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

A Common 3'UTR Variant of the PHOX2B Gene Is Associated With Infant Life-Threatening and Sudden Death Events in the Italian Population

Heterozygous mutations in the Paired like homeobox 2b (PHOX2B) gene are causative of congenital central hypoventilation syndrome (CCHS), a rare monogenic disorder belonging to the family of neurocristopathies and due to a defective development of the autonomic nervous system. Most patients manifest sudden symptoms within 1 year of birth, mainly represented by central apnea and cyanosis episodes. The sudden appearance of hypoxic manifestations in CCHS and their occurrence during sleep resemble two other unexplained perinatal disorders, apparent life-threatening event (ALTE) and sudden and unexpected infant death (SUID), among which the vast majority is represented by sudden infant death syndrome (SIDS). Differently from CCHS, characterized by Mendelian autosomal dominant inheritance, ALTE and SIDS are complex traits, where common genetic variants, together with external factors, may exert an additive effect with symptoms likely manifesting only over a “threshold.” Given the similarities observed among the three abovementioned perinatal disorders, in this work, we have analyzed the frequency of PHOX2B common variants in two groups of Italian idiopathic ALTE (IALTE) and SUIDs/SIDS patients. Here, we report that the c^*161G>A (rs114290493) SNP of the 3′UTR PHOX2B (i) became overrepresented in the two sets of patients compared to population matched healthy controls, and (ii) associated with decreased PHOX2B gene expression, likely mediated by miR-204, a microRNA already known to bind the 3′UTR of the PHOX2B gene. Overall, these results suggest that, at least in the Italian population, the SNP c^*161G>A (rs114290493) does contribute, presumably in association with others mutations or polymorphisms, to confer susceptibility to sudden unexplained perinatal life-threatening or fatal disorders by increasing the effect of miR-204 in inducing PHOX2B expression down-regulation. However, these are preliminary observations that need to be confirmed on larger cohorts to achieve a clinical relevance.

Genetic Factors Underlying Sudden Infant Death Syndrome

Sudden Infant Death syndrome (SIDS) is a diagnosis of exclusion. Decades of research have made steady gains in understanding plausible mechanisms of terminal events. Current evidence suggests SIDS includes heterogeneous biological conditions, such as metabolic, cardiac, neurologic, respiratory, and infectious conditions. Here we review genetic studies that address each of these areas in SIDS cases and cohorts, providing a broad view of the genetic underpinnings of this devastating phenomenon. The current literature has established a role for monogenic genetic causes of SIDS mortality in a subset of cases. To expand upon our current knowledge of disease-causing genetic variants in SIDS cohorts and their mechanisms, future genetic studies may employ functional assessments of implicated variants, broader genetic tests, and the inclusion of parental genetic data and family history information.

The Genetics of Sudden Infant Death Syndrome-Towards a Gene Reference Resource

Sudden infant death syndrome (SIDS) is the unexpected death of an infant under one year of age that remains unexplained after a thorough investigation. Despite SIDS remaining a diagnosis of exclusion with an unexplained etiology, it is widely accepted that SIDS can be caused by environmental and/or biological factors, with multiple underlying candidate genes. However, the lack of biomarkers raises questions as to why genetic studies on SIDS to date are unable to provide a clearer understanding of the disease etiology. We sought to improve the identification of SIDS-associated genes by reviewing the SIDS genetic literature and objectively categorizing and scoring the reported genes based on the strength of evidence (from C1 (high) to C5 (low)). This was followed by analyses of function, associations between genes, the enrichment of gene ontology (GO) terms, and pathways and gender difference in tissue gene expression. We constructed a curated database for SIDS gene candidates consisting of 109 genes, 14 of which received a category 4 (C4) and 95 genes received the lowest category of C5. That none of the genes was classified into the higher categories indicates the low level of supporting evidence. We found that genes of both scoring categories show distinct networks and are highly diverse in function and involved in many GO terms and pathways, in agreement with the perception of SIDS as a heterogeneous syndrome. Genes of both scoring categories are part of the cardiac system, muscle, and ion channels, whereas immune-related functions showed enrichment for C4 genes. A limited association was found with neural development. Overall, inconsistent reports and missing metadata contribute to the ambiguity of genetic studies. Considering those parameters could help improve the identification of at-risk SIDS genes. However, the field is still far from offering a full-pledged genetic test to identify at-risk infants and is still hampered with methodological challenges and misunderstandings of the vulnerabilities of vital biological mechanisms.

A Systematic Review of Molecular Autopsy Studies in Sudden Infant Death Cases

Sudden unexpected death is an upsetting event, which can remain unexplained even after post-mortem investigation. Internationally, molecular autopsies have shown to resolve up to 44% of unexplained cases; however, it is currently unclear how many of these were infants. This systematic literature review showed that significantly fewer infant cases were resolved (median: 4%) compared with cohorts of 1 to 45 years old (median: 32%). Further, no study involving indigenous African participants has yet been published. Overall, molecular autopsies hold immense value to living family members and is motivation to explore new avenues in infant cohorts.

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.

The genetics of the epilepsies

While genetic causes of epilepsy have been hypothesized from the time of Hippocrates, the advent of new genetic technologies has played a tremendous role in elucidating a growing number of specific genetic causes for the epilepsies. This progress has contributed vastly to our recognition of the epilepsies as a diverse group of disorders, the genetic mechanisms of which are heterogeneous. Genotype-phenotype correlation, however, is not always clear. Nonetheless, the developments in genetic diagnosis raise the promise of a future of personalized medicine. Multiple genetic tests are now available, but there is no one test for all possible genetic mutations, and the balance between cost and benefit must be weighed. A genetic diagnosis, however, can provide valuable information regarding comorbidities, prognosis, and even treatment, as well as allow for genetic counseling. In this review, we will discuss the genetic mechanisms of the epilepsies as well as the specifics of particular genetic epilepsy syndromes. We will include an overview of the available genetic testing methods, the application of clinical knowledge into the selection of genetic testing, genotype-phenotype correlations of epileptic disorders, and therapeutic advances as well as a discussion of the importance of genetic counseling.

Novel mutation-deletion in the PHOX2B gene of the patient diagnosed with Neuroblastoma, Hirschsprung's Disease, and Congenital Central Hypoventilation Syndrome (NB-HSCR-CCHS) Cluster

INTRODUCTION

Neuroblastoma (NB), Hirschsprung disease (HSCR), Congenital Central Hypoventilation Syndrome (CCHS), clinically referred as the NB-HSCR-CCHS cluster, are genetic disorders linked to mutations in the PHOX2B gene on chromosome 4p12.

SPECIFIC AIM

The specific aim of this project is to define the PHOX2B gene mutations as the genomic basis for the clinical manifestations of the NB-HSCR-CCHS cluster.

PATIENT

A one day old male patient presented to the Jagiellonian University Medical College (JUMC), American Children Hospital, neonatal Intensive Care Unit (ICU) due to abdominal distention, vomiting, and severe apneic episodes. With the preliminary diagnosis of the NB-HSCR-CCHS, the blood and tissue samples were acquired from the child, as well as from the child's parents. All procedures were pursued in accordance with the Declaration of Helsinki, with the patient's Guardian Informed Consent and the approval from the Institutional Review Board.

GENETIC/GENOMIC METHODS

Karyotyping was analyzed based upon Giemsa banding. The patient's genomic DNA was extracted from peripheral blood and amplified by polymerase chain reaction. Direct microfluidic Sanger sequencing was performed on the genomic DNA amplicons. These procedures were pursued in addition to the routine clinical examinations and tests.

RESULTS

G-banding showed the normal 46 XY karyotype. However, genomic sequencing revealed a novel, heterozygous deletion (8 nucleotides: c.699-706, del8) in exon 3 of the PHOX2B gene on chromosome 4. This led to the frame-shift mutation and malfunctioning gene expression product.

CONCLUSION

Herein, we report a novel PHOX2B gene mutation in the patient diagnosed with the NB-HSCR-CCHS cluster. The resulting gene expression product may be a contributor to the clinical manifestations of these genetic disorders. It adds to the library of the mutations linked to this syndrome. Consequently, we suggest that screening for the PHOX2B mutations becomes an integral part of genetic counseling, genomic sequencing of fetal circulating nucleic acids and / or genomes of circulating fetal cells prenatally, while preparing supportive therapy upon delivery, as well as on neonates' genomes of intubated infants, when breathing difficulties occur upon extubation. Further, we hypothesize that PHOX2B may be considered as a potential target for gene therapy.

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.

Mechanisms of sudden unexplained death in epilepsy

PURPOSE OF REVIEW

Human and experimental research has identified cardioautonomic and respiratory dysfunction as a frequent accompaniment in human and animal model events of sudden unexpected death in epilepsy (SUDEP). This review aims to provide an overview of the scientific evidence behind the currently accepted risk factors and working hypotheses regarding SUDEP pathophysiology.

RECENT FINDINGS

Epidemiological analysis of public health burden of SUDEP has shown that it rates second only to stroke in the years of potential life lost. Clinical and experimental studies uncovered the dynamic cardiorespiratory dysfunction interictally and imminently to SUDEP, and model systems have facilitated discoveries in SUDEP mechanistic understanding and application of pilot therapeutic interventions. Pilot molecular profiling of human SUDEP has uncovered complex genomic structure in the candidate gene network.

SUMMARY

Extensive clinical and experimental work has established a rationale for the conceptual thinking about SUDEP mechanisms. The application of the global molecular profiling will be invaluable in unraveling the individually unique genomic complexities and interactions that underlie the physiological signature of each patient. At the same time, sophisticated model systems will be critical in the iterative translation of human genetics, physiology, pharmacological interventions, and in testing preventive interventions.

Indications, advantages and limitations of perinatal postmortem imaging in clinical practice

Just as there is a range of paediatric imaging techniques available during life, a similar repertoire is available as part of the foetal and perinatal postmortem examination. In this article, we review the literature regarding the diagnostic utility of postmortem radiography, US, CT and MRI in this clinical setting. There is limited direct evidence on the diagnostic utility of any of these techniques, apart from postmortem MRI, which when combined with other noninvasive investigations, has been shown to be highly sensitive and specific for many foetal postmortem diagnoses. The main disadvantages of postmortem MRI include the longer duration of imaging, the need for appropriate training in the interpretation of normal postmortem changes, and possible non-diagnostic imaging examinations in early gestation foetuses. As less-invasive autopsy becomes increasingly available, the true utility of these techniques will evolve, and clinical guidelines for maximal diagnostic yield can be developed.

The Generation R Study: Biobank update 2015

The Generation R Study is a population-based prospective cohort study from fetal life until adulthood. The study is designed to identify early environmental and genetic causes and causal pathways leading to normal and abnormal growth, development and health from fetal life, childhood and young adulthood. In total, 9,778 mothers were enrolled in the study. Data collection in children and their parents include questionnaires, interviews, detailed physical and ultrasound examinations, behavioural observations, Magnetic Resonance Imaging and biological samples. Efforts have been conducted for collecting biological samples including blood, hair, faeces, nasal swabs, saliva and urine samples and generating genomics data on DNA, RNA and microbiome. In this paper, we give an update of the collection, processing and storage of these biological samples and available measures. Together with detailed phenotype measurements, these biological samples provide a unique resource for epidemiological studies focused on environmental exposures, genetic and genomic determinants and their interactions in relation to growth, health and development from fetal life onwards.

Systems-level perspective of sudden infant death syndrome

Sudden infant death syndrome (SIDS) remains one of the primary causes of infant mortality in developed countries. Although the causes of SIDS remain largely inconclusive, some of the most informative associations implicate molecular, genetic, anatomical, physiological, and environmental (i.e., infant sleep) factors. Thus, a comprehensive and evolving systems-level model is required to understand SIDS susceptibility. Such models, by being powerful enough to uncover indirect associations, could be used to expand our list of candidate targets for in-depth analysis. We present an integrated WikiPathways model for SIDS susceptibility that includes associated cell systems, signaling pathways, genetics, and animal phenotypes. Experimental and literature-based gene-regulatory data have been integrated into this model to identify intersecting upstream control elements and associated interactions. To expand this pathway model, we performed a comprehensive analysis of existing proteomics data from brainstem samples of infants with SIDS. From this analysis, we discovered changes in the expression of several proteins linked to known SIDS pathologies, including factors involved in glial cell production, hypoxia regulation, and synaptic vesicle release, in addition to interactions with annotated SIDS markers. Our results highlight new targets for further consideration that further enrich this pathway model, which, over time, can improve as a wiki-based, community curation project.