations between HSCR and CCHS, in addition to recently found genetic mutations in paired-like homeobox 2B that link HSCR, CCHS, and neuroblastoma.

Noninvasive ventilation via bilevel positive airway pressure improved sleep in a child with congenital central hypoventilation syndrome: A case report

We report the polysomnography findings of a 2-year-old girl who was previously diagnosed with CCHS and treated with bilevel positive airway pressure (BiPAP) and O2 supplementation for a year. The girl had convulsions 2 times in the last 10 days. After we replaced her nasal cannula with a nasal mask and adjusted the parameters of the BiPAP, her sleep and ventilation were improved. The polysomnographies measured under spontaneous breathing without oxygen supplementation showed that her sleep structure, heart rate, and oxygen saturation during sleep were improved 1 month and 1 year after effective BiPAP treatment.

A novel case of central hypoventilation syndrome or just heavy breathing?

With the growing prevalence of obesity in the pediatric population, reports of its severe complications are increasing. Obesity hypoventilation syndrome is an uncommon disorder in children with altered respiratory mechanics, sleep-disordered breathing, and impaired ventilatory responses leading to persistent hypercapnia. Presentation is varied, and children may remain relatively asymptomatic until challenged with a respiratory infection, when they may present with acute respiratory failure. With increasing use of genetic testing in pediatric patients, our knowledge of potential contributors to hypoventilation syndromes is growing. Although mutations in the paired-like homeobox 2B gene are known to be causative of congenital central hypoventilation syndrome, other genes may also contribute to hypoventilation phenotypes. We report one of the youngest reported patients with obesity hypoventilation syndrome in pediatrics, with a proposed congenital predisposition for central hypoventilation derived from a deletion in the brain-derived neurotrophic factor gene.

CITATION

McCoy J, Karp N, Brar J, Amin R, St-Laurent A. A novel case of central hypoventilation syndrome or just heavy breathing? J Clin Sleep Med. 2022;18(9):2321-2325.

Neurocognitive monitoring in congenital central hypoventilation syndrome with the NIH Toolbox®

Congenital central hypoventilation syndrome (CCHS) is a rare neurocristopathy, caused by mutations in the paired-like homeobox gene PHOX2B, which alters control of breathing and autonomic nervous system regulation, necessitating artificial ventilation as life-support. A broad range of neurocognitive performance has been reported in CCHS, including an array of cognitive deficits. We administered the NIH Toolbox® Cognition Battery (NTCB), a novel technology comprised of seven tasks presented via an interactive computer tablet application, to a CCHS cohort and studied its convergent and divergent validity relative to traditional clinical neurocognitive measures. The NTCB was administered to 51 CCHS participants, including a subcohort of 24 who also received traditional clinical neurocognitive testing (Wechsler Intelligence Scales). Age-corrected NTCB scores from the overall sample and subcohort were compared to population norms. Associations between NTCB indices and Wechsler Intelligence scores were studied to determine the convergent and divergent validity of the NTCB. NTCB test results indicated reduced Fluid Cognition, which measures new learning and speeded information processing (p < 0.001), but intact Crystallized Cognition, which measures past learning, in CCHS relative to population norms. Moderate to strong associations (r > 0.60) were found between age-corrected NTCB Fluid and Crystallized indices and comparable Wechsler indices, supporting the convergent and discriminant validity of the NTCB. Results reveal deficits of Fluid Cognition in individuals with CCHS and indicate that the NTCB is a valid and sensitive measure of cognitive outcomes in this population. Our findings suggest that the NTCB may play a useful role in tracking neurocognition in CCHS.

Three generations of a family diagnosed with congenital central hypoventilation syndrome: A case series

Congenital central hypoventilation syndrome (CCHS) is an autosomal dominant disorder characterized by alveolar hypoventilation and autonomic dysregulation secondary to mutations of the PHOX2B genes. We present five cases from three generations within the same family with varying degrees of phenotypic expression of the PHOX2B gene mutation. The cases were diagnosed following identification of CCHS in index case at birth. This case series underscores the importance of screening first-degree relatives of individuals with confirmed CCHS and alerts the clinicians to maintain a high degree of suspicion in asymptomatic family members given the high degree of phenotypic variability of CCHS.

Sleep dysregulation in sympathetic-mediated diseases: implications for disease progression

The autonomic nervous system (ANS) plays an important role in the coordination of several physiological functions including sleep/wake process. Significant changes in ANS activity occur during wake-to-sleep transition maintaining the adequate cardiorespiratory regulation and brain activity. Since sleep is a complex homeostatic function, partly regulated by the ANS, it is not surprising that sleep disruption trigger and/or evidence symptoms of ANS impairment. Indeed, several studies suggest a bidirectional relationship between impaired ANS function (i.e. enhanced sympathetic drive), and the emergence/development of sleep disorders. Furthermore, several epidemiological studies described a strong association between sympathetic-mediated diseases and the development and maintenance of sleep disorders resulting in a vicious cycle with adverse outcomes and increased mortality risk. However, which and how the sleep/wake control and ANS circuitry becomes affected during the progression of ANS-related diseases remains poorly understood. Thus, understanding the physiological mechanisms underpinning sleep/wake-dependent sympathetic modulation could provide insights into diseases involving autonomic dysfunction. The purpose of this review is to explore potential neural mechanisms involved in both the onset/maintenance of sympathetic-mediated diseases (Rett syndrome, congenital central hypoventilation syndrome, obstructive sleep apnoea, type 2 diabetes, obesity, heart failure, hypertension, and neurodegenerative diseases) and their plausible contribution to the generation of sleep disorders in order to review evidence that may serve to establish a causal link between sleep disorders and heightened sympathetic activity.

Impaired ventilation during 6-min walk test in congenital central hypoventilation syndrome

BACKGROUND

Patients with congenital central hypoventilation syndrome (CCHS) can develop hypoxemia and hypercapnia during exercise. However, there is limited literature on cardiorespiratory responses during submaximal exercise and their correlation with paired-like homeobox 2B (PHOX2B) genotype.

OBJECTIVES

To assess oxygen saturation (SpO₂ ), end-tidal carbon dioxide (ETCO₂ ), heart rate (HR), and 6-min walk distance (6MWD) during a 6-min walk test (6MWT) in CCHS subjects and to correlate them with PHOX2B genotypes and assisted ventilation (AV) via tracheostomy.

METHODS

In this cross-sectional study, subjects with CCHS performed 6MWT with continuous pulse oximetry, HR, and capnography recorded before and during the 6MWT. Medical records were reviewed for PHOX2B genotype and phenotype data. Patients were categorized based on PHOX2B genotype and AV via tracheostomy.

RESULTS

Fifteen subjects aged 10.5 (interquartile range 7.9-16.2) years completed the 6MWT. Nine subjects used AV via tracheostomy. Seven (47%) subjects developed hypoxemia (SpO₂  ≤ 90%, n = 7) and hypoventilation (ETCO₂  ≥ 50 mmHg, n = 3) during the 6MWT. There was a significant decline from baseline SpO₂ , increase from baseline ETCO₂ , and increase in HR during the 6MWT (all p < 0.05). Subjects had decreased median percent predicted 6MWD (59.7% [50.6%-62.5%]). Nadir SpO₂ (p = 0.029) and peak ETCO₂ (p = 0.046) differed significantly between PHOX2B genotype groups but 6MWD did not (p = 0.8).

CONCLUSION

Despite normal oxygenation and ventilation at rest and during sleep on AV, patients with CCHS can develop hypoxemia and hypercapnia during submaximal exercise. Our study highlights the importance of assessing ventilatory responses during submaximal exercise in patients with CCHS regardless of their PHOX2B genotype.

A Newborn Infant with Congenital Central Hypoventilation Syndrome and Pupillary Abnormalities: A Literature Review

We present a neonate with early onset apnea and bradycardia in the absence of primary cardiorespiratory and central nervous system disorders that eventually required chronic ventilator support starting at 6 hours of life. Molecular testing of paired-like homeobox 2b (PHOX2B) gene mutation confirmed the diagnosis of congenital central hypoventilation syndrome (CCHS). CCHS is a rare genetic disorder characterized by impaired central respiratory control with or without broad spectrum of autonomic nervous system (ANS) dysregulations. Ocular ANS dysregulation is a rare finding in CCHS individuals, and it is usually discovered later in life. However, the ophthalmic evaluation of this neonate on first day of life revealed persistent mild dilated oval pupils with limited light reactivity.

Awake Hypercapnic Ventilatory Response in Obstructive Sleep Apnea Syndrome

Background and Objective Decreased ventilatory response to carbon dioxide or hypercapnic ventilatory response (HCVR) is a feature of pediatric obstructive sleep apnea (OSA) and is also known to diminish during sleep in obese adolescents (age, 12–16 years) with OSA. It reduces minute ventilation, air flow, and tidal volume during inspiration, as well as upper airway obstruction. The purpose of this study was to investigate awake HCVR in adult patients with OSA and to elucidate its association with sleep apnea.Methods HCVR was measured before performing polysomnography (PSG). PSG is performed as the evaluation method during sleep, and the severity of apnea is evaluated by apnea hypopnea index. Patient background, PSG data and HCVR were examined.Results Awake HCVR was greater in patients with severe OSA than in patients with mild and moderate OSA, and in severe OSA patients, the HCVR during awaking was higher in patients with larger changes in saturation of percutaneous oxygen during sleep. Awake HCVR did not differ by age, but it was greater in morbidly obese patients with OSA than in thin patients with OSA. The most frequent apnea pattern of OSA was obstructive, regardless of severity; although with an increasing severity of OSA, the central pattern decreased and the mixed pattern increased in frequency. The appearance of the mixed pattern increased in the augmented HCVR group.Conclusions This study suggested that awake HCVR could be used as an index of progression and a factor to determine the effects of treatment in patients with OSA.

In Transgenic Erythropoietin Deficient Mice, an Increase in Respiratory Response to Hypercapnia Parallels Abnormal Distribution of CO2/H+-Activated Cells in the Medulla Oblongata

Erythropoietin (Epo) and its receptor are expressed in central respiratory areas. We hypothesized that chronic Epo deficiency alters functioning of central respiratory areas and thus the respiratory adaptation to hypercapnia. The hypercapnic ventilatory response (HcVR) was evaluated by whole body plethysmography in wild type (WT) and Epo deficient (Epo-TAg^h) adult male mice under 4%CO₂. Epo-TAg^h mice showed a larger HcVR than WT mice because of an increase in both respiratory frequency and tidal volume, whereas WT mice only increased their tidal volume. A functional histological approach revealed changes in CO₂/H⁺-activated cells between Epo-TAg^h and WT mice. First, Epo-TAg^h mice showed a smaller increase under hypercapnia in c-FOS-positive number of cells in the retrotrapezoid nucleus/parafacial respiratory group than WT, and this, independently of changes in the number of PHOX2B-expressing cells. Second, we did not observe in Epo-TAg^h mice the hypercapnic increase in c-FOS-positive number of cells in the nucleus of the solitary tract present in WT mice. Finally, whereas hypercapnia did not induce an increase in the c-FOS-positive number of cells in medullary raphe nuclei in WT mice, chronic Epo deficiency leads to raphe pallidus and magnus nuclei activation by hyperacpnia, with a significant part of c-FOS positive cells displaying an immunoreactivity for serotonin in the raphe pallidus nucleus. All of these results suggest that chronic Epo-deficiency affects both the pattern of ventilatory response to hypercapnia and associated medullary respiratory network at adult stage with an increase in the sensitivity of 5-HT and non-5-HT neurons of the raphe medullary nuclei leading to stimulation of f_R for moderate level of CO₂.