Health-related quality of life and caregiver burden of pediatric patients with inborn errors of metabolism in Japan using EQ-5D-Y, PedsQL, and J-ZBI.

PURPOSE: Inborn errors of metabolism (IEM) are known with poor long-term health concerns; however, the health-related quality of life (HRQoL) and the burden placed on families remain unclear. This study investigated the self- and proxy-reported HRQoL of pediatric patients with IEM with or without developmental disabilities and the burden placed on their caregivers. METHODS: Patients with IEM aged 8-15 years and their caregivers were asked to respond to the Pediatric Quality of Life Inventory (PedsQL), EuroQoL five-dimension questionnaire for younger populations (EQ-5D-Y), and Japanese version of the Zarit Caregiver Burden Interview (J-ZBI). We compared EQ-5D-Y scores with matched EQ-5D-Y population norms. Intraclass correlation coefficients (ICC) for self and proxy HRQoL scores of those without developmental disabilities were calculated. Correlation coefficients of HRQoL proxy responses with J-ZBI score were estimated. RESULTS: We included 66 patients with IEM (mean age, 11.5 years; males, 41.2%) in the study. The mean (± standard deviation) EQ-5D-Y scores without and with developmental disabilities were 0.957 (± 0.071) and 0.821 (± 0.175), respectively. The EQ-5D-Y scores significantly increased compared with the reference values (p < 0.01, effect size = 0.337). The ICC values were 0.331 and 0.477 for the EQ-5D-Y and PedsQL scores, respectively. HRQoL proxy scores had strong negative correlations with J-ZBI scores. CONCLUSION: The HRQoL of patients with IEM without developmental disabilities in our study was similar to that of the general Japanese population. The HRQoL of patients with IEM with developmental disabilities was low and associated with a tendency towards an increased burden of care.

Phenotypic and genetic spectra of galactose mutarotase deficiency: A nationwide survey conducted in Japan.

PURPOSE: Galactose mutarotase (GALM) deficiency was first reported in 2019 as the fourth type of galactosemia. This study aimed to investigate the clinical and genotypic spectra of GALM deficiency. METHODS: This was a questionnaire-based retrospective survey conducted in Japan between February 2022 and March 2023. RESULTS: We identified 40 patients with GALM deficiency in Japan (estimated prevalence: 1:181,835). Four of 38 patients (10.5%) developed cataracts, which resolved with lactose restriction in 3 out of 4 patients. Transient transaminitis was the most common symptom (23.1%). All of the patients followed lactose restriction; discontinuation of the restriction after infancy did not cause any complications. Moreover, none of the participants experienced long-term complications. Two variants, GALM NM_138801.3: c.294del and c.424G>A, accounted for 72.5% of the identified pathogenic variants. The patients showed moderately elevated blood galactose levels with lactose intake; however, the elevation was lower than that observed in galactokinase deficiency. CONCLUSION: GALM deficiency is characterized by a similar but milder phenotype and lower blood galactose elevation than in galactokinase deficiency. Diagnosis and initiation of lactose restriction in early infancy should be essential for prevention of cataracts, especially in cases of irreversible opacity.

Clinical and molecular analyses of isolated central congenital hypothyroidism based on a survey conducted in Japan.

Central congenital hypothyroidism (CH) can occur as an isolated deficiency or as part of combined pituitary hormone deficiency. Unlike primary CH, central CH cannot be detected by newborn screening (NBS) using dry filter paper blood TSH levels, and early diagnosis remains challenging. In this study, the clinical and genetic backgrounds of patients with isolated central CH were determined through a questionnaire-based survey among members of the Japanese Society for Pediatric Endocrinology. The known causes of isolated central CH were studied in 14 patients, including six with previously reported patient data. The results revealed IGSF1 and TBL1X pathogenic variants in nine and one patient, respectively. All six patients with low free thyroxine (FT4) levels detected in NBS carried IGSF1 pathogenic variants. Five patients with isolated central CH diagnosed after 3 months of age were variant-negative, except for one female patient with a heterozygous IGSF1 variant. Two of the four variant-negative patients and a variant-positive patient were diagnosed with pituitary hypoplasia. One and two patients with IGSF1 variant had obesity and intellectual disability, respectively. Left amblyopia was identified in the patient with a TBL1X variant. The study revalidated that IGSF1 variants comprise the most frequent pathogenic variant in patients with isolated central CH in Japan. The neonatal period is the optimal time for the diagnosis of central CH, particularly IGSF1 abnormalities, and the introduction of T4 screening should be considered in the future, taking cost-effectiveness into consideration.

Identification of causative gene variants for patients with known monogenic diabetes using a targeted next-generation sequencing panel in a single-center study.

Aims: We aimed to verify the usefulness of targeted next-generation sequencing (NGS) technology for diagnosing monogenic diabetes in a single center. Methods: We designed an amplicon-based NGS panel targeting 34 genes associated with known monogenic diabetes and performed resequencing in 56 patients with autoantibody-negative diabetes mellitus diagnosed at < 50 years who had not been highly obese. By bioinformatic analysis, we filtered significant variants based on allele frequency (< 0.005 in East Asians) and functional prediction. We estimated the pathogenicity of each variant upon considering the family history. Results: Overall, 16 candidate causative variants were identified in 16 patients. Among them, two previously known heterozygous nonsynonymous single-nucleotide variants associated with monogenic diabetes were confirmed as causative variants: one each in the GCK and WFS1 genes. The former was found in two independent diabetes-affected families. Two novel putatively deleterious heterozygous variants were also assumed to be causative from the family history: one frameshift and one nonsynonymous single-nucleotide variant in the HNF4A gene. Twelve variants remained as candidates associated with the development of diabetes. Conclusion: Targeted NGS panel testing was useful to diagnose various forms of monogenic diabetes in combination with familial analysis, but additional ingenuity would be needed for practice. Supplementary Information: The online version contains supplementary material available at 10.1007/s13340-023-00669-3.

Incidence and Risk Factors for Adrenal Crisis in Pediatric-onset Adrenal Insufficiency: A Prospective Study.

CONTEXT: Adrenal crisis (AC) is a life-threatening complication that occurs during follow-up of patients with adrenal insufficiency (AI). No prospective study has thoroughly investigated AC in children with primary and secondary AI. OBJECTIVE: This work aimed to determine the incidence and risk factors for AC in patients with pediatric-onset AI. METHODS: This multicenter, prospective cohort study conducted in Japan enrolled patients diagnosed with AI at age ≤15 years. The incidence of AC was calculated as events per person-year (PY), and risk factors for AC were assessed using Poisson regression multivariable analysis. RESULTS: The study population comprised 349 patients (164 male, 185 female) with a total follow-up of 961 PY. The median age at enrollment was 14.3 years (interquartile range [IQR] 8.5-21.2 years), and the median follow-up was 2.8 years (IQR 2.2-3.3 years). Of these patients, 213 (61%) had primary AI and 136 (39%) had secondary AI. Forty-one AC events occurred in 31 patients during the study period. The calculated incidence of AC was 4.27 per 100 PY (95% CI, 3.15-5.75). Poisson regression analysis identified younger age at enrollment (relative risk [RR] 0.93; 95% CI, 0.89-0.97) and increased number of infections (RR 1.17; 95% CI, 1.07-1.27) as significant risk factors. Female sex (RR 0.99; 95% CI, 0.53-1.86), primary AI (RR 0.65; 95% CI, 0.30-1.41), or equivalent dosage of hydrocortisone per square meter of body area (RR 1.02; 95% CI, 0.96-1.08) was not a significant risk factor. CONCLUSION: A substantial proportion of patients with pediatric-onset AI experience AC. Younger age and an increased number of infections are independent risk factors for developing AC in these patients.

Improved sensitivity and specificity for citrin deficiency using selected amino acids and acylcarnitines in the newborn screening.

Citrin deficiency is an autosomal recessive disorder caused by a defect of citrin resulting from mutations in the SLC25A13 gene. Intrahepatic cholestasis and various metabolic abnormalities, including hypoglycemia, galactosemia, citrullinemia, and hyperammonemia may be present in neonates or infants in the "neonatal intrahepatic cholestasis caused by citrin deficiency" (NICCD) form of the disease. Because at present, newborn screening (NBS) for citrin deficiency using citrulline levels in dried blood spots (DBS) can only detect some of the patients, we tried to develop a new evaluation system to more reliably detect newborns with citrin deficiency utilizing parameters already in place in present NBS methods. To achieve this goal, we re-analyzed NBS profiles of amino acids and acylcarnitines in 96 NICCD patients, who were diagnosed through selective screening or positive family history. Hereby, we identified the combined evaluation of arginine (Arg), citrulline (Cit), isoleucine+leucine (Ile + Leu), tyrosine (Tyr), free carnitine (C0) / glutarylcarnitine (C5-DC) ratio in DBS as potentially sensitive to diagnose citrin deficiency in pre-symptomatic newborns. In particular, a scoring system using threshold levels for Arg (≥9 µmol/L), Cit (≥ 39 µmol/L), Ile + Leu (≥ 99 µmol/L), Tyr (≥ 96 µmol/L) and C0/C5-DC ratio (≥327) was significantly effective to detect newborns who later developed NICCD, and could thus be implemented in existing NBS programs at no extra analytical costs whenever citrin deficiency is considered to become a novel target disease.

Association between maternally inherited deafness, epilepsy, and intellectual disability and the m.12207G > A MT-TS2 pathogenic variant in a Japanese family.

The identification of the m.12207G > A variant in MT-TS2, (NC_012920.1:m.12207G > A) was first reported in 2006. The affected individual presented with developmental delay, feeding difficulty, proximal muscle weakness, and lesions within her basal ganglia, with heteroplasmy levels of 92% in muscle and no evidence of maternal inheritance. Herein, we report a case involving a 16-year-old boy with the same pathogenic variation and different phenotype, including sensorineural deafness, epilepsy, and intellectual disability, without diabetes mellitus (DM). His mother and maternal grandmother had similar but milder symptoms with DM. Heteroplasmy levels of the proband in blood, saliva, and urinary sediments were 31.3%, 52.6%, and 73.9%, respectively, while those of his mother were 13.8%, 22.1%, and 29.4%, respectively. The differences in the symptoms might be explained by the different levels of heteroplasmy. To our knowledge, this is the first familial report of the m.12207G > A variant in MT-TS2 that causes DM. The present case showed milder neurological symptoms than did the former report, and suggests the presence of a good phenotype-genotype correlation within this family.

Guidelines for Newborn Screening of Congenital Hypothyroidism (2021 Revision).

Purpose of developing the guidelines: Newborn screening (NBS) for congenital hypothyroidism (CH) was started in 1979 in Japan, and early diagnosis and treatment improved the intelligence prognosis of CH patients. The incidence of CH was once about one in 5,000-8,000 births, but has been increased with diagnosis of subclinical CH. The disease requires continuous treatment and specialized medical facilities should conduct differential diagnosis and treatment in patients who are positive by NBS to avoid unnecessary treatment. The Guidelines for Mass Screening of Congenital Hypothyroidism (1998 version) were developed by the Mass Screening Committee of the Japanese Society for Pediatric Endocrinology in 1998. Subsequently, the guidelines were revised in 2014. Here, we have added minor revisions to the 2014 version to include the most recent findings. Target disease/conditions: Primary congenital hypothyroidism. Users of the Guidelines: Physician specialists in pediatric endocrinology, pediatric specialists, physicians referring pediatric practitioners, general physicians, laboratory technicians in charge of mass screening, and patients.

Clinical manifestation and long-term outcome of citrin deficiency: Report from a nationwide study in Japan.

Citrin deficiency is an autosomal recessive disorder caused by mutations in the SLC25A13 gene. The disease can present with age-dependent clinical manifestations: neonatal intrahepatic cholestasis by citrin deficiency (NICCD), failure to thrive, and dyslipidemia by citrin deficiency (FTTDCD), and adult-onset type II citrullinemia (CTLN2). As a nationwide study to investigate the clinical manifestations, medical therapy, and long-term outcome in Japanese patients with citrin deficiency, we collected clinical data of 222 patients diagnosed and/or treated at various different institutions between January 2000 and December 2019. In the entire cohort, 218 patients were alive while 4 patients (1 FTTDCD and 3 CTLN2) had died. All patients <20 years were alive. Patients with citrin deficiency had an increased risk for low weight and length at birth, and CTLN2 patients had an increased risk for growth impairment during adolescence. Liver transplantation has been performed in only 4 patients (1 NICCD, 3 CTLN2) with a good response thereafter. This study reports the diagnosis and clinical course in a large cohort of patients with citrin deficiency and suggests that early intervention including a low carbohydrate diet and MCT supplementation can be associated with improved clinical course and long-term outcome.

Heterozygous calcyclin-binding protein/Siah1-interacting protein (CACYBP/SIP) gene pathogenic variant linked to a dominant family with paucity of interlobular bile duct.

Paucity of interlobular bile ducts (PILBD) is a heterogeneous disorder classified into two categories, syndromic and non-syndromic bile duct paucity. Syndromic PILBD is characterized by the presence of clinical manifestations of Alagille syndrome. Non-syndromic PILBD is caused by multiple diseases, such as metabolic and genetic disorders, infectious diseases, and inflammatory and immune disorders. We evaluated a family with a dominantly inherited PILBD, who presented with cholestasis at 1-2 months of age but spontaneously improved by 1 year of age. Next-generation sequencing analysis revealed a heterozygous CACYBP/SIP p.E177Q pathogenic variant. Calcyclin-binding protein and Siah1 interacting protein (CACYBP/SIP) form a ubiquitin ligase complex and induce proteasomal degradation of non-phosphorylated ß-catenin. Immunohistochemical analysis revealed a slight decrease in CACYBP and ß-catenin levels in the liver of patients in early infancy, which almost normalized by 13 months of age. The CACYBP/SIP p.E177Q pathogenic variant may form a more active or stable ubiquitin ligase complex that enhances the degradation of ß-catenin and delays the maturation of intrahepatic bile ducts. Our findings indicate that accurate regulation of the ß-catenin concentration is essential for the development of intrahepatic bile ducts and CACYBP/SIP pathogenic variant is a novel cause of PILDB.

Foetal virilisation caused by overproduction of non-aromatisable 11-oxygenated C19 steroids in maternal adrenal tumour.

It is widely believed that adrenal tumours and ovarian luteomas in pregnant women cause virilisation of female foetuses through overproduction of testosterone and/or androstenedione. However, this notion raises a fundamental question as to how these classic androgens pass through the placenta without being converted by aromatase into oestrogens. Here, we report a case of maternal adrenal tumour, in which overproduction of 11-oxygenated C19 steroids (11ox C19s), newly characterised non-aromatisable androgens in humans, caused foetal virilisation. The female proband presented with severely virilised external genitalia at birth. The mother exhibited hirsutism, hyperglycaemia and hypertension and was diagnosed as having adrenal tumour. The mother was subjected to comprehensive steroid measurement. Serum levels of 11ox C19s were markedly elevated. In contrast, testosterone and androstenedione levels remained within the normal range, and levels of most other steroids in the conventional and backdoor androgenic pathways were normal or only mildly elevated. After tumour removal, levels of 11ox C19s were markedly reduced. These results provide the first evidence that 11ox C19s can be synthesised in adrenal adenomas and, due to their non-aromatisable nature, can pass through the placental barrier to cause foetal virilisation. These findings highlight a unique pathogenic property of these newly specified androgens in humans.

Retrospective study of the renal function using estimated glomerular filtration rate and congenital anomalies of the kidney-urinary tract in pediatric Turner syndrome.

Although Turner syndrome (TS) is frequently associated with congenital anomalies of the kidney-urinary tract (CAKUT), which is a major cause of pediatric chronic kidney disease, renal function in TS is usually considered normal. The present study aimed to analyze the frequency of renal dysfunction and CAKUT in pediatric patients with TS. Our study included 122 patients with TS between the ages of 2 and 18 years from 30 hospitals across Japan. Clinical data related to renal function and CAKUT were retrospectively collected. The estimated glomerular filtration rate (eGFR) was calculated using the serum creatinine-based formula recommended by the Japanese Society for Pediatric Nephrology. An eGFR <90 mL/min/1.73 m2 for two consecutive years was defined as renal dysfunction. Fifteen (13.5%) of 122 patients had CAKUT, and four patients had renal dysfunction (3.2%, 95% confidence interval: 0%-6.7%). Three of the four did not have CAKUT. Of the CAKUT manifestations, horseshoe kidney, renal hypodysplasia, and multicystic dysplastic kidney were seen in nine, two, and one patient, respectively. Eight of the nine patients with horseshoe kidney had a normal renal function; however, the remaining patient with renal hypodysplasia had renal dysfunction. A small percentage of patients with pediatric TS may had an eGFR below 90 mL/min/1.73 m2 which was not necessarily associated with CAKUT.

Clinical characteristics of cytochrome P450 oxidoreductase deficiency: a nationwide survey in Japan.

Cytochrome P450 oxidoreductase deficiency (PORD) is a disorder of steroidogenesis that causes various symptoms such as skeletal malformations, disorders of sex development, and adrenal insufficiency. The aim of this study was to elucidate the clinical characteristics, especially age at diagnosis and treatment, of PORD from the perinatal period to adulthood in Japan. The first questionnaire was sent to 183 council members of the Japanese Society for Pediatric Endocrinology on 1 September 2018. The response rate was 65%, and a total of 39 patients with PORD were examined at 20 hospitals. The second questionnaire was sent in November 2018 to the council members examining these 39 patients with PORD. The response rate was 77%, and we received clinical information on 30 of the 39 patients. The two novel clinical findings were the age at diagnosis and the treatment of Japanese patients with PORD. In many cases, PORD can be diagnosed at <3 months of age. Hydrocortisone as the primary treatment during infancy can be used daily or in stressful situations; however, because patients with PORD generally have mild to moderate adrenal insufficiency, some might be able to avoid hydrocortisone treatment. Patients with PORD should be carefully followed up, and treatment should be optimized as for patients with other types of adrenal insufficiency. Other characteristics in the present study were similar to those described in previous reports.

Diabetes mellitus exacerbates citrin deficiency via glucose toxicity.

AIMS: Citrin is an aspartate/glutamate carrier that composes the malate-aspartate reduced nicotinamide adenine dinucleotide (NADH) shuttle in the liver. Citrin deficiency causes neonatal intrahepatic cholestasis (NICCD), failure to thrive and dyslipidemia (FTTDCD) and adult-onset type II citrullinemia (CTLN2). Hepatic glycolysis is essentially impaired in citrin deficiency and a low-carbohydrate diet was recommended. The lethal effect of infusion of glycerol- and fructose-containing osmotic agents was reported in these patients. Hyperalimentation was also reported to exacerbate CTLN2; however, glucose toxicity was unclear in citrin deficiency. METHODS: We studied two CTLN2 patients complicated with type 2 diabetes mellitus (DM), Case 1 presented with hyperammonemic encephalopathy accompanied with DM, while Case 2 presented with hyperammonemic encephalopathy relapse upon the onset of DM after several years' remission following supplementation with medium-chain triglycerides (MCT) and adherence to a low-carbohydrate diet. RESULTS: Insulin therapy with MCT supplementation and a low-carbohydrate diet improved hyperammonemia and liver function in Case 1. Additional insulin therapy improved hyperammonemia in Case 2. CONCLUSION: Glucose is not toxic for citrin deficiency in normoglycemia because glucose uptake and metabolism by hepatocytes are limited in normoglycemia. However, glucose becomes toxic during persistent hyperglycemia and antidiabetic therapy is indispensable for CTLN2 patients with DM.

Three Consecutive Cases of Familial Hemophagocytic Lymphohistiocytosis, Including a Case Due to Maternal Uniparental Disomy.

We have experienced 3 consecutive cases of familial hemophagocytic lymphohistiocytosis (FHL). All affected infants had mutations in exon 3 of the perforin gene. The first had a homozygous mutation, c.1168C>T (p.R390*), caused by maternal uniparental isodisomy. The second and third had compound heterozygous mutations: c.781G>A (p.E261K) and c.1491T>A (p.C497*); c.1724G>T (p.C242G) and p.R390*, respectively. FHL is very rare in Northern Japan but should be suspected if infants exhibit prolonged fever. This is the first report of a relationship of p.R390* with FHL caused by uniparental isodisomy, and the second reported case of FHL type 2 with this form of inheritance.

Genetics of Congenital Isolated TSH Deficiency: Mutation Screening of the Known Causative Genes and a Literature Review.

CONTEXT: Congenital isolated TSH deficiency (i-TSHD) is a rare form of congenital hypothyroidism. Five genes (IGSF1, IRS4, TBL1X, TRHR, and TSHB) responsible for the disease have been identified, although their relative frequencies and hypothalamic/pituitary unit phenotypes have remained to be clarified. OBJECTIVES: To define the relative frequencies and hypothalamic/pituitary unit phenotypes of congenital i-TSHD resulting from single gene mutations. PATIENTS AND METHODS: Thirteen Japanese patients (11 boys and 2 girls) with congenital i-TSHD were enrolled. IGSF1, IRS4, TBL1X, TRHR, and TSHB were sequenced. For a TBL1X mutation (p.Asn382del), its pathogenicity was verified in vitro. For a literature review, published clinical data derived from 74 patients with congenital i-TSHD resulting from single-gene mutations were retrieved and analyzed. RESULTS: Genetic screening of the 13 study subjects revealed six mutation-carrying patients (46%), including five hemizygous IGSF1 mutation carriers and one hemizygous TBL1X mutation carrier. Among the six mutation carriers, one had intellectual disability and the other one had obesity, but the remaining four did not show nonendocrine phenotypes. Loss of function of the TBL1X mutation (p.Asn382del) was confirmed in vitro. The literature review demonstrated etiology-specific relationship between serum prolactin (PRL) levels and TRH-stimulated TSH levels with some degree of overlap. CONCLUSIONS: The mutation screening study covering the five causative genes of congenital i-TSHD was performed, showing that the IGSF1 defect was the leading genetic cause of the disease. Assessing relationships between serum PRL levels and TRH-stimulated TSH levels would contribute to predict the etiologies of congenital i-TSHD.

Growth impairment in individuals with citrin deficiency.

Citrin deficiency causes neonatal intrahepatic cholestasis (NICCD), failure to thrive and dyslipidemia (FTTDCD), and adult-onset type II citrullinemia (CTLN2). Owing to a defect in the NADH-shuttle, citrin deficiency impairs hepatic glycolysis and de novo lipogenesis leading to hepatic energy deficit. To investigate the physiological role of citrin, we studied the growth of 111 NICCD-affected subjects (51 males and 60 females) and 12 NICCD-unaffected subjects (five males and seven females), including the body weight, height, and genotype. We constructed growth charts using the lambda-mu-sigma (LMS) method. The NICCD-affected subjects showed statistically significant growth impairment, including low birth weight and length, low body weight until 6 to 9 months of age, low height until 11 to 13 years of age, and low body weight in 7 to 12-year-old males and 8-year-old females. NICCD-unaffected subjects showed similar growth impairment, including low birth weight and height, and growth impairment during adolescence. In the third trimester, de novo lipogenesis is required for deposition of body fat and myelination of the developing central nervous system, and its impairment likely causes low birth weight and length. The growth rate is the highest during the first 6 months of life and slows down after 6 months of age, which is probably associated with the onset and recovery of NICCD. Adolescence is the second catch-up growth period, and the proportion and distribution of body fat change depending on age and sex. Characteristic growth impairment in citrin deficiency suggests a significant role of citrin in the catch-up growth via lipogenesis.

Clinical characteristics of adolescent cases with Type A insulin resistance syndrome caused by heterozygous mutations in the ß-subunit of the insulin receptor (INSR) gene.

BACKGROUND: Type A insulin resistance (IR) is a rare form of severe congenital IR that is frequently caused by heterozygous mutations in the insulin receptor (INSR) gene. Although Type A IR requires appropriate intervention from the early stages of diabetes, proper diagnosis of this disease is challenging, and accumulation of cases with detailed clinical profiles and genotypes is required. METHODS: Herein we report on six peripubertal patients with clinically diagnosed Type A IR, including four patients with an identified INSR mutation. To clarify the clinical features of Type A IR due to INSR mutation, we validated the clinical characteristics of Type A IR patients with identified INSR mutations by comparing them with mutation-negative patients. RESULTS: Four heterozygous missense mutations within the ß-subunit of INSR were detected: Gly1146Arg, Arg1158Trp, Arg1201Trp, and one novel Arg1201Pro mutation. There were no obvious differences in clinical phenotypes, except for normal lipid metabolism and autosomal dominant inheritance, between Type A IR due to INSR mutations and Type A IR due to other factors. However, our analysis revealed that the extent of growth retardation during the fetal period is correlated with the severity of insulin signaling impairment. CONCLUSIONS: The present study details the clinical features of four patients with genetically proven Type A IR. Further accumulation of genetically proven cases and long-term treatment prognoses following early diagnosis are required to further elucidate the dynamics of this disease.

Adult-onset type II citrullinemia: Current insights and therapy.

Citrin deficiency is a recessively inherited metabolic disorder with age-dependent clinical manifestations. It causes neonatal intrahepatic cholestasis (NICCD) and adult-onset type II citrullinemia (CTLN2). Patients with NICCD present with intrahepatic cholestasis in the neonatal period and usually respond to the treatment with medium-chain triglyceride (MCT) supplement and lactose-restricted formula. In adulthood, CTLN2 develops in <10 % of the patients showing hyperammonemic encephalopathy. Patients with CTLN2 required liver transplantation for the most promising prognosis; however, they were successfully treated with MCT supplement with a low carbohydrate formula. Citrin deficiency is caused by mutations in SLC25A13 on chromosome 7q21.3, with a high frequency in East Asia, including Japan. Citrin is aspartate/glutamate transporter in mitochondria, a component of malate-aspartate nicotinamide adenine dinucleotide hydrogen shuttle, and is essential for the hepatic glycolysis. Although the precise pathophysiology of citrin deficiency remains unclear, recent reports for the effective MCT supplement therapy and downregulation of peroxisome proliferator-activated receptor α suggest that citrin deficiency impairs hepatic de novo lipogenesis coupled with glycolysis leading to the energy deficit of hepatocytes. Herein, we review the current therapeutic and pathological understanding of CTLN2.

Medium-chain triglycerides supplement therapy with a low-carbohydrate formula can supply energy and enhance ammonia detoxification in the hepatocytes of patients with adult-onset type II citrullinemia.

Citrin, encoded by SLC25A13, constitutes the malate-aspartate shuttle, the main NADH-shuttle in the liver. Citrin deficiency causes neonatal intrahepatic cholestasis (NICCD) and adult-onset type II citrullinemia (CTLN2). Citrin deficiency is predicted to impair hepatic glycolysis and de novo lipogenesis, resulting in hepatic energy deficit. Secondary decrease in hepatic argininosuccinate synthetase (ASS1) expression has been considered a cause of hyperammonemia in CTLN2. We previously reported that medium-chain triglyceride (MCT) supplement therapy with a low-carbohydrate formula was effective in CTLN2 to prevent a relapse of hyperammonemic encephalopathy. We present the therapy for six CTLN2 patients. All the patients' general condition steadily improved and five patients with hyperammonemic encephalopathy recovered from unconsciousness in a few days. Before the treatment, plasma glutamine levels did not increase over the normal range and rather decreased to lower than the normal range in some patients. The treatment promptly decreased the blood ammonia level, which was accompanied by a decrease in plasma citrulline levels and an increase in plasma glutamine levels. These findings indicated that hyperammonemia was not only caused by the impairment of ureagenesis at ASS1 step, but was also associated with an impairment of glutamine synthetase (GS) ammonia-detoxification system in the hepatocytes. There was no decrease in the GS expressing hepatocytes. MCT supplement with a low-carbohydrate formula can supply the energy and/or substrates for ASS1 and GS, and enhance ammonia detoxification in hepatocytes. Histological improvement in the hepatic steatosis and ASS1-expression was also observed in a patient after long-term treatment.