PHOX2B mutations in patients with Ondine-Hirschsprung disease and a review of the literature

The Polycomb group gene rnf2 is essential for central and enteric neural system development in zebrafish

The development of central nervous system (CNS) and enteric nervous system (ENS) is under precise and strict control in vertebrates. Whether and how the Polycomb repressive complex 1 (PRC1) is involved in it remain unclear. To investigate the role of PRC1 in the nervous system development, using CRISPR/Cas9 technology, we have generated mutant zebrafish lines for the rnf2 gene which encodes Ring1b, the enzymatic component of the PRC1 complex. We show that rnf2 loss of function leads to abnormal migration and differentiation of neural crest and neural precursor cells. rnf2 mutant embryos exhibit aganglionosis, in which the hindgut is devoid of neurons. In particular, the formation of 5-HT serotonin neurons and myelinating glial cells is defective. Furthermore, ectopic expression of ENS marker genes is observed in forebrain of rnf2 mutant embryos. These findings suggest that the rnf2 gene plays an important role in the migration and differentiation of neural precursor cells, and its absence leads to abnormal development of ENS and CNS in zebrafish.

Research Advances on Therapeutic Approaches to Congenital Central Hypoventilation Syndrome (CCHS)

Congenital central hypoventilation syndrome (CCHS) is a genetic disorder of neurodevelopment, with an autosomal dominant transmission, caused by heterozygous mutations in the PHOX2B gene. CCHS is a rare disorder characterized by hypoventilation due to the failure of autonomic control of breathing. Until now no curative treatment has been found. PHOX2B is a transcription factor that plays a crucial role in the development (and maintenance) of the autonomic nervous system, and in particular the neuronal structures involved in respiratory reflexes. The underlying pathogenetic mechanism is still unclear, although studies in vivo and in CCHS patients indicate that some neuronal structures may be damaged. Moreover, in vitro experimental data suggest that transcriptional dysregulation and protein misfolding may be key pathogenic mechanisms. This review summarizes latest researches that improved the comprehension of the molecular pathogenetic mechanisms responsible for CCHS and discusses the search for therapeutic intervention in light of the current knowledge about PHOX2B function.

New mutations associated with Hirschsprung disease

INTRODUCTION

Hirschsprung Disease is caused by an impairment in cell migration from the neural crest to the gastrointestinal tract, resulting in an absence of neurons in the myenteric plexus. Many mutations in several genes have been associated to Hirschsprung disease; most of them affecting the RET proto-oncogen pathway. The purpose of this study is the description of novel and known mutations in genes associated to Hirschsprung disease and their prognostic implications.

MATERIAL AND METHODS

Retrospective analysis of patients with Hirschsprung disease and positive genetic studies evaluated from 1970 to 2013.

RESULTS

We found 21 positive genetic studies in the global series, 17 of them involving the RET proto-oncogene: Two of the mutations are novel and they have not been reported in the medical literature.

CONCLUSIONS

The RET protooncogene is the main gene associated with Hirschsprung disease. There are still multiple unknown mutations related to the pathogenesis of the disease. The study of this gene must be part of the work-up of all patients with Hirschsprung disease, as well as their first degree relatives if the mutation is associated with MEN2A and MEN2B syndromes.

[New mutations associated with Hirschsprung disease]

INTRODUCTION

Hirschsprung disease is caused by an impairment in cell migration from the neural crest to the gastrointestinal tract, resulting in an absence of neurons in the myenteric plexus. Many mutations in several genes have been associated to Hirschsprung disease; most of them affecting the RET proto-oncogen pathway. The purpose of this study is the description of novel and known mutations in genes associated to Hirschsprung disease and their prognostic implications.

MATERIAL AND METHODS

Retrospective analysis of patients with Hirschsprung disease and positive genetic studies evaluated from 1970 to 2013.

RESULTS

We found 21 positive genetic studies in the global series, 17 of them involving the RET proto-oncogene. Two of the mutations are novel and they have not been reported in the medical literature.

CONCLUSIONS

The RET protooncogene is the main gene associated with Hirschsprung disease. There are still multiple unknown mutations related to the pathogenesis of the disease. The study of this gene must be part of the work-up of all patients with Hirschsprung disease, as well as their first degree relatives if the mutation is associated with MEN2A and MEN2B syndromes.

The genetics of congenital central hypoventilation syndrome: clinical implications

Congenital central hypoventilation syndrome (CCHS) is a rare genetic disorder of the autonomic nervous system (ANS) and respiratory control. This disorder, formerly referred to as Ondine’s curse, is due to a mutation in the PHOX2B gene that affects the development of the neural crest cells. CCHS has an autosomal dominant pattern of inheritance. Majority of the patients have a polyalanine repeat mutation (PARM) of the PHOX2B, while a small group has non-PARM (NPARM). Knowledge of the patient’s PHOX2B gene mutation helps predict a patient’s clinical presentation and outcome and aids in anticipatory management of the respiratory and ANS dysfunction.

Identification of novel pathways and molecules able to down-regulate PHOX2B gene expression by in vitro drug screening approaches in neuroblastoma cells

PHOX2B is a transcription factor involved in the regulation of neurogenesis and in the correct differentiation of the autonomic nervous system. The pathogenetic role of PHOX2B in neuroblastoma (NB) is supported by mutations in familial, sporadic and syndromic cases of NB and overexpression of PHOX2B and its target ALK in tumor samples and NB cell lines. Starting from these observations, we have performed in vitro drug screening approaches targeting PHOX2B overexpression as a potential pharmacological means in NB. In particular, in order to identify molecules able to decrease PHOX2B expression, we have evaluated the effects of 70 compounds in IMR-32 cell line stably expressing the luciferase gene under the control of the PHOX2B promoter. Curcumin, SAHA and trichostatin A showed to down-regulate the PHOX2B promoter activity which resulted in a decrease of both protein and mRNA expressions. In addition, we have observed that curcumin acts by interfering with PBX-1/MEIS-1, NF-κB and AP-1 complexes, in this work demonstrated for the first time to regulate the transcription of the PHOX2B gene. Finally, combined drug treatments showed successful effects in down-regulating the expression of both PHOX2B and its target ALK genes, thus supporting the notion of the effectiveness of molecule combination in tumor therapy.

Congenital hypoventilation syndrome and Hirschsprung's disease - Haddad syndrome: A neonatal case presentation

Congenital central hypoventilation syndrome (CCHS) is an uncommon cause of apnea in the newborn characterized by the occurrence of apnea predominantly during sleep. Haddad syndrome is CCHS with Hirschsprung's disease. We report a newborn with Haddad syndrome that had a family history of spinal muscular atrophy and discuss aspects of CCHS and important considerations in the evaluation of apnea in the term newborn.

Heterozygous 24-polyalanine repeats in the PHOX2B gene with different manifestations across three generations

Congenital central hypoventilation syndrome (CCHS) is an uncommon genetic disorder that is characterized by alveolar hypoventilation and autonomic dysregulation. More than 90% of the patients are heterozygous for polyalanine repeat expansion mutations in the paired-like homeobox 2b (PHOX2B) gene. The normal genotype has a 20-polyalanine sequence whereas expanded alleles are usually 25-33. Heterozygous 24-polyalanine repeat expansion mutation in the PHOX2B gene has rarely been reported. We report three consecutive generations harboring heterozygous 24-polyalanine repeats in the PHOX2B gene with manifestations ranging from apparently asymptomatic to alveolar hypoventilation and apnea requiring mechanical ventilation. The 3-year-old proband developed cor pulmonale and central hypoventilation following an upper respiratory tract infection. Our findings add to the accumulating evidence that the 24-polyalanine repeat in the PHOX2B is a disease-causing mutation. In addition, a high index of suspicion and careful monitoring after anesthesia, sedation, or respiratory illnesses should be exercised when evaluating asymptomatic family members with this genotype.

Advances in Hirschsprung disease genetics and treatment strategies: an update for the primary care pediatrician

Hirschsprung disease (HSCR) is a multigenic condition with variable presentation. Most commonly, it presents in the neonatal period as a functional intestinal obstruction secondary to failure of caudal migration of the enteric nervous system. Classically, this manifests as dilated proximal bowel and constricted distal bowel with absent ganglia and hypertrophic nerve trunks. When recognized early, medical and surgical therapies can be instituted to minimize associated morbidity and mortality. This article reviews current understanding of the etiology of HSCR, its multigenic associations, the historical evolution of HSCR diagnosis and treatment, and current HSCR therapies.

Genetic diseases: congenital central hypoventilation, Rett, and Prader-Willi syndromes

The present review summarizes current knowledge on three rare genetic disorders of respiratory control, congenital central hypoventilation syndrome (CCHS), Rett syndrome (RTT), and Prader-Willi syndrome (PWS). CCHS is characterized by lack of ventilatory chemosensitivity caused by PHOX2B gene abnormalities consisting mainly of alanine expansions. RTT is associated with episodes of tachypneic and irregular breathing intermixed with breathholds and apneas and is caused by mutations in the X-linked MECP2 gene encoding methyl-CpG-binding protein. PWS manifests as sleep-disordered breathing with apneas and episodes of hypoventilation and is caused by the loss of a group of paternally inherited genes on chromosome 15. CCHS is the most specific disorder of respiratory control, whereas the breathing disorders in RTT and PWS are components of a more general developmental disorder. The main clinical features of these three disorders are reviewed with special emphasis on the associated brain abnormalities. In all three syndromes, disease-causing genetic defects have been identified, allowing the development of genetically engineered mouse models. New directions for future therapies based on these models or, in some cases, on clinical experience are delineated. Studies of CCHS, RTT, and PWS extend our knowledge of the molecular and cellular aspects of respiratory rhythm generation and suggest possible pharmacological approaches to respiratory control disorders. This knowledge is relevant for the clinical management of many respiratory disorders that are far more prevalent than the rare diseases discussed here.

Polymorphisms and expression of the WNT8A gene in Hirschsprung's disease

Hirschsprung's disease (HSCR) is a congenital disorder characterized by an absence of intrinsic ganglion cells in the nerves forming the plexus of the lower intestine. The WNT signaling pathway is considered to play an important role in embryonic development. In the present study, we analyzed 2 polymorphisms of the WNT8A gene (rs78301778 and rs6596422) to determine their association with the risk and development of HSCR. Allele frequencies and genotype distributions were analyzed by sequence analysis in patients with HSCR and normal controls. Using real-time PCR, western blot analysis and immunohistochemistry, we detected the mRNA and protein expression of WNT8A in patients with HSCR. The data indicated that the differences in genotype distributions and allele frequencies of rs78301778 and rs6596422 between various clinical classifications were statistically significant. The analysis of the mRNA and protein expression of WNT8A revealed that the expression of WNT8A was increased in the stenotic colon segments compared with the normal colon segments. In conclusion, the data presented in this study suggest that the WNT8A gene is involved in the susceptibility to HSCR, and plays an important role in the occurrence and development of HSCR. These findings warrant further investigation.

Congenital central hypoventilation syndrome

Congenital central hypoventilation syndrome (CCHS) is characterized by hypoventilation during sleep and impaired ventilatory responses to hypercapnia and hypoxemia. Most cases are sporadic and caused by de novo PHOX2B gene mutations, which are usually polyalanine repeat expansions. Physiological and neuroanatomical studies of genetically engineered mice and analyses of cellular responses to mutated Phox2b have shed light on the pathophysiological mechanisms of CCHS. Findings in Phox2b(27Ala/+) knock-in mice consisted of unstable breathing with apneas, absence of the ventilatory response to hypercapnia, death within a few hours after birth, and absence of the retrotrapezoid nucleus (RTN). Conditional mouse mutants in which Phox2b(27Ala) was targeted to the RTN also lacked the ventilatory response to hypercapnia at birth but survived to adulthood and developed a partial hypercapnia response. The therapeutic effects of desogestrel are being evaluated in clinical trials, and recent analyses of cellular responses to polyAla Phox2b aggregates have suggested new pharmacological approaches designed to counteract the toxic effects of mutated Phox2b.

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

Long considered a rare and unique disorder of respiratory control, congenital central hypoventilation syndrome has recently been further distinguished as a disorder of autonomic regulation. Similarly, more recent evidence suggests that sudden infant death syndrome is also a disorder of autonomic regulation. Congenital central hypoventilation syndrome typically presents in the newborn period with alveolar hypoventilation, symptoms of autonomic dysregulation and, in a subset of cases, Hirschsprung disease or tumors of neural crest origin or both. Genetic investigation identified PHOX2B, a crucial gene during early autonomic development, as disease defining for congenital central hypoventilation syndrome. Although sudden infant death syndrome is most likely defined by complex multifactorial genetic and environmental interactions, it is also thought to result from central deficits in the control of breathing and autonomic regulation. The purpose of this article is to review the current understanding of these autonomic disorders and discuss the influence of this information on clinical practice and future research directions.