A respiratory/Hirschsprung phenotype in a three-generation family associated with a novel pathogenic PHOX2B splice donor mutation.

BACKGROUND: Mutations in the PHOX2B gene cause congenital central hypoventilation syndrome (CCHS), a rare autonomic nervous system dysfunction disorder characterized by a decreased ventilatory response to hypercapnia. Affected subjects develop alveolar hypoventilation requiring ventilatory support particularly during the non-REM phase of sleep. In more severe cases, hypoventilation may extend into wakefulness. CCHS is associated with disorders characterized by the defective migration/differentiation of neural crest derivatives, including aganglionic megacolon or milder gastrointestinal phenotypes, such as constipation. Most cases of CCHS are de novo, caused by heterozygosity for polyalanine repeat expansion mutations (PARMs) in exon 3. About 10% of cases are due to heterozygous non-PARM missense, nonsense or frameshift mutations. METHODS: We describe a three-generation Maltese-Caucasian family with a variable respiratory/Hirschsprung phenotype, characterized by chronic constipation, three siblings with Hirschsprung disease necessitating surgery, chronic hypoxia, and alveolar hypoventilation requiring non-invasive ventilation. RESULTS: The sequencing of PHOX2B revealed a novel heterozygous c.241+2delT splice variant in exon 1 that segregates with the CCHS/Hirschsprung phenotype in the family. The mutation generates a non-functional splice site with a deleterious effect on protein structure and is pathogenic according to ACMG P VS1, PM2, and PP1 criteria. CONCLUSION: This report is significant as no PHOX2B splice-site mutations have been reported. Additionally, it highlights the variability in clinical expression and disease severity of non-PARM mutations.

Causative and common PHOX2B variants define a broad phenotypic spectrum.

Paired Like homeobox 2B (PHOX2B) is a gene crucial for the differentiation of the neural lineages of the autonomic nervous system (ANS), whose coding mutations cause congenital central hypoventilation syndrome (CCHS). The vast majority of PHOX2B mutations in CCHS is represented by expansions of a polyalanine region in exon 3, collectively defined PARMs (PolyAlanine Repeat Mutations), the minority being frameshift, missense and nonsense mutations, defined as NPARMs (Non-PARMs). While PARMs are nearly exclusively associated with isolated CCHS, most of NPARMs is detected in syndromic CCHS, presenting with neuroblastoma and/or Hirschsprung disease. More recently, evidence of a complex role of PHOX2B in the pathogenesis of a wider spectrum of ANS disorders has emerged. Indeed, common and hypomorphic PHOX2B variants, including synonymous, polyalanine-contractions, gene deletions may influence the occurrence of either apparent life-threatening event (ALTE), Sudden Infant Death Syndrome (SIDS), neuroblastoma, or isolated HSCR, likely through small effects on PHOX2B expression levels. After an introduction to the role of PHOX2B in the ANS development, causative mutations, common variants, and gene expression deregulation of the PHOX2B gene are discussed, though the involvement of synonymous variants and contractions requires further confirmations with respect to ANS disorders and molecular mechanisms underlying the PHOX2B phenotypic heterogeneity.

Atypical presentations associated with non-polyalanine repeat PHOX2B mutations.

Congenital central hypoventilation syndrome (CCHS) is a disorder of ventilatory control and autonomic dysregulation that can be caused by mutations in the paired-like homeobox 2B (PHOX2B) gene. The majority of CCHS cases are caused by polyalanine repeat mutations (PARMs) in PHOX2B; however, in rare cases, non-polyalanine repeat mutations (NPARMs) have been identified. Here, we report two patients with NPARMs in PHOX2B. Patient 1 has a mild CCHS phenotype seen only on polysomnogram, which was performed for desaturations and stridor following a bronchiolitis episode, and characterized by night-time hypoventilation and a history of ganglioneuroblastoma. She carried a novel de novo missense variant, p.R102S (c.304C > A), in exon 2. Patient 2 has an atypical CCHS phenotype including micrognathia, gastroesophageal reflux, stridor, hypopnea, and intermittent desaturations. Sleep study demonstrated that Patient 2 had daytime and night-time hypercarbia with obstructive sleep apnea, requiring tracheostomy. On PHOX2B sequencing, she carried a recently identified nonsense variant, p.Y78* (c.234C > G), in exon 1. In summary, we present two patients with CCHS and identified NPARMs in PHOX2B who have distinct differences in phenotype severity, further elucidating the range of clinical outcomes in CCHS and illustrating the necessity of considering PHOX2B mutations when encountering atypical CCHS presentations.

Inhalational Anesthetics Induce Neuronal Protein Aggregation and Affect ER Trafficking.

Anesthetic agents have been implicated in the causation of neurological and cognitive deficits after surgery, the exacerbation of chronic neurodegenerative disease, and were recently reported to promote the onset of the neurologic respiratory disease Congenital Central Hypoventilation Syndrome (CCHS), related to misfolding of the transcription factor Phox2B. To study how anesthetic agents could affect neuronal function through alterations to protein folding, we created neuronal cell models emulating the graded disease severity of CCHS. We found that the gas anesthetic isoflurane and the opiate morphine potentiated aggregation and mislocalization of Phox2B variants, similar to that seen in CCHS, and observed transcript and protein level changes consistent with activation of the endoplasmic reticulum (ER) unfolded protein response. Attenuation of ER stress pathways did not result in a correction of Phox2B misfolding, indicating a primary effect of isoflurane on protein structure. We also observed that isoflurane hindered the folding and activity of proteins that rely heavily on ER function, like the CFTR channel. Our results show how anesthetic drugs can alter protein folding and induce ER stress, indicating a mechanism by which these agents may affect neuronal function after surgery.

Nonsense pathogenic variants in exon 1 of PHOX2B lead to translational reinitiation in congenital central hypoventilation syndrome.

Pathogenic variants in PHOX2B lead to congenital central hypoventilation syndrome (CCHS), a rare disorder of the nervous system characterized by autonomic dysregulation and hypoventilation typically presenting in the neonatal period, although a milder late-onset (LO) presentation has been reported. More than 90% of cases are caused by polyalanine repeat mutations (PARMs) in the C-terminus of the protein; however non-polyalanine repeat mutations (NPARMs) have been reported. Most NPARMs are located in exon 3 of PHOX2B and result in a more severe clinical presentation including Hirschsprung disease (HSCR) and/or peripheral neuroblastic tumors (PNTs). A previously reported nonsense pathogenic variant in exon 1 of a patient with LO-CCHS and no HSCR or PNTs leads to translational reinitiation at a downstream AUG codon producing an N-terminally truncated protein. Here we report additional individuals with nonsense pathogenic variants in exon 1 of PHOX2B. In vitro analyses were used to determine if these and other reported nonsense variants in PHOX2B exon 1 produced N-terminally truncated proteins. We found that all tested nonsense variants in PHOX2B exon 1 produced a truncated protein of the same size. This truncated protein localized to the nucleus and transactivated a target promoter. These data suggest that nonsense pathogenic variants in the first exon of PHOX2B likely escape nonsense mediated decay (NMD) and produce N-terminally truncated proteins functionally distinct from those produced by the more common PARMs.

Sleep-disordered breathing and its management in children with achondroplasia.

Sleep-disordered breathing is a common feature in children with achondroplasia. The aim of our study was to review the poly(somno)graphic (P(S)G) findings and consequent treatments in children with achondroplasia followed in the national reference center for skeletal dysplasia. A retrospective review of the clinical charts and P(S)G of 43 consecutive children (mean age 3.9 ± 3.5 years) with achondroplasia seen over a period of 2 years was performed. Twenty four (59%) children had obstructive sleep apnea (OSA). Thirteen children had an obstructive apnea-hypopnea index (OAHI) < 5/hr, four had an OAHI between 5 and 10/hr, and seven had an OAHI ≥ 10/hr. Ten of the 15 children who had previous upper airway surgery still had an abnormal P(S)G. All the patients with an AHI ≥ 10/hr were under 7 years of age and none had a prior tonsillectomy. The children who underwent adeno-tonsillectomy, coupled in most cases with turbinectomy, were significantly older (mean age 7.5 ± 3.5 vs. 3.5 ± 1.7 years old, P = 0.015) and had significantly better P(S)G results than those who underwent only adeno-turbinectomy. No correlation was observed between the mean AHI value at the baseline P(S)G and the type of academic course (standard, supported or specialized). In conclusion, OSA is common in children with achondroplasia. The observation of a reduced prevalence of OSA after (adeno-)tonsillectomy is in favor of this type of surgery when possible.

Association between central sleep apnea and left ventricular structure: the Multi-Ethnic Study of Atherosclerosis.

We assessed whether the presence of central sleep apnea is associated with adverse left ventricular structural changes. We analysed 1412 participants from the Multi-Ethnic Study of Atherosclerosis who underwent both overnight polysomnography and cardiac magnetic resonance imaging. Subjects had been recruited 10 years earlier when free of cardiovascular disease. Our main exposure is the presence of central sleep apnea as defined by central apnea-hypopnea index = 5 or the presence of Cheyne-Stokes breathing. Outcome variables were left ventricular mass/height, left ventricular ejection fraction, and left ventricular mass/volume ratio. Multivariate linear regression models adjusted for age, gender, race, waist circumference, tobacco use, hypertension, and the obstructive apnea-hypopnea index were fit for the outcomes. Of the 1412 participants, 27 (2%) individuals had central sleep apnea. After adjusting for covariates, the presence of central sleep apnea was significantly associated with elevated left ventricular mass/volume ratio (ß = 0.11 ± 0.04 g mL-1 , P = 0.0071), an adverse cardiac finding signifying concentric remodelling.

Oncologic Phenotype of Peripheral Neuroblastic Tumors Associated With PHOX2B Non-Polyalanine Repeat Expansion Mutations.

BACKGROUND: Germline non-polyalanine repeat expansion mutations in PHOX2B (PHOX2B NPARM) predispose to peripheral neuroblastic tumors (PNT), frequently in association with other neurocristopathies: Hirschsprung disease (HSCR) or congenital central hypoventilation syndrome (CCHS). Although PHOX2B polyalanine repeat expansions predispose to a low incidence of benign PNTs, the oncologic phenotype associated with PHOX2B NPARM is still not known in detail. METHODS: We analyzed prognostic factors, treatment toxicity, and outcome of patients with PNT and PHOX2B NPARM. RESULTS: Thirteen patients were identified, six of whom also had CCHS and/or HSCR, one also had late-onset hypoventilation with hypothalamic dysfunction (LO-CHS/HD), and six had no other neurocristopathy. Four tumours were "poorly differentiated," and nine were differentiated, including five ganglioneuromas, three ganglioneuroblastomas, and one differentiating neuroblastoma, hence illustrating that PHOX2B NPARM are predominantly associated with differentiating tumors. Nevertheless, three patients had stage 4 and one patient had stage 3 disease. Segmental chromosomal alterations, correlating with poor prognosis, were found in all the six tumors analyzed by array-comparative genomic hybridization. One patient died of tumor progression, one is on palliative care, one died of hypoventilation, and 10 patients are still alive, with median follow-up of 5 years. CONCLUSIONS: Based on histological phenotype, our series suggests that heterozygous PHOX2B NPARM do not fully preclude ganglion cell differentiation in tumors. However, this tumor predisposition syndrome may also be associated with poorly differentiated tumors with unfavorable genomic profiles and clinically aggressive behaviors. The intrafamilial variability and the unpredictable tumor prognosis should be considered in genetic counseling.

Is MRI Necessary in the Evaluation of Pediatric Central Sleep Apnea?

OBJECTIVES: (1) To determine the prevalence of central nervous system (CNS) pathology identified on head magnetic resonance imaging (MRI) scans in children with central sleep apnea (CSA); (2) to assess the yield of MRI in evaluation of CSA; and (3) to identify factors that predict CNS pathology in children with CSA. STUDY DESIGN: Case series with chart review. SETTING: Tertiary children's hospital. SUBJECTS AND METHODS: A chart review was conducted over 12 years. Patients 6 months to 18 years of age who underwent head MRI for evaluation of CSA were included. CSA was diagnosed on polysomnogram as central apnea index >1. RESULTS: Forty children were included in the CSA group. Twenty-two patients were male, and the mean age was 60 ± 41.5 months. The mean central apnea index was 3.8 ± 1.9, while the mean obstructive apnea hypopnea index was 3.4 (interquartile range, 0.7-3.8). Eighteen percent (7 of 40) of children with CSA had evidence of CNS pathology on MRI, with the most common finding (n = 3) being arachnoid cyst. Children with CSA who had gastroesophageal reflux disease or abnormal neurologic examinations were more likely to have CNS pathology. Other factors, such as prematurity, did not improve the yield of MRI in children with CSA. CONCLUSIONS: While routine evaluation of children with elevated central apnea index by MRI is not indicated, providers should consider neuroimaging in children with CSA and abnormal neurologic examination findings or gastroesophageal reflux disease. Further research is necessary to identify other tests with improved diagnostic yield for evaluation of pediatric CSA.

Brainstem involvement as a cause of central sleep apnea: pattern of microstructural cerebral damage in patients with cerebral microangiopathy.

BACKGROUND: The exact underlying pathomechanism of central sleep apnea with Cheyne-Stokes respiration (CSA-CSR) is still unclear. Recent studies have demonstrated an association between cerebral white matter changes and CSA. A dysfunction of central respiratory control centers in the brainstem was suggested by some authors. Novel MR-imaging analysis tools now allow far more subtle assessment of microstructural cerebral changes. The aim of this study was to investigate whether and what severity of subtle structural cerebral changes could lead to CSA-CSR, and whether there is a specific pattern of neurodegenerative changes that cause CSR. Therefore, we examined patients with Fabry disease (FD), an inherited, lysosomal storage disease. White matter lesions are early and frequent findings in FD. Thus, FD can serve as a "model disease" of cerebral microangiopathy to study in more detail the impact of cerebral lesions on central sleep apnea. PATIENTS AND METHODS: Genetically proven FD patients (n = 23) and age-matched healthy controls (n = 44) underwent a cardio-respiratory polysomnography and brain MRI at 3.0 Tesla. We applied different MR-imaging techniques, ranging from semiquantitative measurement of white matter lesion (WML) volumes and automated calculation of brain tissue volumes to VBM of gray matter and voxel-based diffusion tensor imaging (DTI) analysis. RESULTS: In 5 of 23 Fabry patients (22%) CSA-CSR was detected. Voxel-based DTI analysis revealed widespread structural changes in FD patients when compared to the healthy controls. When calculated as a separate group, DTI changes of CSA-CSR patients were most prominent in the brainstem. Voxel-based regression analysis revealed a significant association between CSR severity and microstructural DTI changes within the brainstem. CONCLUSION: Subtle microstructural changes in the brainstem might be a neuroanatomical correlate of CSA-CSR in patients at risk of WML. DTI is more sensitive and specific than conventional structural MRI and other advanced MR analyses tools in demonstrating these abnormalities.

Prognostic impact of sleep disordered breathing and its treatment in heart failure: an observational study.

AIMS: Sleep disordered breathing (SDB) may contribute to disease progression in patients with chronic heart failure (CHF). The objective of this observational study was to evaluate whether SDB is a risk factor for mortality in CHF patients and whether this risk can be attenuated by treatment with positive airway pressure (PAP). METHODS AND RESULTS: We studied 296 CHF patients (median left ventricular ejection fraction 33%) who underwent in-lab polysomnography between January 2002 and December 2009. We compared (i) mortality between patients with severe SDB [apnoea-hypopnoea index (AHI) ≥ 22.5 h(-1)] vs. those without severe SDB (AHI < 22.5 h(-1)) and (ii) evaluated the impact of PAP treatment on mortality in those with severe SDB. After accounting for significant confounding factors (age, NYHA class, cause of CHF, diabetes, and PAP treatment), patients with severe SDB (n= 176) had a 2.0-fold increased hazard ratio for death compared with those without severe SDB [95% confidence interval (CI) 1.1-3.5, P= 0.023]. In an adjusted on-treatment analysis of the group with severe SDB, mortality was significantly less in patients using PAP (18%) compared with those with untreated SDB (52%; hazard ratio 0.4, 95% CI 0.2-0.6, P= 0.001). Mortality in the PAP-treated group was lower compared with the untreated group at any time-point of the follow-up period. CONCLUSION: The presence of severe SDB in CHF patients constitutes a significantly increased risk for death, independent of established risk factors. In CHF patients with SDB, use of PAP therapy was associated with a decreased mortality rate at any time point of the follow-up, suggesting that PAP can be safely used in such patients.

Redução da prevalência de apneia central em pacientes com insuficiência cardíaca sob uso de betabloqueador / Reducción de la prevalencia de apnea central en pacientes con insuficiencia cardiaca bajo uso de betabloqueante / Reduction of central sleep apnea in heart failure patients with beta-blockers therapy

FUNDAMENTO: As apneias do sono são doenças frequentes em portadores de insuficiência cardíaca (IC). Estimativas da era pré-betabloqueador (BB) apontam para uma prevalência de 45 por cento de apneias centrais nestes pacientes. OBJETIVO: Avaliar a influência dos BB na prevalência das apneias centrais e sua interferência na qualidade do sono e de vida de portadores de IC. MÉTODOS: 65 pacientes portadores de IC foram submetidos a polissonografia diagnóstica.Os resultados da polissonografia foram avaliados de acordo com o uso ou não de BB. No dia do exame os pacientes responderam ao questionário de Minessota para qualidade de vida com IC. Após 6 e 12 meses da data da polissonografia, houve contato telefônico com todos os pacientes, para a repetição do questionário de Minessota. RESULTADOS: A prevalência de apneia do sono (IAH > 15/h) foi de 46,1 por cento na população total, porém a apneia central foi identificada em apenas 18,4 por cento dos pacientes. O uso de BB, em análise multivariada, foi o único preditor de ocorrência de menor índice de apneia e hipopneia (IAH) central (p=0,002), maior saturação (p=0,02) e menor dessaturação média de oxigênio (p=0,03). Além disso, o uso de BB foi preditor de melhor qualidade de vida após 6 e 12 meses (p=0,002 e 0,001 respectivamente) e de menor número de hospitalizações nestes períodos (p=0,001 e p=0,05 respectivamente). CONCLUSÃO: O uso de BB reduziu a incidência de apneia central na população total, se compararmos com os dados da literatura. Além disto, os BB melhoraram parâmetros da qualidade do sono e de vida de portadores de IC.

BACKGROUND: Sleep apneas are frequent in patients with heart failure (HF). Estimate of the pre-beta blocker age (BB) point out to 45 percent of central apneas in these patients. OBJECTIVE: Assess the influence of BB in central apneas and their interference in the quality of sleep and life of patients with heart failure. METHODS: 65 patients with heart failure underwent diagnostic polysomnography. Polysomnography have been assessed according to the use or not of BB. On the day of examination, the patients answered the Minessota questionnaire for quality of life with HF. After 6 and 12 months from the polysomnography date, all patients were contacted by phone, in order to repeat the Minessota questionnaire. RESULTS: The prevalence of sleep apnea (IAH > 15/h) hit 46.1 percent in the total population, however, central sleep apnea was identified in 18.4 percent of patients. The use of BB, in a multivariate analysis, was the only predictor of a minor index of central apnea and hypopnea (IAH) (p=0.002), greater saturation (p=0.02) and smaller average desaturation of oxygen (p=0.03). Additionally, the use of BB could predict a better quality of life after 6 and 12 months (p=0.002 and 0.001 respectively) and a smaller number admissions in these periods (p=0.001 and p=0.05 respectively). CONCLUSION: The use BB reduced the rate of central sleep apnea in total population, if we compare to literature data. Additionally, the BB improved parameters of quality of sleep and life of patients with heart failure.

FUNDAMENTO: Las apneas del sueño son enfermedades frecuentes en portadores de insuficiencia cardiaca (IC). Una estimación de la era pre betabloqueante (BB) señala hacia una prevalencia del 45 por ciento de apneas centrales en estos pacientes. OBJETIVO: Evaluar la influencia de los BB en la prevalencia de las apneas centrales y su interferencia en la calidad del sueño y de vida de portadores de IC. MÉTODOS: 65 pacientes portadores de IC fueron sometidos a polisonografía diagnóstica. Los resultados de la polisonografía se evaluaron según el empleo o no de BB. El día del examen, los pacientes contestaron el cuestionario de Minnesota para la calidad de vida con IC. Tras 6 y 12 meses de la fecha de la polisonografía, hubo contacto telefónico con todos los pacientes, para la repetición del cuestionario de Minnesota. RESULTADOS: La prevalencia de apnea del sueño (IAH > 15/h) fue de un 46,1 por ciento en la población total, además de la apnea central se identificó en solamente un 18,4 por ciento de los pacientes. El empleo de BB, en análisis multivariado, fue el único predictor de ocurrencia de menor índice de apnea e hipopnea (IAH) central (p=0,002), mayor saturación (p=0,02) y menor desaturación promedio de oxígeno (p=0,03). Además de ello, el empleo de BB fue predictor de mejor calidad de vida tras 6 y 12 meses (p=0,002 y 0,001 respectivamente) y de menor número de hospitalizaciones en estos períodos (p=0,001 y p=0,05 respectivamente). CONCLUSIÓN: El empleo de BB reduzco la incidencia de apnea central en la población total, si lo comparamos con los datos de la literatura. Además de esto, los BB mejoran parámetros de la calidad del sueño y de vida de portadores de IC.

PHOX2B in respiratory control: lessons from congenital central hypoventilation syndrome and its mouse models.

Phox2b is a master regulator of visceral reflex circuits. Its role in the control of respiration has been highlighted by the identification of heterozygous PHOX2B mutations as the cause of Central Congenital Hypoventilation Syndrome (CCHS), a rare disease defined by the lack of CO(2) responsiveness and of breathing automaticity in sleep. Phox2b(27Ala/+) mice that bear a frequent CCHS-causing mutation do not respond to hypercapnia and die in the first hour after birth from central apnoea. They are therefore a reliable animal model for CCHS. Neurons of the retrotrapezoïd nucleus/parafacial respiratory group (RTN/pFRG) were found severely depleted in these mice and no other neuronal loss could be identified. Physiological experiments show that RTN/pFRG neurons are crucial to driving proper breathing at birth and are necessary for central chemoreception and the generation of a normal respiratory rhythm. To date, the reason for the selective vulnerability of RTN/pFRG neurons to PHOX2B protein dysfunction remains unexplained.

Changes of neurotransmitters in the brainstem of patients with respiratory-pattern disorders during childhood.

We examined neuropathologically and immunohistochemically the respiratory centers in the brainstem of two patients with Joubert syndrome (JS), three patients with congenital central hypoventilation syndrome (CCHS) and a patient with apneustic breathing (prolonged inspiratory pause) due to unknown etiology. Immunoreactivity (IR) of tryptophan hydroxylase (TPH) was decreased in the dorsal raphe nuclei of two patients with JS compared with age-matched controls, as well as in two patients with Dandy-Walker malformation. The two JS patients showed vermian defect and elongated cerebellar peduncles, and peculiar vascularities in the midline of the whole brainstem were also noted in one of these patients. These findings, as a whole, confirm that the midline structures of brainstem are disordered both structurally and functionally in JS, conceivably resulting in respiratory patterns and psychomotor deficits. IR of serotonin 1A receptor showed no significant changes in the medulla oblongata of these patients, however. In the parabrachial complex, IR of substance P was increased in two patients with CCHS, and one with apneustic breathing. IR of tyrosine hydroxylase was also increased in the latter. The brainstem of these patients showed reactive astrogliosis. These findings suggest preceding hypoxic episodes as well as an increased activity in the parabrachial complex which plays an important role in conducting the driving force to the medullary respiratory neurons from ascending sensory pathways.

Síndrome de ondine: reporte de un caso / Syndrome of ondine's: report of one case

Se reporta un caso de síndrome de hipoventilación central congénita (Síndrome de Ondine). Es una rara enfermedad que cursa con perdida de control automático de la ventilación durante el sueño. Este síndrome aparece en el primer año de vida, estos bebés presentan apnea durante el sueño, tiene constantemente desaturación de O2 (saturación de oxígeno menor de 90 por ciento) y evidencia persistente de hipoventilación durante el sueño (PaCO2 < mmHg), en ausencia de enfermedad pulmonar primaria, disminución neuromuscular o enfermedad cardíaca primaria. Cuando esto sucede, la alta presión de CO2 sanguinea causa dilatación y falla cardíaca derecha. Este síndrome se trata con taqueostomía, ventilación con presión positiva y más recientemente ventilación a presión positiva nasal o combinación de ambas