Congenital central hypoventilation syndrome and sudden infant death syndrome: disorders of autonomic regulation

In vivo evidence for the cellular basis of central hypoventilation of Rett syndrome and pharmacological correction in the rat model

Rett syndrome (RTT) is a neurodevelopmental disorder caused mostly by mutations in the MECP2 gene. RTT patients show periodical hypoventilation attacks. The breathing disorder contributing to the high incidence of sudden death is thought to be due to depressed central inspiratory (I) activity via unknown cellular processes. Demonstration of such processes may lead to targets for pharmacological control of the RTT-type hypoventilation. We performed in vivo recordings from medullary respiratory neurons on the RTT rat model. To our surprise, both I and expiratory (E) neurons in the ventral respiratory column (VRC) increased their firing activity in Mecp2-null rats with severe hypoventilation. These I neurons including E-I phase-spanning and other I neurons remained active during apneas. Consistent with enhanced central I drive, ectopic phrenic discharges during expiration as well as apnea were observed in the Mecp2-null rats. Considering the increased I neuronal firing and ectopic phrenic activity, the RTT-type hypoventilation does not seem to be caused by depression in central I activity, neither reduced medullary I premotor output. This as well as excessive E neuronal firing as shown in our previous studies suggests inadequate synaptic inhibition for phase transition. We found that the abnormal respiratory neuronal firing, ectopic phrenic discharge as well as RTT-type hypoventilation all can be corrected by enhancing GABAergic inhibition. More strikingly, Mecp2-null rats reaching humane endpoints with severe hypoventilation can be rescued by GABAergic augmentation. Thus, defective GABAergic inhibition among respiratory neurons is likely to play a role in the RTT-type hypoventilation, which can be effectively controlled with pharmacological agents.

Firing activity of locus coeruleus noradrenergic neurons decreases in necdin-deficient mice, an animal model of Prader-Willi syndrome

BACKGROUND

Prader-Willi syndrome (PWS) is a neurodevelopmental disorder characterized by multiple respiratory, cognitive, endocrine, and behavioral symptoms, such as central apnea, intellectual disabilities, exaggerated stress responses, and temper tantrums. The locus coeruleus noradrenergic system (LC-NE) modulates a diverse range of behaviors, including arousal, learning, pain modulation, and stress-induced negative affective states, which are possibly correlated with the pathogenesis of PWS phenotypes. Therefore, we evaluated the LC-NE neuronal activity of necdin-deficient mice, an animal model of PWS.

METHODS

Heterozygous necdin-deficient mice (B6.Cg-Ndntm1ky) were bred from wild-type (WT) females to generate WT (+m/+p) and heterozygotes (+m/-p) animals, which were examined of LC-NE neuronal activity, developmental reflexes, and plethysmography.

RESULTS

On slice electrophysiology, LC-NE neurons of Ndntm1ky mice with necdin deficiency showed significantly decreased spontaneous activities and impaired excitability, which was mediated by enhanced A-type voltage-dependent potassium currents. Ndntm1ky mice also exhibited the neonatal phenotypes of PWS, such as hypotonia and blunt respiratory responses to hypercapnia.

CONCLUSIONS

LC-NE neuronal firing activity decreased in necdin-deficient mice, suggesting that LC, the primary source of norepinephrine in the central nervous system, is possibly involved in PWS pathogenesis.

Phrenic-specific transcriptional programs shape respiratory motor output

The precise pattern of motor neuron (MN) activation is essential for the execution of motor actions; however, the molecular mechanisms that give rise to specific patterns of MN activity are largely unknown. Phrenic MNs integrate multiple inputs to mediate inspiratory activity during breathing and are constrained to fire in a pattern that drives efficient diaphragm contraction. We show that Hox5 transcription factors shape phrenic MN output by connecting phrenic MNs to inhibitory premotor neurons. Hox5 genes establish phrenic MN organization and dendritic topography through the regulation of phrenic-specific cell adhesion programs. In the absence of Hox5 genes, phrenic MN firing becomes asynchronous and erratic due to loss of phrenic MN inhibition. Strikingly, mice lacking Hox5 genes in MNs exhibit abnormal respiratory behavior throughout their lifetime. Our findings support a model where MN-intrinsic transcriptional programs shape the pattern of motor output by orchestrating distinct aspects of MN connectivity.

In mammals, air is moved in and out of the lungs by a sheet of muscle called the diaphragm. When this muscle contracts air gets drawn into the lungs and as the muscle relaxes this pushes air back out. Movement of the diaphragm is controlled by a group of nerve cells called motor neurons which are part of the phrenic motor column (or PMC for short) that sits within the spinal cord. The neurons within this column work together with nerve cells in the brain to coordinate the speed and duration of each breath.

For the lungs to develop normally, the neurons that control how the diaphragm contracts need to start working before birth. During development, motor neurons in the PMC cluster together and connect with other nerve cells involved in breathing. But, despite their essential role, it is not yet clear how neurons in the PMC develop and join up with other nerve cells.

Now, Vagnozzi et al. show that a set of genes which make the transcription factor Hox5 control the position and organization of motor neurons in the PMC. Transcription factors work as genetic switches, turning sets of genes on and off. Vagnozzi et al. showed that removing the Hox5 transcription factors from motor neurons in the PMC changed their activity and disordered their connections with other breathing-related nerve cells. Hox5 transcription factors regulate the production of proteins called cadherins which join together neighboring cells. Therefore, motor neurons lacking Hox5 were unable to make enough cadherins to securely stick together and connect with other nerve cells.

Further experiments showed that removing the genes that code for Hox5 caused mice to have breathing difficulties in the first two weeks after birth. Although half of these mutant mice were eventually able to breathe normally, the other half died within a week. These breathing defects are reminiscent of the symptoms observed in sudden infant death syndrome (also known as SIDS).

Abnormalities in breathing occur in many other diseases, including sleep apnea, muscular dystrophy and amyotrophic lateral sclerosis (ALS). A better understanding of how the connections between nerve cells involved in breathing are formed, and the role of Hox5 and cadherins, could lead to improved treatment options for these diseases.

Congenital Central Hypoventilation Syndrome: A Case-Based Learning Opportunity for Neonatal Clinicians

Congenital central hypoventilation syndrome (CCHS) is a rare and sporadic neurocristopathy characterized by alveolar hypoventilation and autonomic nervous system dysfunction. CCHS manifests quickly after birth, initially as respiratory distress. Mortality risk is estimated at 38 percent, with a median age of death of three months of age. A timely and accurate diagnosis is critical. Genetic testing for PHOX2B gene mutations is necessary to confirm the diagnosis; however, laboratory turnaround time often imposes an additional 7-14-day waiting period on an often anxious family. Neonatal clinicians should recognize that families require disease-specific education, emotional support, and time to rehearse daily caregiving in preparation for discharge. Therefore, this article presents the key clinical, pathophysiologic, and diagnostic factors, as well as a discussion of discharge needs. A case report of an infant, born to parents with no known history of CCHS, is included as a case-based learning opportunity for readers.

Medico-legal investigation in an explicable case of congenital central hypoventilation syndrome due to a rare variant of the PHOX2B gene

The heterozygous PHOX2B gene mutation is related to congenital central hypoventilation syndrome (CCHS). It is characterized by defective autonomous nervous system development leading to inadequate breathing response to hypoxia and hypercapnia, leading to hypoventilation especially during non-REM sleep, but also during waking in the more severe cases. Herein we report a case of sudden death in a 28-day-old child. The mother reported the infant was found lying on her own bed in the prone position. The infant was wearing a romper and lying in her crib without any blanket or other objects. At autopsy no significant pathological findings were detected. Histologically, sparse aspirated milk residues were present in some lung fields. Toxicological and microbiological examinations were within the norm. The initial postmortem investigation ruled out any readily identifiable cause of death. However, genetic analysis revealed a rare heterozygous 21bp in-frame deletion of the polyalanine coding sequences of the PHOX2B gene. In-frame contractions of the poly-Ala tract of the PHOX2B gene have already been reported in patients with symptoms suggestive of sporadic hypoventilation, apparent life-threatening events or neonatal respiratory distress.

Sudden Unexpected Death During Sleep in Familial Dysautonomia: A Case-Control Study

Study Objectives

Sudden unexpected death during sleep (SUDS) is the most common cause of death in patients with familial dysautonomia (FD), an autosomal recessive disease characterized by sensory and autonomic dysfunction. It remains unknown what causes SUDS in these patients and who is at highest risk. We tested the hypothesis that SUDS in FD is linked to sleep-disordered breathing.

Methods

We retrospectively identified patients with FD who died suddenly and unexpectedly during sleep and had undergone polysomnography within the 18-month period before death. For each case, we sampled one age-matched surviving subject with FD that had also undergone polysomnography within the 18-month period before study. Data on polysomnography, EKG, ambulatory blood pressure monitoring, arterial blood gases, blood count, and metabolic panel were analyzed.

Results

Thirty-two deceased cases and 31 surviving controls were included. Autopsy was available in six cases. Compared with controls, participants with SUDS were more likely to be receiving treatment with fludrocortisone (odds ratio [OR]; 95% confidence interval) (OR 29.7; 4.1-213.4), have untreated obstructive sleep apnea (OR 17.4; 1.5-193), and plasma potassium levels <4 mEq/L (OR 19.5; 2.36-161) but less likely to use noninvasive ventilation at night (OR 0.19; 0.06-0.61).

Conclusions

Initiation of noninvasive ventilation when required and discontinuation of fludrocortisone treatment may reduce the high incidence rate of SUDS in patients with FD. Our findings contribute to the understanding of the link between autonomic, cardiovascular, and respiratory risk factors in SUDS.

Candidate gene variants of the immune system and sudden infant death syndrome

BACKGROUND

Sudden infant death syndrome (SIDS) causes early infant death with an incidence between 0.5 and 2.5 cases among 1000 live births. Besides central sleep apnea and thermal dysregulation, infections have been repeatedly suggested to be implicated in SIDS etiology.

METHODS

To test the risk contribution of common genetic variants related to infection, we genotyped 40 single-nucleotide polymorphisms (SNPs) from 15 candidate genes for association with SIDS in a total of 579 cases and 1124 controls from Germany and the UK in a two-stage case control design.

RESULTS

The discovery-stage series (267 SIDS cases and 303 controls) revealed nominally significant associations for variants in interleukin 6 (IL6) (rs1880243), interleukin 10 (IL10) (rs1800871, rs1800872), and mannose-binding lectin 2 (MBL2) (rs930506), and for several other variants in subgroups. Meta-analyses were then performed in adding genotype information from a genome-wide association study of another 312 European SIDS cases and 821 controls. Overall associations were observed for two independent variants in MBL2: rs930506 in a co-dominant model (odds ratio (OR) = 0.82, p = 0.04) and rs1838065 in a dominant model (OR = 1.27, p = 0.03).

CONCLUSION

Our study did not replicate published associations of IL10 variants with SIDS. However, the evidence for two independent MBL2 variants in the combined analysis of two large series seems consistent with the hypothesis that infection may play a role in SIDS pathogenesis.

The Clinical Usefulness of Sleep Studies in Children

Sleep disordered breathing is common in children and has the potential to have a significant impact on cognition, activity and social interaction. The overnight in-laboratory polysomnography (PSG) continues to be the gold standard instrument for the investigation of sleep-disordered breathing in children. It has the ability to rule in or rule out the need for intervention for common conditions such as obstructive sleep apnoea, assess the role of sleep quality in children and adolescents with hypersomnolence, provide physiologic data in children with hypoventilation as may be seen in neuromuscular disease and assist in the assessment of children with structural airway and lung abnormalities. Polysomnography is valuable and the only reliable method to differentiate habitual snoring from many levels of sleep apnoea syndrome [1]. The American Academy of Paediatrics recommends that, in order to diagnose and manage OSA syndrome, all children should be screened for snoring and complex cases should be referred to a specialist. PSG is the diagnostic gold standard and adenotonsillectomy is the first line of treatment [2]. There is no evidence to support nap studies or ambulatory sleep studies in children [3]. With adequate staffing, expertise, and a child and family-friendly environment, children of any age can undergo a sleep study.

Hyperplasia of pulmonary neuroendocrine cells in infancy and childhood

Pulmonary neuroendocrine cells (PNEC) are widely distributed throughout the airway mucosa of mammalian lung as solitary cells and as distinctive innervated clusters, neuroepithelial bodies (NEB). These cells differentiate early during lung development and are more prominent in fetal/neonatal lungs compared to adults. PNEC/NEB cells produce biogenic amine (serotonin) and a variety of peptides (i.e., bombesin) involved in regulation of lung function. During the perinatal period, NEB are thought to function as airway O(2)/CO(2) sensors. Increased numbers of PNEC/NEBs have been observed in a variety of perinatal and postnatal lung disorders. Recent advances in cellular and molecular biology of these cells, as they relate to perinatal and postnatal lung disorders associated with PNEC/NEB cell hyperplasia are reviewed and their possible role in pulmonary pathobiology discussed (WC 125).

Polymorphisms in genes of respiratory control and sudden infant death syndrome

Sudden infant death syndrome (SIDS) is a multifactorial syndrome and assumingly, among other mechanisms, a deficit in respiratory control leads to a failure of arousal and autoresuscitation when the child is challenged by a stressful homeostatic event, e.g., hypoxia. We hypothesize that genetic polymorphisms involved in respiratory control mediated in the medulla oblongata contribute to SIDS. Therefore, a total of 366 SIDS cases and 421 controls were genotyped for 48 SNPs in 41 candidate genes. Genotyping was performed using Fluidigm nanofluidic technology. Results were obtained for 356 SIDS and 406 controls and 38 SNPs. After correction for multiple testing, one SNP retained a nominally significant association with seasonal SIDS: rs1801030 in the phenol sulfotransferase 1A1 gene (subgroup: death occurring during summer). A borderline association could be also observed for rs563649 in the opioid receptor μ1 gene in a recessive model (subgroup: death occurring during autumn). As a conclusion, although these data suggest two SNPs to be associated with different subgroups of SIDS cases, none of them can fully explain the SIDS condition, consistent with its multifactorial etiology. Given the great complexity of respiratory control and our initial findings reported here, we believe it is worthwhile to further investigate genes involved in the respiratory system.

That's not it, either-neither polymorphisms in PHOX2B nor in MIF are involved in sudden infant death syndrome (SIDS)

The occurrence of sudden infant death syndrome (SIDS) has been linked to several genetic risk factors, e.g. genes involved in the neuroadrenergic system, variations in serotonin reporter genes or mutations in long-QT syndrome genes. Additionally, polymorphisms in genes with impact in sleep disorder syndromes have been proposed to be of importance as genetic risk factors for SIDS. In this study, we investigated the polyalanine length variation of PHOX2B and the -794 CATT repeat in the MIF promoter region as well as single nucleotide polymorphisms (rs28462174, rs28727473, rs16853571, rs755622, rs12485058, rs12485068, rs4822444, rs4822445, rs4822446, rs4822447 and rs2012124) in both genes in 278 SIDS cases and 240 controls. No significant differences were found in allele distribution of neither length polymorphisms nor single nucleotide polymorphisms between SIDS cases or controls. Therefore, an importance of these variations for the occurrence of SIDS could be ruled out.

Retrospective analysis of prenatal ultrasound of children with Hirschsprung disease

OBJECTIVE

Hirschsprung disease (HD) is a rare gastrointestinal disorder. Our aim was to study the prenatal ultrasound findings of children who were diagnosed with HD after birth.

METHODS

The study population included children who suffered from HD between 1990 and 2008. Data of anomaly scan findings in prenatal ultrasound, demographic and post-natal physical abnormalities and treatment were retrieved from medical files and interviews with the parents.

RESULTS

Twenty-two patients confirmed histopathological diagnosis of HD at age of 1 day to 15 months. Nineteen fetuses had anomaly scan during pregnancy, which revealed minor sonographic abnormalities in three fetuses; two of them had hyperechogenic bowel. One fetus with hyperechogenic bowel had polyhydramnion, and another had a family history of three brothers with HD. A third fetus had dilated pelvic kidney. None of them had sonographic evidence of bowel dilatation. After birth, six patients (31%) were found to have other structural anomalies: ventriculoseptal defect, atriseptal defect, atrio-ventricular septal defect, and pyloric stenosis.

CONCLUSIONS

Abnormal sonographic findings of fetal bowel are absent in the vast majority of fetuses who are diagnosed with HD after birth. In women with a family history of HD, a third trimester anomaly scan may be warranted.

Proceedings of the fourth international conference on central hypoventilation

Central hypoventilation syndromes (CHS) are rare diseases of central autonomic respiratory control associated with autonomous nervous dysfunction. Severe central hypoventilation is the hallmark and the most life-threatening feature. CHS is a group of not-fully defined disorders. Congenital CHS (CCHS) (ORPHA661) is clinically and genetically well-characterized, with the disease-causing gene identified in 2003. CCHS presents at birth in most cases, and associated with Hirschsprung's disease (ORPHA99803) and neural crest tumours in 20% and 5% of cases, respectively. The incidence of CCHS is estimated to be 1 of 200,000 live births in France, yet remains unknown for the rest of the world. In contrast, late-onset CHS includes a group of not yet fully delineated diseases. Overlap with CCHS is likely, as a subset of patients harbours PHOX2B mutations. Another subset of patients present with associated hypothalamic dysfunction. The number of these patients is unknown (less than 60 cases reported worldwide). Treatment of CHS is palliative using advanced techniques of ventilation support during lifetime. Research is ongoing to better understand physiopathological mechanisms and identify potential treatment pathways.The Fourth International Conference on Central Hypoventilation was organised in Warsaw, Poland, April 13-15, 2012, under the patronage of the European Agency for Health and Consumers and Public Health European Agency of European Community. The conference provided a state-of-the-art update of knowledge on all the genetic, molecular, cellular, and clinical aspects of these rare diseases.

A case of congenital central hypoventilation syndrome in a three-generation family with non-polyalanine repeat PHOX2B mutation

We describe a three generation family in whom multiple individuals are variably affected due to a PHOX2B non-polyalanine repeat mutation. This family demonstrates extreme phenotypic variability and autosomal dominant transmission over three generations not previously reported in the wider literature. Novel findings also inclue a history of recurrent second trimester miscarriage. Pediatr Pulmonol. 2014; 49:E140-E143. © 2014 Wiley Periodicals, Inc.

PHOX2B polyalanine repeat length is associated with sudden infant death syndrome and unclassified sudden infant death in the Dutch population

Unclassified sudden infant death (USID) is the sudden and unexpected death of an infant that remains unexplained after thorough case investigation including performance of a complete autopsy and review of the circumstances of death and the clinical history. When the infant is below 1 year of age and with onset of the fatal episode apparently occurring during sleep, this is referred to as sudden infant death syndrome (SIDS). USID and SIDS remain poorly understood despite the identification of several environmental and some genetic risk factors. In this study, we investigated genetic risk factors involved in the autonomous nervous system in 195 Dutch USID/SIDS cases and 846 Dutch, age-matched healthy controls. Twenty-five DNA variants from 11 genes previously implicated in the serotonin household or in the congenital central hypoventilation syndrome, of which some have been associated with SIDS before, were tested. Of all DNA variants considered, only the length variation of the polyalanine repeat in exon 3 of the PHOX2B gene was found to be statistically significantly associated with USID/SIDS in the Dutch population after multiple test correction. Interestingly, our data suggest that contraction of the PHOX2B exon 3 polyalanine repeat that we found in six of 160 SIDS and USID cases and in six of 814 controls serves as a probable genetic risk factor for USID/SIDS at least in the Dutch population. Future studies are needed to confirm this finding and to understand the functional effect of the polyalanine repeat length variation, in particular contraction, in exon 3 of the PHOX2B gene.