Novel PHOX2B mutations in congenital central hypoventilation syndrome.

BACKGROUND: Congenital central hypoventilation syndrome (CCHS) is caused by mutation of paird-like homeobox 2B (PHOX2B). Approximately 90% of patients were found to carry polyalanine repeat expansion mutation (PARM), and the remaining 10% had non-PARM (NPARM). In PARM, the length of the polyalanine expansion correlates with clinical disease severity. Most patients with NPARM have hypoventilation symptoms in the neonatal period and complications of Hirschsprung disease, dysregulation of autonomic nervous system, and tumors of neural crest origin. Data on the genotype-phenotype association may contribute to the clinical management of the disease. METHODS: We studied the genetic background of Japanese CCHS patients according to PHOX2B sequencing. RESULTS: Of 133 Japanese CCHS patients we identified 12 patients carrying 11 different NPARM (approx. 9% of the patients) and described the clinical manifestations in seven of them with the following novel mutations: c.941-945del5, c.678_693dup16, c.609_616del8, c.620_633del14, c.663_711del 49, c.448C>G and c.944G>C. All patients had hypoventilation in the neonatal period and also had Hirschsprung disease, with the exception of two patients carrying c.620_633del14 and c.663_711del49 mutations. The patient carrying the c.609_616del8 mutation also had a benign mediastinal tumor. CONCLUSION: Most patients carrying NPARM had severe symptoms with frequent complications, as in previous reports, and should be carefully monitored for various complications, including neural crest-derived tumor.

Genotype-phenotype relationship in Japanese patients with congenital central hypoventilation syndrome.

Examine the genotype-phenotype relationship in Japanese congenital central hypoventilation syndrome (CCHS) patients and estimate the incidence of CCHS in Japan. Subjects were 92 Japanese patients with PHOX2B mutations; 19 cases carried 25 polyalanine repeat expansion mutations (PARMs); 67 cases carried 26 or more PARMs; and 6 had non-PARMs (NPARMs). We collected clinical data in all patients and estimated the development or intelligent quotients only in the patients carrying 25 PARM. The estimated incidence of CCHS was greater than one case per 148 000 births. Polyhydramnios was observed in three cases. Twelve infants exhibited depressed respiration at birth. In 19 cases carrying 25 PARM, the male-to-female ratio was ~3, no cases had Hirschsprung disease; 7 cases (37%) developed hypoventilation after the neonatal period, and 8 cases (42%) had mental retardation. In other 73 cases carrying 26 or more PARMs or NPARMs, male-to-female ratio was equal; patients frequently complicated with Hirschsprung disease and constipation, and all patients presented with hypoventilation in the neonatal period. Clinical symptoms were severe in most patients carrying long PARMs and NPARMs. In 25 PARM, additional genetic and/or epigenetic factors were required for CCHS development and male sex is likely a predisposing factor. The patients carrying 25 PARM frequently had mental retardation likely because they were not able to receive appropriate ventilation support following a definitive diagnosis owing to subtle and or irregular hypoventilation. Molecular diagnosis provides a definitive diagnosis and enables to receive appropriate ventilator support.

Molecular analysis of the genes causing recessive demyelinating Charcot-Marie-Tooth disease in Japan.

Charcot-Marie-Tooth disease (CMT), the most common hereditary neuropathy, has been classified into two types, demyelinating and axonal types. We previously analyzed the genes causing dominant demyelinating CMT in 227 Japanese patients to identify the genetic background, but could not find any mutations in 110 patients. To investigate the frequency of patients with autosomal recessive demyelinating CMT (CMT4) mutations, we analyzed the coding sequence of known causative genes of CMT4 in 103 demyelinating CMT patients, excluding seven patients owing to lack of specimens. We found one patient with a GDAP1 mutation, one patient with an MTMR2 mutation, two patients with SH3TC2/KIAA1985 mutations and three patients with FGD4 mutations. Twelve patients, including five previously detected patients with PRX mutations, were diagnosed as CMT4, accounting for 5.5% of demyelinating CMT. In the patient with GDAP1 mutation, only one mutation inherited from his mother was detected by genomic sequencing. Analysis by reverse transcription polymerase chain reaction using messenger RNA (mRNA) from the patient's leukocytes revealed the absence of transcription from the allele inherited from his father, suggesting the existence of one more mutation leading to a lack or destabilization of mRNA. Most patients carrying CMT4 gene mutations present with early-onset and slowly progressive symptoms, which may be associated with the function of mutants. We could not identify the disease-causing gene in 96 patients (about 45%). Further studies including studies with next-generation sequencers will be required to identify the causative gene in Japanese CMT.

Inheritance of polyalanine expansion mutation of PHOX2B in congenital central hypoventilation syndrome.

Congenital central hypoventilation syndrome (CCHS; MIM 209880) is caused mostly by dominant alanine expansion (most prevalent is 7-alanine expansion) mutations in PHOX2B. More than 90% of the alanine expansion mutations had been considered to be de novo due to unequal crossover during gametogenesis. However, a recent report stated that 25% of patients inherited the alanine-expanded allele from their parents with somatic mosaicism or constitutive mutation. We studied inheritance in 45 unrelated families, and found that one patient (2%) inherited 5-alanine expansion mutation from a parent with late-onset central hypoventilation syndrome and nine patients (20%) inherited 5- to 7-alanine expansion mutation from apparently asymptomatic parents with somatic mosaicism. Analysis using a sensitive method would be recommended to all parents of CCHS proband due to high incidence of somatic mosaicism. The absence of an alanine-contracted allele (expected counterpart allele in unequal crossover) and the highest prevalence of 6-alanine expansion mutation in somatic mosaicism suggest that the somatic mosaicism is likely caused by a mechanism other than an unequal crossover, such as a replication mechanism.

Compound heterozygous PMP22 deletion mutations causing severe Charcot-Marie-Tooth disease type 1.

We present a 3⅓-year-old girl with severe Charcot-Marie-Tooth disease type 1 (Dejerine-Sottas disease), who was a compound heterozygote carrying a deletion of the whole peripheral myelin protein 22 (PMP22) and a deletion of exon 5 in the other PMP22 allele. Haplotype analyses and sequence determination revealed a 11.2 kb deletion spanning from intron 4 to 3'-region of PMP22, which was likely generated by nonhomologous end joining. Severely affected patients carrying a PMP22 deletion must be analyzed for the mutations of the other copy of PMP22.

Neurofilament light chain polypeptide gene mutations in Charcot-Marie-Tooth disease: nonsense mutation probably causes a recessive phenotype.

The neurofilament light chain polypeptide (NEFL) forms the major intermediate filament in neurons and axons. NEFL mutation is a cause of axonal or demyelinating forms of dominant Charcot-Marie-Tooth disease (CMT). We investigated NEFL in 223 Japanese CMT patients who were negative for PMP22, MPZ, GJB1, LITAF, EGR2, GDAP1, MTMR2 and PRX in the demyelinating form and negative for MFN2, MPZ, GJB1, HSP27, HSP22 and GARS in the axonal form. We detected four heterozygous missense mutations--Pro8Leu, Glu90Lys, Asn98Ser and Glu396Lys--in five unrelated patients and a homozygous nonsense mutation, Glu140Stop, in one other patient. All patients had mildly to moderately delayed nerve conduction velocities, possibly caused by a loss of large diameter fibers. This is the first report of a homozygous nonsense mutation of NEFL. Results of our study show that nonsense NEFL mutations probably cause a recessive phenotype, in contrast to missense mutations, which cause a dominant phenotype.