Knockdown of PHOX2B in the retrotrapezoid nucleus reduces the central CO2 chemoreflex in rats.

PHOX2B is a transcription factor essential for the development of different classes of neurons in the central and peripheral nervous system. Heterozygous mutations in the PHOX2B coding region are responsible for the occurrence of Congenital Central Hypoventilation Syndrome (CCHS), a rare neurological disorder characterised by inadequate chemosensitivity and life-threatening sleep-related hypoventilation. Animal studies suggest that chemoreflex defects are caused in part by the improper development or function of PHOX2B expressing neurons in the retrotrapezoid nucleus (RTN), a central hub for CO2 chemosensitivity. Although the function of PHOX2B in rodents during development is well established, its role in the adult respiratory network remains unknown. In this study, we investigated whether reduction in PHOX2B expression in chemosensitive neuromedin-B (NMB) expressing neurons in the RTN altered respiratory function. Four weeks following local RTN injection of a lentiviral vector expressing the short hairpin RNA (shRNA) targeting Phox2b mRNA, a reduction of PHOX2B expression was observed in Nmb neurons compared to both naive rats and rats injected with the non-target shRNA. PHOX2B knockdown did not affect breathing in room air or under hypoxia, but ventilation was significantly impaired during hypercapnia. PHOX2B knockdown did not alter Nmb expression but it was associated with reduced expression of both Task2 and Gpr4, two CO2/pH sensors in the RTN. We conclude that PHOX2B in the adult brain has an important role in CO2 chemoreception and reduced PHOX2B expression in CCHS beyond the developmental period may contribute to the impaired central chemoreflex function.

PHOX2B: a diagnostic cornerstone in neurocristopathies and neuroblastomas.

Paired-like homeobox 2B (PHOX2B) is a gene essential in the development of the autonomic nervous system. PHOX2B mutations are associated with neurocristopathies-Hirschsprung disease (HSCR) and congenital central hypoventilation syndrome (CCHS)-and peripheral neuroblastic tumours. PHOXB2 plays an important role in the diagnostics of these conditions.Genotyping of a PHOX2B pathogenic variant is required to establish a diagnosis of CCHS. In HSCR patients, PHOX2B immunohistochemical staining has proven to be a valuable tool in identifying this disease. Furthermore, PHOXB2 is a predisposition gene for neuroblastoma, in which PHOX2B immunohistochemical staining can be used as a highly sensitive and specific diagnostic marker. The utility of PHOX2B immunohistochemistry in pheochromocytoma and paraganglioma has also been studied but yields conflicting results.In this review, an overview is given of PHOX2B, its associated diseases and the usefulness of PHOX2B immunohistochemistry as a diagnostic tool.

Recurrence of CCHS-associated PHOX2B Poly-Alanine expansion variant due to paternal mosaicism.

BACKGROUND: Paired-like Homeobox 2B (PHOX2B) is considered the causative gene of Congenital Central Hypoventilation Syndrome (CCHS), a dominant genetic disorder characterized by impaired central respiratory control and subsequent hypoventilation during sleep. METHODS: Herein, we present a family with recurrent severe CCHS. The potential causative genetic variant was confirmed through Whole-Exome Sequencing (WES), Sanger sequencing, and droplet digital PCR (ddPCR). Furthermore, prenatal diagnosis was performed on the proband's mother at 20 weeks of her fourth pregnancy upon request. RESULTS: The proband and her brother were both carriers of the PHOX2B polyalanine expansion variant: c.744_758dupCGCGGCAGCGGCGGCGGCGGC. Sanger sequencing revealed that the proband's father had a small variant peak in the gene position, implying potential somatic mosaicism. In addition, ddPCR results showed that the proband's father had germline mosaicism, with a mosaicism proportion of 14.3%. Notably, the detect p.(Ala241[26]) variant was not detected in the fetus. CONCLUSIONS: These findings have important implications for improving genetic counseling of CCHS families as they suggest that even parents without CCHS symptoms may have somatic chimerism, necessitating careful genetic counseling and consideration of prenatal testing for subsequent pregnancies.

Airway obstruction in two children with congenital central hypoventilation syndrome and review of the literature.

Congenital central hypoventilation syndrome (CCHS) is an autosomal dominant disease that is caused by heterozygous mutations in the paired-like homeobox 2B gene (PHOX2B). Madani et al. described an abnormally high degree of not only central apnea but also obstructive and mixed apnea in Phox2b27Ala/+newborn mice. Newborns with CCHS must undergo polysomnography for obstructive respiratory events in order to guide the optimal ventilation strategy if oxygen desaturation, bradycardia, and malaise persist under noninvasive ventilation. Newborns and infants with CCHS must be systematically tested for obstructive apnea, especially in cases of inefficient noninvasive ventilation.

Diagnosis and Management of Acute Respiratory Failure.

Acute hypoxemic respiratory failure is defined by Pao2 less than 60 mm Hg or SaO2 less than 88% and may result from V/Q mismatch, shunt, hypoventilation, diffusion limitation, or low inspired oxygen tension. Acute hypercapnic respiratory failure is defined by Paco2 ≥ 45 mm Hg and pH less than 7.35 and may result from alveolar hypoventilation, increased fraction of dead space, or increased production of carbon dioxide. Early diagnostic maneuvers, such as measurement of SpO2 and arterial blood gas, can differentiate the type of respiratory failure and guide next steps in evaluation and management.

Alternative low-populated conformations prompt phase transitions in polyalanine repeat expansions.

Abnormal trinucleotide repeat expansions alter protein conformation causing malfunction and contribute to a significant number of incurable human diseases. Scarce structural insights available on disease-related homorepeat expansions hinder the design of effective therapeutics. Here, we present the dynamic structure of human PHOX2B C-terminal fragment, which contains the longest polyalanine segment known in mammals. The major α-helical conformation of the polyalanine tract is solely extended by polyalanine expansions in PHOX2B, which are responsible for most congenital central hypoventilation syndrome cases. However, polyalanine expansions in PHOX2B additionally promote nascent homorepeat conformations that trigger length-dependent phase transitions into solid condensates that capture wild-type PHOX2B. Remarkably, HSP70 and HSP90 chaperones specifically seize PHOX2B alternative conformations preventing phase transitions. The precise observation of emerging polymorphs in expanded PHOX2B postulates unbalanced phase transitions as distinct pathophysiological mechanisms in homorepeat expansion diseases, paving the way towards the search of therapeutics modulating biomolecular condensates in central hypoventilation syndrome.

High-Titer Anti-ZSCAN1 Antibodies in a Toddler Clinically Diagnosed with Apparent Rapid-Onset Obesity with Hypothalamic Dysfunction, Hypoventilation, and Autonomic Dysregulation Syndrome.

Severe obesity in young children prompts for a differential diagnosis that includes syndromic conditions. Rapid-Onset Obesity with Hypothalamic Dysfunction, Hypoventilation, and Autonomic Dysregulation (ROHHAD) syndrome is a potentially fatal disorder characterized by rapid-onset obesity associated with hypoventilation, neural crest tumors, and endocrine and behavioral abnormalities. The etiology of ROHHAD syndrome remains to be established, but recent research has been focusing on autoimmunity. We report on a 2-year-old girl with rapid-onset obesity during the first year of life who progressed to hypoventilation and encephalitis in less than four months since the start of accelerated weight gain. The patient had a high titer of anti-ZSCAN1 antibodies (348; reference range < 40), and the increased values did not decline after acute phase treatment. Other encephalitis-related antibodies, such as the anti-NDMA antibody, were not detected. The rapid progression from obesity onset to central hypoventilation with encephalitis warns about the severe consequences of early-onset ROHHAD syndrome. These data indicate that serial measurements of anti-ZSCAN1 antibodies might be useful for the diagnosis and estimation of disease severity. Further research is needed to determine whether it can predict the clinical course of ROHHAD syndrome and whether there is any difference in antibody production between patients with and without tumors.

A pathogenic P4HTM gene variant in two brothers with autism spectrum disorder.

Autism spectrum disorder is a neurodevelopmental condition that involves limitations in social communication and various stereotypical repetitive behaviors. Genetic and environmental factors both play a role in the etiology. Numerous genetic syndromes accompanying autism spectrum disorders have been reported. Hypoventilation, hypotonia, intellectual disability, epilepsy, eye abnormality (HIDEA) syndrome is a rare genetic condition consisting of a combination of features such as hypoventilation, hypotonia, intellectual disability, eye abnormalities, and epilepsy. Very few cases of HIDEA syndrome have been reported in the literature to date. To the best of our knowledge, no cases of comorbid autism spectrum disorder and HIDEA syndrome have previously been reported. This report describes two brothers with a pathogenic P4HTM gene variant and autism spectrum disorder. One was diagnosed with HIDEA syndrome, while the other was a healthy carrier.

Effects of a 6-Week Repeated-Sprint Training With Voluntary Hypoventilation at Low and High Lung Volume on Repeated-Sprint Ability in Female Soccer Players.

PURPOSE: To investigate the effects of repeated-sprint training with voluntary hypoventilation at low (RSH-VHL) and high (RS-VHH) lung volume on repeated-sprint ability (RSA) in female athletes. METHODS: Over a 6-week period, 24 female soccer players completed 12 sessions of repeated 30-m running sprints with end-expiratory breath holding (RSH-VHL, n = 8), end-inspiratory breath holding (RS-VHH, n = 8), or unrestricted breathing (RS-URB, n = 8). Before and after training, a running RSA test consisting of performing 30-m all-out sprints until exhaustion was implemented. RESULTS: From before to after training, the number of sprints completed during the RSA test was increased in both RSH-VHL (19.3 [0.9] vs 22.6 [0.9]; P < .01) and RS-VHH (19.3 [1.5] vs 20.5 [1.7]; P < .01) but not in RS-URB (19.4 [1.3] vs 19.5 [1.7]; P = .67). The mean velocity and the percentage decrement score calculated over sprints 1 to 17 were, respectively, higher (82.2% [1.8%] vs 84.6% [2.1%] of maximal velocity) and lower (23.7% [3.1%] vs 19.4% [3.2%]) in RSH-VHL (P < .01), whereas they remained unchanged in RS-VHH and RS-URB. The mean arterial oxygen saturation recorded during training at the end of the sprints was lower in RSH-VHL (92.1% [0.4%]) than in RS-VHH (97.3% [0.1%]) and RS-URB (97.8% [0.1%]). CONCLUSIONS: This study shows that female athletes can benefit from the RSH-VHL intervention to improve RSA. The performance gains may have been limited by the short sprinting distance with end-expiratory breath holding, which provoked only moderate hypoxemia. The increase in the number of sprints in RS-VHH seems to show that factors other than hypoxia may have played a role in RSA improvement.

An unusual ophthalmologic finding in a patient with congenital central hypoventilation syndrome.

INTRODUCTION: Congenital Central Hypoventilation Syndrome (CCHS) is a rare disease due to a severely impaired central control of breathing and dysfunction of the autonomic nervous system. Ophthalmologic abnormalities are common in patients with CCHS and include horizontal strabismus, pupil and iris abnormalities and ptosis. We report a unique case of CCHS in association with monocular elevation deficit (MED) in a boy diagnosed with CCHS at birth. CASE DESCRIPTION: We report a case of a boy with a confirmed diagnosis of CCHS (complete sequencing of the paired-like homeobox 2b (PHOX2B) gene) after presenting little respiratory effort and cyanosis at birth. The ophthalmological examination shows an impaired elevation of the left eye, both in adduction and abduction, associated with mild and variable left ptosis. His mother has observed that the left eyelid elevates when the child feeds. A deviation in the primary gaze position or a chin-up position are not present. The funduscopic examination is normal. Given that deviation is limited to upgaze, the ptosis is mild and the patient's age, observation is decided. CONCLUSIONS: Ophthalmologic abnormalities are common in patients with CCHS and include horizontal strabismus, pupil and iris abnormalities and ptosis. To the best of our knowledge, this is the first report of MED in association with CCHS. Further studies are needed to determine if an association between MED and CCHS exists or is just a casual finding in this case.

Anti-ZSCAN1 Autoantibodies Are a Feasible Diagnostic Marker for ROHHAD Syndrome Not Associated with a Tumor.

Recent studies have reported the presence of autoantibodies against zinc finger and SCAN domain-containing protein 1 (ZSCAN1) in the sera of patients with rapid-onset obesity with hypoventilation, hypothalamic and autonomic dysregulation (ROHHAD) syndrome associated with neuroendocrine tumors, suggesting immunologic and paraneoplastic processes as the pathologic underpinnings. Moreover, several hypothalamic regions, including the subfornical organ (SFO), were reported to exhibit antibody reactivity in a patient with ROHHAD syndrome not associated with a tumor. Whether ROHHAD syndrome not associated with a tumor is associated with anti-ZSCAN1 autoantibodies remains unclear. We used a comprehensive protein array analysis to identify candidate molecules in the sera of patients with ROHHAD syndrome and identified ZSCAN1 as a target antigen. We also found that ZSCAN1 was co-expressed at the site of antibody reactivity to the IgG in the patient serum observed in mouse SFOs and an enzyme-linked immunosorbent assay showed that >85% of the patients with ROHHAD syndrome were positive for anti-ZSCAN1 autoantibodies. These results suggest anti-ZSCAN1 autoantibodies as a feasible diagnostic marker in ROHHAD syndrome regardless of the presence of a tumor.

Higher baseline heart rate variability in CCHS patients with progestin-associated recovery of hypercapnic ventilatory response.

After a fortuitous observation of two cases of chemosensitivity recovery in women with congenital central hypoventilation syndrome (CCHS) who took desogestrel, we aimed to evaluate the ventilatory response to hypercapnia of five CCHS patients with or without treatment consisting of desogestrel (DESO) or levonorgestrel (LEVO). Only two patients became responsive to hypercapnia under treatment, according to their basal vagal heart rate variability. These results suggest that heart rate variability may be promising tool to discriminate patients susceptible to become responsive to hypercapnia under DESO-LEVO treatment.Clinical Trials Identifier NCT01243697.

Delineation of ADPRHL2 Variants: Report of Two New Patients with Review of the Literature.

ADPRHL2 is involved in posttranslational modification and is known to have a role in physiological functions such as cell signaling, DNA repair, gene control, cell death, and response to stress. Recently, a group of neurological disorders due to ADPRHL2 variants is described, characterized by childhood-onset, stress-induced variable movement disorders, neuropathy, seizures, and neurodegenerative course. We present the diagnostic pathway of two pediatric patients with episodic dystonia and ataxia, who later had a neurodegenerative course complicated by central hypoventilation syndrome due to the same homozygous ADPRHL2 variant. We conducted a systematic literature search and data extraction procedure following the Preferred Reporting Items for Systematic Review and Meta-Analysis 2020 statement in terms of patients with ADPRHL2 variants, from 2018 up to 3 February, 2023. In total, 12 articles describing 47 patients were included in the final analysis. Median age at symptom onset was 2 (0.7-25) years, with the most common presenting symptoms being gait problems (n = 19, 40.4%), seizures (n = 16, 34%), ataxia (n = 13, 27.6%), and weakness (n = 10, 21.2%). Triggering factors (28/47; 59.5%) and regression (28/43; 60.4%), axonal polyneuropathy (9/23; 39.1%), and cerebral and cerebellar atrophy with white matter changes (28/36; 77.7%) were the other clues. The fatality rate and median age of death were 44.6% (n = 21) and 7 (2-34) years, respectively. ADPRHL2 variants should be considered in the context of episodic, stress-induced pediatric and adult-onset movement disorders and seizures.

Type one chiari malformation as a cause of central sleep apnea and hypoventilation in children.

OBJECTIVES: Chiari type 1 malformation (CM1) may occasionally lead to central sleep apnea (CSA). We studied, in a large clinical cohort of pediatric CM1 patients, the effect of CM1 on breathing during sleep. METHODS: This is a retrospective single pediatric pulmonology center study with a systematic evaluation of pediatric CM1 patients under age 18 with polysomnography (PSG) during 2008-2020. Children with syndromes were excluded. All patients had undergone head and spine magnetic resonance imaging. RESULTS: We included 104 children with CM1 with a median age of 7 (interquartile range (IQR) 5-13) years. The median extent of tonsillar descent (TD) was 13 (IQR 10-18) mm. Syringomyelia was present in 19 children (18%). Of all children, 53 (51%) had normal PSG, 35 (34%) showed periodic breathing or central apnea and hypopnea index ≥5 h-1, and 16 (15%) displayed features of compensated central hypoventilation and end-tidal or transcutaneous carbon dioxide 99th percentile level above 50 mmHg. TD had the best predictive value for central breathing disorders. In a linear model, both age (61%) and TD (39%) predicted median breathing frequency (R = 0.33, p < 0.001). CONCLUSIONS: Although severe CSA is a rare complication of brainstem compression in pediatric patients with CM1, short arousal-triggered episodes of periodic breathing and mild compensated central hypoventilation are common. TD shows the best but still poor prediction of the presence of a central breathing disorder. This highlights the use of PSG in patient evaluation. Posterior fossa decompression surgery effectively treats central breathing disorders.

Etonogestrel promotes respiratory recovery in an in vivo rat model of central chemoreflex impairment.

AIM: The central CO2 chemoreflex is a vital component of respiratory control networks, providing excitatory drive during resting conditions and challenges to blood gas homeostasis. The retrotrapezoid nucleus is a crucial hub for CO2 chemosensitivity; its ablation or inhibition attenuates CO2 chemoreflexes and diminishes restful breathing. Similar phenotypes characterize certain hypoventilation syndromes, suggesting underlying retrotrapezoid nucleus impairment in these disorders. Progesterone stimulates restful breathing and CO2 chemoreflexes. However, its mechanisms and sites of actions remain unknown and the experimental use of synthetic progestins in patients and animal models have been met with mixed respiratory outcomes. METHODS: We investigated whether acute or chronic administration of the progestinic drug, etonogestrel, could rescue respiratory chemoreflexes following selective lesion of the retrotrapezoid nucleus with saporin toxin. Adult female Sprague Dawley rats were grouped based on lesion size determined by the number of surviving chemosensitive neurons, and ventilatory responses were measured by whole body plethysmography. RESULTS: Ventilatory responses to hypercapnia (but not hypoxia) were compromised in a lesion-dependent manner. Chronic etonogestrel treatment improved CO2 chemosensitivity selectively in rats with moderate lesion, suggesting that a residual number of chemosensitive neurons are required for etonogestrel-induced CO2 chemoreflex recovery. CONCLUSION: This study provides new evidence for the use of progestins as respiratory stimulants under conditions of central hypoventilation and provides a new testable model for assessing the mechanism of action of progestins in the respiratory network.

Physiological effect of high flow oxygen therapy measured by electrical impedance tomography in single-lung transplantation.

In patients with chronic obstructive pulmonary disease (COPD), single lung transplantation (SLT) is sometimes performed as an alternative to bilateral lung transplantation due to limited organ availability. However, the postoperative management of SLT presents challenges, including complications related to the distinct compliance of each lung. This case report presents the case of a 65-year-old male patient who underwent SLT and was in the weaning period from mechanical ventilation. High-flow oxygen therapy (HFOT) was administered, and the physiological effects were measured using electrical impedance tomography (EIT). The results demonstrated that the application of HFOT increased air trapping and overdistention in the native lung without benefiting the transplanted lung. HFOT through a tracheostomy tube or nasal cannula resulted in a more heterogeneous distribution of ventilation, with increased end expiratory lung impedance, prolonged expiratory time constants, and an increase in silent spaces. The drop in tidal impedance after applying HFOT did not indicate hypoventilation but rather overdistention and air trapping in the native lung, while the transplanted lung showed evidence of hypoventilation. These findings suggest that HFOT may not be beneficial for SLT patients and could potentially worsen outcomes. However, due to the limited scope of this case report, further prospective studies with larger patient cohorts are needed to confirm these results.

En pacientes con enfermedad pulmonar obstructiva crónica (EPOC), el trasplante pulmonar unilateral (SLT, por sus siglas en inglés) se realiza como alternativa a la disponibilidad limitada de donantes para el trasplante pulmonar bilateral. Sin embargo, el manejo postoperatorio del SLT presenta desafíos, incluyendo complicaciones relacionadas con la distinta complacencia de cada pulmón. Este reporte presenta el caso de un paciente varón de 65 años que fue sometido a un SLT y se encontraba en el proceso de destete de la ventilación mecánica. Se administró terapia de oxígeno de alto flujo (HFOT, por sus siglas en inglés) y se midieron los efectos fisiológicos utilizando la tomografía de impedancia eléctrica (EIT, por sus siglas en inglés). Los resultados demostraron que la aplicación de HFOT aumentó la retención de aire y la hiperinflación en el pulmón nativo sin beneficiar al pulmón trasplantado. Tanto la HFOT a través de un tubo de traqueostomía como a través de cánula nasal resultaron en una distribución más heterogénea de la ventilación, con un aumento en la impedancia pulmonar al final de la espiración, prolongación de las constantes de tiempo espiratorias y un aumento en los espacios silentes. La disminución de la impedancia tidal después de aplicar HFOT no indicó hipoventilación, sino más bien hiperinsuflación y retención de gas en el pulmón nativo, mientras que el pulmón trasplantado mostró evidencia de hipoventilación. Estos hallazgos sugieren que el HFOT puede no ser beneficioso para los pacientes con SLT y podría empeorar los resultados. Sin embargo, debido al alcance limitado de este informe de caso, se necesitan estudios prospectivos con cohortes de pacientes más amplias para confirmar estos resultados.

The Pitfalls of Using Pop-Off Valves in Adult Emergency Airway.

BACKGROUND: Although common in pediatric airway equipment, positive-pressure relief ("pop-off") valves are also present on some adult resuscitator bags. These valves are designed to decrease barotrauma but, in doing so, limit the airway pressure provided during manual bag-assisted ventilation. In critically ill adult patients with high airway pressures, these valves can be detrimental and result in hypoventilation and subsequent hypoxemia. CASE REPORTS: In the 7 days after an unannounced introduction of new resuscitator bags with pop-off valves in the emergency department, there were 3 adult patients for whom an open pop-off valve resulted in hypoventilation and hypoxemia. These cases involved both medical and traumatic pathologies. In each case, there was a delay in discovering the change to a resuscitator bag equipped with a pop-off valve. Once the emergency physicians noticed the pop-off valve and closed them, there was significant improvement in ventilation and oxygenation. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Hand-operated resuscitator bags are an essential tool for airway management. These cases represent two main lessons: changing airway equipment without notifying staff is dangerous, and an open pop-off valve will result in inadequate ventilation when patients have high airway pressures, without the tactile feedback of difficult bagging. Emergency physicians should be aware of equipment changes and know to disable the pop-off valve on resuscitator bags if they find them in their departments.

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

OBJECTIVES: Few data on alveolar hypoventilation in Prader-Willi syndrome (PWS) are available and the respiratory follow-up of these patients is not standardized. The objectives of this study were to evaluate the prevalence of alveolar hypoventilation in children with PWS and identify potential risk factors. STUDY DESIGN: This retrospective study included children with PWS recorded by polysomnography (PSG) with transcutaneous carbon dioxide pressure (PtcCO2) or end-tidal CO2 (ETCO2) measurements, between 2007 and 2021, in a tertiary hospital center. The primary outcome was the presence of alveolar hypoventilation defined as partial pressure of carbon dioxide (pCO2) ≥ 50 mmHg during ≥2% of total sleep time (TST) or more than five consecutive minutes. RESULTS: Among the 57 included children (38 boys, median age 4.8 years, range 0.1-15.6, 60% treated with growth hormone [GH], 37% obese), 19 (33%) had moderate-to-severe obstructive sleep apnea syndrome (defined as obstructive apnea-hypopnea index ≥5/h) and 20 (35%) had hypoventilation. The median (range) pCO2 max was 49 mmHg (38-69). Among the children with hypoventilation, 25% were asymptomatic. Median age and GH treatment were significantly higher in children with hypoventilation compared to those without. There was no significant difference in terms of sex, BMI, obstructive or central apnea-hypopnea index between both groups. CONCLUSION: The frequency of alveolar hypoventilation in children and adolescents with PWS is of concern and may increase with age and GH treatment. A regular screening by oximetry-capnography appears to be indicated whatever the sex, BMI, and rate of obstructive or central apneas.