Idiopathic congenital central hypoventilation syndrome: diagnosis and management. American Thoracic Society

Pediatric disorders with autonomic dysfunction: what role for PHOX2B?

Hirschsprung disease, neuroblastomas, and congenital central hypoventilation syndrome can occur in combination, and familial cases have been reported in all three conditions. This suggests variable expression of a single genetic abnormality as the common cause to these neural crest disorders. Because the PHOX2B gene is pivotal in the development of most relays of the autonomic nervous system, including all autonomic neural crest derivatives, it was considered a candidate gene for the above conditions. Recent studies have shown that 1) PHOX2B is the main disease-causing gene for congenital central hypoventilation syndrome, an autosomal dominant disorder with incomplete penetrance; 2) PHOX2B is the first gene for which germline mutations have been demonstrated to predispose to neuroblastoma; and 3) Hirschsprung disease was associated with an intronic single-nucleotide polymorphism of the PHOX2B gene in a case-control study. For clarifying the variable clinical expression of the autonomic nervous system dysfunction observed in neural crest disorders, international databases of clinical symptoms and molecular test results should be established. Furthermore, the development of genetic mouse models should help to improve our understanding of the molecular mechanisms underlying neural crest disorders.

Congenital central hypoventilation syndrome and Hirschsprung's disease in an extremely preterm infant

Congenital central hypoventilation syndrome with Hirschsprung's disease, also known as Haddad syndrome, is a rare disorder with a variable phenotypic severity. The underlying cause is thought to be an abnormality of neural crest development and/or migration. Surviving neonates can have generalized autonomic nervous system dysfunction. Recent reports have identified mutations in the PHOX2B gene in a significant number of patients with this disorder. Diagnosis and management of this disorder in the setting of extreme prematurity is difficult as the manifestations of failure to maintain breathing effort and failure to establish feeds overlap with the complications of prematurity. We describe an infant who had congenital central hypoventilation syndrome with Hirschsprung's disease and was delivered at 26 weeks' gestational age and had total aganglionosis of the bowel, failure to wean from ventilation, and a mutation in the PHOX2B gene.

Distinct pathogenetic mechanisms for PHOX2B associated polyalanine expansions and frameshift mutations in congenital central hypoventilation syndrome

Congenital central hypoventilation syndrome (CCHS) is a rare neurocristopathy characterized by absence of adequate autonomic control of respiration with decreased sensitivity to hypoxia and hypercapnia. Frameshift mutations and polyalanine triplet expansions in the coding region of PHOX2B have been identified in the vast majority of CCHS patients and a correlation between length of the expanded region and severity of CCHS has been reported. In this work, we have undertaken in vitro analyses aimed at identifying the pathogenetic mechanisms which underlie the effects of PHOX2B mutations in CCHS. According to the known role of this gene, a transcription factor expressed during autonomic nervous system development, we have tested the transcriptional activity of WT and mutant PHOX2B expression constructs on the regulatory regions of two target genes, DbetaH and PHOX2A. We observed that the two sets of mutations play different roles in the transcriptional regulation of these genes, showing a correlation between the length of polyalanine expansions and the severity of reduced transcriptional activity. In particular, although reduced transactivation due to polyalanine expansions may be caused by retention of the mutated protein in the cytoplasm or in the nuclear aggregates, frameshift mutations did not impair the PHOX2B nuclear income, suggesting a different mechanism through which they would exert the observed effects on target promoters. Moreover, the frameshift due to deletion of a cytosine residue seems to cause sequestration of the corresponding mutant PHOX2B in the nucleolar compartment.

FMRI responses to hyperoxia in congenital central hypoventilation syndrome

Congenital Central Hypoventilation Syndrome (CCHS) patients show partial retention of peripheral chemoreception despite impaired ventilatory responses to CO2 and hypoxia. The condition allows examination of central responses to hyperoxia, which minimizes afferent traffic from peripheral chemoreceptors. We used functional magnetic resonance imaging to assess blood oxygen level-dependent signals over the brain during a baseline and subsequent 2-min hyperoxia (100% O2) period in 14 CCHS and 15 control subjects. After partitioning gray matter and correcting for global effects, the images were analyzed using volume-of-interest time trends followed by repeated-measures ANOVA and conventional cluster analyses. Respiratory rates initially (first 20 s) fell in CCHS, but rose in control subjects; CCHS heart rate increased in the first minute, and then decreased in the second minute, as in controls, but with muted rise and extent of decline. Multiple sites within the cerebellum, midbrain, and pons responded similarly to the challenge in both groups. Response patterns differed early in the right amygdala, paralleling initial respiratory pattern deficits, and late in the right insula, concomitant with cardiac rate differences. Signals also differed between groups in the medial and anterior cingulate, hippocampus, head of caudate, and lentiform nuclei, as well as pontine and midbrain structures and regions within the superior temporal and inferior frontal cortical gyri. The findings emphasize that structures that can alter respiratory timing, such as the amygdala, and modulate sympathetic outflow, such as the right insula, are deficient in CCHS. Medullary and pontine areas targeted by PHOX2B expression are also affected.

Aberrant neural responses to cold pressor challenges in congenital central hypoventilation syndrome

Patients with congenital central hypoventilation syndrome (CCHS), a condition characterized by impaired ventilatory responses to chemoreceptor stimulation, do not show the normal increase in respiratory rate and respiratory-related heart rate variation to cold forehead stimulation, a challenge that bypasses central chemoreceptors. We hypothesized that a forehead cold pressor challenge would reveal abnormal neural response patterns, as assessed by functional magnetic resonance imaging, in brain regions that are responsible for the integration of cold afferent stimulation with respiratory and cardiovascular output in patients with CCHS. Primary sensory thalamic and cortical areas for the forehead showed diminished responses in 13 patients with CCHS (ventilator dependent during sleep but not waking, no Hirschsprung's disease) compared with 14 control subjects, despite initial signal changes in the cortex being similar in both groups. Cerebellar cortex and deep nuclei; basal ganglia; and middle to posterior cingulate, insular, frontal, and temporal cortices showed reduced signal rises in patients with CCHS. Areas within the frontal and anterior cingulate cortices exhibited marked signal declines in control subjects but little change in patients with CCHS. No response occurred in either group in the dorsal medulla, but medial and ventral medullary areas showed enhanced signals in patients with CCHS. The cold pressor stimulation did not recruit dorsal medullary sites that would be affected by PHOX2B (a mutation of which is associated with the syndrome) expression in either group but demonstrated deficient cerebellar and medial medullary influences that, by action on rostral sites, may underlie the loss of respiratory responses.

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.

PHOX2B genotype allows for prediction of tumor risk in congenital central hypoventilation syndrome

The Phox2b gene is necessary for autonomic nervous-system development. Phox2b-/- mice die in utero with absent autonomic nervous system circuits, since autonomic nervous system neurons either fail to form or degenerate. We first identified the Phox2b human ortholog, PHOX2B, as the gene underlying congenital central hypoventilation syndrome (CCHS, or Ondine curse), with an autosomal dominant mode of inheritance and de novo mutation at the first generation. We have subsequently shown that heterozygous mutations of PHOX2B may account for several combined or isolated disorders of autonomic nervous-system development--namely, tumors of the sympathetic nervous system (TSNS), such as neuroblastoma and late-onset central hypoventilation syndrome. Here, we report the clinical and molecular assessments of a cohort of 188 probands with CCHS, either isolated or associated with Hirschsprung disease and/or TSNS. The mutation-detection rate was 92.6% (174/188) in our series, and the most prevalent mutation was an in-frame duplication leading to an expansion of +5 to +13 alanines in the 20-alanine stretch at the carboxy terminal of the protein. Such findings suggest PHOX2B mutation screening as a simple and reliable tool for the diagnosis of CCHS, independent of the clinically variable phenotype. In addition, somatic mosaicism was detected in 4.5% of parents. Most interestingly, analysis of genotype-phenotype interactions strongly supports the contention that patients with CCHS who develop malignant TSNS will harbor either a missense or a frameshift heterozygous mutation of the PHOX2B gene. These data further highlight the link between congenital malformations and tumor predisposition when a master gene in development is mutated.

The French Congenital Central Hypoventilation Syndrome Registry: general data, phenotype, and genotype

OBJECTIVE

To analyze the main clinical features, genetic mutations, and outcomes of patients of the French Congenital Central Hypoventilation Syndrome (CCHS) Registry.

DESIGN

A country-wide cohort established throughout a long-term multicenter effort.

PATIENTS

Seventy French patients with CCHS (29 male patients and 41 female patients).

METHODS

The following items were analyzed: the most important moments of the disease course; the main clinical characteristics; associated pathologic conditions; management; clinical outcome; and genetic mutations.

RESULTS

An average of four new cases of CCHS per year was observed in the last 5 years. Thus, the incidence may be estimated to be 1 per 200,000 live births in France. The median age at diagnosis was 3.5 months (range, 0.5 to 15 months) before 1995 and < 2 weeks in the last 5 years (p = 0.01). CCHS occurred in isolation in 58 of 70 patients. In the remainder, it was associated with Hirschsprung disease (HSCR) [nine patients], Hirschsprung and neural crest tumor (two patients), and growth hormone deficiency (one patient). Among the 50 patients who lived beyond 1 year of age, all but one received nighttime ventilation, with 10 of them (20%) receiving it noninvasively. Three patients (6%) required daytime ventilatory support in addition to nighttime ventilation. The overall mortality rate was 38% (95% confidence interval [CI], 27 to 49%). The median age at death was 3 months (range, 0.4 months to 21 years). The 2-year mortality rate was greater in male patients than in female patients (p = 0.02; relative risk [RR], 2.71; 95% CI, 1.14 to 6.47) but was not affected by HSCR (p = 0.93; RR, 0.95; 95% CI, 0.28 to 3.2). The 43 patients who are currently alive (11 men; sex ratio, 0.4) have a mean age of 9 years (range, 2 months to 27 years). Among the 34 patients tested thus far, heterozygous mutations of the paired-like homeobox gene 2B (PHOX2B) gene were found in 31 patients (91%).

CONCLUSION

Our four major findings are the extreme rarity of CCHS, the improved recognition over time, the lack of effect of HSCR on the mortality rate, and the high frequency of PHOX2B mutations.

Short-term blood pressure and heart rate variability in congenital central hypoventilation syndrome (Ondine's curse)

The effect of CCHS (congenital central hypoventilation syndrome, or Ondine's curse) on short-term BP (blood pressure) and HR (heart rate) variability was evaluated in 16-year-old subjects presenting a form of CCHS requiring night ventilatory assistance. The 12 patients were compared with 12 age- and gender-matched healthy volunteers. Recordings were obtained during daytime while the subjects were breathing spontaneously. Continuous BP was measured with a Finapres® device in the supine, head-up tilt and standing positions. The manoeuvre of actively standing was also analysed. HR levels were elevated in CCHS subjects at supine rest (+23%) with a reduced HR overall variability (−88%). The low- and high-frequency components of HR variability were affected. BP levels were preserved at rest, but the manoeuvres demonstrated a limited capacity to elevate BP. There was no overshoot in BP during the manoeuvre of actively standing, and steady standing BP levels in patients were not higher than supine BP levels as usually observed in healthy controls. The spontaneous baroreflex sensitivity estimated using the sequence technique or the cross-spectral analysis fell in the patients to approx. one-third of the sensitivity estimated in the healthy controls whatever the position. This cardiovascular profile suggests a predominant vagal dysfunction with signs of vagal withdrawal and baroreflex failure, and relative preservation of the cardiac and vascular sympathetic function. It is likely that the impaired ontogeny of the visceral reflexes, considered now to cause CCHS syndrome, includes the baroreceptive pathway and mainly its vagal component.

Investigation of sleep disorders

Polysomnography or sleep study is the main investigation for paediatric sleep disorders. It involves the continuous and simultaneous recording of multiple physiological parameters evaluating sleep and respiration. It is most commonly used to diagnose obstructive sleep apnoea and to monitor nocturnal non-invasive ventilation requirements of children. Its role in other sleep related breathing disorders, narcolepsy and parasomnias is discussed.

Hypoxia reveals posterior thalamic, cerebellar, midbrain, and limbic deficits in congenital central hypoventilation syndrome

Congenital central hypoventilation syndrome (CCHS) patients show deficient respiratory and cardiac responses to hypoxia and hypercapnia, despite apparently intact arousal responses to hypercapnia and adequate respiratory motor mechanisms, thus providing a model to evaluate functioning of particular brain mechanisms underlying breathing. We used functional magnetic resonance imaging to assess blood oxygen level-dependent signals, corrected for global signal changes, and evaluated them with cluster and volume-of-interest procedures, during a baseline and 2-min hypoxic (15% O(2), 85% N(2)) challenge in 14 CCHS and 14 age- and gender-matched control subjects. Hypoxia elicited significant (P < 0.05) differences in magnitude and timing of responses between groups in cerebellar cortex and deep nuclei, posterior thalamic structures, limbic areas (including the insula, amygdala, ventral anterior thalamus, and right hippocampus), dorsal and ventral midbrain, caudate, claustrum, and putamen. Deficient responses to hypoxia included no, or late, changes in CCHS patients with declining signals in control subjects, a falling signal in CCHS patients with no change in controls, or absent early transient responses in CCHS. Hypoxia resulted in signal declines but no group differences in hypothalamic and dorsal medullary areas, the latter being a target for PHOX2B, mutations of which occur in the syndrome. The findings extend previously identified posterior thalamic, midbrain, and cerebellar roles for normal mediation of hypoxia found in animal fetal and adult preparations and suggest significant participation of limbic structures in responding to hypoxic challenges, which likely include cardiovascular and air-hunger components. Failing structures in CCHS include areas additional to those associated with PHOX2B expression and chemoreceptor sites.

Hypercapnic exposure in congenital central hypoventilation syndrome reveals CNS respiratory control mechanisms

Congenital central hypoventilation syndrome (CCHS) patients show impaired ventilatory responses and loss of breathlessness to hypercapnia, yet arouse from sleep to high CO2, suggesting intact chemoreceptor afferents. The syndrome provides a means to differentiate brain areas controlling aspects of breathing. We used functional magnetic resonance imaging to determine brain structures responding to inspired 5% CO2-95% O2 in 14 CCHS patients and 14 controls. Global signal changes induced by the challenge were removed on a voxel-by-voxel basis. A priori-defined volume-of-interest time trends (assessed with repeated measures ANOVA) and cluster analysis based on modeling each subject to a step function (individual model parameter estimates evaluated with t-test, corrected for multiple comparisons) revealed three large response clusters to hypercapnia distinguishing the two groups, extending from the 1) posterior thalamus through the medial midbrain to the dorsolateral pons, 2) right caudate nucleus, ventrolaterally through the putamen and ventral insula to the mid-hippocampus, and 3) deep cerebellar nuclei to the dorsolateral cerebellar cortex bilaterally. Smaller clusters and defined areas of group signal differences in the midline dorsal medulla, amygdala bilaterally, right dorsal-posterior temporal cortex, and left anterior insula also emerged. In most sites, early transient or sustained responses developed in controls, with little, or inverse change in CCHS subjects. Limbic and medullary structures regulating responses to hypercapnia differed from those previously shown to mediate loaded breathing ventilatory response processing. The findings show the significant roles of cerebellar and basal ganglia sites in responding to hypercapnia and the thalamic and midbrain participation in breathing control.

fMRI signal changes in response to forced expiratory loading in congenital central hypoventilation syndrome

Congenital central hypoventilation syndrome (CCHS) patients show impaired ventilatory responses to CO2 and hypoxia and reduced drive to breathe during sleep but retain appropriate breathing patterns in response to volition or increased exercise. Breath-by-breath influences on heart rate are also deficient. Using functional magnetic resonance imaging techniques, we examined responses over the brain to voluntary forced expiratory loading, a task that CCHS patients can perform but that results in impaired rapid heart rate variation patterns normally associated with the loading challenge. Increased signals emerged in control ( n = 14) over CCHS ( n = 13; ventilator dependent during sleep but not waking) subjects in the cingulate and right parietal cortex, cerebellar cortex and fastigial nucleus, and basal ganglia, whereas anterior cerebellar cortical sites and deep nuclei, dorsal midbrain, and dorsal pons showed increased signals in the patient group. The dorsal and ventral medulla showed delayed responses in CCHS patients. Primary motor and sensory areas bordering the central sulcus showed comparable responses in both groups. The delayed responses in medullary sensory and output regions and the aberrant reactions in cerebellar and pontine sensorimotor coordination areas suggest that rapid cardiorespiratory integration deficits in CCHS may stem from defects in these sites. Additional autonomic and perceptual motor deficits may derive from cingulate and parietal cortex aberrations.

Sudden infant death syndrome: case-control frequency differences at genes pertinent to early autonomic nervous system embryologic development

We have previously identified polymorphisms in the serotonin transporter gene promoter region and in intron 2 that were more common among sudden infant death syndrome (SIDS) cases compared with control subjects. To elucidate further the genetic profile that might increase an infant's vulnerability to SIDS, we focused on the recognized relationship between autonomic nervous system (ANS) dysregulation and SIDS. We therefore studied genes pertinent to early embryologic development of the ANS, including MASH1, BMP2, PHOX2a, PHOX2b, RET, ECE1, EDN1, TLX3, and EN1 in 92 probands with SIDS and 92 gender- and ethnicity-matched control subjects. Eleven protein-changing rare mutations were identified in 14 of 92 SIDS cases among the PHOX2a, RET, ECE1, TLX3, and EN1 genes. Only 1 of these mutations (TLX3) was identified in 2 of 92 control subjects. Black infants accounted for 10 of these mutations in SIDS cases and 2 control subjects. Four protein-changing common polymorphisms were identified in BMP2, RET, ECE1, and EDN1, but the allele frequency did not differ between SIDS cases and control subjects. However, among SIDS cases, the allele frequency for the BMP2 common polymorphism demonstrated ethnic differences; among control subjects, the allele frequency for the BMP2 and the ECE1 common polymorphisms also demonstrated ethnic differences. These data represent further refinement of the genetic profile that might place an infant at risk for SIDS.

Congenital central hypoventilation syndrome: not just another rare disorder

Congenital central hypoventilation syndrome (CCHS) is a rare syndrome, present from birth, and is defined as the failure of automatic control of breathing. Patients have absent or negligible ventilatory sensitivity to hypercapnia and hypoxaemia during sleep and wakefulness. Therefore, especially while asleep, children with CCHS experience progressive hypercapnia and hypoxaemia. They lack arousal responses and sensations of dyspnoea to the endogenous challenges of isolated hypercapnia and hypoxaemia and to the combined stimulus of hypercapnia and hypoxaemia. Patients with CCHS do not exhibit signs of respiratory distress when challenged with hypercarbia or hypoxia. The diagnosis is one of exclusion, ruling out any primary pulmonary, cardiac, metabolic or neurologic cause for central hypoventilation. CCHS is associated with other manifestations of autonomic nervous system dysfunction, including Hirschsprung's disease. All patients with CCHS require lifelong ventilatory support during sleep but some will be able to maintain adequate ventilation without assistance while awake once past infancy. However, some CCHS patients require ventilatory support for 24h/day. Modalities of home mechanical-assisted ventilation include positive pressure ventilation via tracheostomy, non-invasive positive pressure ventilation (bi-level ventilation), negative pressure ventilation and diaphragmatic pacers. Supplemental oxygen alone is inadequate treatment. With early diagnosis and adequate ventilatory support, these children can have good outcomes and lead productive lives.

Temporal trends of cardiac and respiratory responses to ventilatory challenges in congenital central hypoventilation syndrome

Congenital central hypoventilation syndrome (CCHS) patients exhibit respiratory deficits to ventilatory challenges, diminished breathing drive during sleep, and reduction of respiratory-related heart rate variation, but at least partially preserved peripheral chemoreception. We hypothesized that integration of afferent activity with respiratory motor output is deficient in CCHS, rather than chemoreceptor failure, and that examination of trends in heart and breathing rates and variabilities following ventilatory challenges may clarify the deficient mechanisms. Twelve children with CCHS and 12 age- and gender-matched control cases were subjected to hyperoxic hypercapnic, poikylocapnic hypoxic, and hyperoxic challenges while supine. Heart and respiratory rates and variabilities during 60-s baseline and 120-s challenge periods were assessed. Hypoxia and hypercapnia enhanced breathing rate in control subjects; in CCHS cases, the rise differed during hypercapnia and did not occur to hypoxia. Hyperoxia showed initial transient patterns in breathing rate that differed between groups. A heart rate increase to hypoxia and late decline to hyperoxia were muted in CCHS patients. In hypercapnia, heart rate followed similar rising patterns in both groups. Overall CCHS heart rate variability was lower in baseline and challenge periods, principally due to diminished respiratory-related variation, especially during hypercapnia. No heart rate variability group differences emerged in hypoxia, and only a late increase for CCHS cases developed in hyperoxia. The findings indicate retention of aspects of chemoreceptor sensitivity in CCHS cases. The heart rate alterations to ventilatory challenges suggest specific compensatory responses of a slower nature remain intact in CCHS, whereas other rapidly changing components are deficient.

Genetics and early disturbances of breathing control

Early disturbances in breathing control, including apneas of prematurity and apparently life-threatening events, account for some cases of sudden infant death syndrome and for a rare disorder called congenital central hypoventilation syndrome (CCHS). Data suggesting a genetic basis for CCHS have been obtained. Recently, we found heterozygous de novo mutations of the PHOX2B gene in 18 of 29 individuals with CCHS. Most mutations consisted of five to nine alanine expansions within a 20-residue polyalanine tract, probably resulting from nonhomologous recombination. Other mutations, generally inherited from one of the parents, in the coding regions of genes involved in the endothelin and RET signaling pathways and in the brain-derived-neurotrophic factor (BDNF) gene have been found in a few CCHS patients. Interestingly, all these genes are involved in the development of neural crest cells. Targeted disruption of these genes in mice has provided information on the pathophysiological mechanisms underlying CCHS. Despite the identification of these genes involved in breathing control, none of the genetically engineered mice developed to date replicate the full human CCHS respiratory phenotype. Recent insights into the genetic basis for CCHS may shed light on the genetics of other early disturbances in breathing control, such as apnea of prematurity and sudden infant death syndrome.

Sudden unexpected death and covert homicide in infancy

It is impossible to be certain, but it is estimated that each year in England and Wales there may be about 30-40 infant deaths from covert homicide, which represents about 10% of the current annual total of sudden unexpected deaths in infancy. This paper reviews the features that have been suggested as possible indicators of covert homicide, describes the difficulties in its identification and the need for better evidence, and emphasises the importance of thorough medical investigation of all sudden infant deaths.

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.

Sleep and breathing disturbances in infancy and early childhood

The nature of sleep-related breathing problems varies with age. Ventilatory function may be compromised at the level of the brainstem, the autonomic nerves, or the upper airway musculature. These disorders are state-dependent, being impacted by both rapid eye movement and non-rapid eye movement sleep, and also by the degree of maturation of the nervous system. Many are treatable. An understanding of the molecular basis of these disorders is just now becoming apparent.

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.

24-Hour BP in Children With Congenital Central Hypoventilation Syndrome

OBJECTIVE

To study circadian BP patterns in patients with congenital central hypoventilation syndrome (CCHS).

DESIGN

Case-control study.

SETTING

Teaching hospital in Paris, France.

PATIENTS

Eleven patients with CCHS (median age, 13 years; range, 6 to 18 years) and 11 sex- and height-matched control subjects.

INTERVENTION

None.

METHODS

Each subject underwent 24-h ambulatory BP monitoring. Oxygen saturation and end-tidal PCO(2) were monitored noninvasively. Polysomnography was performed to determine sleep times. All patients with CCHS received mechanical ventilation during sleep. Mean values for systolic BP (SBP) and diastolic BP (DBP) during wakefulness and sleep were analyzed. Nocturnal BP "dipping" was defined as the difference in mean SBP (and/or DBP) between wakefulness and sleep, divided by individual waking mean values. BP "dippers" were defined as subjects showing at least 10% nocturnal dipping.

RESULTS

Patients with CCHS had BPs in the low normal range of normative data. As compared to control subjects, patients with CCHS had lower BP during wakefulness (p = 0.003 and p = 0.016 for SBP and DBP, respectively), and higher BP during sleep (p = 0.016 and p = 0.002). Nocturnal BP dipping was abnormally reduced in patients with CCHS (p = 0.000). Ten of the 11 patients with CCHS were BP nondippers, compared to none of the control subjects.

CONCLUSION

The abnormal circadian BP pattern observed in children and adolescents with CCHS may be related to autonomic nervous dysfunction. Lifelong cardiovascular follow-up is recommended for patients with CCHS.

Genes modulating chemical breathing control: lessons from mutant animals

Genetic factors influence breathing control. Respiratory phenotypes of mutant mice may help to better understand these factors. Congenital central hypoventilation syndrome (CCHS) is a rare disorder defined as failure of chemical control of breathing causing central alveolar hypoventilation, especially during sleep. A genetic basis for CCHS is supported by several arguments, mainly the identification, in a few CCHS patients, of heterozygous mutations of genes contributing to neural crest cell development, namely, genes involved in the endothelin and c-ret pathways. Furthermore, plethysmography studies of the respiratory phenotypes of newborn heterozygous mutant mice have shown that genes in both pathways are involved in breathing control at birth. Nevertheless, no single gene mutation in newborn mice reproduces the human CCHS phenotype. Avenues for future research into the genetics of CCHS include (i) testing of mutant newborn mice for genes in other pathways and (ii) use of microarrays to identify gene clusters that should be associated with abnormal chemical breathing control.

Tracheostomy and home ventilation in children

The last 30 years have brought a significant emphasis on home care for ventilator-dependent children. While the movement was driven by the desire to minimize healthcare costs, the advancements in medical knowledge and technology, and the change in the perception of a ventilator-dependent child have offered a fertile environment for the development of programs that support the chronic care of ventilator-dependent children at home (N. Engl. J. Med. 309(21) (1983) 1319; J. Pediatr. 106(5) (1985) 850; N. Engl. J. Med. 310(17) (1984) 1126; JAMA 258(23) (1987) 3398). In addition, the advances in medical and nursing care have led to the steady increase in the number of children with chronic respiratory failure and development of multi-disciplinary teams experienced and dedicated to the care of these children. Another trend that has also contributed to the rise in the number of pediatric patients using long-term mechanical ventilation is the parental expectation of long-term survival of their child. This parental expectation continues to grow as the effect of long-term mechanical ventilation on quality of life and longer survival becomes more evident. The primary indication for use of home mechanical ventilation is chronic respiratory failure (CRF) as indicated by hypoxemia and or hypercapnia. CRF is considered to be a condition persisting for greater than 1 month and requiring mechanical ventilation during part or all of the day to provide adequate gas exchange for the support of vital function (Chest 103(5) (1993) 1463).

Exclusion of RNX as a major gene in congenital central hypoventilation syndrome (CCHS, Ondine's curse)

Congenital central hypoventilation syndrome (CCHS) is a rare condition for which segregation analyses have suggested genetic factors. The respiratory phenotype of Rnx knock-out mice together with the Rnx expression at the brainstem level prompted us to consider the RNX gene as a candidate for CCHS in human. The screening of the RNX gene in a series of 25 patients with CCHS did not reveal any significant nucleotide variation. We therefore conclude that RNX is not a major gene for CCHS in human.

Mutational analysis of the RNX gene in congenital central hypoventilation syndrome

Congenital central hypoventilation syndrome (CCHS) is a rare syndrome characterized by failure of autonomic respiratory control, often presenting with other dysfunctions of the autonomic nervous system. Segregation analysis suggested a complex model of inheritance with a major locus involved. Disruption of the Rnx gene, a member of the Hox11 family of homeobox genes, in embryonic stem cells produced mice showing a phenotype similar to CCHS. Based on this observation, we have carried out mutation screening of the RNX gene in a set of 13 patients affected with CCHS, 2 of whom showing association with Hirschsprung disease. Single-strand conformational polymorphism analysis and direct sequencing of the whole coding portion of the RNX gene and of 1,311 bp of 5' flanking region were performed. No sequence variant was identified, with the exception of a private nucleotide change at position -874 bp from the ATG codon in two siblings affected with isolated CCHS. A functional test, performed by using the luciferase gene reporter system, has not shown any significant difference in the activity of the promoter region carrying this latter nucleotide change with respect to the wild-type allele. We conclude that RNX, and presumably its expression, are not altered in our index cases of CCHS.

Idiopathic congenital central hypoventilation syndrome: the next generation

Idiopathic congenital central hypoventilation syndrome (CCHS) is a rare disorder in which affected children have a decreased sensitivity of their respiratory centers to hypercarbia and hypoxia, as well as evidence for generalized autonomic nervous system dysfunction. A genetic origin has long been hypothesized for CCHS. Previous reports of the syndrome among twins, siblings, and half siblings, as well as an established association with Hirschsprung disease and neural crest tumors support this genetic hypothesis. Here, we present the first reported offspring born to four women diagnosed with idiopathic CCHS. Their children display a spectrum of abnormalities with one child being diagnosed with CCHS, one child with recurrent apparent life threatening events, one infant born prematurely with severe chronic lung disease and diminished ventilatory responses to carbon dioxide, and one infant who is apparently healthy with no clinical manifestations suggestive of disordered respiratory control to date. Two and potentially three of these patients illustrate transmission of altered respiratory control by CCHS patients into the next generation, furthering the evidence that CCHS is part of a broadly based inherited syndrome of autonomic nervous system dysfunction.

Mother-daughter transmission of congenital central hypoventilation syndrome

The cause of congenital central hypoventilation syndrome (CCHS) is unknown, but a genetic etiology is strongly suspected. We report a 25-year-old woman with CCHS (no Hirschsprung's disease) who gave birth to a daughter who also has CCHS. This suggests a dominant mode of inheritance for CCHS in this family. Pregnancy can be associated with physiologic challenges in CCHS. The increase in endogenous progesterone may stimulate breathing and may possibly improve symptoms of hypoventilation. Although this patient did not have any worsening in symptoms, her hyperoxic hypercapnic rebreathing ventilatory response was not different when pregnant versus when not pregnant. Ventilatory support for the patient was successfully managed with diaphragm pacing throughout the pregnancy without the need to adjust settings, despite the enlarged abdomen during pregnancy. We conclude that CCHS may be an inherited disorder. Increased endogenous progesterone during pregnancy has no effect on the ventilatory response, and diaphragm pacing can successfully provide adequate ventilation throughout pregnancy.

Abnormal esophageal motility in children with congenital central hypoventilation syndrome

BACKGROUND & AIMS

Congenital central hypoventilation syndrome, an unexplained disorder of the central control of breathing that may reflect widespread dysfunction of brainstem structures, is regarded as a form of neuro cristopathy. Because swallowing-induced peristalsis is centrally controlled and depends on neural crest-derived esophageal innervation, we looked for esophageal dysmotility in patients with congenital central hypoventilation syndrome.

METHODS

Seven patients without dysphagia or any other upper gastrointestinal tract symptoms were studied prospectively (5 girls and 2 boys; median age, 14 years; range, 11-18 years). They were compared with 7 age- and sex-matched controls. Esophageal manometry was performed using a low-compliance infusion system and the station pull-through technique. At least 10 wet swallows were analyzed in each subject.

RESULTS

Pressure wave propagation was abnormal in all 7 patients (median percentage of swallows propagated, 18%, and range, 0-66; controls, 90% and 80-100; P < 0.001). Lower esophageal sphincter relaxation was abnormal in 5 patients (patients, 73% and 53-100; controls, 95% and 90-100; P = 0.01). In 2 patients, lower esophageal sphincter pressure was above the 95th percentile of control values.

CONCLUSIONS

These abnormalities are strong evidence of lower esophageal dysfunction in congenital central hypoventilation syndrome. We speculate that the underlying mechanism may be dysfunction of the central structures that control swallowing.

Idiopathic congenital central hypoventilation syndrome: evaluation of brain-derived neurotrophic factor genomic DNA sequence variation

Idiopathic congenital central hypoventilation syndrome (CCHS) is an unique disorder of respiratory control, occurring in association with Hirschsprung disease (HSCR), tumors of neural crest origin, and symptoms of autonomic nervous system dysfunction (ANSD). CCHS is thought to be genetic in origin based upon 1) affected sib pairs, 2) genetic analysis, and 3) identification of genetic mutations in both HSCR and CCHS patients. Because these mutations have been found in but a few cases of CCHS, exploration of other candidate genes has continued. Brain-derived neurotrophic factor (BDNF) represents a potential candidate gene to consider because of altered respiratory control in the BDNF knock-out mouse model and localization to the enteric nervous system in human tissue. The objective of this study was to determine the frequency of BDNF mutations among 19 children with CCHS (five with HSCR) compared to 40 unaffected unrelated controls. Using the known genomic DNA sequence for BDNF, polymerase chain reaction (PCR)-amplified genomic DNA was analyzed by standard sequencing methods. A discrete mutation was identified in one of 19 children with isolated CCHS and the unaffected father. Specifically, an isoleucine was substituted for a threonine or serine in the amino acid sequence. Absence of this mutation in 40 controls confirmed that this mutation was likely not a common polymorphism. These data further support a genetic basis for CCHS, though mutations of BDNF are not consistent in this disorder.

Congenital central hypoventilation syndrome associated with Hirschsprung's disease and neuroblastoma: case of multiple neurocristopathies

We report on a male infant with the rare combined occurrence of congenital central hypoventilation syndrome (CCHS or Ondine's curse), Hirschsprung's disease (HD), and neuroblastoma. Current therapeutical options leave no doubt that children with isolated forms of CCHS, HD, or neuroblastoma must be treated, but management decisions and the ethical dilemma become more difficult with the presence of multiple neurocristopathies. Our patient was dependent on mechanical ventilation and total parenteral nutrition, when a neuroblastoma was diagnosed at age 5 months. We initiated an attempt at curative chemotherapy. The tumor failed to respond to recommended chemotherapeutic regimens, and the patient died at 11 months of age. We emphasize the importance of screening CCHS patients for associated illnesses such as neuroblastoma and ganglioneuroblastoma at time of diagnosis.

Chemoreceptive mechanisms elucidated by studies of congenital central hypoventilation syndrome

Humans born with the condition of central hypoventilation during non-rapid eye movement sleep, termed congenital central hypoventilation syndrome (CCHS), invariably have absent or greatly diminished central hypercapnic ventilatory chemosensitivity. Genetic and pathological studies of CCHS may enable identification of the genes or areas of the central nervous system involved in the syndrome and thus implicated in central hypercapnic ventilatory chemosensitivity. Functional studies of CCHS permit a more quantitative assessment of the importance of ventilatory chemosensitivity in the regulation of breathing during wakefulness and sleep. The experimental evidence suggests that central hypercapnic ventilatory chemosensitivity is crucial in regulating alveolar ventilation during non-rapid eye movement sleep but not during rapid eye movement sleep or during many of the behaviors occurring during wakefulness. Presumably, other neural drives to breathe supervene to enable adequate ventilation. However, although physiological studies in CCHS subjects have been greatly instructive, their accurate interpretation will have to await future determination of the potential genetic and/or neuroanatomic basis of the syndrome.

Case/control family study of autonomic nervous system dysfunction in idiopathic congenital central hypoventilation syndrome

Children with idiopathic congenital central hypoventilation syndrome (CCHS) have a complex phenotype consistent with an imbalance of the autonomic nervous system (ANS). Since CCHS may be genetic in origin, we hypothesized that relatives of individuals with CCHS may exhibit symptoms of ANS dysfunction (ANSD), albeit in a milder form. We tested this hypothesis by assessing aspects of ANS function in relatives of CCHS cases vs. relatives of matched controls with a scripted questionnaire. Only those 35 symptoms of ANSD exhibited by > or =5% of the CCHS cases were included in the analysis as the basis for determining ANSD affection status. Two different arbitrary ANSD affection status definitions are presented in detail: any case, control, or relative with positive findings (1) in two or more symptoms, or (2) in two or more systems. The subjects included in the analysis totaled 2,353, including 56 CCHS cases, 56 age-, gender-, and race-matched controls, and their families. Under each of the two arbitrary ANSD affection statuses, CCHS cases and parents of cases were more likely to be affected than controls and parents of controls (P < 0.001 for both comparisons), 16% of the CCHS siblings had the ANSD phenotype with two or more symptoms, compared to 4% of control siblings (P = 0.03). Aunts and uncles of the CCHS cases were also significantly more likely to have two or more ANSD symptoms than were aunts and uncles of the controls (P= 0.009). These results support our hypothesis and also indicate that relatives of the CCHS cases tended to manifest a milder spectrum of ANSD, with fewer systems and/or fewer symptoms than the cases.

Genetic segregation analysis of autonomic nervous system dysfunction in families of probands with idiopathic congenital central hypoventilation syndrome

Idiopathic congenital central hypoventilation syndrome (CCHS) is a very rare syndrome with major respiratory complications. Hypothesizing that CCHS is the most severe manifestation of general autonomic nervous system dysfunction (ANSD), we applied a case-control family study design to investigate the genetics of ANSD. Fifty-two probands with CCHS were identified, as well as 52 age-, race-, and gender-matched controls. ANSD phenotypic features were characterized in the cases, controls, and their family members. Our earlier studies found that most ANSD symptoms were more likely in CCHS cases and their relatives than in controls and their relatives (P < 0.05). The goal of the current study was to determine if the familiality of ANSD was consistent with a genetic pattern. We performed major locus segregation analysis of ANSD utilizing regressive models. CCHS probands were assumed to be affected; controls and relatives were designated as affected if they had two or more relevant symptoms. The hypothesis of "no transmission and no familial effects" was rejected in both case and control families. Case families were consistent with transmission of a major effect; control families were not (the difference in the pattern of results was significant, P < 0.0001). In the total data set, the best-fitting model was codominant Mendelian inheritance of a major gene for ANSD. These case-control family studies support our hypothesis that CCHS is the most severe manifestation of a general ANSD, with a family pattern consistent with Mendelian transmission, and demonstrate the potential utility of the approach to studies of other, similarly intractable disorders.

Sleep-disordered breathing in children

Sleep-disordered breathing, particularly the obstructive sleep apnea syndrome, is common during childhood. Complications include neurocognitive deficits, growth failure, and pulmonary hypertension. Nevertheless, sleep-disordered breathing is often unrecognized in children. New syndromes, such as the upper airway resistance syndrome, have recently been described. Polysomnography is invaluable for the evaluation of sleep-disordered breathing. Advances in diagnosis and management can alleviate much of the morbidity previously associated with sleep-related respiratory disorders.

Cardiac rhythm disturbances among children with idiopathic congenital central hypoventilation syndrome

The objective of this study was to determine whether subjects with congenital central hypoventilation syndrome (CCHS) had an increased frequency of cardiac arrhythmias and decreased heart rate variability when compared to subjects without a known deficit in control of breathing, and that these abnormalities would be exaggerated by anesthesia. Continuous ambulatory Holter recordings were obtained in patients with CCHS and compared to two otherwise healthy control groups without a deficit in control of breathing: one with an intact airway (n = 11) and a second group with a tracheostomy (n = 6). Holter recordings were obtained before, during (under general anesthesia), and after bronchoscopy. Fourteen children with CCHS (age: 9.3 +/- 4.4 years mean +/- S.D.) were studied, and 7 underwent bronchoscopy. Seventeen control children were studied (age 6.6 +/- 3.6 years): 11 without a tracheostomy, and 6 with a tracheostomy who also underwent bronchoscopy. Maximum heart rate during baseline recording was significantly lower in the CCHS subjects as compared to controls (P = 0.0001). At baseline the difference in the number of arrhythmias/24 hr/subject in all CCHS vs. all control subjects was significant (P = 0.0002); for the subjects who had bronchoscopy, CCHS vs. control, the difference was also significant (P = 0.03). In addition, there was a significant decrease in the number of events/24 hr/subject among the CCHS subjects between baseline and post-bronchoscopy (P = 0.0288). The predominant arrhythmias were sinus bradycardia and transient asystole. The longest asystole in a CCHS subject was 6.50 sec, and in a control subject, 1.42 sec (at baseline the means of the longest asystole were 2.69 +/- 1.4 vs. 1.24 +/- 0.13; P = 0.003 in the CCHS vs. control groups). Other indices of heart rate variability were significantly reduced in the CCHS subjects (P < 0.05). These results substantiate our hypothesis that subjects with CCHS have more arrhythmias than controls, an increased frequency of bradyarrhythmias, and decreased cyclical sinus arrhythmia.

Use of genetic models in respiratory neurobiology and sleep

In this review, two issues are highlighted: 1) the difficulties that can form major hurdles in trying to understand a disease or a fundamental biologic process at the genetic and molecular level and 2) the potential opportunities that genetic models such as the Drosophila or c-elegans can provide in answering clinically or biologically relevant questions. This review also lists in some detail the areas in which these models have been helpful and successes have been scored. For such models to be used, however, requires the "dissection" of a biologic or a disease process into a tractable phenotype that can be assayed in a genetic model and have relevant and interpretable conclusions. The hope is that questions pertaining to sleep, arousal, respiratory neurobiology, and their disorders can be formulated in such a way to be addressed in models that can lend themselves to very exciting discoveries.

Novel insights into congenital hypoventilation syndrome

Congenital central hypoventilation syndrome (CCHS) is a rare and unique condition that may prompt unparalleled approaches to the discovery of genes involved in development of cardiorespiratory control and gas exchange homeostasis. Its higher risk of recurrence in families and its association with Hirschsprung's disease suggest that an underlying genetic mechanism is involved. However, screening for mutations of the receptor tyrosine kinase RET and endothelin 3 has revealed only occasional patients affected by these mutations, therefore suggesting that CCHS may result from disruption of more than a single gene. In recent years, three principal issues have become apparent: 1) the autonomic nervous system is involved universally in CCHS cases, albeit to a varying extent; 2) the use of novel functional imaging approaches incorporating refined stimulus paradigms may provide essential research and clinical insights into localization and assessment of neural sites underlying the phenotypic expression of this syndrome; and 3) efforts to transition patients' nocturnal respiratory support to a noninvasive ventilatory modality should be critically evaluated and pursued, when appropriate, to improve the quality of life for patients and families.