Masayoshi Nagao

Progressive liver fibrosis in late-onset argininosuccinate lyase deficiency.

A 4-month-old boy, with late-onset argininosuccinate lyase (ASL) deficiency with hepatomegaly, was treated by protein restricted diet and arginine supplementation; he was followed for 3 years. Hepatomegaly and mild liver dysfunction persisted without significant hyperammonemia. He maintained normal psychomotor development to the age of 12 months, but, at 3 years of age, his developmental status is in the borderline normal range. Liver biopsy performed at 12 months of age demonstrated swollen and pale hepatocytes with abnormal glycogen deposition and mild periportal fibrosis. A subsequent liver biopsy at 3 years of age showed progressive liver fibrosis in the periportal and central areas, which extended into the liver lobule. These findings suggest that liver impairment in ASL deficiency may advance without significant hyperammonemia and underline the importance of repeated liver biopsy in this disorder, even when the plasma ammonia level is well controlled.

Influence of valproic acid on the expression of various acyl-CoA dehydrogenases in rats.

Abstract Background: Valproic acid (2‐propyl‐N‐pentanoic acid, VPA) causes severe hepatic dysfunction, similar to Reye’s syndrome, in a small number of patients. An enhanced excretion of dicarboxylic acids by patients indicates an interference with mitochondrial β‐oxidation. We investigated the expression of various acyl‐coenzyme A (acyl‐CoA) dehydrogenases (ACD), which catalyze the first step of β‐oxidation in VPA‐treated rats.

Improved neurologic prognosis for a patient with propionic acidemia who received early living donor liver transplantation

Despite medical therapy, patients with propionic academia (PA) still display a tendency to develop epilepsy. Patients with neonatal-onset PA who have received early living donor liver transplantation (LDLT) are limited in number, and the effect on neurologic prognosis, including epilepsy, is not clear. We report a patient with PA whose EEG findings improved dramatically after undergoing LDLT at age 7 months. The patients neurologic development and brain MRI findings were quite satisfactory at age 2 years and 3 months. LDLT is effective not only in preventing metabolic decompensation, but also in improving neurologic function to ensure better quality of life.

Frequency of 985A‐to‐G mutation in medium‐chain acyl‐CoA dehydrogenase gene among patients with sudden infant death syndrome, Reye syndrome, severe motor and intellectual disabilities and healthy newborns in Japan

The prevalence of the 985A‐to‐G mutation in the medium‐chain acyl‐CoA dehydrogenase (MCAD) gene among Japanese patients with sudden infant death syndrome, Reye syndrome, unknown fatty acid oxidation disorders and severe motor and intellectual disabilities was studied using the PCR/Nco‐I method for molecular diagnosis. A frequency study of this common mutation was also conducted on blood samples and left over Guthrie cards from 329 healthy newborns in Japan. Neither heterozygotes nor homozygotes for the 985A‐to‐G mutation were identified among both patients and controls. The result of the present study accord with previous reports that MCAD deficiency is a common disorder in Caucasians, but quite rare among Japanese. Therefore, newborn mass‐screening for MCAD deficiency using this method will not be practical in Japan. However, it still seems necessary to investigate a child with fatty acid oxidation disorder for the presence of MCAD deficiency, using both biochemical and molecular genetic methods.

Spectrum of mutations associated with methionine adenosyltransferase I/III deficiency among individuals identified during newborn screening in Japan

Methionine adenosyltransferase I/III deficiency (MAT I/III deficiency) is an inborn error of metabolism that results in isolated persistent hypermethioninemia. Definitive diagnosis is now possible by molecular analyses of the MAT1A gene. Based on newborn screening (NBS) data collected between 2001 and 2012 in Hokkaido, Japan, the estimated incidence of MAT I/III deficiency was 1 in 107,850. 24 patients (13 males, 11 females) from 11 prefectures in Japan were referred to our laboratory for genetic diagnosis of MAT I/III deficiency. They were all found between 1992 and 2012 by the NBS program in each region. In these 24 individuals, we identified 12 distinct mutations; 14 patients were heterozygous for an R264H mutation; R264H caused an autosomal dominant and clinically benign phenotype in each case. The mutations in the other 10 patients showed autosomal recessive inheritance and included eight novel MAT1A mutations. Putative amino acid substitutions at R356 were observed with six alleles (three R356P, two R356Q, and one R356L). MAT I/III deficiency is not always benign because three of our cases involved brain demyelination or neurological complications. DNA testing early in life is recommended to prevent potential detrimental neurological manifestations.

Rapid Mutation Screening of Phenylketonuria by Polymerase Chain Reaction-Linked Restriction Enzyme Assay and Direct Sequence of the Phenylalanine Hydroxylase Gene: Clinical Application in Northern Japan and Northern China

We describe a simple and technically feasible method for mutation screening of the phenylalanine hydroxylase (PAH) gene and its application to Japanese and Chinese patients with hyperphenylalaninemia. The strategy is based on the identification of a nucleotide substitution by restriction enzyme analysis, coupled with PCR and direct sequencing of exon 7 of the PAH gene. Because the detection of various mutations can proceed simultaneously using the same technique, it is quite rapid and reproducible, making it possible to perform effective molecular diagnosis and carrier screening in most laboratories. Using this procedure, we found that the most common molecular defects were R413P in Hokkaido, Japan (35 %) and R243Q in Heilongjiang, China (50%). R111X, IVS4nt-1, and five mutations in exon 7 (R241C, R243Q, R252W, A259T, and S273P) accounted for 55% of phenylketonuria (PKU) alleles in Hokkaido. In Heilongjiang, the R111X, Y356X, and R408W mutations accounted for 35% of PKU alleles. Clinically, homozygotes or compound heterozygotes of null alleles, which express nonfunctional enzyme activity, were all associated with classic PKU. On the other hand, patients heterozygous for the R241C allele had a benign phenotype of mild hyperphenylalaninemia. The DNA diagnosis in early infancy can predict various PKU phenotypes, and can prove useful in decision-making concerning dietary therapy.

Mutation screening of phenylketonuria in the Far East of Russia

AbstractWe analyzed mutant genotypes at the human phenylalanine hydroxylase (PAH) locus among phenylketonuria (PKU) patients in the Far East of Russia. A total of 60 variant alleles from 30 PKU families were analyzed for prevalent Caucasian mutations and restriction fragment length polymorphism/variable number of tandem repeats (RFLP/VNTR) haplotypes. Seventy-eight percent of all variant alleles carried six mutations. The most prevalent mutation was R408W (63%), with a haplotype background of 2.3. It also showed a very high degree of homozygosity (43%). The other five mutations (R158Q, R261Q, R252W, R261X, and IVS12nt-1) accounted for 1.7%–6.7% of all PKU alleles, and a single haplotype was associated with each genotype, except for R261Q. The genetic structure of PKU patients in the Far East of Russia seems to be relatively homogeneous, compared with that in the other Slavic and Oriental populations of surrounding countries. Prediction of a clinical phenotype and carrier detection will be feasible using DNA tests.

Connatal Pelizaeus-Merzbacher disease : A missense mutation in exon 4 of the proteolipid protein (PLP) gene

AbstractWe investigated the proteolipid protein (PLP) gene in two brothers in a Japanese family with a connatal form of Pelizaeus-Merzbacher disease (PMD). Direct sequencing of the PLP gene revealed an A-to-T transition in exon 4, which led to an Asp-to-Val substitution at re-sidue 202. Their mother was confirmed to be heterozygous for the mutation. The mutation was not found in 78 X-chromosomes of normal Japanese individuals. A correlation between the clinical severity of the disease in the brothers and the Asp202-to-Val mutation in the PLP gene was suggested.

A simple and rapid polymerase chain reaction-based method for detecting a prevalent mutation (R413P) in Japanese phenylketonuria patients

A convenient molecular method for the detection of R413P (1238G←C) mutation in exon 12 of the phenylalanine hydroxylase gene, one of the prevalent mutations among Japanese patients with classical phenylketonuria (PKU) is described. The mutation was previously detected by polymerase chain reaction (PCR)‐direct sequencing or allele specific oligonucleotide hybridization. However, these methods were cumbersome and only a few laboratories could provide such a diagnostic service. An improved version of the method has been developed here, involving 30 cycles of PCR following restriction enzyme digestion. In the upstream primer encompassing G‐1207 to C‐1237, two substitutions are artificially introduced, so that a Bam‐HI site involving C‐1238 is introduced in the copies of the mutant allele. With the use of this method, R413P‐homozygote and ‐heterozygote can be readily and unequivocally distinguished from normal using genomic DNA extracted from peripheral blood leukocytes. Among 10 Japanese PKU patients investigated, three were homozygous and three were heterozygous for the R413P allele, whereas four did not carry this mutant allele, indicating that the prevalence of the mutant allele is 45%. The result suggests that it is technically feasible to develop a program for carrier detection of the mutation in the Japanese population.

Mutation analysis of the phenylalanine hydroxylase gene and its clinical implications in two Japanese patients with non-phenylketonuria hyperphenylalaninemia

AbstractWe describe a mutation analysis for the phenylalanine hydroxylase gene and the clinical outcome of two Japanese patients with non-phenylketonuria (PKU) hyperphenylalaninemia (serum phenylalanine level below 600 μmol/l under a free diet) detected by a mass-screening program. Single strand conformation polynorphism analysis and direct sequencing of their genomic DNAs revealed that non-PKU hyperphenylalaninemia resulted from compound heterozygosity for a mutation causing classical PKU and a mutation with a milder effect on phenylalanine hydroxylase activity. The mutations were R241C and R243Q in exon 7, and R413P in exon 12. The mutation genotypes of the two patients were R241C/R243Q and R241C/R413P. It has been demonstrated that homozygosity for the R243Q or R413P mutation is associated with a severe phenotype of PKU and low in vitro expression activity. In contrast, the R241C mutation has much less effect on phenylalanine hydroxylase activity. The metabolic consequence of each variant allele was confirmed by a phenylalanine loading test in the patients and their parents. The patients achieved normal results in all intellectual and neurologic tests. Brain magnetic resonance imaging revealed no abnormalities. The dietary restriction was continued until 10 years of age in order to maintain the serum phenylalanine level below 400 μmol/l. The genetic analysis to distinguish non-PKU hyperphenylalaninemia from classical PKU helps to determine the principles of dietary management in the early infantile period.