Using the C14:1/Medium-Chain Acylcarnitine Ratio Instead of C14:1 to Reduce False-Positive Results for Very-Long-Chain Acyl-CoA Dehydrogenase Deficiency in Newborn Screening in Japan.

Very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is a long-chain fatty acid oxidation disorder that manifests as either a severe phenotype associated with cardiomyopathy, a hypoglycemic phenotype, or a myopathic phenotype. As the hypoglycemic phenotype can cause sudden infant death, VLCAD deficiency is included in newborn screening (NBS) panels in many countries. The tetradecenoylcarnitine (C14:1) level in dried blood specimens is commonly used as a primary marker for VLCAD deficiency in NBS panels. Its ratio to acetylcarnitine (C2) and various other acylcarnitines is used as secondary markers. In Japan, tandem mass spectrometry-based NBS, initially launched as a pilot study in 1997, was introduced to the nationwide NBS program in 2013. In the present study, we evaluated levels of acylcarnitine with various chain lengths (C18 to C2), free carnitine, and their ratios in 175 infants who tested positive for VLCAD deficiency with C14:1 and C14:1/C2 ratios. Our analyses indicated that the ratios of C14:1 to medium-chain acylcarnitines (C10, C8, and C6) were the most effective markers in reducing false-positive rates. Their use with appropriate cutoffs is expected to improve NBS performance for VLCAD deficiency.

Newborn Screening with (C16 + C18:1)/C2 and C14/C3 for Carnitine Palmitoyltransferase II Deficiency throughout Japan Has Revealed C12/C0 as an Index of Higher Sensitivity and Specificity.

Carnitine palmitoyltransferase (CPT) II deficiency is a long-chain fatty acid oxidation disorder. It manifests as (1) a lethal neonatal form, (2) a hypoglycemic form, or (3) a myopathic form. The second form can cause sudden infant death and is more common among Japanese people than in other ethnic groups. Our study group had earlier used (C16 + C18:1)/C2 to conduct a pilot newborn screening (NBS) study, and found that the use of C14/C3 for screening yielded lower rates of false positivity; in 2018, as a result, nationwide NBS for CPT II deficiency started. In this study, we evaluated the utility of these ratios in 71 NBS-positive infants and found that the levels of both C14/C3 and (C16 + C18:1)/C2 in patients overlapped greatly with those of infants without the disease. Among the levels of acylcarnitines with various chain lengths (C18 to C2) and levels of free carnitine (C0) as well as their ratios of various patterns, C12/C0 appeared to be a promising index that could reduce false-positive results without missing true-positive cases detected by current indices. Although some cases of the myopathic form may go undetected even with C12/C0, its use will help prevent life-threatening onset of the hypoglycemic form of CPT II deficiency.

Low carnitine palmitoyltransferase 1 activity is a risk factor for narcolepsy type 1 and other hypersomnia.

STUDY OBJECTIVES: Narcolepsy type 1 (NT1) is associated with metabolic abnormalities but their etiology remains largely unknown. The gene for carnitine palmitoyltransferase 1B (CPT1B) and abnormally low serum acylcarnitine levels have been linked to NT1. To elucidate the details of altered fatty acid metabolism, we determined levels of individual acylcarnitines and evaluated CPT1 activity in patients with NT1 and other hypersomnia. METHODS: Blood samples from 57 NT1, 51 other hypersomnia patients, and 61 healthy controls were analyzed. The levels of 25 major individual acylcarnitines were determined and the C0/(t[C16] + t[C18]) ratio was used as a CPT1 activity marker. We further performed transcriptome analysis using independent blood samples from 42 NT1 and 42 healthy controls to study the relevance of fatty acid metabolism. NT1-specific changes in CPT1 activity and in expression of related genes were investigated. RESULTS: CPT1 activity was lower in patients with NT1 (p = 0.00064) and other hypersomnia (p = 0.0014) than in controls. Regression analysis revealed that CPT1 activity was an independent risk factor for NT1 (OR: 1.68; p = 0.0031) and for other hypersomnia (OR: 1.64; p = 0.0042). There was a significant interaction between obesity (BMI <25, ≥25) and the SNP rs5770917 status such that nonobese NT1 patients without risk allele had better CPT1 activity (p = 0.0089). The expression levels of carnitine-acylcarnitine translocase (CACT) and CPT2 in carnitine shuttle were lower in NT1 (p = 0.000051 and p = 0.00014, respectively). CONCLUSIONS: These results provide evidences that abnormal fatty acid metabolism is involved in the pathophysiology of NT1 and other hypersomnia.

The frequencies of very long-chain acyl-CoA dehydrogenase deficiency genetic variants in Japan have changed since the implementation of expanded newborn screening.

Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency has been a target of expanded newborn screening (ENBS) using tandem mass spectrometry in Japan. Since the implementation of ENBS, a number of novel ACADVL variants responsible for VLCAD deficiency have been identified. In this study, genotypic differences in Japanese patients with VLCAD deficiency were investigated before and after ENBS. The ACADVL variants in 61 subjects identified through ENBS (ENBS group) and in 40 patients who subsequently developed clinical symptoms without undergoing ENBS (pre-ENBS group) were compared. Subjects in the ENBS group underwent genetic testing and/or VLCAD enzyme activity measurements. Patients in the pre-ENBS group were stratified into three clinical phenotypes and underwent genetic testing. This study revealed that the variants p.K264E, p.K382Q and c.996dupT were found in both groups, but their frequencies were lower in the ENBS group (5.2%, 3.1% and 4.2%, respectively) than in the pre-ENBS group (16.5%, 12.7% and 10.1%, respectively). In addition, p.C607S, p.T409M, p.M478I, p.G289R, p.C237R, p.T260M, and p.R229* were exclusively identified in the ENBS group. Among these variants, p.C607S exhibited the highest frequency (18.8%). The patients who were heterozygous for p.C607S demonstrated 7-42% of control enzyme activity. p.C607S is suspected to be unique to Japanese individuals. According to a comparison of enzyme activity, patients with the p.C607S variant may exhibit higher enzyme activity than those with the p.A416T, p.A180T, p.R450H, and p.K264E variants, which are responsible for the myopathic form of the disease. The VLCAD deficiency genotypes have changed since the initiation of ENBS in Japan.

Severity estimation of very-long-chain acyl-CoA dehydrogenase deficiency via 13C-fatty acid loading test.

BACKGROUND: The clinical severity of very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is difficult to predict using conventional diagnostic methods. METHODS: Peripheral blood mononuclear cells obtained from 14 VLCAD deficiency patients and 23 healthy adults were loaded with carbon-13-universally labeled (U-13C-) fatty acids. Differences in acylcarnitine ratios between the patients and healthy groups and correlations between acylcarnitine ratios and a newly established clinical severity score (CSS) in the patient group were statistically examined. RESULTS: There was a significant decrease in the 13C-C2/13C-C18 and 13C-C12/13C-C14 ratios in the U-13C-stearic acid loading test and in the 13C-C2/13C-C18:1 and 13C-C12:1/13C-C14:1 ratios in the U-13C-oleic acid loading test in the patient group. The values of each ratio were significantly correlated with the CSS, suggesting that they could predict disease severity. Additionally, patients with a higher 13C-C16/13C-C18 ratio than the 13C-C14/13C-C18 ratio in the U-13C-stearic acid loading test had a significantly higher CSS and were presumed to have more severe disease. CONCLUSIONS: Our data indicated that this method could be used to predict the clinical severity of VLCAD deficiency, and identify patients at a risk of severe disease. IMPACT: We established a novel method to predict the severity of VLCAD deficiency by performing a loading test with carbon-13-labeled fatty acids on peripheral blood mononuclear cells. The U-13C-oleic acid loading test was useful for comparing the patient group with the control group in terms of disease severity. The U-13C-stearic acid loading test was useful for identifying the more severely affected patients. These methods are relatively less invasive and enable rapid evaluation of the clinical severity.

Development of Second-Tier Liquid Chromatography-Tandem Mass Spectrometry Analysis for Expanded Newborn Screening in Japan.

To minimize false-positive cases in newborn screening by tandem mass spectrometry in Japan, practical second-tier liquid chromatography-tandem mass spectrometry analyses have been developed using a multimode ODS column with a single set of mobile phases and different gradient elution programs specific to the analysis of acylcarnitines, acylglycines, amino acids, and organic acids. Most analyses were performed using underivatized samples, except for analysis of methylcitric acid, and careful conditioning of the column was necessary for analyses of organic acids. Our second-tier tests enabled us to measure many metabolites useful for detection of target disorders, including allo-isoleucine, homocysteine, methylmalonic acid, and methylcitric acid. We found that accumulation of 3-hydroxyglutaric acid was specific to glutaric acidemia type I and that the ratio of 3-hydroxyisovaleric acid to 3-hydroxyisovalerylcarnitine was useful to detect newborns of mothers with 3-methylcrotonyl-CoA carboxylase deficiency. Data from the analysis of short-chain acylcarnitine and acylglycine were useful for differential diagnosis in cases positive for C5-OH-acylcarnitine or C5-acylcarnitine.

Pilot Study on Neonatal Screening for Methylmalonic Acidemia Caused by Defects in the Adenosylcobalamin Synthesis Pathway and Homocystinuria Caused by Defects in Homocysteine Remethylation.

Neonatal screening (NS) for methylmalonic acidemia uses propionylcarnitine (C3) as a primary index, which is insufficiently sensitive at detecting methylmalonic acidemia caused by defects in the adenosylcobalamin synthesis pathway. Moreover, homocystinuria from cystathionine ß-synthase deficiency is screened by detecting hypermethioninemia, but methionine levels decrease in homocystinuria caused by defects in homocysteine remethylation. To establish NS detection of methylmalonic acidemia and homocystinuria of these subtypes, we evaluated the utility of indices (1) C3 ≥ 3.6 µmol/L and C3/acetylcarnitine (C2) ≥ 0.23, (2) C3/methionine ≥ 0.25, and (3) methionine < 10 µmol/L, by retrospectively applying them to NS data of 59,207 newborns. We found positive results in 116 subjects for index (1), 37 for (2), and 15 for (3). Second-tier tests revealed that for index 1, methylmalonate (MMA) was elevated in two cases, and MMA and total homocysteine (tHcy) were elevated in two cases; for index 2 that MMA was elevated in one case; and for index 3 that tHcy was elevated in one case. Though data were anonymized, two cases identified by index 1 had been diagnosed with maternal vitamin B12 deficiency during NS. Methylene tetrahydrofolate reductase deficiency was confirmed for the case identified by index 3, which was examined because an elder sibling was affected by the same disease. Based on these data, a prospective NS study is underway.

Evaluation of Metabolic Defects in Fatty Acid Oxidation Using Peripheral Blood Mononuclear Cells Loaded with Deuterium-Labeled Fatty Acids.

Because tandem mass spectrometry- (MS/MS-) based newborn screening identifies many suspicious cases of fatty acid oxidation and carnitine cycle disorders, a simple, noninvasive test is required to confirm the diagnosis. We have developed a novel method to evaluate the metabolic defects in peripheral blood mononuclear cells loaded with deuterium-labeled fatty acids directly using the ratios of acylcarnitines determined by flow injection MS/MS. We have identified diagnostic indices for the disorders as follows: decreased ratios of d27-C14-acylcarnitine/d31-C16-acylcarnitine and d23-C12-acylcarnitine/d31-C16-acylcarnitine for carnitine palmitoyltransferase-II (CPT-II) deficiency, decreased ratios of d23-C12-acylcarnitine/d27-C14-acylcarnitine for very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency, and increased ratios of d29-C16-OH-acylcarnitine/d31-C16-acylcarnitine for trifunctional protein (TFP) deficiency, together with increased ratios of d7-C4-acylcarnitine/d31-C16-acylcarnitine for carnitine palmitoyltransferase-I deficiency. The decreased ratios of d1-acetylcarnitine/d31-C16-acylcarnitine could be indicative of ß-oxidation ability in patients with CPT-II, VLCAD, and TFP deficiencies. Overall, our data showed that the present method was valuable for establishing a rapid diagnosis of fatty acid oxidation disorders and carnitine cycle disorders and for complementing gene analysis because our diagnostic indices may overcome the weaknesses of conventional enzyme activity measurements using fibroblasts or mononuclear cells with assumedly uncertain viability.

National survey of Japanese patients with mevalonate kinase deficiency reveals distinctive genetic and clinical characteristics.

OBJECTIVES: Mevalonate kinase deficiency (MKD), a rare autosomal recessive autoinflammatory syndrome, is caused by disease-causing variants of the mevalonate kinase (MVK) gene. A national survey was undertaken to investigate clinical and genetic features of MKD patients in Japan. METHODS: The survey identified ten patients with MKD. Clinical information and laboratory data were collected from medical records and by direct interviews with patients, their families, and their attending physicians. Genetic analysis and measurement of MVK activity and urinary excretion of mevalonic acid were performed. RESULTS: None of the 10 patients harbored MVK disease-causing variants that are common in European patients. However, overall symptoms were in line with previous European reports. Continuous fever was observed in half of the patients. Elevated transaminase was observed in four of the 10 patients, two of whom fulfilled the diagnostic criteria for hemophagocytic lymphohistiocytosis. About half of the patients responded to temporary administration of glucocorticoids and NSAIDs; the others required biologics such as anti-IL-1 drugs. CONCLUSION: This is the first national survey of MKD patients in a non-European country. Although clinical symptoms were similar to those reported in Europe, the incidence of continuous fever and elevated transaminase was higher, probably due to differences in disease-causing variants.

Urea cycle disorders in India: clinical course, biochemical and genetic investigations, and prenatal testing.

BACKGROUND: Urea cycle disorders (UCDs) are inherited metabolic disorders that present with hyperammonemia, and cause significant mortality and morbidity in infants and children. These disorders are not well reported in the Indian population, due to lack of a thorough study of the clinical and molecular profile. RESULTS: We present data from two major metabolic centres in India, including 123 cases of various UCDs. The majority of them (72/123, 58%) presented in the neonatal period (before 30 days of age) with 88% on or before day 7 of life (classical presentation), and had a high mortality (64/72, 88%). Citrullinemia type 1 was the most common UCD, observed in 61/123 patients. Ornithine transcarbamylase (OTC) deficiency was the next most common, seen in 24 cases. Argininosuccinic aciduria was diagnosed in 20 cases. Deficiencies of arginase, N-acetylglutamate synthase, carbamoyl phosphate synthetase, citrin, and lysinuric protein intolerance were also observed. Molecular genetic analysis revealed two common ASS1 mutations: c.470G > A (p.Arg157His) and c.1168G > A (p.Gly390Arg) (36 of 55 tested patients). In addition, few recurrent point mutations in ASL gene, and a deletion of the whole OTC gene were also noted. A total of 24 novel mutations were observed in the various genes studied. We observed a poor clinical outcome with an overall all time mortality of 63% (70/110 cases with a known follow-up), and disability in 70% (28/40) among the survivors. Prenatal diagnosis was performed in 30 pregnancies in 25 families, including one pre-implantation genetic diagnosis. CONCLUSIONS: We report the occurrence of UCDs in India and the spectrum that may be different from the rest of the world. Citrullinemia type 1 was the most common UCD observed in the cohort. Increasing awareness amongst clinicians will improve outcomes through early diagnosis and timely treatment. Genetic diagnosis in the proband will enable prenatal/pre-implantation diagnosis in subsequent pregnancies.

A variant at 9q34.11 is associated with HLA-DQB1*06:02 negative essential hypersomnia.

Essential hypersomnia (EHS) is a lifelong disorder characterized by excessive daytime sleepiness without cataplexy. EHS is associated with human leukocyte antigen (HLA)-DQB1*06:02, similar to narcolepsy with cataplexy (narcolepsy). Previous studies suggest that DQB1*06:02-positive and -negative EHS are different in terms of their clinical features and follow different pathological pathways. DQB1*06:02-positive EHS and narcolepsy share the same susceptibility genes. In the present study, we report a genome-wide association study with replication for DQB1*06:02-negative EHS (408 patients and 2247 healthy controls, all Japanese). One single-nucleotide polymorphism, rs10988217, which is located 15-kb upstream of carnitine O-acetyltransferase (CRAT), was significantly associated with DQB1*06:02-negative EHS (P = 7.5 × 10-9, odds ratio = 2.63). The risk allele of the disease-associated SNP was correlated with higher expression levels of CRAT in various tissues and cell types, including brain tissue. In addition, the risk allele was associated with levels of succinylcarnitine (P = 1.4 × 10-18) in human blood. The leading SNP in this region was the same in associations with both DQB1*06:02-negative EHS and succinylcarnitine levels. The results suggest that DQB1*06:02-negative EHS may be associated with an underlying dysfunction in energy metabolic pathways.

Diversity in the incidence and spectrum of organic acidemias, fatty acid oxidation disorders, and amino acid disorders in Asian countries: Selective screening vs. expanded newborn screening.

BACKGROUND: Expanded newborn screening (ENBS) utilizing tandem mass spectrometry (MS/MS) for inborn metabolic diseases (IMDs), such as organic acidemias (OAs), fatty acid oxidation disorders, (FAODs), and amino acid disorders (AAs), is increasingly popular but has not yet been introduced in many Asian countries. This study aimed to determine the incidence rates of OAs, FAODs, and AAs in Asian countries and Germany using selective screening and ENBS records. MATERIALS AND METHODS: Selective screening for IMDs using gas chromatography-mass spectrometry and MS/MS was performed among patients suspected to be afflicted in Asian countries (including Japan, Vietnam, China, and India) between 2000 and 2015, and the results from different countries were compared. Similarly, ENBS results from Japan, South Korea, Taiwan, and Germany were compared. Additionally, the results of selective screening and ENBS in Japan were compared. RESULTS: Among 39,270 patients who underwent selective screening, IMDs were detected in 1170. Methylmalonic acidemia was frequently identified in several countries, including Japan (81/377 diagnosed IMDs), China (94/216 IMDs), and India (72/293 IMDs). In Vietnam, however, ß-ketothiolase deficiency was particularly frequent (33/250 IMDs). ENBS yielded differences in overall IMD rates by country: 1:8557 in Japan, 1:7030 in Taiwan, 1:13,205 in South Korea, and 1:2200 in Germany. Frequently discovered diseases included propionic acidemia (PPA) and phenylketonuria (PKU) in Japan, 3-methylcrotonyl-CoA carboxylase deficiency (MCCD) and PKU in Taiwan, MCCD and citrullinemia type I in South Korea, and PKU and medium-chain acyl-CoA dehydrogenase deficiency in Germany. Furthermore, in Japan, selective screening and ENBS yielded respective PPA frequencies of 14.7% and 49.4% among all organic acidemias. CONCLUSION: The incidence rates of IMDs vary by country. Moreover, the disease spectra of IMDs detected via selective screening differ from those detected via ENBS.

Acute encephalopathy with biphasic seizures and late reduced diffusion associated with Streptococcus sanguinis sepsis.

Acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) develops in association with systemic as well as central nervous system (CNS) viral or bacterial infections. AESD is most often noted with influenza or human herpesvirus 6 infection in previously healthy infants. However, AESD has also been reported in an infant with developmental retardation and in a mentally and motor-disabled adolescent. Here, we report the case of a 4- year-old female with significant development delay due to spinal muscular atrophy, who developed AESD during Streptococcus sanguinis sepsis with no apparent CNS infection. Although the patient had extremely high serum procalcitonin (45.84 ng/mL, reference; <0.4) on admission indicating a poor prognosis, she was successfully managed for sepsis and AESD.

Newborn screening for carnitine palmitoyltransferase II deficiency using (C16+C18:1)/C2: Evaluation of additional indices for adequate sensitivity and lower false-positivity.

BACKGROUND: Carnitine palmitoyltransferase (CPT) II deficiency is one of the most common forms of mitochondrial fatty acid oxidation disorder (FAOD). However, newborn screening (NBS) for this potentially fatal disease has not been established partly because reliable indices are not available. METHODS: We diagnosed CPT II deficiency in a 7-month-old boy presenting with hypoglycemic encephalopathy, which apparently had been missed in the NBS using C16 and C18:1 concentrations as indices. By referring to his acylcarnitine profile from the NBS, we adopted the (C16+C18:1)/C2 ratio (cutoff 0.62) and C16 concentration (cutoff 3.0nmol/mL) as alternative indices for CPT II deficiency such that an analysis of a dried blood specimen collected at postnatal day five retroactively yielded the correct diagnosis. Thereafter, positive cases were assessed by measuring (1) the fatty acid oxidation ability of intact lymphocytes and/or (2) CPT II activity in the lysates of lymphocytes. The diagnoses were then further confirmed by genetic analysis. RESULTS: The disease was diagnosed in seven of 21 newborns suspected of having CPT II deficiency based on NBS. We also analyzed the false-negative patient and five symptomatic patients for comparison. Values for the NBS indices of the false-negative, symptomatic patient were lower than those of the seven affected newborns. Although it was difficult to differentiate the false-negative patient from heterozygous carriers and false-positive subjects, the fatty acid oxidation ability of the lymphocytes and CPT II activity clearly confirmed the diagnosis. Among several other indices proposed previously, C14/C3 completely differentiated the seven NBS-positive patients and the false-negative patient from the heterozygous carriers and the false-positive subjects. Genetic analysis revealed 16 kinds of variant alleles. The most prevalent, detected in ten alleles in nine patients from eight families, was c.1148T>A (p.F383Y), a finding in line with those of several previous reports on Japanese patients. CONCLUSIONS: These findings suggested that CPT II deficiency can be screened by using (C16+C18:1)/C2 and C16 as indices. An appropriate cutoff level is required to achieve adequate sensitivity albeit at the cost of a considerable increase in the false-positive rate, which might be reduced by using additional indices such as C14/C3.

Tyrosinemia Type I in Japan: A Report of Five Cases.

Tyrosinemia type I in Japan was reported for the first time in 1957 by Sakai et al. (Jikei Med J 2:1-10, 1957) and Kitagawa et al. (Proc Jpn Acad Ser B 88:192-200, 1957). Five cases of patients with tyrosinemia type I were reported to be definitively diagnosed in Japan. The first case was reported by Sakai et al. and Kitagawa et al. To the best of our knowledge, this was the first definite report in the world. The second and third cases were those of a brother and a sister who underwent liver transplantation and who were the children of a Japanese-descent migrant worker; the fourth case was that of a girl who underwent liver transplantation after 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC) treatment, which was reported by Hata et al.; and the fifth case was that of a patient who was administered NTBC, which was reported by Ito et al. These were of the subacute type, wherein residual activity was considerably present. When combined therapy with a low phenylalanine and tyrosine diet and NTBC administration is started after early diagnosis, patients can survive without liver transplantation. Development of liver cancer is not found in the cases in Japan, but performing liver transplantation without delay is necessary when liver cancer is found.

Clinical and molecular investigation of 14 Japanese patients with complete TFP deficiency: a comparison with Caucasian cases.

Mitochondrial trifunctional protein (TFP) deficiency is an inherited metabolic disorder of mitochondrial fatty-acid oxidation. Isolated long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency is often reported in Caucasian countries due to a common mutation. However, the molecular and clinical basis of complete TFP deficiency has not been extensively reported. In this study, 14 Japanese cases (13 families) with complete TFP deficiency, including 9 previously reported cases, were analyzed to clarify the clinical and molecular characteristics of TFP deficiency. The clinical types of the 14 patients were as follows: 12 cases of neonatal (n=7) or myopathic (n=5) types and 2 cases of intermediate type. Peripheral neuropathy was found in four cases and hypocalcemia due to hypoparathyroidism, which is rarely reported in Caucasian patients, had developed in four cases. Maternal hemolysis, elevated liver enzymes and low platelet count syndrome and acute fatty liver of pregnancy were noted in two and one mothers, respectively. Fourteen mutations were identified in 26 alleles in Japanese patients, including two novel mutations (HADHA: c.361C>T, and HADHA-HADHB: g.26233880_ 26248855del), although no common mutations were found. This study suggests that the molecular and clinical aspects of Japanese patients with TFP deficiencies differ from those of Caucasian patients.

Japanese Male Siblings with 2-Methyl-3-Hydroxybutyryl-CoA Dehydrogenase Deficiency (HSD10 Disease) Without Neurological Regression.

2-Methyl-3-hydroxybutyryl-CoA dehydrogenase deficiency (HSD10 disease) is a rare X-linked disorder caused by a mutation in the HSD17B10 gene. Fewer than 30 patients with this disorder have been reported worldwide. The classical infantile form of HSD10 disease is characterized by a progressive neurodegenerative course with retinopathy and cardiomyopathy, although HSD10 disease has broad clinical heterogeneity. However, several male patients have not shown neurological regression. Here, we describe two Japanese siblings with HSD10 disease without neurological regression. A 4-year-old boy presented with unconsciousness due to severe hypoglycemia. Laboratory testing on admission showed mild metabolic acidosis and mild hyperammonemia. Urinary organic acid analysis in the acute phase showed elevated excretion of 2-methyl-3-hydroxybutyric acid, tiglylglycine, and ketones. However, 2-methylacetoacetate was not elevated. HSD10 disease was suspected based on urinary organic acid data. The patient had a novel hemizygous c.470C>T (p.A157V) mutation in the HSD17B10 gene. His mother was a heterozygous carrier of this mutation. The patient's older brother also had the c.470C>T (p.A157V) mutation. Neurological development was normal at the time of evaluation. The pilot newborn screening results using tandem mass spectrometry of the proband were reevaluated retrospectively and showed a high C5:1 carnitine level of 0.070 nmol/mL (upper cutoff limit, 0.05 nmol/mL) and a normal C5-OH carnitine level of 0.290 nmol/mL (upper cutoff limit, 1.0 nmol/mL). His affected brother and another patient with the atypical form of HSD10 disease having p.A154T also showed elevated C5:1 but not C5-OH in serum acylcarnitine analysis. Thus, these data suggested that some patients with this disorder may be identified using newborn screening.