Mitochondrial aspartate glutamate carrier (citrin) deficiency as the cause of adult-onset type II citrullinemia (CTLN2) and idiopathic neonatal hepatitis (NICCD)

Insights into the pathogenesis and treatment of cancer from inborn errors of metabolism

Mutations in genes that play fundamental roles in metabolic pathways have been found to also play a role in tumor development and susceptibility to cancer. At the same time, significant progress has been made in the treatment of patients with inborn errors of metabolism (IEM),(1) resulting in increased longevity and the unmasking of cancer predisposition, frequently hepatocellular carcinoma, in these conditions. These patients offer a potential opportunity to deepen our understanding of how intermediary metabolism impacts tumorigenesis. We provide an overview from the perspective of cancers in patients affected with IEM and discuss how dysregulation of these specific metabolic pathways might contribute to the mechanisms of cancer development and treatment.

Alcohol drinking patterns and the risk of fatty liver in Japanese men

BACKGROUND

Alcohol is considered to be a major cause of fatty liver (FL). In contrast, however, recent investigations have suggested that moderate alcohol consumption is protective against FL. To clarify the role of alcohol consumption in FL development, we examined the association between drinking patterns and FL prevalence.

METHODS

We enrolled 9,886 male participants at regular medical health checks. Each subject's history of alcohol consumption was determined by questionnaire. The subjects were classified according to alcohol consumption as non-, light, moderate, and heavy drinkers (0, <20, 20-59, and ≥60 g/day, respectively). FL was defined by ultrasonography. Independent predictors of FL were determined by logistic regression analysis.

RESULTS

The prevalence of FL displayed a "U-shaped curve" across the categories of daily alcohol consumption (non-, 44.7%; light, 39.3%; moderate, 35.9%; heavy drinkers, 40.1%; P < 0.001). The prevalence of FL was associated positively with body mass index and other obesity-related diseases and inversely with alcohol consumption (light, odds ratio [OR] 0.71, 95% confidence interval [CI] 0.59-0.86; moderate, OR 0.55, CI 0.45-0.67; heavy, OR 0.44, CI 0.32-0.62) as determined by multivariate analysis after adjusting for potential confounding variables. In addition, examination of drinking patterns (frequency and volume) revealed that the prevalence of FL was inversely associated with the frequency of alcohol consumption (≥21 days/month) (OR 0.62, CI 0.53-0.71) but not with the volume of alcohol consumed.

CONCLUSIONS

Our observations suggest that alcohol consumption plays a protective role against FL in men, and consistent alcohol consumption may contribute to this favorable effect.

Hypermethioninemias of genetic and non-genetic origin: A review

This review covers briefly the major conditions, genetic and non-genetic, sometimes leading to abnormally elevated methionine, with emphasis on recent developments. A major aim is to assist in the differential diagnosis of hypermethioninemia. The genetic conditions are: (1) Homocystinuria due to cystathionine β-synthase (CBS) deficiency. At least 150 different mutations in the CBS gene have been identified since this deficiency was established in 1964. Hypermethioninemia is due chiefly to remethylation of the accumulated homocysteine. (2) Deficient activity of methionine adenosyltransferases I and III (MAT I/III), the isoenzymes the catalytic subunit of which are encoded by MAT1A. Methionine accumulates because its conversion to S-adenosylmethionine (AdoMet) is impaired. (3) Glycine N-methyltrasferase (GNMT) deficiency. Disruption of a quantitatively major pathway for AdoMet disposal leads to AdoMet accumulation with secondary down-regulation of methionine flux into AdoMet. (4) S-adenosylhomocysteine (AdoHcy) hydrolase (AHCY) deficiency. Not being catabolized normally, AdoHcy accumulates and inhibits many AdoMet-dependent methyltransferases, producing accumulation of AdoMet and, thereby, hypermethioninemia. (5) Citrin deficiency, found chiefly in Asian countries. Lack of this mitochondrial aspartate-glutamate transporter may produce (usually transient) hypermethioninemia, the immediate cause of which remains uncertain. (6) Fumarylacetoacetate hydrolase (FAH) deficiency (tyrosinemia type I) may lead to hypermethioninemia secondary either to liver damage and/or to accumulation of fumarylacetoacetate, an inhibitor of the high K(m) MAT. Additional possible genetic causes of hypermethioninemia accompanied by elevations of plasma AdoMet include mitochondrial disorders (the specificity and frequency of which remain to be elucidated). Non-genetic conditions include: (a) Liver disease, which may cause hypermethioninemia, mild, or severe. (b) Low-birth-weight and/or prematurity which may cause transient hypermethioninemia. (c) Ingestion of relatively large amounts of methionine which, even in full-term, normal-birth-weight babies may cause hypermethioninemia.

A case of adult-onset type II citrullinemia induced by hospital diet

A 47-year-old Japanese man was first admitted to our hospital for 8 days because of an asthma attack. After discharge he changed his diet. On the 12th day after his discharge, he was re-admitted to our hospital because he exhibited transient loss of consciousness with flapping tremor. His plasma ammonia level was extremely high (245 μg/dL; normal, <90 μg/dL), suggesting hepatic encephalopathy. He underwent intravenous administration of branched-chain amino acids (Aminoleban(®)) and oral administration of lactulose and kanamycin sulfate; however, the hyperammonemia did not improve. Analysis of the amino acids and citrin gene led to the diagnosis of adult-onset type II citrullinemia (CTLN2). Following this diagnosis, the carbohydrate content of his diet was mildly restricted. As a result, his plasma ammonia level markedly improved (ammonia, 40-60 μg/dL) and he became symptom-free without any medication. CTLN2 is a metabolic disorder characterized by increased plasma concentrations of citrulline and ammonia, which occurs by the failure of compensatory mechanisms associated with diet. Here, we report a case of a patient for whom a change in eating habits during his hospitalization disturbed his compensatory mechanism resulting in clinical CTLN2, which was reversed with an appropriate diet.

Genetic determinants of hepatic steatosis in man

Hepatic steatosis is one of the most common liver disorders in the general population. The main cause of hepatic steatosis is nonalcoholic fatty liver disease (NAFLD), representing the hepatic component of the metabolic syndrome, which is characterized by type 2 diabetes, obesity, and dyslipidemia. Insulin resistance and excess adiposity are considered to play key roles in the pathogenesis of NAFLD. Although the risk factors for NAFLD are well established, the genetic basis of hepatic steatosis is largely unknown. Here we review recent progress on genomic variants and their association with hepatic steatosis and discuss the potential impact of these genetic studies on clinical practice. Identifying the genetic determinants of hepatic steatosis will lead to a better understanding of the pathogenesis and progression of NAFLD.

Neonatal intrahepatic cholestasis associated with citrin deficiency (NICCD): a case series of 11 Malaysian patients

Citrin deficiency, aetiologically linked to mutations of SLC25A13 gene, has two clinical phenotypes, namely adult-onset type II citrullinaemia (CTLN2) and neonatal/infantile intrahepatic cholestasis, caused by citrin deficiency (NICCD). Malaysian patients with NICCD, especially of Malay and East Malaysian indigenous descent, have never been reported in the literature. We present the clinical features, biochemical findings and results of molecular analysis in 11 Malaysian children with NICCD. In this case series, all patients manifested prolonged cholestatic jaundice and elevated citrulline levels. The other more variable features included failure to thrive, bleeding diathesis, hypoproteinaemia, abnormal liver enzymes, prolonged coagulation profile, hyperammonaemia, hypergalactosaemia, multiple aminoacidaemia, elevated α-feto protein and urinary orotic acid as well as liver biopsies showing hepatitis and steatosis. DNA analysis of SLC25A13 revealed combinations of 851del4(Ex9), IVS16ins3kb and 1638ins23. Most of our patients recovered completely by the age of 22 months. However, one patient had ongoing symptoms at the time of reporting and one had died of liver failure. Since a small percentage of children with NICCD will develop CTLN2 and the mechanisms leading to this is yet to be defined, ongoing health surveillance into adulthood is essential.

[Therapeutic approaches for patients with adult-onset type II citrullinemia (CTLN2): effectiveness of treatment with low-carbohydrate diet and sodium pyruvate]

Adult-onset type II citrullinemia (CTLN2) is an autosomal recessive disease characterized by highly elevated plasma levels of citrulline and ammonia due to the urea cycle dysfunction associated with citrin deficiency. Patients with CTLN2 show various neurological symptoms with hyperammonemia closely resembling those of hepatic encephalopathy. Since 1990, 26 CTLN2 patients (17 males and 9 females) have been admitted and treated at Shinshu University Hospital. Twelve of the 26 patients received living related partial liver transplantation (LRLT). After LRLT, neurological symptoms soon disappeared, and all patients returned to their previous social lives. Among the 14 patients that did not undergo LRLT, 6 died of intractable encephalopathy or the development of hepatic cancer, but 8 patients have had relatively good clinical courses (follow-up range 0.5-8 years) with oral intake of L-arginine and low-carbohydrate and relatively protein-rich diet. Six patients have been also given sodium pyruvate and the frequency of attacks of encephalopathy markedly decreased in 5 of 6 patients. Our observations indicated that liver transplantation is a very promising type of therapy but that other therapeutic approaches, including low-carbohydrate diet and pyruvate, are being established.

Liver transplantation for an infant with neonatal intrahepatic cholestasis caused by citrin deficiency using heterozygote living donor

NICCD is an autosomal recessive genetic disorder, characterized by cholestasis, coagulopathy, hypoglycemia, fatty liver and multiple amino acidemia. NICCD develops in the neonatal/infantile period and has been reported as a "naturally curable" disease within one yr of life. Recently, we experienced an infantile NICCD who developed progressive liver failure, and required subsequent LT using a heterozygote living donor at eight months of age. Diagnosis of NICCD was established before transplantation, and donor evaluation included mutation in the SLC25A13 gene for exclusion of individuals with citrin deficiency citrullinemia. LDLT, from blood type identical mother using a left lateral segment graft, was performed without serious complication. Plasma amino acid concentration was normalized rapidly, and the patient was discharged 30 days after transplant. During one yr follow up, the recipient has been doing well without additional medication for NICCD. NICCD should be considered in the differential diagnosis as a cause of neonatal/infantile cholestatic disease. LT using a heterozygote living donor is an effective alternative in countries where a deceased donor is not available.

Recurrent liver failure in a 25-year-old female

Acute liver failure (ALF) is defined as severe and sudden liver dysfunction leading to coagulopathy and encephalopathy in a previously healthy person without preexisting liver disease. Almost half of adult cases of ALF are due to acetaminophen toxicity, with 21% labeled indeterminate or other. We present a patient with a second episode of ALF, both episodes being initiated by catabolic stress. Elevated aminotransferases, jaundice, an elevated international normalized ratio, and confusion were typical of idiopathic ALF, and a low serum ceruloplasmin level initially led to a misdiagnosis of acute Wilson disease. Citrullinemia type I, a urea cycle defect caused by a deficiency of argininosuccinate synthetase, was diagnosed on the basis of plasma amino acids and was confirmed by molecular testing. Urea cycle defects are not generally considered causes of ALF in adults and are described rarely in children beyond the neonatal period. Our case illustrates the importance of screening patients with idiopathic ALF for a metabolic disorder. A prompt diagnosis and timely treatment enabled her to recover fully without the need for liver transplantation.

Most common SLC25A13 mutation in 400 Chinese infants with intrahepatic cholestasis

AIM: To establish the real time fluorescence polymerase chain reaction (RT-PCR) with dual labeled probes for fast detection of SLC25A13 gene mutation 851del4.

METHODS: Four hundred infants (< 1 year of age) with unexplained intrahepatic cholestasis from 18 provinces or municipalities in China were enrolled in this study for detecting their SLC25A13 gene mutation 851del4. Suitable primers and fluorescence-labeled probes for detecting SLC25A13 gene mutation 841del4 were designed. Normal and mutant sequences were detected by PCR with two fluorescence-labeled probes. After a single RT-PCR, results were obtained by analyzing the take-off curves. Twenty-four positive and 14 negative samples were retested by direct sequencing.

RESULTS: Eight homozygous and 30 heterozygous mutations were detected in 46 mutant alleles with a 851del4 mutation rate of 5.8% (46/800). Twenty-six and 20 mutant alleles were observed respectively, in 474 and 242 alleles from the intermediate and southern areas of China. No mutant allele was detected in 84 alleles from northern China. Twenty-four positive samples including 4 homozygous and 20 heterozygous mutations, and 14 negative samples were retested by direct sequencing, which confirmed that the accuracy of RT-PCR was 100%.

CONCLUSION: RT-PCR can detect the mutation 851del4 in infants with intrahepatic cholestasis with an accuracy of 100%.

Histological findings in the livers of patients with neonatal intrahepatic cholestasis caused by citrin deficiency

AIM

To characterize the histological features of the livers of patients with neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD), we studied specimens from 30 patients diagnosed with NICCD by genetically analyzing the SLC25A13 gene.

METHODS

Liver biopsy specimens were subjected to hematoxylin-eosin, Azan, and Berlin-blue staining.

RESULTS

Most specimens showed varying degrees of fibrosis. The degree of inflammation varied among the specimens, with half showing moderate or severe inflammatory changes. Fat deposition in hepatocytes was observed in almost all of the specimens, and severe fatty liver was noted in 20 (67%) of them. There was a mixture of two types of hepatocytes with macrovesicular or microvesicular fat droplets, and cholestasis was observed at a rate of 77%. Hemosiderin deposition, mostly mild and localized in periportal hepatocytes and macrophages in portal areas, was observed in 57% of the specimens.

CONCLUSION

A combination of mixed macrovesicular and microvesicular fatty hepatocytes and the above-described findings, such as fatty liver, cholestasis, necroinflammatory reaction and iron deposition, are almost never observed in other liver diseases in infants and adults. We believe that NICCD is a disease with characteristic hepatopathological features.

Interpreting metabolomic profiles using unbiased pathway models

Human disease is heterogeneous, with similar disease phenotypes resulting from distinct combinations of genetic and environmental factors. Small-molecule profiling can address disease heterogeneity by evaluating the underlying biologic state of individuals through non-invasive interrogation of plasma metabolite levels. We analyzed metabolite profiles from an oral glucose tolerance test (OGTT) in 50 individuals, 25 with normal (NGT) and 25 with impaired glucose tolerance (IGT). Our focus was to elucidate underlying biologic processes. Although we initially found little overlap between changed metabolites and preconceived definitions of metabolic pathways, the use of unbiased network approaches identified significant concerted changes. Specifically, we derived a metabolic network with edges drawn between reactant and product nodes in individual reactions and between all substrates of individual enzymes and transporters. We searched for "active modules"--regions of the metabolic network enriched for changes in metabolite levels. Active modules identified relationships among changed metabolites and highlighted the importance of specific solute carriers in metabolite profiles. Furthermore, hierarchical clustering and principal component analysis demonstrated that changed metabolites in OGTT naturally grouped according to the activities of the System A and L amino acid transporters, the osmolyte carrier SLC6A12, and the mitochondrial aspartate-glutamate transporter SLC25A13. Comparison between NGT and IGT groups supported blunted glucose- and/or insulin-stimulated activities in the IGT group. Using unbiased pathway models, we offer evidence supporting the important role of solute carriers in the physiologic response to glucose challenge and conclude that carrier activities are reflected in individual metabolite profiles of perturbation experiments. Given the involvement of transporters in human disease, metabolite profiling may contribute to improved disease classification via the interrogation of specific transporter activities.

Conventional diet therapy for hyperammonemia is risky in the treatment of hepatic encephalopathy associated with citrin deficiency

Citrin deficiency caused by SLC25A13 gene mutations develops into adult-onset type II citrullinemia (CTLN2) presenting with hepatic encephalopathy. Recent studies have suggested that excessive loading of carbohydrates is harmful in citrin-deficient individuals. Here we report a CTLN2 patient who showed further deterioration of encephalopathy after the employment of conventional low-protein diet therapy for chronic liver failure. Owing to the high carbohydrate content, the conventional low-protein diet therapy should be avoided in patients with hepatic encephalopathy associated with citrin deficiency. In addition, our observation may suggest that carbohydrate-restricted diet in which the content of carbohydrate is below 50% of daily energy intake can have therapeutic efficacy in CTLN2 patients.

Citrin deficiency and current treatment concepts

In this paper, we describe the historical aspects of citrin and citrin deficiency, characteristic food preference and food aversion of citrin-deficient subjects, and carbohydrate toxicity in relation to ureogenesis and issues of the conventional treatment procedures for hyperammonemia in citrin deficiency, leading to current treatment concepts for citrin deficiency. We also emphasize the importance of a citrin deficiency mouse model in elucidating the pathophysiology and developing novel therapeutics based on the pathophysiology, such as sodium pyruvate.

Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) as a cause of liver disease in infants in the UK

Citrin deficiency is a disorder with two phenotypes: neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD), and adult-onset type II citrullinaemia (CTLN2). NICCD presents in the first few weeks of life with prolonged cholestasis and metabolic abnormalities including aminoacidaemia (notably citrulline, tyrosine, threonine, arginine and methionine) and galactosuria. Symptoms resolve within the first year of life, thus making a diagnosis difficult after this time. Although patients subsequently remain generally healthy, some may develop more severe symptoms of CTLN2, characterized by neurological changes, one or more decades later. To date more than 400 cases have been reported, almost all from East Asia (mainly Japan). Here we describe the first two cases of NICCD in infants from the UK, one of caucasian origin and one of Pakistani origin. Both showed typical clinical and biochemical changes with a diagnosis confirmed by the presence of previously unreported mutations in the SLC25A13 gene. The presence of citrin deficiency in other ethnic groups means that NICCD needs to be considered in the diagnosis of any neonate with an unexplained cholestasis. We discuss both the difficulties in diagnosing these patients in populations where very few DNA mutations have been identified and the problems faced in the management of these patients. These findings also raise the possibility of adults with CTLN2 in whom a diagnosis has yet to be made.

Neonatal intrahepatic cholestasis caused by citrin deficiency: clinical and laboratory investigation of 13 subjects in mainland of China

BACKGROUND

Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) is a novel inborn error of metabolism due to dysfunction of citrin protein, and much more information about this new disease is still needed for its clinical management.

AIMS

To investigate in detail the clinical and laboratory features of NICCD.

PATIENTS

13 NICCD subjects in mainland of China diagnosed in our department since 2006.

METHODS

The anthropometric parameters of the patients at birth were compared with controls, representative biochemical changes and metabolome findings were investigated cross-sectionally, and mutations in the causative gene SLC25A13 were analyzed by protocols established previously.

RESULTS

The patients showed reduced birth weight, length and ponderal index. Main clinical manifestations consisted of jaundice, hepato/hepatosplenomegaly and steatohepatosis on ultrasonography. Biochemical analysis revealed intrahepatic cholestasis, delayed switch of AFP to albumin, and elevated triglyceride, total cholesterol and LDL-cholesterol together with reduced HDL-cholesterol. Metabolome findings included co-existence of markers for galactosemia and tyrosinemia in urine, and elevated Cit, Met, Thr, Tyr, Lys, Arg and Orn in blood. Mutations of 851-854del, IVS6+5G>A, 1638-1660dup, A541D, IVS16ins3kb, R319X and G333D were detected in the gene SLC25A13.

CONCLUSIONS

The diagnosis of NICCD cannot be established based just on the numerous but non-specific clinical manifestations and biochemical changes. The relatively specific metabolome features provide valuable tools for its screening and diagnosis, while SLC25A13 mutation analysis should be taken as one of the reliable tools for the definitive diagnosis. The body proportionality at birth, steatohepatosis on ultrasonography, delayed switch of AFP to albumin, dyslipidemia pattern, urinary metabolome features and the novel mutation G333D expanded the clinical spectrum of NICCD.

Sustaining hypercitrullinemia, hypercholesterolemia and augmented oxidative stress in Japanese children with aspartate/glutamate carrier isoform 2-citrin-deficiency even during the silent period

Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) shows diverse metabolic abnormalities such as urea cycle dysfunction together with citrullinemia, galactosemia, and suppressed gluconeogenesis. Such abnormalities apparently resolve during the first year of life. However, metabolic profiles of the silent period remain unknown. We analyzed oxidative stress markers and profiles of amino acids, carbohydrates, and lipids in 20 asymptomatic children with aspartate/glutamate carrier isoform 2-citrin-deficiency aged 1-10 years, for whom tests showed normal liver function. Despite normal plasma ammonia levels, the affected children showed higher blood levels of ornithine (p<0.001) and citrulline (p<0.01)--amino acids involved in the urea cycle--than healthy children. Blood levels of nitrite/nitrate, metabolites of nitric oxide (NO), and asymmetric dimethylarginine inhibiting NO production from arginine were not different between these two groups. Blood glucose, galactose, pyruvate, and lactate levels after 4-5h fasting were not different between these groups, but the affected group showed a significantly higher lactate to pyruvate ratio. Low-density and high-density lipoprotein cholesterol levels in the affected group were 1.5 times higher than those in the controls. Plasma oxidized low-density lipoprotein apparently increased in the affected children; their levels of urinary oxidative stress markers such as 8-hydroxy-2'-deoxyguanosine and acrolein-lysine were significantly higher than those in the controls. Results of this study showed, even during the silent period, sustained hypercitrullinemia, hypercholesterolemia, and augmented oxidative stress in children with citrin deficiency.

Citrin deficiency, a perplexing global disorder

Citrin deficiency, caused by mutations in SLC25A13, can present with neonatal intrahepatic cholestasis or with adult onset neuropsychiatric, hepatic and pancreatic disease. Until recently, it had been thought to be found mostly in individuals of East Asian ancestry. A key diagnostic feature has been the deficient argininosuccinate synthetase (ASS) activity (E.C. 6.3.4.5) in liver, with normal activity in skin fibroblasts. In this series we describe the clinical presentation of 10 patients referred to our laboratories for sequence analysis of the SCL25A13 gene, including several patients who presented with elevated citrulline on newborn screening. In addition to sequence analysis performed on all patients, ASS enzyme activity, citrulline incorporation and Western blot analysis for ASS and citrin were performed on skin fibroblasts if available. We have found 5 unreported mutations including two apparent founder mutations in three unrelated French-Canadian patients. In marked contrast to previous cases, these patients have a markedly reduced ASS activity in skin fibroblasts. The presence of citrin protein on Western blot in three of our cases reduces the sensitivity of a screening test based on protein immunoblotting. The finding of citrin mutations in patients of Arabic, Pakistani, French Canadian and Northern European origins supports the concept that citrin deficiency is a panethnic disease.

Treatment of a citrin-deficient patient at the early stage of adult-onset type II citrullinaemia with arginine and sodium pyruvate

Citrin deficiency is a common congenital metabolic defect not only in East Asian populations but also in other populations around the world. It has been shown that although liver transplantation is ultimately required in many patients to prevent neurological decompensation associated with hyperammonaemia, arginine is effective in lowering ammonia in hyperammonaemic patients, and a high-protein low-carbohydrate diet may provide some benefit to infants in improving failure to thrive. In the present study, the clinical symptoms and laboratory findings are reported for a 13-year-old citrin-deficient girl in the early stage of adult-onset type II citrullinaemia (CTLN2), and the therapeutic effect of orally administered arginine and sodium pyruvate was investigated. The patient complained of anorexia, lethargy, fatigue and poor growth, and showed laboratory findings typical of CTLN2; elevated levels of plasma citrulline, threonine-to-serine ratio, and serum pancreatic secretory trypsin inhibitor. Oral administration of arginine and sodium pyruvate for over 3 years improved her clinical symptoms and has almost completely normalized her laboratory findings. It is suggested that the administration of arginine and sodium pyruvate with low-carbohydrate meals may be an effective therapy in patients with citrin deficiency in order either to prolong metabolic normalcy or to provide a safer and more affordable alternative to liver transplantation.

Citrin deficiency as a cause of chronic liver disorder mimicking non-alcoholic fatty liver disease

BACKGROUND/AIMS

Citrin deficiency caused by SLC25A13 gene mutations develops into adult-onset type II citrullinemia (CTLN2) and may be accompanied with hepatic steatosis and steatohepatitis. As its clinical features remain unclear, we aimed to explore the characteristics of fatty liver disease associated with citrin deficiency.

METHODS

The prevalence of hepatic steatosis in 19 CTLN2 patients was examined, and clinical features were compared with those of non-alcoholic fatty liver disease (NAFLD) patients without known SLC25A13 gene mutations.

RESULTS

Seventeen (89%) CTLN2 patients had steatosis, and 4 (21%) had been diagnosed as having NAFLD before appearance of neuropsychological symptoms. One patient had steatohepatitis. Citrin deficiency-associated fatty livers showed a considerably lower prevalence of accompanying obesity and metabolic syndrome, higher prevalence of history of pancreatitis, and higher serum levels of pancreatic secretory trypsin inhibitor (PSTI) than fatty livers without the mutations. Receiver operating characteristic curve analyses revealed that a body mass index < 20kg/m(2) and serum PSTI>29ng/mL were associated with citrin deficiency.

CONCLUSIONS

Patients presenting with non-alcoholic fatty liver unrelated to obesity and metabolic syndrome might have citrin deficiency, and serum PSTI may be a useful indicator for distinguishing this from conventional NAFLD.

Primary liver carcinoma exhibiting dual hepatocellular-biliary epithelial differentiations associated with citrin deficiency: a case report

We report a 50-year-old male patient with primary liver carcinoma exhibiting dual hepatocellular and biliary epithelial differentiations associated with citrin deficiency (asymptomatic adult-onset type II citrullinemia, CTLN2). Although so far 14 CTLN2 patients with hepatocellular carcinoma have been reported, this report describes a unique case of liver carcinoma showing the features of both hepatocellular and cholangiocellular carcinoma. In addition to the clinical data of the 14 patients reported previously, the findings in our patient suggest that the citrin deficiency might be one of the key disorders causing hepatocellular carcinoma especially at younger ages and can also play an important role in hepatocarcinogenesis of the hepatic progenitor cells, which have the bipotential to differentiate into both hepatocytes and cholangiocytes.

Chubby face and the biochemical parameters for the early diagnosis of neonatal intrahepatic cholestasis caused by citrin deficiency

OBJECTIVES

To identify facial and biochemical characteristics as early clinical features of neonatal intrahepatic cholestasis due to citrin deficiency (NICCD).

PATIENTS AND METHODS

Ten patients with diagnoses of NICCD by SLC25A13 mutation analysis in Taiwan were recruited. A "Chubby Index" was developed for objective measurement of their facial characteristics. Liver function profiles were analyzed and compared with data on neonatal hepatitis and biliary atresia.

RESULTS

Chubby face was observed in early infancy in all 5 patients whose serial photographs were taken. A significant difference in the Chubby Index was seen between NICCD infants and healthy infants (1.331 +/- 0.07 vs 1.068 +/- 0.059; P < 0.05). NICCD is characterized by an aspartate aminotransferase-to-alanine aminotransferase ratio of 2 or greater, a direct bilirubin-to-total bilirubin ratio under 0.67, and a standard deviation score for alpha-fetoprotein of 4 or greater, with respect to neonatal hepatitis and biliary atresia. Although chubby face, abnormal liver function profiles, and multiple amino acidemia gradually disappeared after age 1 year, an increase in hepatic echogenicity was observed in most patients in long-term follow-up.

CONCLUSIONS

Our Chubby Index is an informative measurement of the facial characteristics of infants with NICCD. The chubby face features, along with an aspartate aminotransferase-to-alanine aminotransferase ratio of 2 or greater, a direct bilirubin-to-total bilirubin ratio under 0.67, and a standard deviation score for alpha-fetoprotein of 4 or greater, may serve as useful clinical indicators for diagnosing NICCD early in infancy.

Reduced carbohydrate intake in citrin-deficient subjects

Citrin is the liver-type aspartate-glutamate carrier that resides within the inner mitochondrial membrane. Citrin deficiency (due to homozygous or compound heterozygous mutations in the gene SLC25A13) causes both adult-onset type II citrullinaemia (CTLN2) and neonatal intrahepatic cholestasis (NICCD). Clinically, CTLN2 is characterized by hyperammonaemia and citrullinaemia, whereas NICCD has a much more varied and transient presentation that can include multiple aminoacidaemias, hypoproteinaemia, galactosaemia, hypoglycaemia, and jaundice. Personal histories from CTLN2 patients have repeatedly described an aversion to carbohydrate-rich foods, and clinical observations of dietary and therapeutic outcomes have suggested that their unusual food preferences may be directly related to their pathophysiology. In the present study, we monitored the food intake of 18 Japanese citrin-deficient subjects whose ages ranged from 1 to 33 years, comparing them against published values for the general Japanese population. Our survey confirmed a marked decrease in carbohydrate intake, which accounts for a smaller proportion of carbohydrates contributing to the total energy intake (PFC ratio) as well as a shift towards a lower centile distribution for carbohydrate intake relative to age- and sex-matched controls. These results strongly support an avoidance of carbohydrate-rich foods by citrin-deficient patients that may lead to worsening of symptoms.

Tissue specificity of mitochondrial glutamate pathways and the control of metabolic homeostasis

Glutamate is implicated in numerous metabolic and signalling functions that vary according to specific tissues. Glutamate metabolism is tightly controlled by activities of mitochondrial enzymes and transmembrane carriers, in particular glutamate dehydrogenase and mitochondrial glutamate carriers that have been identified in recent years. It is remarkable that, although glutamate-specific enzymes and transporters share similar properties in most tissues, their regulation varies greatly according to particular organs in order to achieve tissue specific functions. This is illustrated in this review when comparing glutamate handling in liver, brain, and pancreatic beta-cells. We describe the main cellular glutamate pathways and their specific functions in different tissues, ultimately contributing to the control of metabolic homeostasis at the organism level.

Identification of 13 novel mutations including a retrotransposal insertion in SLC25A13 gene and frequency of 30 mutations found in patients with citrin deficiency

Deficiency of citrin, liver-type mitochondrial aspartate-glutamate carrier, is an autosomal recessive disorder caused by mutations of the SLC25A13 gene on chromosome 7q21.3 and has two phenotypes: neonatal intrahepatic cholestatic hepatitis (NICCD) and adult-onset type II citrullinemia (CTLN2). So far, we have described 19 SLC25A13 mutations. Here, we report 13 novel SLC25A13 mutations (one insertion, two deletion, three splice site, two nonsense, and five missense) in patients with citrin deficiency from Japan, Israel, UK, and Czech Republic. Only R360X was detected in both Japanese and Caucasian. IVS16ins3kb identified in a Japanese CTLN2 family seems to be a retrotransposal insertion, as the inserted sequence (2,667-nt) showed an antisense strand of processed complementary DNA (cDNA) from a gene on chromosome 6 (C6orf68), and the repetitive sequence (17-nt) derived from SLC25A13 was found at both ends of the insert. All together, 30 different mutations found in 334 Japanese, 47 Chinese, 11 Korean, four Vietnamese and seven non-East Asian families have been summarized. In Japan, IVS16ins3kb was relatively frequent in 22 families, in addition to known mutations IVS11 + 1G > A, 851del4, IVS13 + 1G > A, and S225X in 189, 173, 48 and 30 families, respectively; 851del4 and IVS16ins3kb were found in all East Asian patients tested, suggesting that these mutations may have occurred very early in some area of East Asia.

[Urea cycle disorders in adult patients]

INTRODUCTION

Urea cycle disorders (UCD) usually present after 24 h to 48 h of life with failure to thrive, lethargy and coma leading to death, but milder forms may occur from infancy to adulthood.

STATE OF THE ART

Survival of children with UCD has significantly improved and the need for transitional care to adulthood has emerged. Adult onset UCD present with chronic or acute neurological, psychiatric and digestive symptoms associated with protein avoidance. Ornithine transcarbamylase (OTC) deficiency, which is inherited as an X-linked disorder, is the most well-described UCD in adults. Acute decompensations associate the triad of encephalopathy, respiratory alkalosis and hyperammonemia. Acute encephalopathy is characterized by brain edema, which is life-threatening without treatment. Specific urea cycle enzyme deficiency can be suspected in the presence of abnormal plasma amino acids concentrations and urinary excretion of orotic acid. A measurement enzyme activity in appropriate tissue, or DNA analysis if available, is required for diagnosis. Treatment requires restriction of dietary protein intake and the use of alternative pathways of waste nitrogen excretion with sodium benzoate and sodium phenylbutyrate. Patients with acute forms may need hemodialysis or hemodiafiltration. Therapeutic goals for OTC deficiency are to maintain plasma ammonia<80 micromol/L, plasma glutamine<1,000 micromol/L, argininemia 80-150 micromol/L and branched chain amino acids within the normal range, in order to prevent episodes of potentially lethal acute hyperammonemia.

CONCLUSION

Potentially fatal acute hyperammonemia may occur in male or female patients at any age. Ammonia should be measured promptly in case of acute neurological and psychiatric symptoms or coma.

Neonatal intrahepatic cholestasis caused by citrin deficiency in Korean infants

Citrin is a liver-type mitochondrial aspartate-glutamate carrier encoded by the SLC25A13 gene, and its deficiency causes adult-onset type II citrullinemia and neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD). Here, the authors investigated clinical findings in Korean infants with NICCD and performed mutation analysis on the SLC25A13 gene. Of 47 patients with neonatal cholestasis, three infants had multiple aminoacidemia (involving citrulline, methionine, and arginine) and galactosemia, and thus were diagnosed as having NICCD. Two of these three showed failure to thrive. The laboratory findings showed hypoproteinemia and hyperammonemia, and liver biopsies revealed micro-macrovesicular fatty liver and cholestasis. The three patients each harbored compound heterozygous 1,638-1,660 dup/ S225X mutation, compound heterozygous 851del4/S225X mutation, and heterozygous 1,638-1,660 dup mutation, respectively. With nutritional manipulation, liver functions were normalized and catch-up growth was achieved. NICCD should be considered in the differential diagnosis of cholestatic jaundice in Korean infants.

Citrin/Mitochondrial Glycerol-3-phosphate Dehydrogenase Double Knock-out Mice Recapitulate Features of Human Citrin Deficiency

Citrin is the liver-type mitochondrial aspartate-glutamate carrier that participates in urea, protein, and nucleotide biosynthetic pathways by supplying aspartate from mitochondria to the cytosol. Citrin also plays a role in transporting cytosolic NADH reducing equivalents into mitochondria as a component of the malate-aspartate shuttle. In humans, loss-of-function mutations in the SLC25A13 gene encoding citrin cause both adult-onset type II citrullinemia and neonatal intrahepatic cholestasis, collectively referred to as human citrin deficiency. Citrin knock-out mice fail to display features of human citrin deficiency. Based on the hypothesis that an enhanced glycerol phosphate shuttle activity may be compensating for the loss of citrin function in the mouse, we have generated mice with a combined disruption of the genes for citrin and mitochondrial glycerol 3-phosphate dehydrogenase. The resulting double knock-out mice demonstrated citrullinemia, hyperammonemia that was further elevated by oral sucrose administration, hypoglycemia, and a fatty liver, all features of human citrin deficiency. An increased hepatic lactate/pyruvate ratio in the double knock-out mice compared with controls was also further elevated by the oral sucrose administration, suggesting that an altered cytosolic NADH/NAD(+) ratio is closely associated with the hyperammonemia observed. Microarray analyses identified over 100 genes that were differentially expressed in the double knock-out mice compared with wild-type controls, revealing genes potentially involved in compensatory or downstream effects of the combined mutations. Together, our data indicate that the more severe phenotype present in the citrin/mitochondrial glycerol-3-phosphate dehydrogenase double knock-out mice represents a more accurate model of human citrin deficiency than citrin knock-out mice.

Simple and quantitative analysis of urinary sulfated tauro- and glycodihydroxycholic acids in infant with cholestasis by electrospray ionization mass spectrometry

Here we report a simple, sensitive, and accurate method for detecting urinary sulfated tauro- and glyco-bile acids that uses electrospray ionization mass spectrometry. The sulfated tauro- and glycodihydroxycholic acids mainly generated [M-2H](2-) negative ions at m/z 288.6 and m/z 263.6, respectively. These doubly charged ions appeared primarily in samples prepared from the urine of patients with cholestasis and were detected quantitatively. Cholestatic jaundice is the primary clinical sign of biliary atresia. The measurement of doubly charged negative ions, especially of sulfated taurodihydroxycholic acid (principally taurochenodeoxycholate-3-sulfate), is a useful screening modality for biliary atresia in neonates.

Clinical pictures of 75 patients with neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD)

We clarified the clinical features of NICCD (neonatal intrahepatic cholestasis caused by citrin deficiency) by retrospective review of symptoms, management and long-term outcome of 75 patients. The data were generated from questionnaires to paediatricians in charge of the patients. Thirty of the patients were referred to hospitals before 1 month of age because of positive results in newborn screening (hypergalactosaemia, hypermethioninaemia, and hyperphenylalaninaemia). The other 45, the screen-negative patients, were referred to hospitals with suspected neonatal hepatitis or biliary atresia because of jaundice or discoloured stool. Most of the screen-negative patients presented before 4 months of age, and 11 had failure to thrive. Laboratory data showed elevated serum bile acid concentrations, hypoproteinaemia, low levels of vitamin K-dependent coagulation factors and hypergalactosaemia. Hypoglycaemia was detected in 18 patients. Serum amino acid analyses showed significant elevation of citrulline and methionine concentrations. Most of the patients were given a lactose-free and/or medium-chain triglyceride-enriched formula and fat-soluble vitamins. Symptoms resolved in all but two of the patients by 12 months of age. The two patients with unresolved symptoms suffered from progressive liver failure and underwent liver transplantation before their first birthday. Another patient developed citrullinaemia type II (CTLN2) at age 16 years. It is important to recognize that NICCD is not always a benign condition.

Citrin deficiency: a novel cause of failure to thrive that responds to a high-protein, low-carbohydrate diet

The proband was born at 36 weeks, appropriate for gestational age, to nonconsanguineous white parents. There was no evidence of hyperbilirubinemia or intrahepatic cholestasis in the neonatal period, and she had normal newborn screen results. She presented with 3 episodes of life-threatening bleeding and anemia. The diagnostic evaluation for her bleeding diathesis revealed an abnormal clotting profile with no biochemical evidence for hepatocellular damage. She was incidentally noted to have severe growth deceleration that failed to respond to 502 kJ/kg (120 kcal/kg) per day of protein-hydrolyzed formula. An extensive diagnostic workup for failure to thrive, which was otherwise normal, included plasma amino acid analysis that revealed hyperglutaminemia and citrulline levels within the reference range. Testing of a repeat sample revealed isolated hypercitrullinemia. No argininosuccinic acid was detected. Her ammonia level and urine orotic acid were within the reference ranges. Subsequent plasma amino acid analysis exhibited a profile suggestive of neonatal intrahepatic cholestasis caused by citrin deficiency with elevations in citrulline, methionine, and threonine. Western blotting of fibroblasts demonstrated citrin deficiency, and a deletion for exon 3 was found in the patient's coding DNA of the SLC25A13 gene. On the basis of the experience with adults carrying this condition, the patient was given a high-protein, low-carbohydrate diet. The failure to thrive and bleeding diathesis resolved. When compliance with the dietary prescription was relaxed, growth deceleration was again noted, although significant bleeding did not recur. This is the first report of an infant of Northern European descent with citrin deficiency. The later age at presentation with failure to thrive and bleeding diathesis and without obvious evidence of neonatal intrahepatic cholestasis expands the clinical spectrum of citrin deficiency. This case emphasizes the importance of continued dietary control and growth monitoring in children with neonatal intrahepatic cholestasis caused by citrin deficiency and identifies a new metabolic entity responsible for failure to thrive.

Clinical pictures of 75 patients with neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD)

We clarified the clinical features of NICCD (neonatal intrahepatic cholestasis caused by citrin deficiency) by retrospective review of symptoms, management and long-term outcome of 75 patients. The data were generated from questionnaires to paediatricians in charge of the patients. Thirty of the patients were referred to hospitals before 1 month of age because of positive results in newborn screening (hypergalactosaemia, hypermethioninaemia, and hyperphenylalaninaemia). The other 45, the screen-negative patients, were referred to hospitals with suspected neonatal hepatitis or biliary atresia because of jaundice or discoloured stool. Most of the screen-negative patients presented before 4 months of age, and 11 had failure to thrive. Laboratory data showed elevated serum bile acid concentrations, hypoproteinaemia, low levels of vitamin K-dependent coagulation factors and hypergalactosaemia. Hypoglycaemia was detected in 18 patients. Serum amino acid analyses showed significant elevation of citrulline and methionine concentrations. Most of the patients were given a lactose-free and/or medium-chain triglyceride-enriched formula and fat-soluble vitamins. Symptoms resolved in all but two of the patients by 12 months of age. The two patients with unresolved symptoms suffered from progressive liver failure and underwent liver transplantation before their first birthday. Another patient developed citrullinaemia type II (CTLN2) at age 16 years. It is important to recognize that NICCD is not always a benign condition.

Mitochondrial Transporters as Novel Targets for Intracellular Calcium Signaling

Ca2+signaling in mitochondria is important to tune mitochondrial function to a variety of extracellular stimuli. The main mechanism is Ca2+entry in mitochondria via the Ca2+uniporter followed by Ca2+activation of three dehydrogenases in the mitochondrial matrix. This results in increases in mitochondrial NADH/NAD ratios and ATP levels and increased substrate uptake by mitochondria. We review evidence gathered more than 20 years ago and recent work indicating that substrate uptake, mitochondrial NADH/NAD ratios, and ATP levels may be also activated in response to cytosolic Ca2+signals via a mechanism that does not require the entry of Ca2+in mitochondria, a mechanism depending on the activity of Ca2+-dependent mitochondrial carriers (CaMC). CaMCs fall into two groups, the aspartate-glutamate carriers (AGC) and the ATP-Mg/Picarriers, also named SCaMC (for short CaMC). The two mammalian AGCs, aralar and citrin, are members of the malate-aspartate NADH shuttle, and citrin, the liver AGC, is also a member of the urea cycle. Both types of CaMCs are activated by Ca2+in the intermembrane space and function together with the Ca2+uniporter in decoding the Ca2+signal into a mitochondrial response.

Novel diagnostic approach to citrin deficiency: analysis of citrin protein in lymphocytes

Citrin deficiency induces two clinical features; namely neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) and adult-onset type II citrullinemia. Hypercitrullinemia is the most characteristic feature, whereas there are non-citrullinemic individuals. Diagnosis of citrin deficiency is performed by genetic analysis, although the 12 known mutations in the alleles are not detected in about 15% of cases. Thus, we aimed to examine citrin protein in lymphocytes isolated from peripheral blood as an alternative diagnostic method. We examined 38 children having an episode of cholestatic liver dysfunction, 8 heterozygotes, and 11 healthy individuals. All subjects were evaluated for citrin protein by Western blotting and for the 12 known mutations by gene analysis. Citrin protein was detected in 15 of 38 children with cholestatic liver dysfunction. Fourteen of them were negative for 12 known mutations in both alleles, whereas one patient was found to have a known mutation in one allele. Citrin protein was absent in 23 of the 38 patients. Among these 23, gene analysis diagnosed citrin deficiency in 19, whereas 2 patients were later revealed to be NICCD with novel mutations. In the remaining 2 patients, who exhibit the clinical features of NICCD, a known mutation was detected in one allele but no mutation was identified in another allele. Citrin protein was also detected in the 8 heterozygotes and 11 healthy individuals. We disclosed that citrin was deficient in lymphocytes among patients with citrin deficiency. Analysis of citrin is useful to diagnose citrin deficiency even in patients without known mutations or hypercitrullinemia.

Time course of acylcarnitine elevation in neonatal intrahepatic cholestasis caused by citrin deficiency

Citrin is a mitochondrial membrane aspartate-glutamate carrier, and citrin deficiency causes both hyperammonaemia in adults (adult-onset type II citrullinaemia, CTLN2) and neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD), with metabolic derangements in gluconeogenesis, aerobic glycolysis, urea synthesis, UDP-galactose epimerase activity, and possibly fatty acid synthesis and utilization. Through neonatal screening and case review, four patients with NICCD who had an acylcarnitine profile during infancy were all found to have an elevation of free carnitine, C2-carnitine, and long-chain acylcarnitines. These metabolic abnormalities appeared after the rise of citrulline and bilirubin, but before the elevation of alanine aminotransferase and aspartate aminotransferase. Although the rise of free carnitine and acylcarnitines seems to be a benign condition, the sequential changes of these metabolic derangements may give clues to the pathogenesis of this interesting disorder.

The human mitochondrial transport/carrier protein family. Nonsynonymous single nucleotide polymorphisms (nsSNPs) and mutations that lead to human diseases

There are 67 proteins in the human mitochondrial transport protein family. They have been identified from among the proteins of the RefSeq database on the basis of sequence similarity to proteins that have been functionally identified as mitochondrial transport proteins. They have also been identified by matching their predicted structure to the high resolution structure of the bovine ADP/ATP T1 transporter subunit/carboxyatractyloside complex. 74 nonsynonymous single nucleotide polymorphisms (nsSNP) have been identified in their gene sequences. These nsSNPs are present in genes of 30 of the proteins. No nsSNP has been found in 24 of the protein genes and no search has as yet been carried out on the rest (13) of them. The largest number of nsSNPs are in the ADP/ATP T3 transporter, the uncoupling protein 3 L, and the phosphate transporter genes with 7, 6, and 6, respectively. nsSNPs are located in groups along the protein sequence suggesting that certain protein domains are too critical for transport function to tolerate mutations. This interpretation has been validated with mutation and function studies of the phosphate transporter. Human diseases have been identified with replacement mutations in seven of these proteins. Their genes are not abnormally susceptible to mutations since they have the smallest number of nsSNPs. Disease causing mutations have also been observed as: substitution, silent (may affect stability of messages), frameshift (protein truncation or elongation), splicing (exon skipping), residue deletion. Disease causing mutations have only been identified in few transporter genes because others do not yield dramatic symptoms or are essential and thus lethal. Mutations in other transporter genes may also only have a major impact through their combination with other genes and their nsSNPs.

Proteomic analysis of iron overload in human hepatoma cells

Iron-mediated organ damage is common in patients with iron overload diseases, namely, hereditary hemochromatosis. Massive iron deposition in parenchymal organs, particularly in the liver, causes organ dysfunction, fibrosis, cirrhosis, and also hepatocellular carcinoma. To obtain deeper insight into the poorly understood and complex cellular response to iron overload and consequent oxidative stress, we studied iron overload in liver-derived HepG2 cells. Human hepatoma HepG2 cells were exposed to a high concentration of iron for 3 days, and protein expression changes initiated by the iron overload were studied by two-dimensional electrophoresis and mass spectrometry. From a total of 1,060 spots observed, 21 spots were differentially expressed by iron overload. We identified 19 of them; 11 identified proteins were upregulated, whereas 8 identified proteins showed a decline in response to iron overload. The differentially expressed proteins are involved in iron storage, stress response and protection against oxidative stress, protein folding, energy metabolism, gene expression, cell cycle regulation, and other processes. Many of these molecules have not been previously suggested to be involved in the response to iron overload and the consequent oxidative stress.

Hepatic steatosis and neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) in Taiwanese infants

OBJECTIVES

To explore the prevalence of hepatic steatosis and neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) in Taiwanese infants with idiopathic intrahepatic cholestasis.

STUDY DESIGN

The liver specimens from 69 infants with idiopathic intrahepatic cholestasis were reviewed (1993-2004); 11 of them (14.7%) had hepatic steatosis. Six patients with hepatic steatosis participated in the genetic study for the SLC25A13 gene under parental consent.

RESULTS

Infants with cholestasis and hepatic steatosis had lower aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels than those with cholestasis alone. Three of the six infants in the genetic study had homozygous 851del4 mutation; for the others, homozygous 1638ins23 mutation, compound heterozygous 851del4/IVS6+5G-->A mutation, and heterozygous IVS6+5G-->A mutation were found for each one. Eleven of the total 12 alleles (91.7%) were demonstrated to have SLC25A13 gene mutations.

CONCLUSIONS

Metabolic and genetic studies for NICCD should be performed in Asian infants with idiopathic intrahepatic cholestasis and hepatic steatosis. The 851del4 mutation on the SLC25A13 gene accounts for the major genotype expression of patients with NICCD in Taiwan.

Pyruvate ameliorates the defect in ureogenesis from ammonia in citrin-deficient mice

BACKGROUND/AIMS

Mutations in SLC25A13, encoding the mitochondrial aspartate-glutamate carrier citrin, cause adult-onset type II citrullinemia (CTLN2) in humans. We have previously reported that although citrin-knockout (Ctrn-/-) mice fail to display symptoms of CTLN2, liver perfusion revealed a deficit in ureogenesis from ammonia accompanied by an increase in the perfusate lactate-to-pyruvate (L/P) ratio. The present study explores the effects of pyruvate, aspartate and citrate on improving the abnormalities observed in the Ctrn-/- liver.

METHODS

We measured the rate of ureogenesis from ammonium chloride using the liver-perfusion system.

RESULTS

Pyruvate infusion lowered the L/P ratio and corrected the deficit in ureogenesis in the Ctrn-/- liver. This effect was found to be dose-dependent in both instances. Phenazine methosulfate, a cytosolic oxidant, also improved the rate of ureogenesis in the Ctrn-/- liver and led to a fall in the L/P ratio. The addition of aspartate or citrate did not change either the rate of ureogenesis or the L/P ratio in the Ctrn-/- liver.

CONCLUSIONS

Citrin deficiency disturbs urea synthesis primarily as a result of an elevated cytosolic NADH/NAD+ ratio owing to limited reoxidation of reducing equivalents. Clinically, pyruvate may have a therapeutic benefit for CTLN2 patients.

Unmasked adult-onset urea cycle disorders in the critical care setting

Most often, urea cycle disorders have been described as acute onset hyperammonemia in the newborn period; however, there is a growing awareness that urea cycle disorders can present at almost any age, frequently in the critical care setting. This article presents three cases of adult-onset hyperammonemia caused by inherited defects in nitrogen processing in the urea cycle, and reviews the diagnosis, management, and pathophysiology of adult-onset urea cycle disorders. Individuals who have milder molecular urea cycle defects can lead a relatively normal life until a severe environmental stress triggers a hyperammonemic crisis. Comorbid conditions such as physical trauma often delay the diagnosis of the urea cycle defect. Prompt recognition and treatment are essential in determining the outcome of these patients.

Homozygous SLC25A13 Mutation in a Taiwanese Patient with Adult-onset Citrullinemia Complicated with Steatosis and Hepatocellular Carcinoma

Citrullinemia is a metabolic disorder characterized by elevated plasma concentrations of citrulline and ammonia. Adult-onset citrullinemia (type II, CTLN2) has been attributed to citrin deficiency caused by mutations in the SLC25A13 gene. CTLN2 is associated with a high incidence of hepatocellular carcinoma (HCC) in Japanese. We report a 48-year-old Taiwanese man with citrullinemia, who was in good health until the age of 34 when he had repeated episodes of consciousness disturbance. Hyperammonia (201 micromol/L) was found during an episode of coma. Liver function and electrolyte levels were normal at that time. Serologic markers of viral hepatitis B and C were negative. Analysis of genomic DNA extracted from peripheral blood leukocytes showed homozygous 851del4 mutation in exon 9 of the SLC25A13 gene on chromosome 7q21.3. Fourteen years after disease onset, at the age of 48, he was admitted due to an episode of coma. Abdominal sonography and computed tomography showed a 2.5 cm tumor in the left lobe of the liver, without evidence of liver cirrhosis. Wedge resection of the tumor was performed and grade 2 HCC was diagnosed. The nontumor part of the resected specimen showed chronic persistent hepatitis with moderate steatosis. The results in this case support that both citrin deficiency and steatohepatitis may contribute to hepatocarcinogenesis.

Cirrhosis in an infant heterozygous for classical citrullinaemia

Classical citrullinaemia is caused by the inherited deficiency of argininosuccinate synthetase. Although varying degrees of liver involvement have been observed in urea cycle defects, including classical citrullinaemia, the co-existence of liver failure in a patient heterozygous for the disease has not been reported before. A female infant was investigated to find out the aetiology of early infantile liver failure. She was later found to be a heterozygote for the G390R mutation found in severe citrullinaemia patients.

CONCLUSION

Classical citrullinaemia is a phenotypically heterogeneous disease, and observations for signs of its presence should be made even in heterozygotes.

Variant clinical courses of 2 patients with neonatal intrahepatic cholestasis who have a novel mutation of SLC25A13

Deficiency of citrin due to mutations of the SLC25A13 gene causes not only adult-onset type II citrullinemia, but also neonatal intrahepatic cholestasis. Neonatal intrahepatic cholestasis is a self-limiting condition and spontaneously disappears by 12 months of age without special treatment. The natural history of patients with SLC25A13 mutations is not clear. Two patients with infantile hepatic dysfunction were found to have a novel mutation of the SLC25A13 gene. DNA analyses of SLC25A13 disclosed that the first patient was a compound heterozygote for the Ex16+74_IVS17-32del516 (del516-Ex16/IVS17) and IVS11+1G-->A mutations and the second one a homozygote for the del516-Ex16/IVS17 mutation. It is predicted that the 516-base pair deletion mutation leads to a frameshift from codons 556 to 564, a premature termination at codon 565, and a truncated form of the citrin protein (normal, 675 amino acids). The first patient had disseminated intravascular coagulation associated with hepatic dysfunction in the neonatal period. The other patient had persistent cholestatic jaundice and underwent an operation to rule out bile duct atresia. Without specific treatment, both patients had a favorable clinical course. In conclusion, citrin deficiency resulting from the mutation of SLC25A13 presented variant clinical courses, followed by hypercitrullinemia and intrahepatic cholestasis in infancy. The conditions in the patients were self-limiting and spontaneously disappeared.

Living Donor Liver Transplantation for Noncirrhotic Inheritable Metabolic Liver Diseases: Impact of the Use of Heterozygous Donors

BACKGROUND

In living donor liver transplantation (LDLT), the liver donor is almost always a blood relative; therefore, the donor is sometimes a heterozygous carrier of inheritable diseases. The use of such carriers as donors has not been validated. The aim of the present study was to evaluate the outcome of LDLT for noncirrhotic inheritable metabolic liver disease (NCIMLD) to clarify the effects of using a heterozygous carrier as a donor.

METHODS

Between June 1990 and December 2003, 21 patients with NCIMLD underwent LDLT at our institution. The indications for LDLT included type II citrullinemia (n = 7), ornithine transcarbamylase deficiency (n = 6), propionic acidemia (n = 3), Crigler-Najjar syndrome type I (n = 2), methylmalonic acidemia (n = 2), and familial amyloid polyneuropathy (n = 1). Of these 21 recipients, six underwent auxiliary partial orthotopic liver transplantation.

RESULTS

The cumulative survival rate of the recipients was 85.7% at both 1 and 5 years after operation. All surviving recipients are currently doing well without sequelae of the original diseases, including neurological impairments or physical growth retardation. Twelve of the 21 donors were considered to be heterozygous carriers based on the modes of inheritance of the recipients' diseases and preoperative donor medical examinations. All donors were uneventfully discharged from the hospital and have been doing well since discharge. No mortality or morbidity related to the use of heterozygous donors was observed in donors or recipients.

CONCLUSIONS

Our results suggest that the use of heterozygous donors in LDLT for NCIMLD has no negative impact on either donors or recipients, although some issues remain unsolved and should be evaluated in further studies.

Reduced N-Acetylaspartate Levels in Mice Lacking Aralar, a Brain- and Muscle-type Mitochondrial Aspartate-glutamate Carrier

Aralar is a mitochondrial calcium-regulated aspartate-glutamate carrier mainly distributed in brain and skeletal muscle, involved in the transport of aspartate from mitochondria to cytosol, and in the transfer of cytosolic reducing equivalents into mitochondria as a member of the malate-aspartate NADH shuttle. In the present study, we describe the characteristics of aralar-deficient (Aralar-/-) mice, generated by a gene-trap method, showing no aralar mRNA and protein, and no detectable malate-aspartate shuttle activity in skeletal muscle and brain mitochondria. Aralar-/- mice were growth-retarded, exhibited generalized tremoring, and had pronounced motor coordination defects along with an impaired myelination in the central nervous system. Analysis of lipid components showed a marked decrease in the myelin lipid galactosyl cerebroside. The content of the myelin lipid precursor, N-acetylaspartate, and that of aspartate are drastically decreased in the brain of Aralar-/- mice. The defect in N-acetylaspartate production was also observed in cell extracts from primary neuronal cultures derived from Aralar-/- mouse embryos. These results show that aralar plays an important role in myelin formation by providing aspartate for the synthesis of N-acetylaspartate in neuronal cells.