Myocerebrohepatopathy spectrum disorder due to POLG mutations: A clinicopathological report.

We report on the clinical, neuropathological, and genetic findings of a Japanese case with myocerebrohepatopathy spectrum (MCHS) disorder due to polymerase gamma (POLG) mutations. A girl manifested poor sucking and failure to thrive since 4 months of age and had frequent vomiting and developmental regression at 5 months of age. She showed significant hypotonia and hepatomegaly. Laboratory tests showed hepatocellular dysfunction and elevated protein and lactate levels in the cerebrospinal fluid. Her liver function and neurologic condition exacerbated, and she died at 8 months of age. At autopsy, fatty degeneration and fibrosis were observed in the liver. Neuropathological examination revealed white matter-predominant spongy changes with Alzheimer type II glia and loss of myelin. Enzyme activities of the respiratory chain complex I, III, and IV relative to citrate synthase in the muscle were normal in the biopsied muscle tissue, but they were reduced in the liver to 0%, 10%, and 14% of normal values, respectively. In the liver, the copy number of mitochondrial DNA compared to nuclear DNA was reduced to 3.3% of normal values as evaluated by quantitative polymerase chain reaction. Genetic analysis revealed compound heterozygous mutations for POLG (I1185T/A957V). This case represents the differential involvement of multiple organs and phenotype-specific distribution of brain lesions in mitochondrial DNA depletion disorders.

Molecular diagnosis of mitochondrial respiratory chain disorders in Japan: focusing on mitochondrial DNA depletion syndrome.

BACKGROUND: Although mitochondrial respiratory chain disorders (MRCD) are one of the most common congenital metabolic diseases, there is no cumulative data on enzymatic diagnosis and clinical manifestation for MRCD in Japan and Asia. METHODS: We evaluated 675 Japanese patients having profound lactic acidemia, or patients having symptoms or signs of multiple-organ origin simultaneously without lactic acidemia on respiratory chain enzyme activity assay and blue native polyacrylamide gel electrophoresis. Quantitative polymerase chain reaction was used to diagnose mitochondrial DNA depletion syndrome (MTDPS). Mutation analysis of several genes responsible for MTDPS was also performed. RESULTS: A total of 232 patients were diagnosed with a probable or definite MRCD. MRCD are common, afflicting one in every several thousand people in Japan. More than one in 10 of the patients diagnosed lacked lactic acidemia. A subsequent analysis of the causative genes of MTDPS identified novel mutations in six of the patients. A 335 bp deletion in deoxyguanosine kinase (DGUOK; g.11692_12026del335 (p.A48fsX90)) was noted in two unrelated families, and may therefore be a common mutation in Japanese people. The proportion of all patients with MTDPS, and particularly those with recessive DNA polymerase γ (POLG) mutations, appears to be lower in Japan than in other studies. This is most likely due to the relatively high prevalence of ancient European POLG mutations in Caucasian populations. No other significant differences were identified in a comparison of the enzymatic diagnoses, disease classifications or prognoses in Japanese and Caucasian patients with MRCD. CONCLUSION: MTDPS and other MRCD are common, but serious, diseases that occur across all races.

Tysnd1 deficiency in mice interferes with the peroxisomal localization of PTS2 enzymes, causing lipid metabolic abnormalities and male infertility.

Peroxisomes are subcellular organelles involved in lipid metabolic processes, including those of very-long-chain fatty acids and branched-chain fatty acids, among others. Peroxisome matrix proteins are synthesized in the cytoplasm. Targeting signals (PTS or peroxisomal targeting signal) at the C-terminus (PTS1) or N-terminus (PTS2) of peroxisomal matrix proteins mediate their import into the organelle. In the case of PTS2-containing proteins, the PTS2 signal is cleaved from the protein when transported into peroxisomes. The functional mechanism of PTS2 processing, however, is poorly understood. Previously we identified Tysnd1 (Trypsin domain containing 1) and biochemically characterized it as a peroxisomal cysteine endopeptidase that directly processes PTS2-containing prethiolase Acaa1 and PTS1-containing Acox1, Hsd17b4, and ScpX. The latter three enzymes are crucial components of the very-long-chain fatty acids ß-oxidation pathway. To clarify the in vivo functions and physiological role of Tysnd1, we analyzed the phenotype of Tysnd1(-/-) mice. Male Tysnd1(-/-) mice are infertile, and the epididymal sperms lack the acrosomal cap. These phenotypic features are most likely the result of changes in the molecular species composition of choline and ethanolamine plasmalogens. Tysnd1(-/-) mice also developed liver dysfunctions when the phytanic acid precursor phytol was orally administered. Phyh and Agps are known PTS2-containing proteins, but were identified as novel Tysnd1 substrates. Loss of Tysnd1 interferes with the peroxisomal localization of Acaa1, Phyh, and Agps, which might cause the mild Zellweger syndrome spectrum-resembling phenotypes. Our data established that peroxisomal processing protease Tysnd1 is necessary to mediate the physiological functions of PTS2-containing substrates.

Association of UGT2B7 and ABCB1 genotypes with morphine-induced adverse drug reactions in Japanese patients with cancer.

PURPOSE: To investigate the effects of genetic polymorphisms on morphine-induced adverse events in cancer patients. METHODS: We examined the relation of morphine-related adverse events to polymorphisms in UDP-glucuronosyltransferase (UGT) 2B7, ATP-binding cassette, sub-family B, number 1 (ABCB1), and µ-opioid receptor 1 genes in 32 Japanese cancer patients receiving oral controlled-release morphine sulfate tablets. RESULTS: The T/T genotype at 1236 or TT/TT diplotype at 2677 and 3435 in ABCB1 was associated with significantly lower frequency of fatigue (grades 1-3) (P = 0.012 or 0.011, Fisher's exact test). The UGT2B7*2 genotype was associated with the frequency of nausea (grades 1-3) (P = 0.023). The frequency of nausea was higher in patients without UGT2B7*2 allele than others. The diplotype at 2677 and 3435 in ABCB1 was associated with the frequency of vomiting (grades 1-3) (P = 0.011). No patient whose diplotype was consisted of no GC allele at 2677 and 3435 suffered from vomiting. CONCLUSION: Our findings suggest that pharmacogenetics can be used to predict the risk of morphine-induced adverse events.

Fluctuating liver functions in siblings with MPV17 mutations and possible improvement associated with dietary and pharmaceutical treatments targeting respiratory chain complex II.

BACKGROUND/AIMS: To describe the clinical and biological findings of two Japanese siblings with novel MPV17 gene mutations (c.451insC/c.509C > T) manifesting hepatic mitochondrial DNA depletion syndrome. METHODS: We observed these brothers and sought to determine the efficacy of treatment targeting respiratory chain complex II for the younger brother. RESULTS: A 3-month-old boy had presented with profound liver dysfunction, failure to thrive, and watery diarrhea. Although he was then placed on a carbohydrate-rich diet, his liver function thereafter fluctuated greatly in association with viral infections, and rapidly deteriorated to liver failure. He underwent liver transplantation at 17 months of age but died at 22 months of age. The younger brother, aged 47 months at the time of this writing, presented with liver dysfunction from 8 months of age. His transaminase levels also fluctuated considerably fluctuations in association with viral infections. At 31 months of age, treatment with succinate and ubiquinone was initiated together with a lipid-rich diet using ketone milk. Thereafter, his transaminase levels normalized and never fluctuated, and the liver histology improved. CONCLUSIONS: These cases suggested that the clinical courses of patients with MPV17 mutations are greatly influenced by viral infections and that dietary and pharmaceutical treatments targeting the mitochondrial respiratory chain complex II may be beneficial in the clinical management of MPV17 mutant patients.

Homozygosity haplotype allows a genomewide search for the autosomal segments shared among patients.

A promising strategy for identifying disease susceptibility genes for both single- and multiple-gene diseases is to search patients' autosomes for shared chromosomal segments derived from a common ancestor. Such segments are characterized by the distinct identity of their haplotype. The methods and algorithms currently available have only a limited capability for determining a high-resolution haplotype genomewide. We herein introduce the homozygosity haplotype (HH), a haplotype described by the homozygous SNPs that are easily obtained from high-density SNP genotyping data. The HH represents haplotypes of both copies of homologous autosomes, allowing for direct comparisons of the autosomes among multiple patients and enabling the identification of the shared segments. The HH successfully detected the shared segments from members of a large family with Marfan syndrome, which is an autosomal dominant, single-gene disease. It also detected the shared segments from patients with model multigene diseases originating with common ancestors who lived 10-25 generations ago. The HH is therefore considered to be useful for the identification of disease susceptibility genes in both single- and multiple-gene diseases.

Twenty single-nucleotide polymorphisms in four genes encoding cardiac ion channels.

We here report 20 novel single-nucleotide polymorphisms in four genes that are potentially involved in the excitement of cardiomyocytes: 1 in KCNA5 (encoding Kv1.5), 5 in KCNAB1 (encoding Kvbeta1.3), 5 in KCNIP2 (encoding KChIP2), and 9 in CACNA1C (encoding a cardiac L-type voltage-dependent calcium ion channel, dihydropyridine receptor). We also examined their allelic frequencies in Japanese individuals. These data will be useful for genetic association studies designed to investigate secondary long QT syndrome or other circulatory disorders.

[Genetics and genomics of long QT syndrome].

In the past decade, molecular genetics has revealed that some life-threatening arrhythmogenic disorders, such as long QT syndrome, are due to mutated genes encoding ion channels that generate the cardiac action potential. Great efforts made in various fields have partly solved problems caused by unforeseen genetic diversity of these congenital arrhythmogenic disorders, while the genetics of these disorders has recently proved to be applicable to very wide-ranging conditions associated with sudden cardiac death, and increased knowledge about the human genome will revolutionize researches into arrhythmic diseases in future. The purpose of this review is to outline the recent advances and problems in the molecular genetics in long QT syndrome.