The obesity hypoventilation syndrome in children with the Prader-Willi syndrome: a possible role for familial decreased response to carbon dioxide

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.

Breathing disorders in Prader-Willi syndrome: the role of obesity, growth hormone treatment and upper respiratory tract infections

Prader-Willi syndrome is a neurogenetic disorder characterized by a number of signs and symptoms, including muscular hypotonia in infancy, hypogonadism, obesity and short stature. Neurobehavioral abnormalities and cognitive impairment are common. In addition, breathing abnormalities have been described, including sleep-related breathing disorders, abnormal chemoreceptor sensitivity and pulmonary function abnormalities. Growth hormone treatment is now widely used in children with Prader-Willi syndrome to improve growth and body composition. Over the last 4 years, case reports have been published concerning unexpected death, many of which were related to respiratory abnormalities. This review focuses on breathing abnormalities in Prader-Willi syndrome individuals and the influence of obesity, growth hormone treatment and upper respiratory tract infections.

Sleep-disordered breathing in Prader-Willi syndrome and its association with neurobehavioral abnormalities

OBJECTIVES

To determine the prevalence and type of sleep-disordered breathing among patients with Prader-Willi syndrome (PWS) and its relationship to such neurobehavioral abnormalities as mental retardation, obsessive-compulsive behavior, and conduct disorders.

STUDY DESIGN

Polysomnography (PSG) studies were conducted in 13 unselected subjects with PWS (age 1.5 to 28 years). PSG results were compared with tests of behavior and cognition (Development Behavior Checklist [DBC], Auditory Continuous Performance Test [ACPT], and Wechsler Intelligence Scale appropriate for age).

RESULTS

Nine of 13 (69%) subjects had > 10 apneas and hypopneas per hour of sleep. Apart from a 2-year-old subject with normal body weight who demonstrated severe central hypopnea in rapid eye movement sleep, the sleep-breathing disturbance was due to upper airway obstruction. Age-adjusted body mass index was associated with more severe hypoxemia during sleep (min SaO2, r = -.87, P < .005) and more sleep disruption (arousals/hour of sleep, r = .62, P < .05; sleep efficiency, r = -.66, P < .05). Increasing severity of obstructive sleep apnea (OSA) or sleep disturbance was associated with daytime inactivity/sleepiness and autistic-relating behavior (DBC) and with impulsiveness (ACPT). Unexpectedly, sleep hypoxemia appeared to be predictive of increased performance IQ.

CONCLUSIONS

OSA is prevalent among subjects with PWS and is associated with increased body mass, daytime inactivity/ sleepiness, and some behavioral disturbances.

Hypercapnic arousal responses in Prader-Willi syndrome

STUDY OBJECTIVE

Prader-Willi syndrome (PWS) is characterized by a number of abnormalities of hypothalamic function, such as hyperphagia, short stature, temperature instability, hypogonadotropic hypogonadism, and neurosecretory growth hormone deficiency. Patients with PWS are reported to have sleep-disordered breathing and have blunted hypercapnic ventilatory responses secondary to abnormal peripheral chemoreceptor function. Thus, we hypothesized that hypercapnic arousal responses would be abnormal in PWS.

DESIGN

Hypercapnic arousal responses were tested in ten nonobese children and adults with PWS, aged 17.7 +/- 2.5 (SEM) years, 70% female, and nine control subjects, aged 14.2 +/- 2.6 years, 67% female. Hypercapnic challenges were performed during stage 3/4 non-rapid eye movement sleep.

RESULTS

The PWS subjects had a significantly higher arousal threshold to hypercapnia compared with the controls (53 +/- 1.0 vs 46 +/- 1.7 mm Hg; p < 0.01). The PWS subjects had significantly higher baseline end-tidal CO2 levels (42 +/- 0.8 vs 38 +/- 1.1 mm Hg; p < 0.01) and more central apneas greater than 15 s/h of sleep (1.5 +/- 0.3 vs 0.1 +/- 0.1; p < 0.01).

CONCLUSIONS

Elevated hypercapnic arousal thresholds during sleep are found in PWS subjects; these may be a manifestation of abnormal peripheral chemoreceptor function and may further contribute to sleep-disordered breathing in PWS patients.

Sleep and breathing in patients with the Prader-Willi syndrome

The Prader-Willi syndrome is characterized by infantile hypotonia, early childhood obesity, mental deficiency, short stature, small hands and feet, and hypogonadism. Many patients also have hypersomnolence, experience daytime hypoventilation, and subsequently die prematurely of cardiorespiratory failure. Hypersomnolence and daytime hypoventilation are also common occurrences in the sleep apnea syndrome. For a better understanding of the relationship of sleep to the features of the Prader-Willi syndrome, we retrospectively reviewed five patients (two adults, one adolescent, and two children) with this syndrome who underwent polysomnography. All patients were obese; they had hypersomnolence and daytime hypoxemia, and they nored. In all patients, the apnea plus hypopnea index was less than 10 episodes per hour of sleep. During rapid eye movement sleep, nonapneic reductions in oxyhemoglobin saturation were detected in one adult and in one child. Despite the presence of morbid obesity and a history of snoring, patients with Prader-Willi syndrome seem to have only mild sleep-disordered breathing.

Premature coronary artery disease and the Prader-Willi syndrome

A 28 year old woman with the Prader-Willi syndrome developed chest pain and loss of anterior R wave amplitude on the electrocardiogram. Cardiac catheterization demonstrated a severe proximal stenosis of the left anterior descending artery with delayed antegrade flow together with antero-apical akinesia consistent with myocardial infarction. Physicians involved in the management of patients with the Prader-Willi syndrome should be aware of this association with premature coronary artery disease.

The obesity hypoventilation syndrome and the Prader-Willi syndrome

Fourteen children with the Prader-Willi syndrome have been managed at the Royal Alexandra Hospital for Children between the years 1964-1980--twelve male, two female. Six male children developed features of the obesity hypoventilation syndrome. The age of onset of this complication ranged from 4.0 to 12.6 years. With one exception those children with the obesity hypoventilation syndrome were more obese than those without it. At the time of onset of the syndrome, five of six patients had weights greater than or equal to 6.5 standard deviations above ideal body weight. Those children without the obesity hypoventilation syndrome had a range of standard deviations 1.0 to 4.2 above the ideal body weight. In four of six cases weight reduction and a cardiac failure regimen resulted in reversal of the obesity hypoventilation syndrome. With two of the six children there had been cardiomegaly and increased pulmonary venous vascularity on x-ray at a chronological age of three months. Two of the six children died.

Anaesthetic considerations in the Prader-Willi syndrome: report of four cases

The anaesthetic management of four paediatric patients with the Prader-Willi syndrome is reported. The syndrome is characterized by obesity, mental retardation, genital hypoplasia, hypotonia, and diabetes mellitus. All patients were anaesthetized with halothane. Succinylcholine or pancuronium were used for muscle relaxation, without evidence of abnormal response. Common anaesthetic difficulties in this syndrome are obesity, hypotonia, disturbance in thermoregulation, arrhythmias, diabetes mellitus and convulsions.