Polyalanine expansion and frameshift mutations of the paired-like homeobox gene PHOX2B in congenital central hypoventilation syndrome

Hospital Universitario Cruces, Bilbo, Basque Country, Spain
Nature Genetics (Impact Factor: 29.65). 05/2003; 33(4):459-61. DOI: 10.1038/ng1130
Source: PubMed

ABSTRACT Congenital central hypoventilation syndrome (CCHS or Ondine's curse; OMIM 209880) is a life-threatening disorder involving an impaired ventilatory response to hypercarbia and hypoxemia. This core phenotype is associated with lower-penetrance anomalies of the autonomic nervous system (ANS) including Hirschsprung disease and tumors of neural-crest derivatives such as ganglioneuromas and neuroblastomas. In mice, the development of ANS reflex circuits is dependent on the paired-like homeobox gene Phox2b. Thus, we regarded its human ortholog, PHOX2B, as a candidate gene in CCHS. We found heterozygous de novo mutations in PHOX2B in 18 of 29 individuals with CCHS. Most mutations consisted of 5-9 alanine expansions within a 20-residue polyalanine tract probably resulting from non-homologous recombination. We show that PHOX2B is expressed in both the central and the peripheral ANS during human embryonic development. Our data support an essential role of PHOX2B in the normal patterning of the autonomous ventilation system and, more generally, of the ANS in humans.

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    ABSTRACT: 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.
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    ABSTRACT: To investigate the role of IKBKAP (inhibitor of kappa light polypeptide gene enhancer in B-cells, kinase complex-associated protein) in the development of enteric nervous system (ENS) and Hirschsprung disease (HSCR). In this study, we injected a morpholino that blocked the translation of ikbkap protein to 1-cell stage zebrafish embryos. The phenotype in the ENS was analysed by antibody staining of the pan-neuronal marker HuC/D followed by enteric neuron counting. The mean numbers of enteric neurons were compared between the morphant and the control. We also studied the expressions of ret and phox2bb, which are involved in ENS development, in the ikbkap morpholino injected embryos by quantitative reverse transcriptase polymerase chain reaction and compared them with the control. We observed aganglionosis (χ (2), P < 0.01) and a reduced number of enteric neurons (38.8 ± 9.9 vs 50.2 ± 17.3, P < 0.05) in the zebrafish embryos injected with ikbkap translation-blocking morpholino (morphant) when compared with the control embryos. Specificity of the morpholino was confirmed by similar results obtained using a second non-overlapping morpholino that blocked the translation of ikbkap. We further studied the morphant by analysing the expression levels of genes involved in ENS development such as ret, phox2bb and sox10, and found that phox2bb, the ortholog of human PHOX2B, was significantly down-regulated (0.51 ± 0.15 vs 1.00 ± 0, P < 0.05). Although we also observed a reduction in the expression of ret, the difference was not significant. Loss of IKBKAP contributed to HSCR as demonstrated by functional analysis in zebrafish embryos.
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    ABSTRACT: Purpose: Congenital central hypoventilation syndrome (CCHS), or Ondine's curse, is a rare disorder affecting central respiratory drive. Patients with this disorder fail to ventilate adequately and require lifelong ventilatory support. Diaphragm pacing is a form of ventilatory support which can improve mobility and/or remove the tracheostomy from CCHS patients. Little is known about complications and long-termoutcomes of this procedure. Methods: A single-center retrospective review was performed of CCHS patients undergoing placement of phrenic nerve electrodes for diaphragm pacing between 2000 and 2012. Data abstracted from the medical record included operation duration, ventilationmethod, number of trocars required, and postoperative and pacing outcomes. Results: Charts of eighteen patients were reviewed. Mean surgical time was 3.3 +/- 0.7 hours. In all cases except one, three trocars were utilized for each hemithorax, with no conversions to open procedures. Five patients (27.8%) experienced postoperative complications. The mean ICU stay was 4.3 +/- 0.5 days, and the mean hospital stay is 5.7 +/- 0.3 days. Eleven patients (61.1%) achieved their daily goal pacing times within the follow- up period. Conclusions: Thoracoscopic placement of phrenic nerve electrodes for diaphragmatic pacing is a safe and effective treatmentmodality for CCHS. Observed complications were temporary, and the majority of patientswere able to achieve pacing goals.
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May 31, 2014