Respiratory and autonomic dysfunction in congenital central hypoventilation syndrome

A Case of Fulminant Listeria Rhombencephalitis with Brainstem Abscesses in a 37-Year-Old Immunocompetent Patient: From Vestibular Neuritis to Ondine's Curse

We present a rare case of Listeria monocytogenes (LM) rhombencephalitis with the formation of multifocal abscesses in a young immunocompetent patient. His initial symptoms of dizziness, headache, and feeling generally unwell were put down to a coincidental coinfection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The unfortunate rapid progression to trigeminal, hypoglossal, vagal, facial, and abducens nuclei palsies, and then an acquired central hypoventilation syndrome, known as Ondine's curse, required a prolonged intensive care unit (ICU) stay, and prolonged mechanical ventilation. As they continued to deteriorate despite targeted antibiotic treatment, surgical drainage of the abscesses was seen as the only meaningful available treatment option left to contain the disease. Postoperatively, the patient's strength rapidly improved as well as the severity of the cranial nerve palsies. After prolonged rehabilitation, at 3 months of follow-up, the patient was weaned off mechanical ventilation, independently mobile, and was left with only minor residual neurologic deficits. This case highlights a number of interesting findings only touched upon in current literature including the route of entry of LM into the central nervous system, the rare entity of acquired central hypoventilation syndrome, and finally the use of surgical intervention in cerebral LM infections.

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.

Ampakine CX614 increases respiratory rate in a mouse model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by progressive loss of dopaminergic neurons in the substantia nigra compacta (SNpc). In a mouse model of PD induced by the injection of 6-hydroxydopamine (6-OHDA) into the caudate putamen (CPu) dyspnea events are very common. Neuroanatomical and functional studies show that the number of glutamatergic neurons in the pre-Bötzinger Complex (preBötC) are reduced. We hypothesize that the neuronal loss, and consequently loss of glutamatergic connections in the respiratory network previously investigated, are responsible for the breathing impairment in PD. Here, we tested whether ampakines (CX614), a subgroup of AMPA receptor positive allosteric modulators, could stimulate the respiratory activity in PD-induced animals. CX614 (50 µM) injected intraperitoneally or directly into the preBötC region reduced the irregularity pattern and increased the respiratory rate by 37% or 82%, respectively, in PD-induced animals. CX614 also increased the respiratory frequency in healthy animals. These data suggest that ampakine CX614 could become a tool to restore breathing in PD.

Organoid models of breathing disorders reveal patterning defect of hindbrain neurons caused by PHOX2B-PARMs

Retrotrapezoid nucleus (RTN) neurons in the brainstem regulate the ventilatory response to hypercarbia. It is unclear how PHOX2B-polyalanine repeat mutations (PHOX2B-PARMs) alter the function of PHOX2B and perturb the formation of RTN neurons. Here, we generated human brainstem organoids (HBSOs) with RTN-like neurons from human pluripotent stem cells. Single-cell transcriptomics revealed that expression of PHOX2B+7Ala PARM alters the differentiation trajectories of the hindbrain neurons and hampers the formation of the RTN-like neurons in HBSOs. With the unguided cerebral organoids (HCOs), PHOX2B+7Ala PARM interrupted the patterning of PHOX2B+ neurons with dysregulation of Hedgehog pathway and HOX genes. With complementary use of HBSOs and HCOs with a patient and two mutant induced pluripotent stem cell lines carrying different polyalanine repetition in PHOX2B, we further defined the association between the length of polyalanine repetition and malformation of RTN-respiratory center and demonstrated the potential toxic gain of function of PHOX2B-PARMs, highlighting the uniqueness of these organoid models for disease modeling.

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.

Developmental disorders affecting the respiratory system: CCHS and ROHHAD

Rapid-onset Obesity with Hypothalamic dysfunction, Hypoventilation, and Autonomic Dysregulation (ROHHAD) and Congenital Central Hypoventilation Syndrome (CCHS) are ultra-rare distinct clinical disorders with overlapping symptoms including altered respiratory control and autonomic regulation. Although both disorders have been considered for decades to be on the same spectrum with necessity of artificial ventilation as life-support, recent acquisition of specific knowledge concerning the genetic basis of CCHS coupled with an elusive etiology for ROHHAD have definitely established that the two disorders are different. CCHS is an autosomal dominant neurocristopathy characterized by alveolar hypoventilation resulting in hypoxemia/hypercarbia and features of autonomic nervous system dysregulation (ANSD), with presentation typically in the newborn period. It is caused by paired-like homeobox 2B (PHOX2B) variants, with known genotype-phenotype correlation but pathogenic mechanism(s) are yet unknown. ROHHAD is characterized by rapid weight gain, followed by hypothalamic dysfunction, then hypoventilation followed by ANSD, in seemingly normal children ages 1.5-7 years. Postmortem neuroanatomical studies, thorough clinical characterization, pathophysiological assessment, and extensive genetic inquiry have failed to identify a cause attributable to a traditional genetic basis, somatic mosaicism, epigenetic mechanism, environmental trigger, or other. To find the key to the ROHHAD pathogenesis and to improve its clinical management, in the present chapter, we have carefully compared CCHS and ROHHAD.

Effects of Cervical Spine Mobilization on Respiratory Function and Cervical Angles of Stroke Patients: A Pilot Study

The forward head posture (FHP) of stroke patients has a negative impact on respiratory function. Cervical spine mobilization is a manual therapy technique that used to prevent and treat FHP and respiratory function. This pilot study investigated whether cervical spine mobilization can effectively improve outcomes following FHP and respiratory function of stroke patients. Twenty-four patients participated in our assessor-blinded randomized controlled trial. All the participants received neurodevelopmental treatments (gait training and trunk rehabilitation). The experimental group additionally received 15-min sessions of cervical spine mobilization three times per week for 4 weeks. The control group received cervical spine sham mobilization during the same period. For the cervical angles, the cranial vertebral angle (CVA) and cranial rotation angle (CRA) were measured. A respiratory function test was performed to measure the forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), peak expiratory flow (PEF), maximal inspiratory pressure (MIP), maximal expiratory pressure (MEP), and chest circumferences (upper and lower chest sizes). Except for MIP, there was no significant difference between the experimental group and the control group. The CVA and CRA were significantly increased in the experimental group only. Cervical spine mobilization improved cervical angles and inspiratory function of the stroke patients in this study. However, a comparative study with a larger number of patients is needed to confirm this finding from our pilot study, which had a small sample size.

Research Advances on Therapeutic Approaches to Congenital Central Hypoventilation Syndrome (CCHS)

Congenital central hypoventilation syndrome (CCHS) is a genetic disorder of neurodevelopment, with an autosomal dominant transmission, caused by heterozygous mutations in the PHOX2B gene. CCHS is a rare disorder characterized by hypoventilation due to the failure of autonomic control of breathing. Until now no curative treatment has been found. PHOX2B is a transcription factor that plays a crucial role in the development (and maintenance) of the autonomic nervous system, and in particular the neuronal structures involved in respiratory reflexes. The underlying pathogenetic mechanism is still unclear, although studies in vivo and in CCHS patients indicate that some neuronal structures may be damaged. Moreover, in vitro experimental data suggest that transcriptional dysregulation and protein misfolding may be key pathogenic mechanisms. This review summarizes latest researches that improved the comprehension of the molecular pathogenetic mechanisms responsible for CCHS and discusses the search for therapeutic intervention in light of the current knowledge about PHOX2B function.

Machine learning-based data analytic approaches for evaluating post-natal mouse respiratory physiological evolution

Respiratory parameters change during post-natal development, but the nature of their changes have not been well-described. The advent of commercially available plethysmographic instruments provided improved repeatability of measurements and standardization of measured breathing in mice across laboratories. These technologies thus allowed for exploration of more precise respiratory pattern changes during the post-natal developmental epoch. Current methods to analyze respiratory behavior utilize plethysmography to acquire standing values of frequency, volume and flow at specific time points in murine maturation. These metrics have historically been independently analyzed as a function of time with no further analysis examining the interplay these variables have with each other and in the context of postnatal maturation or during blood gas homeostasis. We posit that machine learning workflows can provide deeper physiological understanding into the postnatal development of respiration. In this manuscript, we delineate a machine learning workflow based on the R-statistical programming language to examine how variation and relationships of frequency (f) and tidal volume (TV) change with respect to inspiratory and expiratory parameters. Our analytical workflows could successfully predict age and found that the variation and relationships between respiratory metrics are dynamically shifting with age and during hypercapnic breathing. Thus, our work demonstrates the utility of high dimensional analyses to provide reliable class label predictions using non-invasive respiratory metrics. These approaches may be useful in large-scale phenotyping across development and in disease.

Recognizing genetic disease: A key aspect of pediatric pulmonary care

Advancement in technology has improved recognition of genetic etiologies of disease, which has impacted diagnosis and management of rare disease patients in the pediatric pulmonary clinic. This review provides an overview of genetic conditions that are likely to present with pulmonary features and require extensive care by the pediatric pulmonologist. Increased familiarity with these conditions allows for improved care of these patients by reducing time to diagnosis, tailoring management, and prompting further investigation into these disorders.

Respiratory Control by Phox2b-expressing Neurons in a Locus Coeruleus-preBötzinger Complex Circuit

The locus coeruleus (LC) has been implicated in the control of breathing. Congenital central hypoventilation syndrome results from mutation of the paired-like homeobox 2b (Phox2b) gene that is expressed in LC neurons. The present study was designed to address whether stimulation of Phox2b-expressing LC (Phox2b^LC) neurons affects breathing and to reveal the putative circuit mechanism. A Cre-dependent viral vector encoding a Gq-coupled human M3 muscarinic receptor (hM3Dq) was delivered into the LC of Phox2b-Cre mice. The hM3Dq-transduced neurons were pharmacologically activated while respiratory function was measured by plethysmography. We demonstrated that selective stimulation of Phox2b^LC neurons significantly increased basal ventilation in conscious mice. Genetic ablation of these neurons markedly impaired hypercapnic ventilatory responses. Moreover, stimulation of Phox2b^LC neurons enhanced the activity of preBötzinger complex neurons. Finally, axons of Phox2b^LC neurons projected to the preBötzinger complex. Collectively, Phox2b^LC neurons contribute to the control of breathing most likely via an LC-preBötzinger complex circuit.

Insights into the dynamic control of breathing revealed through cell-type-specific responses to substance P

The rhythm generating network for breathing must continuously adjust to changing metabolic and behavioral demands. Here, we examined network-based mechanisms in the mouse preBötzinger complex using substance P, a potent excitatory modulator of breathing frequency and stability, as a tool to dissect network properties that underlie dynamic breathing. We find that substance P does not alter the balance of excitation and inhibition during breaths or the duration of the resulting refractory period. Instead, mechanisms of recurrent excitation between breaths are enhanced such that the rate that excitation percolates through the network is increased. We propose a conceptual framework in which three distinct phases of inspiration, the burst phase, refractory phase, and percolation phase, can be differentially modulated to control breathing dynamics and stability. Unraveling mechanisms that support this dynamic control may improve our understanding of nervous system disorders that destabilize breathing, many of which involve changes in brainstem neuromodulatory systems.

Differential Role of Pontomedullary Glutamatergic Neuronal Populations in Sleep-Wake Control

Parafacial zone (PZ) GABAergic neurons play a major role in slow-wave-sleep (SWS), also called non-rapid eye movement (NREM) sleep. The PZ also contains glutamatergic neurons expressing the vesicular transporter for glutamate, isoform 2 (Vglut2). We hypothesized that PZ Vglut2-expressing (PZ^Vglut2) neurons are also involved in sleep control, playing a synergistic role with PZ GABAergic neurons. To test this hypothesis, we specifically activated PZ^Vglut2 neurons using the excitatory chemogenetic receptor hM3Dq. Anatomical inspection of the injection sites revealed hM3Dq transfection in PZ, parabrachial nucleus (PB), sublaterodorsal nucleus (SLD) or various combinations of these three brain areas. Consistent with the known wake- and REM sleep-promoting role of PB and SLD, respectively, chemogenetic activation of PB^Vglut2 or SLD^Vglut2 resulted in wake or REM sleep enhancement. Chemogenetic activation of PZ^Vglut2 neurons did not affect sleep-wake phenotype during the mouse active period but increased wakefulness and REM sleep, similar to PB^Vglut2 and SLD^Vglut2 activation, during the rest period. To definitively confirm the role of PZ^Vglut2 neurons, we used a specific marker for PZ^Vglut2 neurons, Phox2B. Chemogenetic activation of PZ^Phox2B neurons did not affect sleep-wake phenotype, indicating that PZ glutamatergic neurons are not sufficient to affect sleep-wake cycle. These results indicate that PZ glutamatergic neurons are not involved in sleep-wake control.

Hydrogen sulfide ameliorates disorders in the parafacial respiratory group region of neonatal rats caused by prenatal cigarette smoke exposure via an antioxidative effect

We previously found that hydrogen sulfide (H₂S) ameliorated the dysfunction of central chemoreception caused by prenatal cigarette smoke exposure (CSE). In the present study, we further explored whether the parafacial respiratory group (pFRG) is involved in the protection of central chemoreception by H₂S against prenatal CSE-induced injury. We found that NaHS, a donor of H₂S, restored the expression of Phox2b, which was downregulated by prenatal CSE, in the pFRG region of neonatal rats. NaHS also relieved the prenatal CSE-induced excitatory synapse disturbance in the pFRG region of neonatal rats. Additionally, NaHS prevented the increase in the malondialdehyde level and suppression of antioxidase activity in the pFRG region of neonatal rats induced by prenatal CSE. Furthermore, NaHS prevented the downregulation of the expression of antioxidases and Nrf2 in the pFRG region of neonatal rats with prenatal CSE. These results suggest that H₂S can protect the pFRG of neonatal rats against prenatal CSE-induced injury via an antioxidative effect.

Individual long non-coding RNAs have no overt functions in zebrafish embryogenesis, viability and fertility

Hundreds of long non-coding RNAs (lncRNAs) have been identified as potential regulators of gene expression, but their functions remain largely unknown. To study the role of lncRNAs during vertebrate development, we selected 25 zebrafish lncRNAs based on their conservation, expression profile or proximity to developmental regulators, and used CRISPR-Cas9 to generate 32 deletion alleles. We observed altered transcription of neighboring genes in some mutants, but none of the lncRNAs were required for embryogenesis, viability or fertility. Even RNAs with previously proposed non-coding functions (cyrano and squint) and other conserved lncRNAs (gas5 and lnc-setd1ba) were dispensable. In one case (lnc-phox2bb), absence of putative DNA regulatory-elements, but not of the lncRNA transcript itself, resulted in abnormal development. LncRNAs might have redundant, subtle, or context-dependent roles, but extrapolation from our results suggests that the majority of individual zebrafish lncRNAs have no overt roles in embryogenesis, viability and fertility.

Neonatal Congenital Central Hypoventilation Syndrome: Why We Should not Sleep on it. Literature Review of Forty-two Neonatal Onset Cases

Congenital Central Hypoventilation Syndrome (CCHS), also referred with the expression "Ondine's Curse", is a rare genetic life-long disease resulting from the mutation of PHOX2B gene on chromosome 4p12.3. CCHS represents an autonomic nervous system disorder; its more fearsome manifestation is central hypoventilation, due to a deficient response of chemoreceptors to hypercapnia and hypoxia. Several associated symptoms can occur, such as pupillary anomalies, arrhythmias, reduced heart rate variability, esophageal dysmotility, and structural comorbidities (Hirschsprung's Disease or neural crest tumours). CCHS typical onset is during the neonatal period, but cases of delayed diagnosis have been reported; moreover, both sporadic or familial cases can occur. In preterm newborns, asphyxia and typical prematurity-related findings may overlap CCHS clinical manifestations and make it harder to formulate a correct diagnosis. The early recognition of CCHS allows appropriate management, useful to reduce immediate and long- term consequences.

The genetics of congenital central hypoventilation syndrome: clinical implications

Congenital central hypoventilation syndrome (CCHS) is a rare genetic disorder of the autonomic nervous system (ANS) and respiratory control. This disorder, formerly referred to as Ondine’s curse, is due to a mutation in the PHOX2B gene that affects the development of the neural crest cells. CCHS has an autosomal dominant pattern of inheritance. Majority of the patients have a polyalanine repeat mutation (PARM) of the PHOX2B, while a small group has non-PARM (NPARM). Knowledge of the patient’s PHOX2B gene mutation helps predict a patient’s clinical presentation and outcome and aids in anticipatory management of the respiratory and ANS dysfunction.

The role of the hypothalamus in modulation of respiration

The hypothalamus is a higher center of the autonomic nervous system and maintains essential body homeostasis including respiration. The paraventricular nucleus, perifornical area, dorsomedial hypothalamus, and lateral and posterior hypothalamus are the primary nuclei of the hypothalamus critically involved in respiratory control. These hypothalamic nuclei are interconnected with respiratory nuclei located in the midbrain, pons, medulla and spinal cord. We provide an extensive review of the role of the above hypothalamic nuclei in the maintenance of basal ventilation, and modulation of respiration in hypoxic and hypercapnic conditions, during dynamic exercise, in awake and sleep states, and under stress. Dysfunction of the hypothalamus causes abnormal breathing and hypoventilation. However, the cellular and molecular mechanisms how the hypothalamus integrates and modulates autonomic and respiratory functions remain to be elucidated.

Genetic factors in sleep-disordered breathing

Sleep-disordered breathing (SDB) is characterized by repetitive episodes of decreased or arrested respiratory airflow during sleep. SDB is common and affects approximately 20% of the Japanese general population. Most traits of normal sleep and SDB show familial aggregation, suggesting significant effects of genetic factors. Obstructive sleep apnea (OSA) is the most common type of SDB and has a high heritability. Regardless of high heritability, no risk locus for OSA has reached a genome-wide level of significance (P < 5×10^-8) in linkage or candidate gene analysis. However, a recent genome-wide association study identified some genetic risks for OSA with P < 5×10^-8 for the first time. The identified genes are associated with inflammation, hypoxia signaling, and sleep pathways. The effects of genetic factors on the consequences of OSA has not been determined, although a correlation between OSA and cardiovascular disease may differ across races. Congenital central hypoventilation syndrome (CCHS) is a genetically inherited disorder caused by mutations in the paired-like homeobox 2B (PHOX2B) gene of polyalanine repeat mutations in the 20-alanine repeat or non-polyalanine repeat mutations. PHOX2B genotypes are also associated with clinical phenotypes of CCHS, including severity of hypoventilation. SDB, including obesity hypoventilation syndrome, is often seen in genetic obesity-associated disorders such as Prader-Willi syndrome. Although advances in genetics have resulted in identification of some genetic causes of SDB, further studies are required to elucidate the cellular and molecular mechanisms between genetic risks and clinical manifestations.

Congenital central hypoventilation syndrome: An overview of etiopathogenesis, associated pathologies, clinical presentation, and management

Congenital central hypoventilation syndrome (CCHS), known colloquially as Ondine's curse, is a rare disorder characterized by impaired autonomic control of breathing during sleep from the loss of vagal input and diminished sensitivity of CO₂ receptors in the medulla. CCHS correlates to the malformation of the neural crest located in the brainstem; this consequently affects the loss of sensitivity of CO₂ chemoreceptors, bringing about hypoventilation during sleep. The primary cause of CCHS is the mutation of the paired-like homeobox PHO2XB gene, found in 90% of the patients. This mutation not only affects breathing but also drives neurological abnormalities such as autonomic and neurocognitive dysfunction. Though typically congenital, there have been late-onset (i.e., acquired) cases reported. It is vital for physicians and clinicians to be able to diagnose CCHS due to its similar presentation to other syndromes and disorders, which may cause it to be misdiagnosed and may account for its deleterious effects. CCHS can lead to a constellation of symptoms, and consideration of diseases that present concomitantly with CCHS affords us a better understanding of the etiology of this illness. Although a rare syndrome, we aim to review the current literature to emphasize the pathogenesis, etiology, clinical presentation, symptoms, diagnosis, and current treatment methods of CCHS for clinicians to better identify and understand this condition.