Genotype-phenotype correlation of PHOX2B in two independent neonates with congenital central hypoventilation syndrome

Abstract

Objective To identify variants in the coding sequence of PHOX2B and RET using Sanger sequencing in two independent neonates with congenital central hypoventilation syndrome (CCHS) and to evaluate genotype-phenotype relationships.Methods Genomic DNA samples were obtained from two CCHS neonates admitted to Department of Neonatology,Children's Hospital of Fudan University in January and August of 2013.The coding regions in PHOX2B and RET were screened using Sanger sequencing.Genotype-phenotype analysis was performed on the basis of extensive literature search.Results Two male patients with CCHS were included in this study.Case 1 was a premature newborn with asphyxia at birth who showed subsequent ventilator dependence and abdominal distension.Hirschsprung disease was confirmed by surgery.Despite active treatment the patient died.Case 2 was a mature newborn who had multiple episodes of cyanosis and showed ventilator dependence.DNA sequencing demonstrated a heterozygous 38 bp deletion within exon 3 from bp 722-759 of the coding region [non-polyalanine repeat expansion mutations (NPARMs) ; genotype c.722_759het_del] in Case 1 and a heterozygous 21 bp polyalanine repeat expansion mutation (PARMs; genotype c.776_777het_dup) in Case 2.A homozygous c.1296 A＞G nucleotide change in RET was detected in both patients which was a common single nucleotide polymorphism (rs1800860).Following a literature review,mutations in PHOX2B were identified in 670 patients with CCHS.Over 90％ of CCHS cases were heterozygous for polyalanine expansion repeat mutations.The remaining patients with a CCHS phenotype were heterozygous for non-polyalanine expansion repeat mutations.Conclusions CCHS may be characterized by ventilator dependence in the neonatal period.Some of CCHS patients are likely to develop Hirschsprung disease.Symptoms of autonomic nervous system dysregulation such as diminished heart rate variability,esophageal dysmotility,and reduced basal body temperature may be atypical.The type of PHOX2B mutation and the length of PARMs determine the severity of CCHS.Patients with NPARMs show a more severe phenotype.Hirschsprung disease is more prevalent in cases with NPARMs.Individuals with genotypes from 20/27 to 20/33 often require continuous ventilatory support,especially as the expanded allele becomes larger.Genetic testing can not only provide evidence for definite diagnosis,but also guide treatment. Key words: Sleep apnea, central; Hypoventilation; Genetic association studies