Congenital central hypoventilation syndrome: ocular findings in 37 children

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

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

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.

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.

Elevated transaminases in congenital central hypoventilation syndrome

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

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

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

How the Management of Children With Congenital Central Hypoventilation Syndrome Has Changed Over Time: Two Decades of Experience From an Italian Center

Background: Congenital central hypoventilation syndrome (CCHS) is a rare disorder whose clinical phenotype is closely related to genotype. Methods: A retrospective analysis has been conducted on 22 patients with CCHS, who were referred to the Pediatric Pulmonology and Respiratory Intermediate Care Unit of Bambino Gesù Children's Hospital (Italy) for a multidisciplinary follow-up program between 2000 and 2020. Results: Apnea and cyanosis were the most frequent symptoms at onset (91%). Overall, 59% of patients required tracheostomy and invasive mechanical ventilation (IMV) in the first months of life. Thirty-two percent of patients had Hirschsprung disease (HSCR) that was associated with longer polyalanine repetitions or non-polyalanine repeat expansion mutations (NPARMs). Polyalanine repeat expansion mutations (PARMs) were more frequent and two novel NPARMs (c.780dupT and C.225-256delCT) were described in 14% of patients. Focal epilepsy was first described in 14% of patients and neurocognitive and neuromotor impairment involved 27% and 23% of children, respectively. Symptoms due to autonomic nervous system dysfunction/dysregulation (ANSD)-including strabismus (27%), dysphagia (27%), abnormal heart rhythm (10%), breath-holding spells (9%), and recurrent seizures due to hypoglycemia (9%)-were associated with an increased number of polyalanine repetitions of exon 3 or NPARMs of PHOX2B gene. Overall, the number of patients with moderate to severe phenotype initially treated with non-invasive ventilation (NIV) increased over time, and the decannulation program was concluded with 3 patients who started with IMV. Conclusions: Our study confirms that more severe phenotypes of CCHS are related to the number of polyalanine repetitions or to NPARMs. Although invasive ventilation is often required by patients with severe genotype/phenotype, gradual acquisition of specific skills in the management of patients with CCHS and technological improvements in mechanical ventilation allowed us to improve our therapeutic approach in this population.

Guidelines for diagnosis and management of congenital central hypoventilation syndrome

BACKGROUND

Congenital Central Hypoventilation Syndrome (CCHS) is a rare condition characterized by an alveolar hypoventilation due to a deficient autonomic central control of ventilation and a global autonomic dysfunction. Paired-like homeobox 2B (PHOX2B) mutations are found in most of the patients with CCHS. In recent years, the condition has evolved from a life-threatening neonatal onset disorder to include broader and milder clinical presentations, affecting children, adults and families. Genes other than PHOX2B have been found responsible for CCHS in rare cases and there are as yet other unknown genes that may account for the disease. At present, management relies on lifelong ventilatory support and close follow up of dysautonomic progression. BODY: This paper provides a state-of-the-art comprehensive description of CCHS and of the components of diagnostic evaluation and multi-disciplinary management, as well as considerations for future research.

CONCLUSION

Awareness and knowledge of the diagnosis and management of this rare disease should be brought to a large health community including adult physicians and health carers.

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.

Congenital central hypoventilation syndrome: a bedside-to-bench success story for advancing early diagnosis and treatment and improved survival and quality of life

The "bedside-to-bench" Congenital Central Hypoventilation Syndrome (CCHS) research journey has led to increased phenotypic-genotypic knowledge regarding autonomic nervous system (ANS) regulation, and improved clinical outcomes. CCHS is a neurocristopathy characterized by hypoventilation and ANS dysregulation. Initially described in 1970, timely diagnosis and treatment remained problematic until the first large cohort report (1992), delineating clinical presentation and treatment options. A central role of ANS dysregulation (2001) emerged, precipitating evaluation of genes critical to ANS development, and subsequent 2003 identification of Paired-Like Homeobox 2B (PHOX2B) as the disease-defining gene for CCHS. This breakthrough engendered clinical genetic testing, making diagnosis exact and early tracheostomy/artificial ventilation feasible. PHOX2B genotype-CCHS phenotype relationships were elucidated, informing early recognition and timely treatment for phenotypic manifestations including Hirschsprung disease, prolonged sinus pauses, and neural crest tumors. Simultaneously, cellular models of CCHS-causing PHOX2B mutations were developed to delineate molecular mechanisms. In addition to new insights regarding genetics and neurobiology of autonomic control overall, new knowledge gained has enabled physicians to anticipate and delineate the full clinical CCHS phenotype and initiate timely effective management. In summary, from an initial guarantee of early mortality or severe neurologic morbidity in survivors, CCHS children can now be diagnosed early and managed effectively, achieving dramatically improved quality of life as adults.

[Spanish patients with central hypoventilation syndrome included in the European Registry. The 2015 data]

INTRODUCTION

Congenital Central Hypoventilation Syndrome (CCHS) is a very rare genetic disease. In 2012 the European Central Hypoventilation Syndrome (EuCHS) Consortium created an online patient registry in order to improve care.

AIM

To determine the characteristics and outcomes of Spanish patients with CCHS, and detect clinical areas for improvement.

MATERIALS AND METHOD

An assessment was made on the data from Spanish patients in the European Registry, updated on December 2015.

RESULTS

The Registry contained 38 patients, born between 1987 and 2013, in 18 hospitals. Thirteen (34.2%) were older than 18 years. Three patients had died. Genetic analysis identified PHOX2B mutations in 32 (86.5%) out of 37 patients assessed. The 20/25, 20/26 and 20/27 polyalanine repeat mutations (PARMs) represented 84.3% of all mutations. Longer PARMs had more, as well as more severe, autonomic dysfunctions. Eye diseases were present in 47%, with 16% having Hirschsprung disease, 13% with hypoglycaemia, and 5% with tumours. Thirty patients (79%) required ventilation from the neonatal period onwards, and 8 (21%) later on in life (late onset/presentation). Eight children (21%) were using mask ventilation at the first home discharge. Five of them were infants with neonatal onset, two of them, both having a severe mutation, were switched to tracheostomy after cardiorespiratory arrest at home. Approximately one-third (34.3%) of patients were de-cannulated and switched to mask ventilation at a mean age of 13.7 years. Educational reinforcement was required in 29.4% of children attending school.

CONCLUSION

The implementation of the EuCHS Registry in Spain has identified some relevant issues for optimising healthcare, such as the importance of genetic study for diagnosis and assessment of severity, the high frequency of eye disease and educational reinforcement, as well as some limitations in ventilatory techniques.

Congenital Tonic Pupils Associated With Congenital Central Hypoventilation Syndrome and Hirschsprung Disease

Autonomic dysfunction can be associated with pupillary abnormalities. We describe a rare association of tonic pupils, congenital central hypoventilation syndrome, and Hirschsprung disease in a newborn with a mutation in the PHOX2B gene, a key regulator of neural crest cells. Hirschsprung disease is characterized by the congenital absence of neural crest-derived intrinsic ganglion cells. Tonic pupils may result from an abnormality of the ciliary ganglion, another structure of neural crest origin. The close association of these conditions in this child suggests a common abnormality in neural crest migration and differentiation.

Dysregulation of locus coeruleus development in congenital central hypoventilation syndrome

Human congenital central hypoventilation syndrome (CCHS), resulting from mutations in transcription factor PHOX2B, manifests with impaired responses to hypoxemia and hypercapnia especially during sleep. To identify brainstem structures developmentally affected in CCHS, we analyzed two postmortem neonatal-lethal cases with confirmed polyalanine repeat expansion (PARM) or Non-PARM (PHOX2B∆8) mutation of PHOX2B. Both human cases showed neuronal losses within the locus coeruleus (LC), which is important for central noradrenergic signaling. Using a conditionally active transgenic mouse model of the PHOX2B∆8 mutation, we found that early embryonic expression (<E10.5) caused failure of LC neuronal specification and perinatal respiratory lethality. In contrast, later onset (E11.5) of PHOX2B∆8 expression was not deleterious to LC development and perinatal respiratory lethality was rescued, despite failure of chemosensor retrotrapezoid nucleus formation. Our findings indicate that early-onset mutant PHOX2B expression inhibits LC neuronal development in CCHS. They further suggest that such mutations result in dysregulation of central noradrenergic signaling, and therefore, potential for early pharmacologic intervention in humans with CCHS.

Genotype-phenotype relationship in Japanese patients with congenital central hypoventilation syndrome

Examine the genotype-phenotype relationship in Japanese congenital central hypoventilation syndrome (CCHS) patients and estimate the incidence of CCHS in Japan. Subjects were 92 Japanese patients with PHOX2B mutations; 19 cases carried 25 polyalanine repeat expansion mutations (PARMs); 67 cases carried 26 or more PARMs; and 6 had non-PARMs (NPARMs). We collected clinical data in all patients and estimated the development or intelligent quotients only in the patients carrying 25 PARM. The estimated incidence of CCHS was greater than one case per 148 000 births. Polyhydramnios was observed in three cases. Twelve infants exhibited depressed respiration at birth. In 19 cases carrying 25 PARM, the male-to-female ratio was ~3, no cases had Hirschsprung disease; 7 cases (37%) developed hypoventilation after the neonatal period, and 8 cases (42%) had mental retardation. In other 73 cases carrying 26 or more PARMs or NPARMs, male-to-female ratio was equal; patients frequently complicated with Hirschsprung disease and constipation, and all patients presented with hypoventilation in the neonatal period. Clinical symptoms were severe in most patients carrying long PARMs and NPARMs. In 25 PARM, additional genetic and/or epigenetic factors were required for CCHS development and male sex is likely a predisposing factor. The patients carrying 25 PARM frequently had mental retardation likely because they were not able to receive appropriate ventilation support following a definitive diagnosis owing to subtle and or irregular hypoventilation. Molecular diagnosis provides a definitive diagnosis and enables to receive appropriate ventilator support.

Ophthalmologic impairment during adulthood in central congenital hypoventilation syndrome: a longitudinal cohort analysis of nine patients

BACKGROUND

Congenital central hypoventilation syndrome (CCHS) is a rare dysgenetic form of neurocristopathy associated with dysfunction of the autonomic nervous system. Ophthalmologic abnormalities are reported in CCHS children, and range from pupillary and iris abnormalities to ptosis, strabismus and convergence deficiency. Since earlier CCHS diagnosis and multidisciplinary management, combined with improved ventilatory support techniques, the lifespan of children with CCHS has been considerably lengthened. The oldest of them have now reached adult age and we report in this study the results of their ophthalmologic examination.

MATERIALS AND METHODS

Nine CCHS adult patients were prospectively included during a 14-month period. Each patient underwent complete ophthalmologic examination, static pupillometry with scotopic and photopic pupillary diameter (PD) measures, Humphrey 24-2 visual field analysis, macular OCT and complete orthoptic assessment including a Hess-Lancaster test.

RESULTS

Ophthalmologic abnormalities were found in six of the nine patients (66%). The main features were strabismus in six patients (66%). Four patients (44%) displayed abnormal pupillary function, with a decrease in average scotopic PD (3.8 ± 1.4 mm), average photopic PD (3.5 ± 1.2 mm), and average percentage of pupillary constriction (7.6 ± 8.5%). Three patients (33%) exhibited iris abnormalities such as iris atrophy, smooth iris surface and atrophic sphincter.

CONCLUSION

This study allowed the description of ophthalmologic abnormalities occurring in CCHS in a series of adult patients, thus improving current knowledge of the disease. The prevalence of pupillary and iris lesions were lower than those observed in a series of children, suggesting that they could be considered as systemic disease severity markers.

Germline mosaicism of PHOX2B mutation accounts for familial recurrence of congenital central hypoventilation syndrome (CCHS)

Congenital central hypoventilation syndrome (CCHS), a rare disorder characterized by alveolar hypoventilation and autonomic dysregulation, is caused by mutations in the PHOX2B gene. Most mutations occur de novo, but recent evidence suggests that up to 25% are inherited from asymptomatic parents with somatic mosaicism for these mutations. However, to date, germline mosaicism has not been reported. This report describes a family with recurrence of PHOX2B mutation-confirmed CCHS due to germline mosaicism. The first occurrence was a baby girl, noted on day 2 of life to have multiple episodes of apnea, bradycardia, and cyanosis while breathing room air. PHOX2B gene testing confirmed the diagnosis of CCHS with a heterozygous polyalanine repeat expansion mutation (PARM); genotype 20/27 (normal 20/20). Both parents tested negative for this mutation using fragment analysis (limit of detection<1%). Upon subsequent pregnancy [paternity confirmed using short tandem repeat (STR) analysis], amniocentesis testing identified the PHOX2B 20/27 genotype, confirmed with repeat testing. Elective abortion was performed at 21.5 weeks gestation. Testing of abortus tissue confirmed amniocentesis testing. The PHOX2B 20/27 expansion was not observed in a paternal sperm sample. This case represents the first reported family with recurrence of PHOX2B mutation-confirmed CCHS without detection of a parental carrier state or mosaicism, confirming the previously hypothesized possibility of germline mosaicism for PHOX2B mutations. This is an important finding for genetic counseling of CCHS families, suggesting that even if somatic mosaicism is not detected in parental samples, there is still reason for careful genetic counseling and consideration of prenatal testing during subsequent pregnancies.

Progressive gray matter changes in patients with congenital central hypoventilation syndrome

INTRODUCTION

Patients with congenital central hypoventilation syndrome (CCHS) show brain injury in areas that control chemosensory, autonomic, motor, cognitive, and emotion functions, which are deficient in the condition. Many of these abnormal characteristics are present from the neonatal period; however, it is unclear whether tissue injury underlying the characteristics progressively worsens with time. We hypothesized that several brain areas in subjects with CCHS would show increased gray matter volume loss over time.

METHODS

We collected high-resolution T1-weighted images twice (4 years apart) from seven subjects with CCHS (age at first study, 16.1 ± 2.7 years; four males) and three control subjects (15.9 ± 2.1 years; three males) using a 3.0-Tesla magnetic resonance imaging (MRI) scanner, and evaluated regional gray matter volume changes with voxel-based morphometry (VBM) procedures.

RESULTS

Multiple brain sites in CCHS, including frontal, prefrontal, insular, and cingulate cortices; caudate nuclei and putamen; ventral temporal and parietal cortices; and cerebellar cortices showed significantly reduced gray matter volume over time. Only limited brain areas, including sensory, temporal, and medullary regions, emerged with increased gray matter at the later age.

DISCUSSION

Patients with CCHS show reduced gray matter volume with age progression in autonomic, respiratory, and cognitive regulatory areas, an outcome that may contribute to deterioration of functions found in the syndrome with increasing age.

Case reports of congenital central hypoventilation syndrome

Congenital central hypoventilation syndrome (CCHS), which occurs in less than 1 in every 50,000 infants and children, is a rare syndrome first noted in literature by Mellins in 1970. Congenital central hypoventilation syndrome is a condition in which the patient loses the drive to breathe during deep sleep and can mimic many diseases. Until recently, CCHS has largely been a diagnosis of exclusion; fortunately, there is now a genetic test available to confirm the diagnosis. The purpose of this article is to discuss the steps taken to confirm the diagnosis of CCHS. In addition to the history of the disease and clinical manifestations, genetics and prognosis of children with CCHS will be discussed. Two cases are presented for illustration of hospital course and preparation for discharge.

Pupillometry in congenital central hypoventilation syndrome (CCHS): quantitative evidence of autonomic nervous system dysregulation

INTRODUCTION

Congenital central hypoventilation syndrome (CCHS) is characterized by alveolar hypoventilation, autonomic nervous system (ANS) dysregulation (ANSD), and mutations in the paired-like homeobox 2B (PHOX2B) gene. ANSD in CCHS affects multiple systems and includes ophthalmologic abnormalities. We hypothesized that quantitative pupil measures, obtained using pupillometry, would vary between cases with CCHS and controls and within those with CCHS by PHOX2B genotype.

RESULTS

Measures known to be illustrative of sympathetic and parasympathetic response (prestimulus, maximum pupil diameter, percentage of pupil constriction after light stimulus, and average constriction and dilation velocities) were significantly reduced in those with CCHS as compared with controls (all P < 0.05).

DISCUSSION

These reductions are indicative of both sympathetic and parasympathetic deficits in CCHS, which is in keeping with the role of PHOX2B in ANS development. An inverse linear relationship was apparent in pupil diameter and velocity measurements among the cases with CCHS with the most common heterozygous PHOX2B polyalanine expansion repeat mutations, suggesting a graded phenotype/genotype dose response based on polyalanine repeat length. These results confirm our central hypotheses while offering the first objective measures of pupillary dysfunction and ophthalmologic-specific ANSD in CCHS.

METHODS

A total of 316 monocular measurements were taken under dark-adapted conditions with a fixed light stimulus from 22 PHOX2B mutation-confirmed cases with CCHS and 68 healthy controls.

Variable human phenotype associated with novel deletions of the PHOX2B gene

BACKGROUND

Clinical testing for PHOX2B mutations is widely used for patients with any symptoms suggestive of hypoventilation (with/without anatomic/physiologic autonomic dysregulation), though not necessarily with the congenital central hypoventilation syndrome (CCHS) phenotype. Consequently, a multitude of referrals for clinical PHOX2B testing (fragment analysis of the 20 polyalanine repeat region and/or sequencing of entire coding region) have no identifiable mutation. Whole gene deletions/duplications have recently been identified as a common disease-causing mechanism, but have not been reported in a clinical population referred for PHOX2B testing. The objective of this study was to determine if PHOX2B exon or whole gene deletion/duplication would be identified in a subset of patients referred for PHOX2B testing.

HYPOTHESIS

We hypothesized that PHOX2B exon or whole gene deletion or duplication would be identified in a subset of cases who were referred for genetic testing but not found to have a PHOX2B mutation with currently available clinical PHOX2B testing.

METHODS

Genomic DNA samples from patients that tested negative for PHOX2B mutations using fragment analysis and/or sequencing, and control samples, were screened for PHOX2B exon deletions/duplications by multiplex ligation-dependent probe amplification with confirmation by array comparative genomic hybridization.

RESULTS

Deletions of/in PHOX2B were identified in 4/250 patients and 0/261 controls. The deletions ranged from 6,216 base pairs (involving only PHOX2B exon 3) to 2.6 megabases (involving all of PHOX2B and 12 other genes). The case with PHOX2B partial exon 3 deletion had a CCHS-compatible phenotype (hypoventilation, Hirschsprung disease). Phenotypes for the other three cases, all PHOX2B whole-gene deletions, were varied including: (1) apparent life threatening event, (2) full CCHS necessitating artificial ventilation with ganglioneuroblastoma, and (3) hypoventilation during sleep. Family studies of two of the four probands showed these deletions to be maternally inherited; the mothers also had phenotypic findings of autonomic dysfunction.

CONCLUSIONS

PHOX2B exon or whole gene deletion should be considered as another mechanism of disease which may include CCHS, Hirschsprung disease, and/or tumors of neural crest origin, although the genotype-phenotype relationship requires further clarification. Pediatr Pulmonol. 2012; 47:153-161. © 2011 Wiley Periodicals, Inc.

Congenital central hypoventilation syndrome in children

Congenital central hypoventilation syndrome (CCHS) is a rare, lifelong condition wherein control of breathing is abnormal and patients present with symptoms of alveolar hypoventilation. The severity of hypoventilation varies and although most patients present in the neonatal period, late onset cases have been reported. In 2003, it was discovered that mutations in the PHOX2B gene were responsible for CCHS. This gene also plays a role in neural crest cell migration, and many patients present with symptoms of autonomic dysfunction in addition to hypoventilation. The pathophysiology responsible for hypoventilation remains unclear although a unifying hypothesis is that the abnormality is located in areas of the brain involved in integration of chemoreceptor afferent pathways for ventilation. The goal of treatment for CCHS is to ensure adequate ventilation during wakefulness and sleep. A variety of ventilation modalities are available including positive pressure ventilation via tracheostomy, non-invasive ventilation via nasal mask, and diaphragmatic pacing. With close monitoring and support, children with CCHS can be expected to function well in society and have a good quality of life.

Late onset congenital central hypoventilation syndrome after exposure to general anesthesia

PURPOSE

Prolonged postoperative hypoventilation presents a challenge to anesthesiologists with regard to assessing etiology and related treatment. We present a case of recurrent episodes of postoperative hypoventilation in a previously asymptomatic child after uneventful general anesthesia. In this case, the child eventually required lifelong ventilatory support during sleep.

CLINICAL FEATURES

A case of postoperative hypoventilation in a previously asymptomatic six-year-old child was investigated to determine the possible etiology. After uneventful general anesthesia for dental surgery, the child experienced recurrent episodes of hypoventilation associated with sleep. The child's lungs were mechanically ventilated due to failure of all trials of weaning. Clinical examination was unremarkable and laboratory investigations excluded the possibility of thyroid, hepatic, renal, and neuromuscular diseases. Computerized tomography, magnetic resonance imaging, and electroencephalogram studies were within normal limits. A negative pyridostigmine trial ruled out myasthenia. The child was finally diagnosed as having "late onset congenital central hypoventilation syndrome". Genetic testing revealed a PHOX2B mutation consistent with this diagnosis. The child was discharged home on mechanical ventilatory support during sleep.

CONCLUSION

Congenital central hypoventilation syndrome is a rare lifelong multisystem disorder which may occur during the neonatal period as a result of severe genetic mutation in the PHOX2B gene. In mild mutations, a triggering factor, such as sedation or anesthesia, may be required for the syndrome to manifest itself. These patients often require lifelong mechanical ventilatory support, particularly during sleep.

Selectively diminished corpus callosum fibers in congenital central hypoventilation syndrome

Congenital central hypoventilation syndrome (CCHS), a condition associated with mutations in the PHOX2B gene, is characterized by loss of breathing drive during sleep, insensitivity to CO2 and O2, and multiple somatomotor, autonomic, neuropsychological, and ophthalmologic deficits, including impaired intrinsic and extrinsic eye muscle control. Brain structural studies show injury in peri-callosal regions and the corpus callosum (CC), which has the potential to affect functions disturbed in the syndrome; however, the extent of CC injury in CCHS is unclear. Diffusion tensor imaging (DTI)-based fiber tractography procedures display fiber directional information and allow quantification of fiber integrity. We performed DTI in 13 CCHS children (age, 18.2±4.7 years; eight male) and 31 control (17.4±4.9 years; 18 male) subjects using a 3.0-Tesla magnetic resonance imaging scanner; CC fibers were assessed globally and regionally with tractography procedures, and fiber counts and densities compared between groups using analysis-of-covariance (covariates; age and sex). Global CC evaluation showed reduced fiber counts and densities in CCHS over control subjects (CCHS vs. controls; fiber-counts, 4490±854 vs. 5232±777, P<0.001; fiber-density, 10.0±1.5 vs. 10.8±0.9 fibers/mm2, P<0.020), and regional examination revealed that these changes are localized to callosal axons projecting to prefrontal (217±47 vs. 248±32, P<0.005), premotor (201±51 vs. 241±47, P<0.012), parietal (179±64 vs. 238±54, P<0.002), and occipital regions (363±46 vs. 431±82, P<0.004). Corpus callosum fibers in CCHS are compromised in motor, cognitive, speech, and ophthalmologic regulatory areas. The mechanisms of fiber injury are unclear, but may result from hypoxia or perfusion deficits accompanying the syndrome, or from consequences of PHOX2B action.

Congenital central hypoventilation syndrome and the PHOX2B gene: a model of respiratory and autonomic dysregulation

The paired-like homeobox 2B gene (PHOX2B) is the disease-defining gene for congenital central hypoventilation syndrome (CCHS). Individuals with CCHS typically present in the newborn period with alveolar hypoventilation during sleep and often during wakefulness, altered respiratory control including reduced or absent ventilatory responses to hypercarbia and hypoxemia, and autonomic nervous system (ANS) dysregulation; however, a subset of individuals present well into adulthood. Thermoregulation is altered and perception of shortness of breath is absent, but voluntary breathing is retained. Structural and functional magnetic resonance imaging (MRI) and limited post-mortem studies in subjects with CCHS reveal abnormalities in both forebrain and brainstem. MRI changes appear in the hypothalamus (responsible for thermal drive to breathing), posterior thalamus and midbrain (mediating O(2) and oscillatory motor patterns), caudal raphé and locus coeruleus (regulating serotonergic and noradrenergic systems), the lateral medulla, parabrachial pons, and cerebellum (coordinating chemoreceptor and somatic afferent activity with breathing), and insular and cingulate cortices (mediating shortness of breath perception). Structural and functional alterations in these sites may result from PHOX2B mutations or be secondary to hypoxia/perfusion alterations from suboptimal management/compliance. The study of CCHS, with collaboration between physician-scientists and basic scientists, offers a rare opportunity to investigate control of breathing within the complex physiological network of the ANS.

International Classification of Functioning, Disability and Health in children with congenital central hypoventilation syndrome

PURPOSE

The main aim of this study is to examine the functioning of children with congenital central hypoventilation syndrome (CCHS), a rare disorder of respiratory control associated with physiological and anatomical manifestations of a generalised autonomic nervous system dysfunction, using WHO's International Classification of Functioning, Disability and Health, Children and Youth version (ICF-CY).

METHOD

The data of 26 children, (F = 17) aged 1.5-17.5 years, were collected. Data were analysed in the following four age groups: <3, 3-6, 7-12 and 13-18 years, using only the ICF-CY questionnaires' cross-age items.

RESULTS

In the body functions, component breathing and paying attention were common problems for four age groups. In the activity and participation component, all children, except adolescents, showed problems with language. Furthermore, problems in social interaction were evident for all age ranges, except the youngest. Finally, in the environmental factors component, parents reported limitations concerning the natural environment and human-made changes to the environment that were common to all ages.

CONCLUSIONS

The study supports the usefulness of supplementing diagnostic classifications with functional classifications to obtain complete information on health-related conditions in children with CCHS.

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

BACKGROUND

Congenital central hypoventilation syndrome (CCHS) is characterized by alveolar hypoventilation and autonomic dysregulation.

PURPOSE

(1) To demonstrate the importance of PHOX2B testing in diagnosing and treating patients with CCHS, (2) to summarize recent advances in understanding how mutations in the PHOX2B gene lead to the CCHS phenotype, and (3) to provide an update on recommendations for diagnosis and treatment of patients with CCHS.

METHODS

Committee members were invited on the basis of their expertise in CCHS and asked to review the current state of the science by independently completing literature searches. Consensus on recommendations was reached by agreement among members of the Committee.

RESULTS

A review of pertinent literature allowed for the development of a document that summarizes recent advances in understanding CCHS and expert interpretation of the evidence for management of affected patients.

CONCLUSIONS

A PHOX2B mutation is required to confirm the diagnosis of CCHS. Knowledge of the specific PHOX2B mutation aids in anticipating the CCHS phenotype severity. Parents of patients with CCHS should be tested for PHOX2B mutations. Maintaining a high index of suspicion in cases of unexplained alveolar hypoventilation will likely identify a higher incidence of milder cases of CCHS. Recommended management options aimed toward maximizing safety and optimizing neurocognitive outcome include: (1) biannual then annual in-hospital comprehensive evaluation with (i) physiologic studies during awake and asleep states to assess ventilatory needs during varying levels of activity and concentration, in all stages of sleep, with spontaneous breathing, and with artificial ventilation, and to assess ventilatory responsiveness to physiologic challenges while awake and asleep, (ii) 72-hour Holter monitoring, (iii) echocardiogram, (iv) evaluation of ANS dysregulation across all organ systems affected by the ANS, and (v) formal neurocognitive assessment; (2) barium enema or manometry and/or full thickness rectal biopsy for patients with a history of constipation; and (3) imaging for neural crest tumors in individuals at greatest risk based on PHOX2B mutation.

Novel neuropathologic findings in the Haddad syndrome

Haddad syndrome (congenital central hypoventilation syndrome and Hirschsprung's disease) is a rare disorder for which in-depth neuropathologic analysis is lacking. We report the brain findings in a full-term male infant with Haddad syndrome who died at 27 days of life. Bilateral hypoplasia of the superior temporal lobe and gyral anomalies in the frontal cortex were present. Immunohistochemistry with an antibody to tyrosine hydroxylase (noradrenaline synthesis) demonstrated hypoplasia of the locus coeruleus (implicated in chemoreception) and A5 region. Other findings included delayed maturation of the arcuate nucleus (putative human homologue of ventral medullary neurons in animals critical for chemoreception) and aberrant fascicles in the nucleus of the solitary tract. Efforts to determine the putative gene mutation were unsuccessful. This study implicates novel brain findings in Haddad syndrome mimicking those in murine Phox2b null mutants. This case suggests that abnormalities occur in CCHS in a network of sites critical to chemoreception.

Carbon dioxide chemoreception and hypoventilation syndromes with autonomic dysregulation

Respiratory and autonomic disorders of infancy, childhood, and adulthood are a group of disorders that have varying presentation, combined with a range of severity of respiratory control and autonomic nervous system dysfunction. Within this group, congenital central hypoventilation syndrome and rapid onset obesity with hypothalamic dysfunction, hypoventilation, and autonomic dysregulation, exhibit the greatest respiratory control deficits, requiring supported ventilation as a mainstay of care. The discovery of the key role of the paired-like homeobox 2B gene in autonomic nervous system development, along with the identification of paired-like homeobox 2B gene mutations causing congenital central hypoventilation syndrome, has led to a fruitful dialog between basic scientists and physician-scientists, producing an explosion of knowledge regarding genotype-phenotype correlations in this disorder, as well as important animal models of chemosensory regulation deficit. Though the etiology of rapid onset obesity with hypothalamic dysfunction, hypoventilation, and autonomic dysregulation is still to be determined, recent studies have begun to carefully delineate the phenotype, suggesting that it too may provide fertile ground for research that both advances our knowledge and improves patient care.

Congenital central hypoventilation syndrome: neurocognitive functioning in school age children

OBJECTIVE

Examine indices of neurocognitive functioning in children with PHOX2B mutation-confirmed neonatal onset congenital central hypoventilation syndrome (CCHS) and relate them to indices of PHOX2B genotype, demographics, and disease severity.

METHODS

Subjects were 20 patients with PHOX2B mutation-confirmed CCHS diagnosed as neonates who had undergone neurocognitive assessment in the course of clinical care at the Rush Children's Hospital CCHS Center between 1990 and 2006. Neurocognitive variables of interest included Full Scale IQ (FSIQ) and Wechsler-derived marker indices (subtests) of verbal comprehension (Vocabulary), visuoperceptual reasoning (Block Design), working memory (Digit Span), and clerical/processing speed (Coding).

RESULTS

Single sample t-tests revealed participants' general intelligence index (FSIQ; mean 84.9, SD 23.6) to be lower than the general population, though the range of FSIQ observed was broad. Visuoperceptual reasoning and clerical/visuographic speed marker indices were similarly depressed. These deficits were related to special education participation but not to PHOX2B genotype status or other demographic and clinical risk factors.

CONCLUSIONS

PHOX2B mutation-confirmed CCHS confers risk for adverse neurocognitive outcome, though the range of functioning observed raises questions about factors that may contribute to neurocognitive variability. Visuoperceptual reasoning and clerical/visuographic speed appear particularly vulnerable. PHOX2B genotype and disease severity indicators were unrelated to neurocognitive indices, possibly due to our modest sample. Future research should employ comprehensive neurocognitive assessment emphasizing visuoperceptual ability, mental speed, attention, and information processing efficiency. Increased recognition and expedited diagnosis with PHOX2B testing should allow larger studies of the relationship between neurocognitive functioning, PHOX2B genotype/mutation, and disease severity and management.

Breathing with phox2b

In the last few years, elucidation of the architecture of breathing control centres has reached the cellular level. This has been facilitated by increasing knowledge of the molecular signatures of various classes of hindbrain neurons. Here, we review the advances achieved by studying the homeodomain factor Phox2b, a transcriptional determinant of neuronal identity in the central and peripheral nervous systems. Evidence from human genetics, neurophysiology and mouse reverse genetics converges to implicate a small population of Phox2b-dependent neurons, located in the retrotrapezoid nucleus, in the detection of CO(2), which is a paramount source of the 'drive to breathe'. Moreover, the same and other studies suggest that an overlapping or identical neuronal population, the parafacial respiratory group, might contribute to the respiratory rhythm at least in some circumstances, such as for the initiation of breathing following birth. Together with the previously established Phox2b dependency of other respiratory neurons (which we review briefly here), our new data highlight a key role of this transcription factor in setting up the circuits for breathing automaticity.

Congenital central hypoventilation syndrome from past to future: model for translational and transitional autonomic medicine

The modern story of CCHS began in 1970 with the first description by Mellins et al., came most visibly to the public eye with the ATS Statement in 1999, and continues with increasingly fast paced advances in genetics. Affected individuals have diffuse autonomic nervous system dysregulation (ANSD). The paired-like homeobox gene PHOX2B is the disease-defining gene for CCHS; a mutation in the PHOX2B gene is requisite to the diagnosis of CCHS. Approximately 90% of individuals with the CCHS phenotype will be heterozygous for a polyalanine repeat expansion mutation (PARM); the normal allele will have 20 alanines and the affected allele will have 24-33 alanines (genotypes 20/24-20/33). The remaining approximately 10% of individuals with CCHS will have a non-PARM (NPARM), in the PHOX2B gene; these will be missense, nonsense, or frameshift. CCHS and PHOX2B are inherited in an autosomal dominant manner with a stable mutation. Approximately 8% of parents of a CCHS proband will be mosaic for the PHOX2B mutation. A growing number of cases of CCHS are identified after the newborn period, with presentation from infancy into adulthood. An improved understanding of the molecular basis of the PHOX2B mutations and of the PHOX2B genotype/CCHS phenotype relationship will allow physicians to anticipate the clinical phenotype for each affected individual. To best convey the remarkable history of CCHS, and to describe the value of recognizing CCHS as a model for translational and transitional autonomic medicine, we present this review article in the format of a chronological story, from 1970 to the present day.

Congenital central hypoventilation syndrome (CCHS) and sudden infant death syndrome (SIDS): kindred disorders of autonomic regulation

Congenital central hypoventilation syndrome (CCHS) and sudden infant death syndrome (SIDS) were long considered rare disorders of respiratory control and more recently have been highlighted as part of a growing spectrum of disorders within the rubric of autonomic nervous system (ANS) dysregulation (ANSD). CCHS typically presents in the newborn period with a phenotype including alveolar hypoventilation, symptoms of ANSD and, in a subset of cases, Hirschsprung disease and later tumors of neural crest origin. Study of genes related to autonomic dysregulation and the embryologic origin of the neural crest led to the discovery of PHOX2B as the disease-defining gene for CCHS. Like CCHS, SIDS is thought to result from central deficits in control of breathing and ANSD, although SIDS risk is most likely defined by complex multifactorial genetic and environmental interactions. Some early genetic and neuropathological evidence is emerging to implicate serotonin systems in SIDS risk. The purpose of this article is to review the current understanding of the genetic basis for CCHS and SIDS, and discuss the impact of this information on clinical practice and future research directions.

Congenital central alveolar hypoventilation syndrome (Ondine's curse) with survival into adulthood

Ondine's curse or central alveolar hypoventilation (CCAH) syndrome is a disorder of the autonomic nervous system resulting in respiratory dysregulation. The clinical outcome is typically poor, with few individuals living into adulthood and even fewer surviving to adulthood with normal neurological function. Our patient initially presented following an uncomplicated delivery with hypotonia, poor respiratory effort, and hypoxemia that required ventilatory support. Laboratory workup, radiographic evaluation, and ancillary testing ruled out brain stem lesions, neuromuscular diseases, cardiovascular and pulmonary disease, and metabolic disorders, resulting in a diagnosis of CCAH syndrome. The patient underwent tracheotomy and chronic ventilatory support. Close long-term management and appropriate treatment modifications have provided for an excellent outcome and good quality of life. The patient is currently 22 years old and is earning her teaching degree for K-12 art education. A combination of early recognition and a multidisciplinary approach may lead to a successful outcome in patients with CCAH syndrome.

[Ondine's Curse and rare oculomotor abnormalities: a case report]

Ondine's Curse or congenital central hypoventilation syndrome (CCHS) is a neurocristopathy (failure of migration or differentiation of neural crest-derived precursor cells) and is characterized by hypoventilation or apnea, which is most pronounced during sleep, with no other abnormalities of the neuro-respiratory system. Because of respiratory distress soon after birth, patients must be intubated and ventilated for a long time. This disorder may be associated with other symptoms of neurocristopathy (Hirschsprung disease, neuroblastoma, neuroganglioma) and other abnormalities of the autonomic nervous system (vasomotor dysfunctions or ophthalmic abnormalities: abnormal pupils, insufficient convergence, strabismus, or ptosis). We report the original case of a CCHS patient who presented with alternative ptosis of both the right and left eyes and esotropia. The ocular findings should lead to earlier diagnosis and speedier adequate treatment.

Pediatric autonomic disorders

The scope of pediatric autonomic disorders is not well recognized. The goal of this review is to increase awareness of the expanding spectrum of pediatric autonomic disorders by providing an overview of the autonomic nervous system, including the roles of its various components and its pervasive influence, as well as its intimate relationship with sensory function. To illustrate further the breadth and complexities of autonomic dysfunction, some pediatric disorders are described, concentrating on those that present at birth or appear in early childhood.

Sleep-related breathing disorders

Sleep-related breathing disorders are a heterogeneous group of conditions that may be associated with alterations in the structure of sleep, in sleep quality, and in gas exchange during sleep. Obstructive sleep apnea represents the most frequent cause of sleep-related breathing disorders, which encompass a diversity of conditions that either complicate coexisting disease or present as primary disorders. Many of these disorders have consequences during both sleep and wakefulness and may produce substantial burden of symptoms and disease in untreated individuals.

Autonomic Function in Children With Congenital Central Hypoventilation Syndrome and Their Families

STUDY OBJECTIVES

Congenital central hypoventilation syndrome (CCHS) is a genetic disorder characterized by failure of automatic control of breathing in the absence of obvious anatomic lesions. There have been several reports suggesting that CCHS patients display autonomic dysregulation. Pulse arterial tonometry (PAT) is a novel technique that provides noninvasive moment-to-moment measurements of sympathetic tone changes to the cutaneous vascular bed. We hypothesized that autonomic function as measured by PAT would be altered in children with CCHS.

DESIGN

Prospective study.

SETTING

CCHS Family Conference, Orlando, FL, and the local community in Louisville, KY.

PARTICIPANTS

Nineteen CCHS patients and 31 parents as well as 24 control children and 15 adult control subjects.

INTERVENTIONS

Children with CCHS and their parents underwent sympathetic challenges (vital capacity sigh and cold hand pressor test) and a test of reactive hyperemia (brachial artery occlusion) while PAT was continuously monitored from the right hand. Control children and control adults underwent the same procedure.

MEASUREMENTS AND RESULTS

The maximal change of the PAT signal compared to the preceding baseline was averaged and expressed as percentage change for each of the challenges. The magnitude of sympathetic discharge-induced attenuation of PAT signal following a sigh was reduced in CCHS children compared to control subjects for both the vital capacity sighs and the cold hand pressor test. There were no differences observed in the magnitude of PAT attenuation between parents of children with CCHS and control adults. No differences were observed between either CCHS and control subjects or CCHS parents and adult control subjects for the brachial artery occlusion test.

CONCLUSION

CCHS patients show an attenuated response to endogenous sympathetic stimulation, supporting the presence of autonomic nervous system dysfunction as a consistent feature of this condition. No differences were found in parents of children with CCHS compared to control adults, consistent with the finding that CCHS is primarily the result of a de novo gene mutation.

In pursuit (and discovery) of a genetic basis for congenital central hypoventilation syndrome

Congenital central hypoventilation syndrome (CCHS) typically presents in the newborn period with a phenotype including alveolar hypoventilation, symptoms of autonomic nervous system dysregulation, and in a subset of cases Hirschsprung disease and later tumors of neural crest origin. Study of genes related to the autonomic dysregulation and the embryologic origin of the neural crest has led to identification of the genetic basis for CCHS, the mode of inheritance, and the presence of mosaicism in a subset of parents. Polyalanine expansion mutations in PHOX2B have been identified to be the disease-defining mutation in CCHS, with a small subset of patients having other mutations in PHOX2B. Further, the size of the polyalanine repeat mutation in PHOX2B is correlated with the severity of the phenotype in CCHS, and non-polyalanine repeat mutations appear to, in general, result in CCHS phenotypes at the severe end of the spectrum. These studies highlight the utility of PHOX2B genetic testing for confirmation of the CCHS diagnosis, for prenatal diagnosis, and for identification of previously undiagnosed adults with unexplained hypercarbia or control of breathing deficits. This diagnostic approach may be a consideration for other complex, seemingly undecipherable diseases that affect infants and children. The purpose of this article is to provide a comprehensive review of current research into the genetic basis for CCHS, an explanation for how these studies evolved, recent studies that begin to explain the mechanisms through which mutations in PHOX2B exert their effects, and clinical application of the genetic testing.

Cough in children with congenital central hypoventilation syndrome

Congenital central hypoventilation syndrome (CCHS) is defined as failure of the chemical (autonomic) control of breathing causing alveolar hypoventilation in the absence of pulmonary, cardiac, neuromuscular or patent brainstem lesions. Hypoventilation is predominant in non-rapid-eye-movement sleep, during which breathing is primarily under chemical control. Failure of the central integration of chemosensory inputs is proposed as the putative defect. A genetic basis for CCHS is supported by lines of evidence. In some diseases of the central nervous system there is more or less complete depression of the cough reflex, whereas spontaneous ventilation is generally preserved. Little is known regarding cough in CCHS patients. Parents consistently report that their children cough 'normally' during airway infections; in contrast, experimental lines of evidence suggest that CCHS children lack a cough response following inhalation of a tussigenic agent. Although several factors may account for the discrepancy, the possibility of a weakened or even absent cough reflex remains to be fully ascertained. Conceivably, a defective cough reflex, in conjunction with the well established lack of perception of respiratory discomfort, might result in an increased risk of potentially serious respiratory complications in CCHS patients.

Epidemiologic survey of 196 patients with congenital central hypoventilation syndrome

This study examined the cross-sectional medical and social characteristics of children diagnosed with congenital central hypoventilation syndrome (CCHS). A detailed questionnaire was mailed to all families with a child with CCHS who are affiliated with a family network or support group. The questionnaire response rate was >75% (n=196). Mean age was 10.22 years +/- 6.6 years (SD) (range, 0.4-38 years), with a 1:1 sex ratio. Multisystem involvement was almost universal among the cohort, with Hirschsprung's disease (HD) present in 16.3%; 61.7% of the children had a tracheotomy, but 14.3% were never tracheotomized, with 77 subjects (39.3%) not having a tracheostomy tube at time of survey. Respiratory support approaches varied but clearly reflected the trend towards earlier and more widespread transition to noninvasive ventilatory modalities. Significant developmental problems were noted, but attendance in regular classes occurred in the majority. Significant deficiencies in routine periodic evaluation and management were reported. In addition, the presence of CCHS was associated with a significant financial and psychosocial burden to the families. In conclusion, a comprehensive survey of 196 CCHS children and their families revealed a cross-sectional picture of substantial medical and psychosocial complexities associated with this disorder, and pointed out substantial inadequacies in routine preventive care that appear to impose stress on the families. The emerging trend of earlier transition to noninvasive ventilatory support warrants future studies. Implementation of recommended guidelines for diagnosis and multidisciplinary follow-up of CCHS should ultimately ameliorate the long-term outcome of this lifelong condition.

Global BOLD MRI changes to ventilatory challenges in congenital central hypoventilation syndrome

We evaluated global blood oxygen level dependent (BOLD) signal changes in gray and white matter in 14 congenital central hypoventilation syndrome (CCHS) and 14 control subjects. One baseline image series with room air and three series with 30 s room air followed by 120 s hypercapnia (5% CO2/95% O2), hypoxia (15% O2/85% N2) or hyperoxia (100% O2) were collected. Hypercapnia and hyperoxia raised, and hypoxia lowered gray and white matter global signal in both groups, with smaller changes in white matter. Signal changes in CCHS cases were lower than control subjects for hypercapnia in gray and white matter, slightly more-enhanced in hypoxia, and, except for initial transient responses, were nearly comparable during hyperoxia. Initial signal rate or pattern changes emerged in all three challenges in gray or white matter in control, but not CCHS cases. Neural or vascular mechanisms mediate perfusion differently in CCHS; the aberrant initial transient responses may reflect deficiencies in rapidly-varying physiologic interactions in the syndrome.

Idiopathic congenital central hypoventilation syndrome: Analysis of genes pertinent to early autonomic nervous system embryologic development and identification of mutations in PHOX2b

Idiopathic congenital central hypoventilation syndrome (CCHS) has been linked to autonomic nervous system dysregulation and/or dysfunction (ANSD) since it was first described in 1970. A genetic basis of CCHS has been proposed because of the reports of four families with two affected children, because of mother-child transmission, and because of a recent report of a polyalanine expansion mutation in PHOX2b in a subset of CCHS subjects. We, therefore, studied genes pertinent to early embryologic development of the ANS including mammalian achaete-scute homolog-1 (MASH1), bone morphogenic protein-2 (BMP2), engrailed-1 (EN1), TLX3, endothelin converting enzyme-1 (ECE1), endothelin-1 (EDN1), PHOX2a, and PHOX2b in 67 probands with CCHS, and gender- and ethnicity-matched controls. No disease-defining mutations were identified in MASH1, BMP2, EN1, TLX3, ECE1, EDN1, or PHOX2a. The 65/67 CCHS probands (97%) were found to be heterozygous for the exon 3 polyalanine expansion mutation identified previously in PHOX2b. Further, there was an association between repeat mutation length and severity of the CCHS/ANSD phenotype. Of the two probands who did not carry the expansion mutation, one had a nonsense mutation in exon 3 which truncated the protein and the other had no mutation in PHOX2b but had a previously reported EDN3 frameshift point mutation. The polyalanine expansion mutation was not found in any of 67 matched controls. Of 54 available families (including 97 unaffected parents), whose child carried the PHOX2b mutation, 4 parents demonstrated mosaicism for an expansion mutation identical to that seen in the CCHS cases, suggesting that not all mutations in affected probands with unaffected parents are de novo. We also studied four women with CCHS who were heterozygous for the PHOX2b mutation, each with one child. Three of the four children were also affected and had the same mutation, demonstrating autosomal dominant inheritance of the mutation. Assay of the PHOX2b polyalanine repeat mutation represents a highly sensitive and specific technique for confirming the diagnosis of CCHS. Identification of the CCHS mutation will lead to clarification of the phenotype, allow for prenatal diagnosis for parents of CCHS probands and adults with CCHS in future pregnancies, and potentially direct intervention strategies for the treatment of CCHS.