Phox2b mutation mediated by Atoh1 expression impaired respiratory rhythm and ventilatory responses to hypoxia and hypercapnia.

Mutations in the transcription factor Phox2b cause congenital central hypoventilation syndrome (CCHS). The syndrome is characterized by hypoventilation and inability to regulate breathing to maintain adequate O2 and CO2 levels. The mechanism by which CCHS impact respiratory control is incompletely understood, and even less is known about the impact of the non-polyalanine repeat expansion mutations (NPARM) form. Our goal was to investigate the extent by which NPARM Phox2b mutation affect (a) respiratory rhythm; (b) ventilatory responses to hypercapnia (HCVR) and hypoxia (HVR); and (c) number of chemosensitive neurons in mice. We used a transgenic mouse line carrying a conditional Phox2bΔ8 mutation (same found in humans with NPARM CCHS). We crossed them with Atoh1cre mice to introduce mutation in regions involved with respiratory function and central chemoreflex control. Ventilation was measured by plethysmograph during neonatal and adult life. In room air, mutation in neonates and adult did not greatly impact basal ventilation. However, Phox2bΔ8, Atoh1cre increased breath irregularity in adults. The HVR and HCVR were impaired in neonates. The HVR, but not HCVR, was still partially compromised in adults. The mutation reduced the number of Phox2b+/TH--expressing neurons as well as the number of fos-activated cells within the ventral parafacial region (also named retrotrapezoid nucleus [RTN] region) induced by hypercapnia. Our data indicates that Phox2bΔ8 mutation in Atoh1-expressing cells impaired RTN neurons, as well as chemoreflex under hypoxia and hypercapnia specially early in life. This study provided new evidence for mechanisms related to NPARM form of CCHS neuropathology.

Congenital central hypoventilation syndrome associated with Hirschsprung's Disease: case report and literature review / Síndrome de hipoventilação central congênita associada à doença de Hirschsprung: relato de caso e revisão de literatura

Abstract Objective: To report the case of a newborn with recurrent episodes of apnea, diagnosed with Congenital Central hypoventilation syndrome (CCHS) associated with Hirschsprung's disease (HD), configuring Haddad syndrome. Case description: Third child born at full-term to a non-consanguineous couple through normal delivery without complications, with appropriate weight and length for gestational age. Soon after birth he started to show bradypnea, bradycardia and cyanosis, being submitted to tracheal intubation and started empiric antibiotic therapy for suspected early neonatal sepsis. During hospitalization in the NICU, he showed difficulty to undergo extubation due to episodes of desaturation during sleep and wakefulness. He had recurrent episodes of hypoglycemia, hyperglycemia, metabolic acidosis, abdominal distension, leukocytosis, increase in C-reactive protein levels, with negative blood cultures and suspected inborn error of metabolism. At 2 months of age he was diagnosed with long-segment Hirschsprung's disease and was submitted to segment resection and colostomy through Hartmann's procedure. A genetic research was performed by polymerase chain reaction for CCHS screening, which showed the mutated allele of PHOX2B gene, confirming the diagnosis. Comments: This is a rare genetic, autosomal dominant disease, caused by mutation in PHOX2B gene, located in chromosome band 4p12, which results in autonomic nervous system dysfunction. CCHS can also occur with Hirschsprung's disease and tumors derived from the neural crest. There is a correlation between phenotype and genotype, as well as high intrafamilial phenotypic variability. In the neonatal period it can simulate cases of sepsis and inborn errors of metabolism.

Resumo Objetivo: Relatar caso de neonato com episódios de apneias recorrentes, diagnosticado com síndrome de hipoventilação central congênita (SHCC) associada à doença de Hirschsprung (DH), o que configurou síndrome de Haddad. Descrição do caso: Terceiro filho de casal não consanguíneo, nascido a termo, parto normal sem intercorrências, peso e comprimento adequados para idade gestacional. Logo após o nascimento apresentou bradipneia, bradicardia e cianose, foi submetido à intubação orotraqueal e iniciada antibioticoterapia empírica devido à suspeita de sepse neonatal precoce. Durante internação em UTI neonatal evoluiu com dificuldade de extubação devido a episódios de dessaturação durante sono e vigília. Apresentou quadros recorrentes de hipoglicemia, hiperglicemia, acidose metabólica, distensão abdominal, leucocitose, aumento de proteína C reativa, com hemoculturas negativas e suspeita de erro inato do metabolismo. Aos dois meses foi diagnosticada doença de Hirschsprung de segmento longo, foi submetido à ressecção do segmento e colostomia à Hartmann. Feita pesquisa genética por reação em cadeia da polimerase para pesquisa de SHCC, que evidenciou alelo mutado do gene PHOX2B e confirmou o diagnóstico. Comentários: Trata-se de doença genética rara, de herança autossômica dominante, causada por mutação no gene PHOX2B, localizado na banda cromossômica 4p12, que resulta em disfunção do sistema nervoso autônomo. A SHCC também pode cursar com doença de Hirschsprung e tumores derivados da crista neural. Há correlação entre fenótipo e genótipo, além de grande variabilidade fenotípica intrafamiliar. No período neonatal pode simular quadros de sepse e erros inatos do metabolismo.

Congenital central hypoventilation syndrome associated with Hirschsprung's Disease: case report and literature review. / Síndrome de hipoventilação central congênita associada à doença de Hirschsprung: relato de caso e revisão de literatura.

OBJECTIVE: To report the case of a newborn with recurrent episodes of apnea, diagnosed with Congenital Central hypoventilation syndrome (CCHS) associated with Hirschsprung's disease (HD), configuring Haddad syndrome. CASE DESCRIPTION: Third child born at full-term to a non-consanguineous couple through normal delivery without complications, with appropriate weight and length for gestational age. Soon after birth he started to show bradypnea, bradycardia and cyanosis, being submitted to tracheal intubation and started empiric antibiotic therapy for suspected early neonatal sepsis. During hospitalization in the NICU, he showed difficulty to undergo extubation due to episodes of desaturation during sleep and wakefulness. He had recurrent episodes of hypoglycemia, hyperglycemia, metabolic acidosis, abdominal distension, leukocytosis, increase in C-reactive protein levels, with negative blood cultures and suspected inborn error of metabolism. At 2 months of age he was diagnosed with long-segment Hirschsprung's disease and was submitted to segment resection and colostomy through Hartmann's procedure. A genetic research was performed by polymerase chain reaction for CCHS screening, which showed the mutated allele of PHOX2B gene, confirming the diagnosis. COMMENTS: This is a rare genetic, autosomal dominant disease, caused by mutation in PHOX2B gene, located in chromosome band 4p12, which results in autonomic nervous system dysfunction. CCHS can also occur with Hirschsprung's disease and tumors derived from the neural crest. There is a correlation between phenotype and genotype, as well as high intrafamilial phenotypic variability. In the neonatal period it can simulate cases of sepsis and inborn errors of metabolism.

Síndrome de hipoventilación alveolar central congénita / Congenital central alveolar hypoventilation syndrome

ResumenIntroducción: El síndrome de hipoventilación alveolar central congénita (SHACC) es un raro trastorno respiratorio del dormir, aunque cada vez más frecuentemente diagnosticado en clínicas de sueño y servicios de neumología pediátrica. Si bien se desconoce su epidemiología, en la literatura médica existen cerca de 300 casos reportados, y su incidencia es de 1 caso por cada 200,000 recién nacidos vivos. Se caracteriza por hipoventilación alveolar que se presenta o empeora durante el sueño. Es secundario a la disminución/ausencia de la respuesta ventilatoria a la hipercapnia o hipoxemia, y en el 90% de los casos es debido a una mutación tipo PARM del gen PHOX2B. Su tratamiento incluye ventilación mecánica y marcapasos diafragmático. Si la terapéutica no se inicia en forma temprana, el paciente desarrollará insuficiencia respiratoria crónica, hipertensión arterial pulmonar, cor pulmonale y la muerte.Casos clínicos: Se presentan tres casos de SHACC diagnosticados, tratados y en seguimiento en la Clínica de Trastornos Respiratorios del Dormir del Instituto Nacional de Enfermedades Respiratorias.Conclusiones: El diagnóstico temprano es importante para el inicio del soporte ventilatorio, y para prevenir el desarrollo de complicaciones y reducir la mortalidad.

AbstractBackground: Congenital central alveolar hypoventilation syndrome (CCAHS) is a rare sleep-related breathing disorder. Although increasingly frequently diagnosed in sleep clinics and pediatric pulmonology services, its epidemiology is not known. There are about 300 reported cases reported in the literature with an incidence of 1 case per 200,000 live births. CCAHS is characterized by alveolar hypoventilation that occurs or worsens during sleep and is secondary to a reduction/absence of the ventilatory response to hypercapnia and/or hypoxemia. In 90% of the cases it is due to a PARM-type mutation of the PHOX2B gene. Treatment includes mechanical ventilation and diaphragmatic pacemaker. If therapy is not initiated promptly the patient can evolve to chronic respiratory failure, pulmonary hypertension, cor pulmonale and death.Case reports: In this paper we present three cases of CCAHS diagnosed, treated and followed up at the Sleep Disorders Clinic of the National Institute of Respiratory Diseases in Mexico.Conclusions: Early diagnosis is important to initiate ventilatory support so as to prevent any complications and to reduce mortality.

[Congenital central alveolar hypoventilation syndrome]. / Síndrome de hipoventilación alveolar central congénita.

BACKGROUND: Congenital central alveolar hypoventilation syndrome (CCAHS) is a rare sleep-related breathing disorder. Although increasingly frequently diagnosed in sleep clinics and pediatric pulmonology services, its epidemiology is not known. There are about 300 reported cases reported in the literature with an incidence of 1 case per 200,000 live births. CCAHS is characterized by alveolar hypoventilation that occurs or worsens during sleep and is secondary to a reduction/absence of the ventilatory response to hypercapnia and/or hypoxemia. In 90% of the cases it is due to a PARM-type mutation of the PHOX2B gene. Treatment includes mechanical ventilation and diaphragmatic pacemaker. If therapy is not initiated promptly the patient can evolve to chronic respiratory failure, pulmonary hypertension, cor pulmonale and death. CASE REPORTS: In this paper we present three cases of CCAHS diagnosed, treated and followed up at the Sleep Disorders Clinic of the National Institute of Respiratory Diseases in Mexico. CONCLUSIONS: Early diagnosis is important to initiate ventilatory support so as to prevent any complications and to reduce mortality.

Acute exercise-induced activation of Phox2b-expressing neurons of the retrotrapezoid nucleus in rats may involve the hypothalamus.

The rat retrotrapezoid nucleus (RTN) contains neurons that have a well-defined phenotype characterized by the presence of vesicular glutamate transporter 2 (VGLUT2) mRNA and a paired-like homeobox 2b (Phox2b)-immunoreactive (ir) nucleus and the absence of tyrosine hydroxylase (TH). These neurons are important to chemoreception. In the present study, we tested the hypothesis that the chemically-coded RTN neurons (ccRTN) (Phox2b(+)/TH(-)) are activated during an acute episode of running exercise. Since most RTN neurons are excited by the activation of perifornical and lateral hypothalamus (PeF/LH), a region that regulates breathing during exercise, we also tested the hypothesis that PeF/LH projections to RTN neurons contribute to their activation during acute exercise. In adult male Wistar rats that underwent an acute episode of treadmill exercise, there was a significant increase in c-Fos immunoreactive (c-Fos-ir) in PeF/LH neurons and RTN neurons that were Phox2b(+)TH(-) (p<0.05) compared to rats that did not exercise. Also the retrograde tracer Fluoro-Gold that was injected into RTN was detected in c-Fos-ir PeF/LH (p<0.05). In summary, the ccRTN neurons (Phox2b(+)TH(-)) are excited by running exercise. Thus, ccRTN neurons may contribute to both the chemical drive to breath and the feed-forward control of breathing associated with exercise.