Novel PHOX2B mutations in congenital central hypoventilation syndrome

Hirschsprung disease

Hirschsprung disease (HSCR) is a rare congenital intestinal disease that occurs in 1 in 5,000 live births. HSCR is characterized by the absence of ganglion cells in the myenteric and submucosal plexuses of the intestine. Most patients present during the neonatal period with the first meconium passage delayed beyond 24 h, abdominal distension and vomiting. Syndromes associated with HSCR include trisomy 21, Mowat-Wilson syndrome, congenital central hypoventilation syndrome, Shah-Waardenburg syndrome and cartilage-hair hypoplasia. Multiple putative genes are involved in familial and isolated HSCR, of which the most common are the RET proto-oncogene and EDNRB. Diagnosis consists of visualization of a transition zone on contrast enema and confirmation via rectal biopsy. HSCR is typically managed by surgical removal of the aganglionic bowel and reconstruction of the intestinal tract by connecting the normally innervated bowel down to the anus while preserving normal sphincter function. Several procedures, namely Swenson, Soave and Duhamel procedures, can be undertaken and may include a laparoscopically assisted approach. Short-term and long-term comorbidities include persistent obstructive symptoms, enterocolitis and soiling. Continued research and innovation to better understand disease mechanisms holds promise for developing novel techniques for diagnosis and therapy, and improving outcomes in patients.

Non-polyalanine repeat mutation in PHOX2B is detected in autopsy cases of sudden unexpected infant death

Background

Congenital central hypoventilation syndrome (CCHS), which is caused by PHOX2B with phenotypic variations, has a point of controversy: CCHS is putatively involved in autopsy cases of sudden unexpected infant death (SUID) including sudden infant death syndrome.

Objective

The relation of CCHS to SUID cases was investigated by extensive genotyping of PHOX2B.

Methods

We analyzed 93 DNA samples of less than one-year-old SUID cases that were autopsied in our department. Unrelated adult volunteers (n = 942) were used as the control.

Results

No polyalanine tract expansion was detected in the SUID cases. The allelic frequencies of repeat contractions and SNP (rs28647582) in intron 2 were not significantly different from that in those control group. Further extensive sequencing revealed a non-polyalanine repeat mutation (NPARM) of c.905A>C in a sudden death case of a one-month-old male infant. This missense mutation (p.Asn302Thr), registered as rs779068107, was annotated to ‘Affected status is unknown’, but it might be associated with the sudden death.

Conclusion

NPARM was more plausibly related to sudden unexpected death than expansions because of severe clinical complications. This finding indicates possible CCHS involvement in forensic autopsy cases without ante-mortem diagnosis.

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.

Paired-like homeobox gene (PHOX2B) nonpolyalanine repeat expansion mutations (NPARMs): genotype-phenotype correlation in congenital central hypoventilation syndrome (CCHS)

PURPOSE

CCHS is an extremely rare congenital disorder requiring artificial ventilation as life support. Typically caused by heterozygous polyalanine repeat expansion mutations (PARMs) in the PHOX2B gene, identification of a relationship between PARM length and phenotype severity has enabled anticipatory management. However, for patients with non-PARMs in PHOX2B (NPARMs, ~10% of CCHS patients), a genotype-phenotype correlation has not been established. This comprehensive report of PHOX2B NPARMs and associated phenotypes, aims at elucidating potential genotype-phenotype correlations that will guide anticipatory management.

METHODS

An international collaboration (clinical, commercial, and research laboratories) was established to collect/share information on novel and previously published PHOX2B NPARM cases. Variants were categorized by type and gene location. Categorical data were analyzed with chi-square and Fisher's exact test; further pairwise comparisons were made on significant results.

RESULTS

Three hundred two individuals with PHOX2B NPARMs were identified, including 139 previously unreported cases. Findings demonstrate significant associations between key phenotypic manifestations of CCHS and variant type, location, and predicted effect on protein function.

CONCLUSION

This study presents the largest cohort of PHOX2B NPARMs and associated phenotype data to date, enabling genotype-phenotype studies that will advance personalized, anticipatory management and help elucidate pathological mechanisms. Further characterization of PHOX2B NPARMs demands longitudinal clinical follow-up through international registries.

Congenital central hypoventilation syndrome in neonates: report of fourteen new cases and a review of the literature

BACKGROUND

Congenital central hypoventilation syndrome (CCHS) is a rare autosomal dominant disorder caused by pathogenic variants in paired-like homeobox 2B (PHOX2B) gene. Characteristics of neonatal-onset CCHS cases have not been well assessed. The aim of this study is to expand current knowledge of clinical and genetic features of neonates with CCHS and provide data on the genotype-phenotype correlation.

METHODS

We made a retrospective analysis of 14 neonates carrying PHOX2B pathogenic variants from 2014 to 2019 and we reviewed previously published neonatal-onset cases. Clinical and genetic data were analyzed. Moreover, genotype-phenotype correlation analysis was performed.

RESULTS

We identified a total of 60 neonatal-onset CCHS cases (35 males and 25 females) including 14 novel cases from our local cohort. Nearly 20% (18.2%) of the patients were born prematurely. Nearly half (46.2%) of the patients had abnormal family history. Polyhydramnios was observed in 21.3% (10/47) of the patients. About 90% of the patients manifested symptoms of hypoventilation in the first week of life. Fourteen patients (23.3%) were classified as mild-CCHS and the rest were severe-CCHS. Gastrointestinal manifestations were observed in 71.7% of the patients. Approximately twofold more males than females were affected by Hirschprung disease (HSCR)/variant HSCR (75.8% vs. 35%, P=0.003). Neural crest tumor occurred in 9.1% (4/44) patients. Half patients had polyalanine repeat expansion mutations (PARMs) in PHOX2B (seven with 25 PARM, nine with 26 PARM, twelve with 27 PARM, one with 28 PARM and one with 31 PARM) and the other half patients had 23 distinct non-polyalanine repeat expansion mutations (NPARMs) with one novel pathogenic variant (c.684dup). The prevalence of HSCR and mild-CCHS among patients with NPARMs was significantly greater than that of the patients with PARMs.

CONCLUSIONS

This report provides a large cohort of neonatal-onset CCHS cases. The results indicate that severe hypoventilation and HSCR are frequently observed in this group. NPARMs accounted for half of the cohort with some genotypes tend to be associated with mild phenotype. Molecular testing in neonates with suspicion of CCHS and genetic counseling for CCHS families are highly recommended.