Keiichi Hara1, Go Tajima2, Satoshi Okada3, Miyuki Tsumura3, Reiko Kagawa3, Kenichiro Shirao4, Yoshinori Ohno5, Shin'ichiro Yasunaga6, Motoaki Ohtsubo7, Ikue Hata8, Nobuo Sakura9, Yosuke Shigematsu10, Yoshihiro Takihara11, Masao Kobayashi3. 1. Department of Pediatrics, National Hospital Organization Kure Medical Center, Kure 737-0023, Japan; Department of Pediatrics, Hiroshima University Graduate School of Biomedical & Health Sciences, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan. 2. Department of Pediatrics, Hiroshima University Graduate School of Biomedical & Health Sciences, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan. Electronic address: isleofmaple@me.com. 3. Department of Pediatrics, Hiroshima University Graduate School of Biomedical & Health Sciences, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan. 4. Shirao Clinic of Pediatrics and Pediatric Allergy, Department of Pediatrics, Hiroshima 734-0023, Japan. 5. Department of Stem Cell Biology, Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima 734-8553, Japan. 6. Department of Biochemistry, Faculty of Medicine, Fukuoka University, Fukuoka 814-0180, Japan. 7. Department of Food and Nutrition, Beppu University, Ooita 874-0501, Japan. 8. Department of Pediatrics, Faculty of Medical Sciences, University of Fukui, Fukui 910-1193, Japan. 9. Nursing House for Severe Motor and Intellectual Disabilities SUZUGAMINE, Hiroshima 731-5122, Japan. 10. Department of Health Science, Faculty of Medical Sciences, University of Fukui, Fukui 910-1193, Japan. 11. Department of Stem Cell Biology, Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima 734-8553, Japan. Electronic address: takihara@hiroshima-u.ac.jp.
Abstract
BACKGROUND: Since the first case was detected in 2000, there has been a remarkable increase in Japanese patients diagnosed with medium-chain acyl-CoA dehydrogenase (MCAD) deficiency. Genetic analysis has revealed a spectrum of mutations that is quite different from those observed in Caucasian populations. In 2014, Japan initiated nationwide newborn screening (NBS) for MCAD using tandem mass spectrometry (MS/MS). It is an urgent issue to assess the risk of acute metabolic decompensation from the respective novel mutations found thus far. METHODS: To evaluate the pathogenic effect of each mutation, we established a eukaryotic cell expression system and prepared 11 mutant proteins identified in five symptomatic patients and eight MS/MS-NBS-positive newborns, as well as two common Caucasian mutations, p.K329E (c.985G>A) and p.Y67H (c.157C>T) for comparison. RESULTS: The expression of four mutant proteins (p.Q45R, p.P92L, p.P128X and p.Y397N) were severely impaired, whereas the others expressed normally, as did p.K329E and p.Y67H. Based on their dehydrogenase activities toward n-octanoyl-CoA, we determined three mutations (p.R53C, p.R281S and p.G362E) to be disease-causing, two mutations having (p.R17H and p.M274V) to be of marginal risk, and two mutations (p.K271E and p.I416T) as benign. Their allele-specific activities were as a whole in accordance with those estimated from the results of measurement in peripheral blood mononuclear cells. CONCLUSION: As most of the mutations detected in the Japanese population are unique, prudent genetic and enzymatic analysis is essential to precisely evaluate the latent risk of clinical onset for screening-positive newborns.
BACKGROUND: Since the first case was detected in 2000, there has been a remarkable increase in Japanese patients diagnosed with medium-chain acyl-CoA dehydrogenase (MCAD) deficiency. Genetic analysis has revealed a spectrum of mutations that is quite different from those observed in Caucasian populations. In 2014, Japan initiated nationwide newborn screening (NBS) for MCAD using tandem mass spectrometry (MS/MS). It is an urgent issue to assess the risk of acute metabolic decompensation from the respective novel mutations found thus far. METHODS: To evaluate the pathogenic effect of each mutation, we established a eukaryotic cell expression system and prepared 11 mutant proteins identified in five symptomatic patients and eight MS/MS-NBS-positive newborns, as well as two common Caucasian mutations, p.K329E (c.985G>A) and p.Y67H (c.157C>T) for comparison. RESULTS: The expression of four mutant proteins (p.Q45R, p.P92L, p.P128X and p.Y397N) were severely impaired, whereas the others expressed normally, as did p.K329E and p.Y67H. Based on their dehydrogenase activities toward n-octanoyl-CoA, we determined three mutations (p.R53C, p.R281S and p.G362E) to be disease-causing, two mutations having (p.R17H and p.M274V) to be of marginal risk, and two mutations (p.K271E and p.I416T) as benign. Their allele-specific activities were as a whole in accordance with those estimated from the results of measurement in peripheral blood mononuclear cells. CONCLUSION: As most of the mutations detected in the Japanese population are unique, prudent genetic and enzymatic analysis is essential to precisely evaluate the latent risk of clinical onset for screening-positive newborns.