Ayako Sasaki

Neonatal hyperbilirubinemia and mutation of the bilirubin uridine diphosphate‐glucuronosyltransferase gene: a common missense mutation among Japanese, Koreans and Chinese

We analyzed the bilirubin uridine diphosphate‐glucuronosyltransferase (B‐UGT) gene in 42 Japanese newborns with hyperbilirubinemia and determined that 21 infants were heterozygous while 3 was homozygous for Gly71Arg. Allele frequency of Gly71Arg was 0.32 in newborns with hyperbilirubinemia, which was significantly higher than 0.13 in healthy Japanese controls. This mutant allele is also prevalent among Korean and Chinese healthy controls with a frequency of 0.23 in both populations. However, this mutation was not detected in 50 healthy German controls. These data suggest that the high frequency of the Gly71Arg mutation of the B‐UGT gene is associated with high incidence of neonatal hyperbilirubinemia in Japanese, Korean and Chinese populations.

Neonatal hyperbilirubinemia and a common mutation of the bilirubin uridine diphosphate-glucuronosyltransferase gene in Japanese

AbstractNeonatal hyperbilirubinemia, which is prevalent among Asian peoples, has been considered as a physiological phenomenon, and its metabolic basis has not been clearly explained. Gilbert syndrome is a common inherited disease of unconjugated hyperbilirubinemia due to decreased bilirubin uridine diphosphate-glucuronosyltransferase (B-UGT), and its role in neonatal jaundice has recently been considered. We have previously reported that the Gly71Arg mutation of the B-UGT gene associated with Gilbert syndrome is prevalent in Japanese, Korean, and Chinese populations and was more frequently detected in neonates with severe hyperbilirubinemia than in control subjects. We have studied 159 Japanese full-term neonates, evaluating the relationship between the B-UGT genotype and the severity of jaundice, as assessed with a transcutaneous bilirubinometer. The gene frequency of the Gly71Arg mutation in these neonates was 0.19, and neonates carrying the Gly71Arg mutation had significantly increased bilirubin levels on days 2–4, manifested in a gene dose-dependent manner. The frequency of the Gly71Arg mutation was 0.47 in the neonates who required phototherapy (i.e., those with more severe hyperbilirubinemia), significantly higher than 0.16 in the neonates who did not require the therapy. The gene frequency of the TA repeat promoter polymorphism, the (TA)7 mutation, was 0.07, and neonates carrying this mutation did not have an increase in bilirubin. These results suggested that the Gly71Arg mutation contributes to the high incidence of neonatal hyperbilirubinemia in Japanese.

Neonatal hyperbilirubinemia in Japanese neonates: Analysis of the heme oxygenase-1 gene and fetal hemoglobin composition in cord blood

Neonatal hyperbilirubinemia is frequent and severe in Japanese infants. Although the G71R mutation of the bilirubin uridine diphosphate-glucuronosyltransferase gene is associated with severe neonatal hyperbilirubinemia in this population, it accounts for only half of the neonates with severe hyperbilirubinemia. It was suggested that increased bilirubin production would also be associated with severe neonatal hyperbilirubinemia in Japanese infants. To elucidate the genetic factors causing severe hyperbilirubinemia in these patients, we studied two notable factors associated with bilirubin production: heme oxygenase-1, a key enzyme of heme metabolism, and fetal Hb composition, a factor possibly associated with heme load in neonates. We first determined the sequences of promoter and all coding regions of the heme oxygenase-1 gene in Japanese neonates who had undergone phototherapy, but found no mutation except for the polymorphic (GT)n repeats in the promoter region. These repeats modulate the transcription of the heme oxygenase-1 gene, and the longer repeat sequences are known to reduce the transcription. We detected a significant difference in the allele frequencies of each number of (GT)n repeats between Japanese and German populations. However, we could not find a relation between those polymorphisms and neonatal hyperbilirubinemia. We next analyzed the state of Hb switching of the γ- to β-globin chain and the phenotype of γ-globin chain isoforms in cord blood. We found no relation between fetal Hb composition and neonatal hyperbilirubinemia. Further studies are required to elucidate genetic or environmental factors in neonatal hyperbilirubinemia in Japanese infants.

Three siblings of fatal infantile encephalopathy with olivopontocerebellar hypoplasia and microcephaly

We report three male siblings born with fatal encephalopathy comprising microcephaly, myoclonus and muscle hypertonia. All three patients died during infancy. Postmortem examination on the brain revealed that all infants had neuronal loss in the cerebellar cortex, inferior olivary and pontine nuclei, which were more pronounced in the older subject than the younger ones. In addition, they were associated with polymicrogyria in the cerebral cortex of the insula, olivary and dentate nuclear dysplasia, and a hypoplastic corticospinal tract. The clinical and neuropathological findings in our cases were identical to those in fatal infantile encephalopathy with olivopontocerebellar hypoplasia and microencephaly [Albrecht et al., Acta Neuropathol 1993;85:394-399], but an association of malformations suggests a new genetic factor in pathogenesis of olivopontocerebellar hypoplasia.

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.

Neonatal hyperbilirubinemia and the bilirubin uridine diphosphate‐glucuronosyltransferase gene: The common −3263T > G mutation of phenobarbital response enhancer module is not associated with the neonatal hyperbilirubinemia in Japanese

Abstract Background : Neonatal hyperbilirubinemia is frequent and severe in Japanese newborns. Previously, it has been reported that half of the Japanese neonates with severe hyperbilirubinemia carried the 211G > A (p.G71R) mutation of the bilirubin uridine diphosphate‐glucuronosyltransferase (UGT1A1) gene causing Gilbert syndrome. Recently, it was reported that the −3263T > G mutation in the phenobarbital response enhancer module in UGT1A1 was associated with the majority of cases of Gilbert syndrome. The gene frequency of the −3263T > G mutation was determined and the relation with neonatal hyperbilirubinemia in Japanese was studied.

Sensitive Detection of Polyalanine Expansions in PHOX2B by Polymerase Chain Reaction Using Bisulfite-Converted DNA

Congenital central hypoventilation syndrome, also known as Ondines curse, is characterized by idiopathic abnormal control of respiration during sleep. Recent studies indicate that a polyalanine expansion of PHOX2B is relevant to the pathogenesis of this disorder. However, it is difficult to detect the repeated tract because its high GC content inhibits conventional polymerase chain reaction (PCR) amplification. Here, we describe a bisulfite treatment for DNA in which uracil is obtained by deamination of unmethylated cytosine residues. Deamination of DNA permitted direct PCR amplification that yielded a product of 123 bp for the common 20-residue repetitive tract with replacement of C with T by sequencing. It settled allele dropouts accompanied by insufficient amplification of expanded alleles. The defined procedure dramatically improved detection of expansions to 9 of 10 congenital central hypoventilation syndrome patients examined in a previous study. The chemical conversion of DNA before PCR amplification facilitates effective detection of GC-rich polyalanine tracts.

De novo polyalanine expansion of PHOX2B in congenital central hypoventilation syndrome: unequal sister chromatid exchange during paternal gametogenesis

AbstractThe expansion of polyalanine repeats is known to cause at least nine disorders, including congenital central hypoventilation syndrome (CCHS). Unequal crossover has been speculated as the expanding mechanism, in contrast to strand slippage in polyglutamine expansion disorders. We carried out segregation analysis of PHOX2B in 13 de novo families with CCHS and found that 6 families were informative regarding a parental origin of polyalanine expansion, with all 6 mutants being of paternal origin. Four of them were also informative regarding a chromosomal event and their mutants were derived from unequal sister chromatid exchange. It is probable that de novo expansion of polyalanine repeats in CCHS results mainly from unequal sister chromatid exchange during spermatogenesis due to the secondary DNA structure of imperfect trinucleotide repeats encoding polyalanine tracts.

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.

Polyalanine expansion of PHOX2B in congenital central hypoventilation syndrome: rs17884724:A>C is associated with 7-alanine expansion

With congenital central hypoventilation syndrome (CCHS), most patients have a de novo 5–13 polyalanine expansion mutation in PHOX2B. We reported previously that de novo polyalanine expansion mutations were of paternal origin and were derived from unequal sister chromatid exchange during spermatogenesis in six and four informative families, respectively. In this study, we analyzed the relationship between haplotypes and de novo polyalanine expansion in PHOX2B and found that haplotypes carrying rs17884724:A>C were detected frequently in 7-alanine expanded (27-alanine) mutant alleles, which are the most prevalent mutations in CCHS. The allele with rs17884724:A>C made fewer nucleotide mismatches in the misalignment at crossing-over than the allele without rs17884724:A>C. The high frequency of rs17884724:A>C in 7-alanine expansion (27-alanine) mutations also supported the unequal crossover mechanism for polyalanine expansion. We also confirmed the paternal origin of de novo polyalanine expansion mutation and unequal sister chromatid exchange association in three more patients. In spite of paternal bias, the paternal age effect on CCHS incidence was not observed. De novo polyalanine expansion mutations are mainly derived from unequal sister chromatid exchange during spermatogenesis because of replication and/or repair systems that are specific for spermatogenesis.