Adult cases of late-onset congenital central hypoventilation syndrome and paired-like homeobox 2B-mutation carriers: an additional case report and pooled analysis

Later Onset Congenital Central Hypoventilation Syndrome

Congenital central hypoventilation syndrome (CCHS) is a rare disorder of the autonomic nervous system involving multiple organ systems, with the hallmark symptom of respiratory failure due to aberrant central control of breathing resulting in hypoxemia and hypercapnia. Later onset CCHS (LOCCHS) is defined as the diagnosis of CCHS in children older than 1 month. Molecular genetic testing for PHOX2B variants has led not only to increased diagnosis of neonates with CCHS but also the increased identification of older children, adolescents, and adults with LOCCHS who may have a milder clinical presentation of this multisystem disease.

Post-mortem genetic analysis of sudden unexplained death in a young cohort: a whole-exome sequencing study

Sudden unexplained death (SUD) constitutes a considerable portion of unexpected sudden death in the young. Molecular autopsy has proved to be an efficient diagnostic tool in the multidisciplinary management of SUD. Yet, many cases remain undiagnosed using the widely adopted targeted genetic screening strategies. Here, we investigated the genetic substrates of a young SUD cohort (18-40 years old) from China using whole-exome sequencing (WES), with the primary aim to identify novel SUD susceptibility genes. Within 255 previously acknowledged SUD-associated genes, 21 variants with likely functional effects (pathogenic/likely pathogenic) were identified in 51.9% of the SUD cases. More importantly, a set of 33 candidate genes associated with myopathy were identified to be novel susceptibility genes for SUD. Comparative analysis of the cumulative PHRED-scaled CADD score and polygenetic burden score showed that the amount and deleteriousness of variants in the 255 SUD-associated genes and the 33 candidate genes identified by this study were significantly higher compared with 289 randomly selected genes. A significantly higher genetic burden of rare variants (MAF < 0.1%) in the 33 candidate genes also highlighted putative roles of these genes in SUD. After incorporating these novel genes, the genetic testing yields of the current SUD cohort elevated from 51.9 to 66.7%. Our study expands understanding of the genetic variants underlying SUD and presents insights that improve the utility of genetic screenings.

Transitional care and clinical management of adolescents, young adults, and suspected new adult patients with congenital central hypoventilation syndrome

PURPOSE

With contemporaneous advances in congenital central hypoventilation syndrome (CCHS), recognition, confirmatory diagnostics with PHOX2B genetic testing, and conservative management to reduce the risk of early morbidity and mortality, the prevalence of identified adolescents and young adults with CCHS and later-onset (LO-) CCHS has increased. Accordingly, there is heightened awareness and need for transitional care of these patients from pediatric medicine into a multidisciplinary adult medical team. Hence, this review summarizes key clinical and management considerations for patients with CCHS and LO-CCHS and emphasizes topics of particular importance for this demographic.

METHODS

We performed a systematic review of literature on diagnostics, pathophysiology, and clinical management in CCHS and LO-CCHS, and supplemented the review with anecdotal but extensive experiences from large academic pediatric centers with expertise in CCHS.

RESULTS

We summarized our findings topically for an overview of the medical care in CCHS and LO-CCHS specifically applicable to adolescents and adults. Care topics include genetic and embryologic basis of the disease, clinical presentation, management, variability in autonomic nervous system dysfunction, and clarity regarding transitional care with unique considerations such as living independently, family planning, exposure to anesthesia, and alcohol and drug use.

CONCLUSIONS

While a lack of experience and evidence exists in the care of adults with CCHS and LO-CCHS, a review of the relevant literature and expert consensus provides guidance for transitional care areas.

Central sleep apnea: pathophysiologic classification

Central sleep apnea is not a single disorder; it can present as an isolated disorder or as a part of other clinical syndromes. In some conditions, such as heart failure, central apneic events are due to transient inhibition of ventilatory motor output during sleep, owing to the overlapping influences of sleep and hypocapnia. Specifically, the sleep state is associated with removal of wakefulness drive to breathe; thus, rendering ventilatory motor output dependent on the metabolic ventilatory control system, principally PaCO2. Accordingly, central apnea occurs when PaCO2 is reduced below the "apneic threshold". Our understanding of the pathophysiology of central sleep apnea has evolved appreciably over the past decade; accordingly, in disorders such as heart failure, central apnea is viewed as a form of breathing instability, manifesting as recurrent cycles of apnea/hypopnea, alternating with hyperpnea. In other words, ventilatory control operates as a negative-feedback closed-loop system to maintain homeostasis of blood gas tensions within a relatively narrow physiologic range, principally PaCO2. Therefore, many authors have adopted the engineering concept of "loop gain" (LG) as a measure of ventilatory instability and susceptibility to central apnea. Increased LG promotes breathing instabilities in a number of medical disorders. In some other conditions, such as with use of opioids, central apnea occurs due to inhibition of rhythm generation within the brainstem. This review will address the pathogenesis, pathophysiologic classification, and the multitude of clinical conditions that are associated with central apnea, and highlight areas of uncertainty.

Congenital Central Hypoventilation Syndrome: Optimizing Care with a Multidisciplinary Approach

Congenital central hypoventilation syndrome (CCHS) is a rare genetic disorder affecting respiratory control and autonomic nervous system function caused by variants in the paired-like homeobox 2B (PHOX2B) gene. Although most patients are diagnosed in the newborn period, an increasing number of patients are presenting later in childhood, adolescence, and adulthood. Despite hypoxemia and hypercapnia, patients do not manifest clinical features of respiratory distress during sleep and wakefulness. CCHS is a lifelong disorder. Patients require assisted ventilation throughout their life delivered by positive pressure ventilation via tracheostomy, noninvasive positive pressure ventilation, and/or diaphragm pacing. At different ages, patients may prefer to change their modality of assisted ventilation. This requires an individualized and coordinated multidisciplinary approach. Additional clinical features of CCHS that may present at different ages and require periodic evaluations or interventions include Hirschsprung’s disease, gastrointestinal dysmotility, neural crest tumors, cardiac arrhythmias, and neurodevelopmental delays. Despite an established PHOX2B genotype and phenotype correlation, patients have variable and heterogeneous clinical manifestations requiring the formulation of an individualized plan of care based on collaboration between the pulmonologist, otolaryngologist, cardiologist, anesthesiologist, gastroenterologist, sleep medicine physician, geneticist, surgeon, oncologist, and respiratory therapist. A comprehensive multidisciplinary approach may optimize care and improve patient outcomes. With advances in CCHS management strategies, there is prolongation of survival necessitating high-quality multidisciplinary care for adults with CCHS.

Variable phenotypes in congenital central hypoventilation syndrome with PHOX2B nonpolyalanine repeat mutations

STUDY OBJECTIVES

Congenital central hypoventilation syndrome (CCHS) is a rare disorder affecting the autonomic nervous system that is caused by variants in the PHOX2B gene. About 10% of patients with CCHS have nonpolyalanine repeat mutations (NPARM) that are associated with severe phenotypes requiring continuous assisted ventilation, Hirschsprung's disease, and increased neural crest tumor risk. However, some patients with NPARMs have milder phenotypes. Our objective was to describe the phenotypes in patients with CCHS PHOX2B NPARM.

METHODS

Retrospective case series of patients with CCHS PHOX2B NPARM was conducted at two children's hospitals to evaluate their phenotypes.

RESULTS

We identified eight patients with CCHS PHOX2B NPARM aged 3-31 years. Seven patients were diagnosed in infancy and one patient at two years of age. All patients presented with respiratory depression in the first two months of life. Only one patient was identified with a severe phenotype requiring continuous assisted ventilation, Hirschsprung's disease, and a neural crest tumor, that was resected. Five patients required positive pressure ventilation via tracheostomy only during sleep and two patients required oxygen only during sleep. Four patients had Hirschsprung's disease and one patient had a cardiac pacemaker due to a bradyarrhythmia. None of the patients had echocardiographic abnormalities.

CONCLUSIONS

Patients with CCHS PHOX2B NPARM can have variable phenotypes emphasizing the importance of implementing a plan of care that is individualized for each patient. The type of NPARM and its respective location on the PHOX2B gene may play a critical role in the severity of phenotypes displayed by each patient.