CCHS is a rare disorder characterized by abnormal ventilatory response to hypoxia and hypercapnia, often associated with other autonomic nervous system dysfunctions. Clinical diagnosis of CCHS is based on the presence of central alveolar hypoventilation in the absence of primary pulmonary, cardiac, neuromuscular, or neurologic disease. However, diagnosis is confounded in a critically ill neonate when phenotype is not typical or when the patient is complicated with other conditions predispose to respiratory insufficiency, which is further accentuated in premature newborns, as premature infants often have problems of recurrent central apneas and feeding intolerance. Diagnosing CCHS in NICUs for critically ill babies is challenging and molecular analysis may help to diagnose this disorder in this age group.
In this study, we gave the first comprehensive report on 14 Chinese CCHS neonates and reviewed published data on 46 neonatal cases with genetic diagnosis. It includes the largest number of neonatal-onset CCHS reported to date with PHOX2B mutations.
Prenatal/intrapartum history is essential to diagnosis in newborn area. It is noteworthy that, polyhydramnios was observed in 21.3% (10/47) of the patients, higher than reported (3.3%), together with high occurrence of postnatal dysphagia, we speculate the complication of polyhydramnios might be derived from a dysfunction of swallowing control. Abnormal family history including affected patients, abnormal miscarriages and early death was observed in 46.2% (18/39) of the patients. In addition, a few patients presented decreased fetal movements poor fetal heart rate variability in fetal period. These findings would provide clues for the diagnosis and they emphasized the need for a careful review of the neonates’ history.
CCHS patients suffer a broad spectrum of severity. In the current cohort, about three quarters cases presented as severe-CCHS. Compared with mild-CCHS group, neonates in severer-CCHS group may manifest hypoventilation earlier, be complicated with longer segment HSCR. They may predispose to harbor de novo PHOX2B variants. And their parents tend to choose withdrawn of life thus a higher mortality may occur in the first year of life. Correlations between PHOX2B genotype and CCHS phenotype have been described before. Patients carrying more PARMs or NPARMs appear to produce severer phenotypes with continuous ventilatory support, HSCR with extensive gut involvement, and an increased tumor risk.  However, several recent studies have identified novel NPARMs in CCHS patients who have a milder clinical presentation and delayed diagnosis, suggesting that NPARM may have widely variable phenotypic expressivity which was associated with the type and location of the mutation[30, 31]. Our results revealed that HSCR was indeed more prevalent among NPARMs subjects than among those with PARMs, though no evident correlation between genotype and the extent of HD was observed owing to the small sample size. However, a higher proportion of severe-CCHS patients was observed in the PARMs group which was different from previous reports. There are two possible explanations. First, patients with 20/26 PARMs and more PARMs account for majority of this group who present sever hypoventilation extent in neonatal period. Second, patients with NPARMs can present with a diverse range of respiratory phenotypes. We identified 14 mild-CCHS patients from the 60 neonates, apart from 3 patients with 20/25 PARM, we found other 8 NPARMs (c.234C>G, c.255_256delCT, c.391delC, c.448C>G, c.481del, c.663_711del49, c.691_698dup8, c.944G>C) in 11 patients appear to be associated with the mild-CCHS. Among the 11 patients, nine of them had HSCR and another one had neural crest tumor. So, it is currently difficult to assess severity and prognosis based on specific NPARM genotype. In the future, more research is needed on patients with NPARMs to further understand and characterize the variety of associated clinical presentations and elucidate the underlying molecular mechanism.
Neural crest tumors are more frequently diagnosed among CCHS patients over 1 year of age. Four patients harboring frameshift PHOX2B mutations were identified having tumor in this study. Interestingly, there was no evidence of tumor in one of the babies through initial abdominal ultrasound screening. While measurements of the catecholamines’ metabolites strongly suggested neuroblastoma and then CT scans were performed to confirm the diagnosis. These findings emphasize the need of metabolites tests and CT scans in CCHS neonates especially those patients with frameshift PHOX2B mutations who are at very high risk for developing tumors.
Recurrent episodes of apnea and cyanosis in a newborn should be distinguished from seizure which is a common neurological condition in NICU. Neurological complications were observed in 34.1% (15/44) CCHS neonates, and about half of them presented as seizure. It is unclear whether this is due to hypoxemia or a direct result of the primary neurologic problem associated with CCHS. Thus CCHS should be suspected by neonatologists when confronted with seizure in NICU.
The association between cardiovascular defects and mutations in PHOX2B had been previously assessed by Lombardo et al. Congenital heart disease (CHD) was found in 30% of CCHS patients which was higher than general population (0.8%). The majority of patients had anomalies involving the proximal aortic arch and/or proximal coronary arteries. Similar prevalence of CHD in our cohort was observed (23.7%, 9/38) but anomalies including patent ductus arteriosus and atrial septal defect appears to be more common. In the previous study, five of seven patients identified with CHD had either NPARMs or whole-gene deletion, while in the current cohort, more patients with PARMs were identified with CHD, though without significantly difference (P=0.055). Considering the small sample size of both studies, we suggest a large-scale, multicenter study in this field.
Pertaining to genetic findings, higher frequency of NPARMs (50%) was identified in this group of neonates than previous data (10%). This may be explained by the previous finding that patients carrying shorter PARMs like 20/24, 20/25 PARM may have a mild phenotypic consequence who exhibit hypoventilation in late childhood or adulthood, while our study was specific to newborns. Triplet expansion of 27 nucleotides (20/27) was the most frequent mutation (20.0%) identified in our cohort. Thus far, nearly 200 cases associated with NPARMs have been reported, with about 100 unique variants identified. Here, we reported a novel NPARM of PHOX2B (c.684dup) which was predicted to cause frameshift and produce prolonged protein in a preterm neonate with sever CCHS and HSCR. This finding contributes to accumulating data on the genotype-phenotype correlations and providing useful information for clinical practice.
CCHS is typically inherited in an autosomal dominant pattern, and most mutations occur de novo. Recent evidence indicates that a subset is inherited from parents carrying somatic or germline mosaicism for these PHOX2B mutations, thus the prevalence of de novo mutations may be overestimated. In this study, fourteen cases showed a familiar pattern, thirteen represented sporadic mutations while in 33 cases familiarity was not reported. Among them, CCHS was observed in one pair of Chinese siblings with the same CCHS-causing PHOX2B 20/26 PARM, as this 20/26 genotype is rare, with about 200 cases identified and reported worldwide, the recurrence of the same disease in this family strongly indicated inheritance of the PHOX2B mutation from an asymptomatic parent. However, this 20/26 mutation could not be found on testing PHOX2B gene in the parents’ blood samples thus germline mosaicism had been hypothesized to explain sibling recurrence for CCHS in this family which deserved further investigations. These findings highlighted the importance of family planning and genetic counseling for families of a PHOX2B mutation confirmed proband.
The current study also indicates that there are ethical problems in decision making in this group of neonates, and death occurrence is highly related to ethical decisions, especially in China. Mortality rates of 8% to 38% have been documented in various CCHS patient cohorts. In this cohort, available data showed that 35.3% (18/51) of the parents chose to withdraw of treatment and 39.4% (13/33) of the patients were deceased in the first year after birth. A striking finding was that nearly all the Chinese parents (92.9%, 13/14) elected withdrawal of treatment. Long-term outcome is the issue that most concerns parents. Babies with CCHS are routinely managed with a tracheostomy and ventilation, parents do not want their children to suffer with a lifetime of ventilation and they doubt their ability to care for them at home. They are also concerned about the impact of this child’s illness on other children and their family. At the same time, the medical and homecare requirements of CCHS children impose significant annual healthcare costs that few family incomes would cover without financial support in China. On the other side, neonatologists are generally pessimistic about medical outcomes and they tend to give parents the option to withdrawal of life support in this situation. In developed countries such as America, France and Japan, specialized centers were established to promote CCHS care and research. With advances in early diagnosis and home ventilation, CCHS patients are surviving into adulthood and reporting good quality of life. From a long-term follow-up of 196 children with CCHS in North America and Europe, vast majority (88%) of parents stated that things got better with time. As a developing country, China has much work to do to help healthcare professionals and parents gain confidence and comfort in managing CCHS such as providing optimal training and education.
As the present study was a single-center report with literature reviewing combination, methodological issues like skewed patient recruitment may limit our conclusions. First, this survey only targeted those CCHS neonates with genetic diagnosis, we may have missed relevant information on CCHS cases without genetic data. Secondly, for cases with genetic data, we could not obtain relevant clinical information that were not reported in the literatures, thus some phenotypic characteristics may have been underrepresented in this study. Considering sampling bias, these results should be confirmed in more patients. At the same time, large-scale follow-up studies are required for further information on disease progression.