The genetics of congenital central hypoventilation syndrome: clinical implications

Zebrafish Congenital Heart Disease Models: Opportunities and Challenges

Congenital heart defects (CHDs) are common human birth defects. Genetic mutations potentially cause the exhibition of various pathological phenotypes associated with CHDs, occurring alone or as part of certain syndromes. Zebrafish, a model organism with a strong molecular conservation similar to humans, is commonly used in studies on cardiovascular diseases owing to its advantageous features, such as a similarity to human electrophysiology, transparent embryos and larvae for observation, and suitability for forward and reverse genetics technology, to create various economical and easily controlled zebrafish CHD models. In this review, we outline the pros and cons of zebrafish CHD models created by genetic mutations associated with single defects and syndromes and the underlying pathogenic mechanism of CHDs discovered in these models. The challenges of zebrafish CHD models generated through gene editing are also discussed, since the cardiac phenotypes resulting from a single-candidate pathological gene mutation in zebrafish might not mirror the corresponding human phenotypes. The comprehensive review of these zebrafish CHD models will facilitate the understanding of the pathogenic mechanisms of CHDs and offer new opportunities for their treatments and intervention strategies.

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.

[Two children with late-onset congenital central hypoventilation syndrome]

Two children with late-onset congenital central hypoventilation syndrome were reported, one of whom was male and had no abnormal manifestations after birth, respiratory failure occurs at the age of 1 year and 6 months. After being hospitalized, he was treated with oxygen inhalation and non-invasive ventilation, but carbon dioxide retention could not be corrected. After one month of tracheal intubation, he was failure to wean from ventilator, so tracheostomy was performed. He needs a ventilator to help breath while sleeping, and can breath autonomously during the day without ventilator. The other case was a female, with no abnormalities after birth. At the age of 11 months, she developed respiratory failure. During sleep, the child needs non-invasive assisted ventilation through a nasal mask, and during the day, she breathed autonomously.Two patients were followed up forever 2 years and their growth and development were normal.

Ventilatory and Orthostatic Challenges Reveal Biomarkers for Neurocognition in Children and Young Adults With Congenital Central Hypoventilation Syndrome

BACKGROUND

Children and young adults with congenital central hypoventilation syndrome (CCHS) are at risk of cognitive deficits. They experience autonomic dysfunction and chemoreceptor insensitivity measured during ventilatory and orthostatic challenges, but relationships between these features are undefined.

RESEARCH QUESTION

Can a biomarker be identified from physiologic responses to ventilatory and orthostatic challenges that is related to neurocognitive outcomes in CCHS?

STUDY DESIGN AND METHODS

This retrospective study included 25 children and young adults with CCHS tested over an inpatient stay. Relationships between physiologic measurements during hypercarbic and hypoxic ventilatory challenges, hypoxic ventilatory challenges, and orthostatic challenges and neurocognitive outcomes (by Wechsler intelligence indexes) were examined. Independent variable inclusion was determined by significant associations in Pearson's analyses. Multivariate linear regressions were used to assess relationships between measured physiologic responses to challenges and neurocognitive scores.

RESULTS

Significant relationships were identified between areas of fluid intelligence and measures of oxygen saturation (SpO2) and heart rate (HR) during challenges. Specifically, perceptual reasoning was related to HR (adjusted regression [β] coefficient, -0.68; 95% CI, 1.24 to -0.12; P = .02) during orthostasis. Working memory was related to change in HR (β, -1.33; 95% CI, -2.61 to -0.05; P = .042) during the hypoxic ventilatory challenge. Processing speed was related to HR (β, -1.19; 95% CI, -1.93 to -0.46; P = .003) during orthostasis, to baseline SpO2 (hypercarbic and hypoxic β, 8.57 [95% CI, 1.63-15.51]; hypoxic β, 8.37 [95% CI, 3.65-13.11]; P = .002 for both) during the ventilatory challenges, and to intrachallenge SpO2 (β, 5.89; 95% CI, 0.71-11.07; P = .028) during the hypoxic ventilatory challenge.

INTERPRETATION

In children and young adults with CCHS, SpO2 and HR-or change in HR-at rest and as a response to hypoxia and orthostasis are related to cognitive outcomes in domains of known risk, particularly fluid reasoning. These findings can guide additional research on the usefulness of these as biomarkers in understanding the impact of daily physical stressors on neurodevelopment in this high-risk group.

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.

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.

Non-polyalanine repeat mutation in PHOX2B is detected in autopsy cases of sudden unexpected infant death

Background

Congenital central hypoventilation syndrome (CCHS), which is caused by PHOX2B with phenotypic variations, has a point of controversy: CCHS is putatively involved in autopsy cases of sudden unexpected infant death (SUID) including sudden infant death syndrome.

Objective

The relation of CCHS to SUID cases was investigated by extensive genotyping of PHOX2B.

Methods

We analyzed 93 DNA samples of less than one-year-old SUID cases that were autopsied in our department. Unrelated adult volunteers (n = 942) were used as the control.

Results

No polyalanine tract expansion was detected in the SUID cases. The allelic frequencies of repeat contractions and SNP (rs28647582) in intron 2 were not significantly different from that in those control group. Further extensive sequencing revealed a non-polyalanine repeat mutation (NPARM) of c.905A>C in a sudden death case of a one-month-old male infant. This missense mutation (p.Asn302Thr), registered as rs779068107, was annotated to ‘Affected status is unknown’, but it might be associated with the sudden death.

Conclusion

NPARM was more plausibly related to sudden unexpected death than expansions because of severe clinical complications. This finding indicates possible CCHS involvement in forensic autopsy cases without ante-mortem diagnosis.

Congenital Central Hypoventilation Syndrome: Optimizing Care with a Multidisciplinary Approach

Congenital central hypoventilation syndrome (CCHS) is a rare genetic disorder affecting respiratory control and autonomic nervous system function caused by variants in the paired-like homeobox 2B (PHOX2B) gene. Although most patients are diagnosed in the newborn period, an increasing number of patients are presenting later in childhood, adolescence, and adulthood. Despite hypoxemia and hypercapnia, patients do not manifest clinical features of respiratory distress during sleep and wakefulness. CCHS is a lifelong disorder. Patients require assisted ventilation throughout their life delivered by positive pressure ventilation via tracheostomy, noninvasive positive pressure ventilation, and/or diaphragm pacing. At different ages, patients may prefer to change their modality of assisted ventilation. This requires an individualized and coordinated multidisciplinary approach. Additional clinical features of CCHS that may present at different ages and require periodic evaluations or interventions include Hirschsprung’s disease, gastrointestinal dysmotility, neural crest tumors, cardiac arrhythmias, and neurodevelopmental delays. Despite an established PHOX2B genotype and phenotype correlation, patients have variable and heterogeneous clinical manifestations requiring the formulation of an individualized plan of care based on collaboration between the pulmonologist, otolaryngologist, cardiologist, anesthesiologist, gastroenterologist, sleep medicine physician, geneticist, surgeon, oncologist, and respiratory therapist. A comprehensive multidisciplinary approach may optimize care and improve patient outcomes. With advances in CCHS management strategies, there is prolongation of survival necessitating high-quality multidisciplinary care for adults with CCHS.

The genetic basis of sudden death in young people - Cardiac and non-cardiac

Sudden death is one of the major causes of death in young adults. Sudden death could be a result from both genetic and environmental or acquired factors. Understanding the genetic etiology is crucial to prevent preventable sudden death for those who are not aware of their genetic condition. In fact, the spectrum of causes of sudden death is complex and varied. In this study, we reviewed the genes that are associated with multiple causes of sudden death in terms of both sudden cardiac death and sudden noncardiac death. A summary of genetic risk factors of the major causes of genetic relevant sudden death is also provided. We believe this review could benefit the researchers who are interested in sudden death genetic studies or the young people who are concerning about their own risk on sudden death.

Case Report: A novel PHOX2B p.Ala248_Ala266dup variant causing congenital central hypoventilation syndrome

INTRODUCTION

Congenital central hypoventilation syndrome (CCHS) is a rare disease characterized by central alveolar hypoventilation and impaired autonomic regulation, caused by pathogenic variants of PHOX2B gene. More than 90% of patients have a polyalanine repeat mutation (PARM) in the heterozygous state, characterized by the expansion of GCN repeats and an increase in the number of alanine repeats, so that genotypes 20/24-20/33 are formed (the normal genotype is 20/20). The remaining 10% of patients harbor non-PARMs.

CASE DESCRIPTION

We present a clinical case of a girl with a novel PHOX2B heterozygous genetic variant in the exon 3: NM_003924.4: c.735_791dup, p.Ala248_Ala266dup. The duplication includes 16 GCN (alanine) repeats and 3 adjacent amino acids. Both clinically healthy parents demonstrated a normal PHOX2B sequence. In addition, the girl has a variant of unknown significance in RYR1 gene and a variant of unknown significance in NKX2-5 gene. The child's phenotype is quite special. She needs ventilation during sleep, and has Hirschsprung's disease type I, arteriovenous malformation S4 of the left lung, ventricular and atrium septal defects, coronary right ventricular fistula, hemodynamically nonsignificant, episodes of sick sinus and atrioventricular dissociation with bradycardia, divergent alternating strabismus, and oculus uterque (both eyes) (OU) retinal angiopathy. Two episodes of hypoglycemic seizures were also registered. Severe pulmonary hypertension resolved after appropriate ventilation adjustment. Diagnostic odyssey was quite dramatic.

CONCLUSION

Detection of a novel PHOX2B variant expands the understanding of molecular mechanisms of CCHS and genotype-phenotype correlations.

Genetic study of a patient with congenital central hypoventilation syndrome in Iran: a case report

BACKGROUND

Congenital central hypoventilation syndrome (CCHS) is an extremely rare genetic disorder characterized by Autonomic nervous system dysregulation caused by mutations in the PHOX2B gene. Here we introduce the first genetic analysis of a one-month-old CCHS baby girl in Iran.

METHODS AND RESULTS

Genetic analysis of the PHOX2B gene was performed by Sanger sequencing and interpreted using the American College of Medical Genetics and Genomics (ACMG) guideline. The results showed a heterozygous duplication in exon 3, causing a polyalanine repeat expansion mutation to 27 repeats in thePHOX2B gene (20/27 genotype).The patient's parents did not demonstrate this mutation on genetic studies.

CONCLUSIONS

According to the ACMG guideline, the mutation is pathogenic, and it was a denovo mutation in the family. The genetic study can help the family for prenatal diagnosis or pre-implantation diagnosis if the parents have gonadal mosaicism.

Congenital central hypoventilation syndrome: a life-threatening cause of neonatal apnoea

Congenital central hypoventilation syndrome (CCHS) is an uncommon genetic disease characterised by an autonomic nervous system dysfunction that affects ventilatory homeostasis. Involvement of other systems is also described, mainly cardiovascular, gastrointestinal and central nervous systems. We describe a rare case of CCHS diagnosed in a term newborn who presented with persistent apnoea in the first hours of life. After an exhaustive aetiological study excluding primary pulmonary, cardiac, metabolic and neurological diseases, this diagnosis was confirmed by a paired-like homeobox 2B gene sequence analysis. During hospitalisation, ventilation was optimised and multidisciplinary follow-up was initiated, including genetic counselling. At 2 months old, the child was discharged under non-invasive ventilation during sleep. This case illustrates the importance of early diagnosis, including genetic study and advances in home ventilation. These factors allow early hospital discharge and timely multidisciplinary intervention, which is crucial for patients' quality of life and outcome optimisation.

The Emerging Genetic Landscape of Hirschsprung Disease and Its Potential Clinical Applications

Hirschsprung disease (HSCR) is the leading cause of neonatal functional intestinal obstruction. It is a rare congenital disease with an incidence of one in 3,500-5,000 live births. HSCR is characterized by the absence of enteric ganglia in the distal colon, plausibly due to genetic defects perturbing the normal migration, proliferation, differentiation, and/or survival of the enteric neural crest cells as well as impaired interaction with the enteric progenitor cell niche. Early linkage analyses in Mendelian and syndromic forms of HSCR uncovered variants with large effects in major HSCR genes including RET, EDNRB, and their interacting partners in the same biological pathways. With the advances in genome-wide genotyping and next-generation sequencing technologies, there has been a remarkable progress in understanding of the genetic basis of HSCR in the past few years, with common and rare variants with small to moderate effects being uncovered. The discovery of new HSCR genes such as neuregulin and BACE2 as well as the deeper understanding of the roles and mechanisms of known HSCR genes provided solid evidence that many HSCR cases are in the form of complex polygenic/oligogenic disorder where rare variants act in the sensitized background of HSCR-associated common variants. This review summarizes the roadmap of genetic discoveries of HSCR from the earlier family-based linkage analyses to the recent population-based genome-wide analyses coupled with functional genomics, and how these discoveries facilitated our understanding of the genetic architecture of this complex disease and provide the foundation of clinical translation for precision and stratified medicine.

Congenital central hypoventilation syndrome and ventilatory responses during cardiopulmonary exercise testing

BACKGROUND

Previous studies have shown evidence of hypoxemia and hypercapnia during cardiopulmonary exercise test (CPET) evaluation in children with congenital central hypoventilation syndrome (CCHS). However, there are no longitudinal studies which compared CPET findings to polysomnogram (PSG) or PHOX2B mutation, to date.

OBJECTIVES

To describe the longitudinal CPET findings in a cohort of children with CCHS and correlate the findings to the PSG results.

METHODS

This retrospective study was conducted in children with CCHS followed in the Long-term Ventilation Program at SickKids, Toronto, Canada between September, 2013 and January, 2020. CCHS genetic mutation, age of diagnosis, ventilatory support, family history, disease associations of CCHS, CPETs, and PSG parameters were recorded and analyzed.

RESULTS

A total of nine patients with CCHS (46 CPETs and 46 PSGs) were enrolled. Four (44.4%) children had polyalanine repeat mutations. The mean (SD) age at the time of diagnosis and duration of ventilatory usage were 3.2 ± 3.4 years and 11.5 ± 2.8 years, respectively. All abnormal CPETs had hypercapnia in at least 1 phase of the exercise test. Hypercapnia (12/46; 26.1%) at peak of exercise was the most common abnormality. None of the children experienced an oxygen desaturation below 90%. End-tidal CO₂ (PetCO₂ ) at rest and at peak exercise in the CPETs were significantly correlated with PSG TcCO₂ while PetCO₂ at anaerobic threshold was correlated with CO₂ in pre-PSG capillary blood gas.

CONCLUSION

Nocturnal hypoventilation may impact the CPET results in CCHS children. Serial CPETs should be considered standard clinical care for all CCHS children.

Altered Mental Status and Respiratory Failure in an 11-Year-Old Female

Congenital central hypoventilation syndrome (CCHS) is a rare disorder that results in profound hypoventilation that is most prominent during periods of sleep. Caused by a genetic mutation in the PHOX2B gene, CCHS typically presents in the newborn period with symptoms of hypoventilation. However, there is a subset of patients with the same genetic mutation who present much later in life, which is termed late-onset congenital central hypoventilation syndrome (LO-CCHS). The reason for its late presentation is unclear but is often dramatic. Given its rarity, the diagnosis can be difficult to establish but can be accomplished by using a systematic approach. Here, we present a case of LO-CCHS in an 11-year-old female who presented with respiratory failure and altered mental status.

Variable phenotypes in congenital central hypoventilation syndrome with PHOX2B nonpolyalanine repeat mutations

STUDY OBJECTIVES

Congenital central hypoventilation syndrome (CCHS) is a rare disorder affecting the autonomic nervous system that is caused by variants in the PHOX2B gene. About 10% of patients with CCHS have nonpolyalanine repeat mutations (NPARM) that are associated with severe phenotypes requiring continuous assisted ventilation, Hirschsprung's disease, and increased neural crest tumor risk. However, some patients with NPARMs have milder phenotypes. Our objective was to describe the phenotypes in patients with CCHS PHOX2B NPARM.

METHODS

Retrospective case series of patients with CCHS PHOX2B NPARM was conducted at two children's hospitals to evaluate their phenotypes.

RESULTS

We identified eight patients with CCHS PHOX2B NPARM aged 3-31 years. Seven patients were diagnosed in infancy and one patient at two years of age. All patients presented with respiratory depression in the first two months of life. Only one patient was identified with a severe phenotype requiring continuous assisted ventilation, Hirschsprung's disease, and a neural crest tumor, that was resected. Five patients required positive pressure ventilation via tracheostomy only during sleep and two patients required oxygen only during sleep. Four patients had Hirschsprung's disease and one patient had a cardiac pacemaker due to a bradyarrhythmia. None of the patients had echocardiographic abnormalities.

CONCLUSIONS

Patients with CCHS PHOX2B NPARM can have variable phenotypes emphasizing the importance of implementing a plan of care that is individualized for each patient. The type of NPARM and its respective location on the PHOX2B gene may play a critical role in the severity of phenotypes displayed by each patient.

Congenital central hypoventilation syndrome in neonates: report of fourteen new cases and a review of the literature

BACKGROUND

Congenital central hypoventilation syndrome (CCHS) is a rare autosomal dominant disorder caused by pathogenic variants in paired-like homeobox 2B (PHOX2B) gene. Characteristics of neonatal-onset CCHS cases have not been well assessed. The aim of this study is to expand current knowledge of clinical and genetic features of neonates with CCHS and provide data on the genotype-phenotype correlation.

METHODS

We made a retrospective analysis of 14 neonates carrying PHOX2B pathogenic variants from 2014 to 2019 and we reviewed previously published neonatal-onset cases. Clinical and genetic data were analyzed. Moreover, genotype-phenotype correlation analysis was performed.

RESULTS

We identified a total of 60 neonatal-onset CCHS cases (35 males and 25 females) including 14 novel cases from our local cohort. Nearly 20% (18.2%) of the patients were born prematurely. Nearly half (46.2%) of the patients had abnormal family history. Polyhydramnios was observed in 21.3% (10/47) of the patients. About 90% of the patients manifested symptoms of hypoventilation in the first week of life. Fourteen patients (23.3%) were classified as mild-CCHS and the rest were severe-CCHS. Gastrointestinal manifestations were observed in 71.7% of the patients. Approximately twofold more males than females were affected by Hirschprung disease (HSCR)/variant HSCR (75.8% vs. 35%, P=0.003). Neural crest tumor occurred in 9.1% (4/44) patients. Half patients had polyalanine repeat expansion mutations (PARMs) in PHOX2B (seven with 25 PARM, nine with 26 PARM, twelve with 27 PARM, one with 28 PARM and one with 31 PARM) and the other half patients had 23 distinct non-polyalanine repeat expansion mutations (NPARMs) with one novel pathogenic variant (c.684dup). The prevalence of HSCR and mild-CCHS among patients with NPARMs was significantly greater than that of the patients with PARMs.

CONCLUSIONS

This report provides a large cohort of neonatal-onset CCHS cases. The results indicate that severe hypoventilation and HSCR are frequently observed in this group. NPARMs accounted for half of the cohort with some genotypes tend to be associated with mild phenotype. Molecular testing in neonates with suspicion of CCHS and genetic counseling for CCHS families are highly recommended.

Recurrent apnoea and respiratory failure in an infant: congenital central hypoventilation syndrome with a novel PHOX2B gene variant

A 20-day-old term infant presented with recurrent apnoea, lethargy and respiratory failure. Examination revealed episodes of apnoea and desaturation to 85% without any signs of respiratory distress requiring initiation of non-invasive positive pressure ventilation (NPPV). Capillary blood gas was indicative of respiratory acidosis and serum bicarbonate was elevated at 35 mmol/L. Chest radiograph, echocardiogram and evaluations for infectious aetiologies resulted normal. Due to inability to wean off NPPV with ensuing apnoea and desaturation, polysomnogram was performed and showed central and obstructive sleep apnoea, hypoxaemia and hypoventilation. Central apnoeas and hypoventilation were worse in non-rapid eye movement sleep. Paired-like homeobox 2B genetic studies showed a novel non-polyalanine repeat mutation (c.429+1G>A) establishing the diagnosis of congenital central hypoventilation syndrome (CCHS). Our case highlights the utility of polysomnography in the evaluation of term infants with apnoea. Although rare, clinicians should consider a diagnosis of CCHS in the evaluation of infants with apnoea and hypoventilation.

A Variant in SLC25A4 Leads to Mitochondrial DNA-Depletion Syndrome-12A Causing Neonatal Hypotonia and Hypoventilation

Congenital hypotonia and hypoventilation is a rare association. We report a rare case of a female newborn with poor respiratory drive, ventilator dependency, severe hypotonia, cardiomyopathy, and premature death. Clinical-exome-sequencing revealed SLC25A4-related mitochondrial deoxyribonucleic acid (DNA) depletion syndrome-12A (cardiomyopathic type). This syndrome is apparent at birth and carries a poor prognosis.

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.

Neonatal Metabolic Acidosis in the Neonatal Intensive Care Unit: What Are the Genetic Causes?

Neonatal metabolic acidosis (NMA) is a common problem, particularly in critically ill patients in neonatal intensive care units (NICUs). Complex etiologies and atypical clinical signs make diagnosis difficult; thus, it is crucial to investigate the underlying causes of NMA rapidly and provide disorder-specific therapies. Our study aims to provide an overview of the genetic causes of NMA in patients from NICUs. We performed next-generation sequencing (NGS) on neonates with NMA from January 2016 to December 2019. Clinical features, genetic diagnoses, and their effects on clinical interventions were collected for analysis. In the 354 enrolled patients, 131 (37%) received genetic diagnoses; 95 (72.5%) of them were autosomal recessively inherited diseases. Two hundred and fifteen variants spanning 57 genes were classified as pathogenic (P) or likely pathogenic (LP) in 131 patients. The leading cause was metabolic disorders due to 35 genes found in 89 patients (68%). The other 42 NMA patients (32%) with 22 genes had malformations and renal, neuromuscular, and immune-hematological disorders. Seven genes (MMUT, MMACHC, CHD7, NPHS1, OTC, IVD, and PHOX2B) were noted in more than four patients, accounting for 48.9% (64/131) of the identified P/LP variants. Forty-six diagnosed patients with uncorrected NMA died or gave up. In conclusion, 37% of neonates with metabolic acidosis had genetic disorders. Next-generation sequencing should be considered when investigating the etiology of NMA in NICUs. Based on early molecular diagnoses, valuable treatment options can be provided for some genetic diseases to achieve better outcomes.

Pregnancy in congenital central hypoventilation syndrome

BACKGROUND

Congenital central hypoventilation syndrome is a rare genetic disorder of autonomic regulation of breathing resulting from mutations in the paired-like homeobox gene. Individuals with congenital central hypoventilation syndrome demonstrate an absent or diminished physiological response to hypercapnia and hypoxia that is most severe during sleep and depend on mechanical ventilation to maintain normal gas exchange. Increased disease awareness and availability of paired-like homeobox gene testing has improved congenital central hypoventilation syndrome morbidity and mortality, and patients are now living into adulthood. During pregnancy, delivery, and the postpartum period, women with congenital central hypoventilation syndrome are vulnerable to developing respiratory insufficiency. Currently, there is no standardized approach to monitoring ventilatory status and anticipating the need for changes to existing ventilatory support for women with congenital central hypoventilation syndrome during pregnancy, labor, and delivery.

OBJECTIVE

This study aimed to characterize current practices for monitoring ventilatory status and managing ventilatory needs in women with congenital central hypoventilation syndrome during pregnancy; identify specific circumstances through which ventilation may be compromised during pregnancy, delivery, and postpartum; evaluate utilization of prenatal congenital central hypoventilation syndrome testing; and report any adverse pregnancy outcomes.

STUDY DESIGN

We conducted an anonymous cross-sectional survey of women with congenital central hypoventilation syndrome with current or prior pregnancy. The 26-item electronic questionnaire included questions on congenital central hypoventilation syndrome genotype; number and outcome of pregnancies; use of mechanical ventilation; and issues with or adjustments made to ventilation during pregnancy, delivery, and the postpartum period.

RESULTS

We received 10 responses. Three patients were not diagnosed with congenital central hypoventilation syndrome until after pregnancy and delivery. The 7 patients with a preexisting congenital central hypoventilation syndrome diagnosis reported information on 10 total pregnancies. At baseline, patients relied on various types of ventilatory support including positive pressure ventilation via tracheostomy, bilevel noninvasive positive pressure ventilation, and diaphragm pacing by phrenic nerve stimulation. Polysomnography for objective assessment of nocturnal ventilation was not consistently utilized. Changes to baseline ventilatory support were required during 3 out of 10 pregnancies. In addition, 2 patients using diaphragm pacing reported discomfort with pacing during the third trimester or after cesarean delivery, prompting discontinuation of diaphragm pacing. In 1 instance, discontinuation of diaphragm pacing and lack of recognition of need for an alternative support method led to respiratory arrest and need for emergent resuscitation. All patients who were offered prenatal congenital central hypoventilation syndrome testing chose to undergo testing. Of note, 9 out of 10 pregnancies were carried successfully to term and 5 infants were diagnosed with congenital central hypoventilation syndrome.

CONCLUSION

Women with congenital central hypoventilation syndrome may experience issues maintaining adequate ventilation during pregnancy, necessitating an adjustment of ventilator settings or use of an alternative type of ventilation. Objective assessment of nocturnal ventilation by means of polysomnography is an important part of congenital central hypoventilation syndrome pregnancy care to optimize maintenance of adequate gas exchange. Patients who rely on diaphragm pacing may experience discomfort with pacing during the later stages of pregnancy and after cesarean delivery. Anticipatory guidance and contingency planning for changing ventilatory needs should be discussed early in pregnancy. Prenatal congenital central hypoventilation syndrome testing should be offered to pregnant patients with congenital central hypoventilation syndrome to inform delivery decisions and prepare for the provision of advanced neonatal care.

Long Term Non-invasive Ventilation in Children With Central Hypoventilation

Central hypoventilation (CH) is a quite rare disorder caused by some congenital or acquired conditions. It is featured by increased arterial concentration of serum carbon dioxide related to an impairment of respiratory drive. Patients affected by CH need to be treated by mechanical ventilation in order to achieve appropriate ventilation and oxygenation both in sleep and wakefulness. In fact, in severe form of Congenital Central Hypoventilation Syndrome (CCHS) hypercarbia can be present even during the day. Positive pressure ventilation via tracheostomy is the first therapeutic option in this clinical condition, especially in congenital forms. Non-Invasive ventilation is a an option that must be reserved for more stable clinical situations and that requires careful monitoring over time.

Noninvasive ventilation in a young infant with congenital central hypoventilation and 7-year follow-up

INTRODUCTION

Congenital central hypoventilation syndrome (CCHS) is a rare disorder characterized by alveolar hypoventilation and autonomic system dysregulation secondary to mutations of the PHOX2B gene. Treatment consists of assisted ventilation using positive-pressure ventilators via tracheostomy, bi-level positive airway pressure (BPAP) via a noninvasive interface, negative-pressure ventilators, or diaphragm pacing. The long-term use of BPAP in younger children at home has been less frequently reported.

CASE PRESENTATION

We present a case of a 2-month-old infant with CCHS who was successfully managed by BPAP without the need for tracheostomy and followed up for 7 years.

CONCLUSION

CCHS is a rare disease that manifests as nocturnal desaturation and carbon dioxide retention in early life. Noninvasive ventilation can be successfully used in young infants via an appropriate mask.