Case report of Haddad syndrome in a newborn: congenital central hypoventilation syndrome and Hirschsprung's disease

A novel PHOX2B gene mutation in an extremely low birth weight infant with congenital central hypoventilation syndrome and variant Hirschsprung's disease

Congenital central hypoventilation syndrome is a disorder of respiratory control caused by mutations in the paired-like homeobox 2B gene. Mutations in the paired-like homeobox 2B gene are also responsible for Hirschsprung's disease. Variant Hirschsprung's disease is a rarer disorder that does not meet the diagnostic criteria of Hirschsprung's disease, although severe functional bowel obstruction persists. We present a case of an extremely low birth weight infant with congenital central hypoventilation syndrome and variant Hirschsprung's disease. A male infant who was diagnosed to have fetal growth restriction and polyhydramnios was delivered by emergency cesarean section at 30 weeks and 3 days of gestational age due to non-reassuring fetal status. The birth weight was 979 g, and intensive care was started immediately following delivery. The patient exhibited refractory apnea and was diagnosed with congenital central hypoventilation syndrome by genetic testing of the paired-like homeobox 2B gene. The patient also exhibited refractory functional bowel obstruction and was diagnosed to have variant Hirschsprung's disease through pathological examination of his intestinal specimens. The patient grew slowly but surely with intensive care including mechanical ventilation and parenteral nutrition. However, the patient repeatedly suffered from sepsis and died of fungemia at 197 days of age. This is the first congenital central hypoventilation syndrome case that was accompanied with variant Hirschsprung's disease, and the paired-like homeobox 2B mutation detected in this case (NM_003924.3: c.441G > C; p.(Gln147His)) is novel. This case suggests that the paired-like homeobox 2B mutation causes not only congenital central hypoventilation syndrome and Hirschsprung's disease, but also variant Hirschsprung's disease in humans. It also highlights the extreme difficulty in treating premature infants with severe and prolonged functional bowel obstruction.

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.

Hypoventilation syndromes

A wide variety of mechanisms can lead to the hypoventilation associated with various medical disorders, including derangements in central ventilatory control, mechanical impediments to breathing, and abnormalities in gas exchange leading to increased dead space ventilation. The pathogenesis of hypercapnia in obesity hypoventilation syndrome remains somewhat obscure, although in many patients comorbid obstructive sleep apnea appears to play an important role. Hypoventilation in neurologic or neuromuscular disorders is primarily explained by weakness of respiratory muscles, although some central nervous system diseases may affect control of breathing. In other chest wall disorders, obstructive airways disease, and cystic fibrosis, much of the pathogenesis is explained by mechanical impediments to breathing, but an element of increased dead space ventilation also often occurs. Central alveolar hypoventilation syndrome involves a genetically determined defect in central respiratory control. Treatment in all of these disorders involves coordinated management of the primary disorder (when possible) and, increasingly, the use of noninvasive positive pressure ventilation.

Sleep-related hypoventilation/hypoxemic syndromes

The latest edition of The International Classification of Sleep Disorders: Diagnostic and Coding Manual subsumes a broad range of disorders under the heading "Sleep Related Hypoventilation/Hypoxemic Syndromes." Some are quite common, such as COPD with worsening gas exchange during sleep; while some are exceedingly rare, such as congenital central hypoventilation syndrome. All share the attribute of abnormal gas exchange that worsens, or may only be present, during sleep. The sleep state, the sleeping posture, and the circadian rhythm driving sleep all may affect respiration by altering control of breathing and/or pulmonary mechanics. These changes are largely inconsequential in the normal individual but interact with respiratory, neurologic, or neuromuscular disease to manifest as the sleep-related hypoventilation/hypoxemic syndromes. In addition to optimal treatment of the underlying disorder (when known and when possible), treatment usually involves nocturnal ventilatory support that is now most commonly provided by noninvasive positive pressure ventilation.