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

The therapeutic landscape of citrin deficiency

Citrin deficiency (CD) is a recessive, liver disease caused by sequence variants in the SLC25A13 gene encoding a mitochondrial aspartate-glutamate transporter. CD manifests as different age-dependent phenotypes and affects crucial hepatic metabolic pathways including malate-aspartate-shuttle, glycolysis, gluconeogenesis, de novo lipogenesis and the tricarboxylic acid and urea cycles. Although the exact pathophysiology of CD remains unclear, impaired use of glucose and fatty acids as energy sources due to NADH shuttle defects and PPARα downregulation, respectively, indicates evident energy deficit in CD hepatocytes. The present review summarizes current trends on available and potential treatments for CD. Baseline recommendation for CD patients is dietary management, often already present as a self-selected food preference, that includes protein and fat-rich food, and avoidance of excess carbohydrates. At present, liver transplantation remains the sole curative option for severe CD cases. Our extensive literature review indicated medium-chain triglycerides (MCT) as the most widely used CD treatment in all age groups. MCT can effectively improve symptoms across disease phenotypes by rapidly supplying energy to the liver, restoring redox balance and inducing lipogenesis. In contrast, sodium pyruvate restored glycolysis and displayed initial preclinical promise, with however limited efficacy in adult CD patients. Ursodeoxycholic acid, nitrogen scavengers and L-arginine treatments effectively address specific pathophysiological aspects such as cholestasis and hyperammonemia and are commonly administered in combination with other drugs. Finally, future possibilities including restoring redox balance, amino acid supplementation, enhancing bioenergetics, improving ureagenesis and mRNA/DNA-based gene therapy are also discussed.

Adult Onset Episodic Encephalopathy Due to Citrin Deficiency-A Case Report

Hyperammonemia is a rare cause of adult episodic encephalopathy. Citrin deficiency resulting in citrullinemia type 2 (CTLN2) can lead to recurrent delirium in adults. Here we report a case of adult onset episodic encephalopathy due to citrin deficiency. A 40 years old male presented with one-year history of episodic encephalopathy triggered by high protein and fat diet. He also had chronic pancreatitis and subacute intestinal obstruction which is a novel manifestation of CTLN2. Evaluation showed elevated blood liver enzymes, ammonia, and citrulline. MRI brain showed frontal hyperintensities and bulky basal ganglia which have not been reported. Diagnosis was confirmed by next-generation sequencing which showed a novel variant c. 1591G > A in exon15 of SLC25A13. Hyperammonemic syndromes should be considered in differential diagnosis of episodic encephalopathy in adults. This report shows novel features of subacute intestinal obstruction and MRI findings in CTLN2 expanding spectrum of manifestation.

Challenges in pediatric inherited/metabolic liver disease: Focus on the disease spectrum, diagnosis and management of relatively common disorders

The clinical scenario of pediatric liver disease is becoming more intricate due to changes in the disease spectrum, in which an increasing number of inherited/ metabolic liver diseases are reported, while infectious diseases show a decreasing trend. The similar clinical manifestations caused by inherited/metabolic diseases might be under-recognized or misdiagnosed due to nonspecific characteristics. A delayed visit to a doctor due to a lack of symptoms or mild symptoms at an early stage will result in late diagnosis and treatment. Moreover, limited diagnostic approaches, especially liver biopsy, are not easily accepted by pediatric patients, leading to challenges in etiological diagnosis. Liver dysfunction due to inherited/metabolic diseases is often caused by a variety of metabolites, so precision treatment is difficult; symptomatic treatment is a compelling option for inherited disorders.

Anesthetic Management of a Patient With Citrullinemia Type I During Dental Treatment

We report a case involving intravenous sedation for third molar extractions in a 32-year-old man with citrullinemia type I (CTLN1), a genetic disorder that affects the urea cycle. The patient was diagnosed with CTLN1 after he exhibited seizures soon after birth and was intellectually disabled because of persistent hyperammonemia, although his recent serum ammonia levels were fairly well controlled. We planned to minimize his preoperative fasting, continue his routine oral medications, and monitor his serum ammonia levels at least twice. Sedation with midazolam and a propofol infusion was planned to suppress his gag reflex and reduce protein hypercatabolism due to stress. Epinephrine-containing local anesthetics, which enhance protein catabolism, were avoided, replaced by plain lidocaine for blocks and prilocaine with felypressin for infiltration anesthesia. No significant elevation in ammonia levels was observed. In patients with CTLN1, sedation can be useful for preventing hyperammonemia. Patients who develop symptomatic hyperammonemia may require urgent/emergent treatment involving other medical specialists. Therefore, preoperative endocrinology consultation, perioperative monitoring of serum ammonia levels, and preemptively coordinating for appropriate care in the event hyperammonemia occurs should all be considered.

Citrin deficiency mimicking mitochondrial depletion syndrome

Background

Neonatal intrahepatic cholestasis caused by citrin deficiency (CD) is a rare inborn error of metabolism due to variants in the SLC25A13 gene encoding the calcium-binding protein citrin. Citrin is an aspartate-glutamate carrier located within the inner mitochondrial membrane.

Case presentation

We report on two siblings of Romanian-Vietnamese ancestry with citrin deficiency. Patient 1 is a female who presented at age 8 weeks with cholestasis, elevated lactate levels and recurrent severe hypoglycemia. Diagnosis was made by whole exome sequencing and revealed compound heterozygosity for the frameshift variant c.852_855del, p.Met285Profs*2 and a novel deletion c.(69 + 1_70–1)_(212 + 1_231–1)del in SLC25A13. The girl responded well to dietary treatment with a lactose-free, MCT-enriched formula. Her younger brother (Patient 2) was born 1 year later and also found to be carrying the same gene variants. Dietary treatment from birth was able to completely prevent clinical manifestation until his current age of 4.5 months.

Conclusions

As CD is a well-treatable disorder it should be ruled out early in the differential diagnosis of neonatal cholestasis. Due to the combination of hepatopathy, lactic acidosis and recurrent hypoglycemia the clinical presentation of CD may resemble hepatic mitochondrial depletion syndrome.

Dietary Management, Clinical Status and Outcome of Patients with Citrin Deficiency in the UK

Background: Little is known about the optimal dietary treatment for citrin deficiency. Our aim is to describe the management of UK citrin deficiency patients. Methods: A longitudinal retrospective review was performed. Data were collected from medical records on presenting signs and symptoms, dietary management and clinical outcome. Results: data were collected on 32 patients from 21 families. 50% were females (16/32). Median age at diagnosis was 4 y (5 days–35 y) with 12 patients diagnosed in the neonatal period with neonatal intrahepatic cholestasis (NICCD), eight later in childhood (FTTDCD) and 12 by family screening based on index cases from five families. No patient had adult-onset type II citrullinemia. The patient age at the time of data collection was a median of 11 y (1–44 y). 91% (29/32) of patients had normal physical and neurological development, 47% (15/32) experienced recurrent unexplained abdominal pain and 9% (3/32) episodes of hypoglycaemia. Siblings had different phenotypes (5 families had > 1 affected patient). Most patients preferred high protein foods, limiting sugar-containing foods. Only 41% (13/32) were prescribed a low CHO, high protein, high fat diet (restriction varied) and two used medium chain triglyceride (MCT) supplements. No patient was prescribed drug therapy. Twenty-five per cent (8/32) of patients were underweight and 41% (13/32) had height <−1 z-scores. Conclusions: patients presented with various phenotypes, symptoms and suboptimal growth. Symptoms and biochemical markers improved with age, but height remained low in some. More research is necessary to assess the effectiveness of dietary approaches in improving clinical outcomes and symptoms in citrin deficiency.

AGC2 (Citrin) Deficiency-From Recognition of the Disease till Construction of Therapeutic Procedures

Can you imagine a disease in which intake of an excess amount of sugars or carbohydrates causes hyperammonemia? It is hard to imagine the intake causing hyperammonemia. AGC2 or citrin deficiency shows their symptoms following sugar/carbohydrates intake excess and this disease is now known as a pan-ethnic disease. AGC2 (aspartate glutamate carrier 2) or citrin is a mitochondrial transporter which transports aspartate (Asp) from mitochondria to cytosol in exchange with glutamate (Glu) and H⁺. Asp is originally supplied from mitochondria to cytosol where it is necessary for synthesis of proteins, nucleotides, and urea. In cytosol, Asp can be synthesized from oxaloacetate and Glu by cytosolic Asp aminotransferase, but oxaloacetate formation is limited by the amount of NAD⁺. This means an increase in NADH causes suppression of Asp formation in the cytosol. Metabolism of carbohydrates and other substances which produce cytosolic NADH such as alcohol and glycerol suppress oxaloacetate formation. It is forced under citrin deficiency since citrin is a member of malate/Asp shuttle. In this review, we will describe history of identification of the SLC25A13 gene as the causative gene for adult-onset type II citrullinemia (CTLN2), a type of citrin deficiency, pathophysiology of citrin deficiency together with animal models and possible treatments for citrin deficiency newly developing.

Successful treatment of adult-onset type II citrullinemia with a low-carbohydrate diet and L-arginine after DNA analysis produced a definitive diagnosis

A 60-year-old male, who exhibited finger tremors, obnubilation, and hyperammonemia (409 μg/dL), was admitted to our hospital. Initially, we suspected that a portosystemic shunt had caused his hyperammonemia. However, his symptoms did not improve after balloon-occluded retrograde transvenous obliteration. He was subsequently found to have some peculiar eating habits, including a fondness for bean curd and peanuts, and an aversion to alcohol and sweets. Furthermore, marked citrullinemia (454.2 nmol/mL) was revealed, which led us to suspect adult-onset type II citrullinemia (CTLN2). DNA analysis of the patient and his mother, son, and daughter confirmed that he was homozygous for the c.852_855del mutation in the SLC25A13 gene, and his relatives were heterozygous for the c.852_855del mutation, which led to a definitive diagnosis. A low-carbohydrate diet and the administration of L-arginine ameliorated his symptoms. It is important to be aware that CTLN2 can occur in elderly patients. Thus, patients who exhibit symptoms of CTLN2 should be interviewed about their dietary habits and subjected to plasma amino acid analysis.In this report, we consider the metabolic disorders seen in citrin deficiency and the associated compensatory mechanisms in relation to the clinical features and treatment of CTLN2.

Chronic pancreatitis and pancreatic pseudocyst with adult-onset type II citrullinemia

Citrin deficiency, which is caused by a mutation of SCL25A13, can manifest in older children as failure to thrive and dyslipidemia caused by citrin deficiency (FTTDCD) and in adults as recurrent hyperammonemia with neuropsychiatric symptoms in adult-onset type II citrullinemia (CTLN2). FTTDCD and CTLN2 are known to complicate hypertriglyceridemia and chronic pancreatitis. Here we report, for the first time, the case of a patient with chronic pancreatitis and pancreatic pseudocyst with CTLN2 who was treated using endoscopic ultrasound-guided cyst drainage (EUS-CD). A 33-year-old woman with down syndrome presented to our hospital with complaints of fever, abdominal distention, and biliary vomiting for the previous 2 weeks. Owing to her difficulties in communication, although she had been taking a nutritionally balanced diet regardless of her preference, chronic pancreatitis and pancreatic stones had already been observed at the time of CTLN2 diagnosis at the age of 30 years. Three years later, a merged pancreatic pseudocyst was detected, and EUS-CD was successfully performed. A high-fat diet therapy for FTTDCD and CTLN2 may have caused the development of the pancreatic pseudocyst combined with chronic pancreatitis in this case. Pancreatic pseudocysts associated with FTTDCD or CTLN2 can be treated in a similar manner to those resulting from other causes.

Pivotal role of inter-organ aspartate metabolism for treatment of mitochondrial aspartate-glutamate carrier 2 (citrin) deficiency, based on the mouse model

Previous studies using citrin/mitochondrial glycerol-3-phosphate (G3P) dehydrogenase (mGPD) double-knockout mice have demonstrated that increased dietary protein reduces the extent of carbohydrate-induced hyperammonemia observed in these mice. This study aimed to further elucidate the mechanisms of this effect. Specific amino acids were initially found to decrease hepatic G3P, or increase aspartate or citrulline levels, in mGPD-knockout mice administered ethanol. Unexpectedly, oral glycine increased ammonia in addition to lowering G3P and increasing citrulline. Subsequently, simultaneous glycine-plus-sucrose (Gly + Suc) administration led to a more severe hyperammonemic state in double-KO mice compared to sucrose alone. Oral arginine, ornithine, aspartate, alanine, glutamate and medium-chain triglycerides all lowered blood ammonia following Gly + Suc administration, with combinations of ornithine-plus-aspartate (Orn + Asp) or ornithine-plus-alanine (Orn + Ala) suppressing levels similar to wild-type. Liver perfusion and portal vein-arterial amino acid differences suggest that oral aspartate, similar to alanine, likely activated ureagenesis from ammonia and lowered the cytosolic NADH/NAD⁺ ratio through conversion to alanine in the small intestine. In conclusion, Gly + Suc administration induces a more severe hyperammonemic state in double-KO mice that Orn + Asp or Orn + Ala both effectively suppress. Aspartate-to-alanine conversion in the small intestine allows for effective oral administration of either, demonstrating a pivotal role of inter-organ aspartate metabolism for the treatment of citrin deficiency.

Sudden development of adult-onset type II citrullinemia after total gastrectomy: a case report

Background

Adult-onset type II citurullinemia is an autosomal recessive disorder characterized by recurrent encephalopathy with hyperammonemia resulting from high plasma citrulline and ammonium levels. This report describes a rare case of adult-onset type II citurullinemia that occurred in a patient who only had the heterozygote mutation, and had never presented with any symptoms before surgery.

Case presentation

A 56-year-old man underwent a total gastrectomy for stomach cancer. On postoperative Day 13, he suddenly developed presyncope, and blood tests showed hyperammonemia and high levels of serum citrulline. He was diagnosed with hepatic encephalopathy. DNA analysis revealed a heterozygote mutation in Solute Carrier Family 25. Although the patient received a conservative treatment, episodes of loss of consciousness and abnormality of behavior repeatedly occurred.

Conclusion

Abdominal surgery involving the reconstruction of digestive tract alters the mechanisms of absorption and/or metabolism such that the symptoms of adult-onset type II citurullinemia may arise. Liver transplantation should be performed if all conservative treatments are unsuccessful.

Oral aversion to dietary sugar, ethanol and glycerol correlates with alterations in specific hepatic metabolites in a mouse model of human citrin deficiency

Mice carrying simultaneous homozygous mutations in the genes encoding citrin, the mitochondrial aspartate-glutamate carrier 2 (AGC2) protein, and mitochondrial glycerol-3-phosphate dehydrogenase (mGPD), are a phenotypically representative model of human citrin (a.k.a., AGC2) deficiency. In this study, we investigated the voluntary oral intake and preference for sucrose, glycerol or ethanol solutions by wild-type, citrin (Ctrn)-knockout (KO), mGPD-KO, and Ctrn/mGPD double-KO mice; all substances that are known or suspected precipitating factors in the pathogenesis of human citrin deficiency. The double-KO mice showed clear suppressed intake of sucrose, consuming less with progressively higher concentrations compared to the other mice. Similar observations were made when glycerol or ethanol were given. The preference of Ctrn-KO and mGPD-KO mice varied with the different treatments; essentially no differences were observed for sucrose, while an intermediate intake or similar to that of the double-KO mice was observed for glycerol and ethanol. We next examined the hepatic glycerol 3-phosphate, citrate, citrulline, lysine, glutamate and adenine nucleotide levels following forced enteral administration of these solutions. A strong correlation between the simultaneous increased hepatic glycerol 3-phosphate and decreased ATP or total adenine nucleotide content and observed aversion of the mice during evaluation of their voluntary preferences was found. Overall, our results suggest that the aversion observed in the double-KO mice to these solutions is initiated and/or mediated by hepatic metabolic perturbations, resulting in a behavioral response to increased hepatic cytosolic NADH and a decreased cellular adenine nucleotide pool. These findings may underlie the dietary predilections observed in human citrin deficient patients.

Anesthetic experience of an adult male with citrullinemia type II: a case report

Background

Citrullinemia type II is an autosomal recessive urea cycle disorder and a subtype of citrin deficiency. However, the management of recurrent hyperammonemia with neurologic symptoms in patients with citrullinemia type II is quite different from the management of other types of urea cycle disorders. In pats with citrullinemia type II, regional anesthesia might be a good choice for the early detection of hyperammonemic symptoms and addressing psychic stress.

Case presentation

A 48-year-old male with adult onset citrullinemia type II was scheduled for urethral scrotal fistula repair. During the first operation, spinal anesthesia with conscious sedation using dexmedetomidine was used, a second operation was performed after confirmation of infection control and a stable neurologic condition. In this patient, dietary planning with close monitoring of serum ammonia level and close observation of neurologic conditions might lead to successful perioperative care.

Conclusion

For anesthesia of patients with adult onset citrullinemia type II, close monitoring of neurologic signs and serum ammonia are important to reduce neurologic complications induced by hyperammonemia. Regional anesthesia with a proper dietary plan might reduce patient stress and prevent metabolic tragedy.

Adult liver disorders caused by inborn errors of metabolism: review and update

Inborn errors of metabolism (IEMs) are a group of genetic diseases that have protean clinical manifestations and can involve several organ systems. The age of onset is highly variable but IEMs afflict mostly the pediatric population. However, in the past decades, the advancement in management and new therapeutic approaches have led to the improvement in IEM patient care. As a result, many patients with IEMs are surviving into adulthood and developing their own set of complications. In addition, some IEMs will present in adulthood. It is important for internists to have the knowledge and be familiar with these conditions because it is predicted that more and more adult patients with IEMs will need continuity of care in the near future. The review will focus on Wilson disease, alpha-1 antitrypsin deficiency, citrin deficiency, and HFE-associated hemochromatosis which are typically found in the adult population. Clinical manifestations and pathophysiology, particularly those that relate to hepatic disease as well as diagnosis and management will be discussed in detail.

Steatogenesis in adult-onset type II citrullinemia is associated with down-regulation of PPARα

SLC25A13 (citrin or aspartate-glutamate carrier 2) is located in the mitochondrial membrane in the liver and its genetic deficiency causes adult-onset type II citrullinemia (CTLN2). CTLN2 is one of the urea cycle disorders characterized by sudden-onset hyperammonemia due to reduced argininosuccinate synthase activity. This disorder is frequently accompanied with hepatosteatosis in the absence of obesity and ethanol consumption. However, the precise mechanism of steatogenesis remains unclear. The expression of genes associated with fatty acid (FA) and triglyceride (TG) metabolism was examined using liver samples obtained from 16 CTLN2 patients and compared with 7 healthy individuals. Although expression of hepatic genes associated with lipogenesis and TG hydrolysis was not changed, the mRNAs encoding enzymes/proteins involved in FA oxidation (carnitine palmitoyl-CoA transferase 1α, medium- and very-long-chain acyl-CoA dehydrogenases, and acyl-CoA oxidase 1), very-low-density lipoprotein secretion (microsomal TG transfer protein), and FA transport (CD36 and FA-binding protein 1), were markedly suppressed in CTLN2 patients. Serum concentrations of ketone bodies were also decreased in these patients, suggesting reduced mitochondrial β-oxidation activity. Consistent with these findings, the expression of peroxisome proliferator-activated receptor α (PPARα), a master regulator of hepatic lipid metabolism, was significantly down-regulated. Hepatic PPARα expression was inversely correlated with severity of steatosis and circulating ammonia and citrulline levels. Additionally, phosphorylation of c-Jun-N-terminal kinase was enhanced in CTLN2 livers, which was likely associated with lower hepatic PPARα. Collectively, down-regulation of PPARα is associated with steatogenesis in CTLN2 patients. These findings provide a novel link between urea cycle disorder, lipid metabolism, and PPARα.

Liver transplantation versus conservative treatment for adult-onset type II citrullinemia: our experience and a review of the literature

Adult-onset type II citrullinemia (CTLN2), an autosomal recessive disorder caused by a mutation in the SLC25A13 gene, is characterized by increased serum citrulline and ammonia levels. Patients with CTLN2 also display various neuropsychiatric symptoms. Many individuals with CTLN2 are fond of protein-rich and/or lipid-rich foods with an aversion to carbohydrate-rich foods. We herein report two cases of CTLN2 treated with living donor liver transplantation (LDLT) and provide a review of the pertinent literature. Case 1 was a 43-year-old man admitted to our hospital for repetitive episodes of consciousness disturbance. Case 2 was a 37-year-old man admitted to our hospital because of abnormal behavior associated with hyperammonemia. A definitive diagnosis of CTLN2 was accomplished by DNA analysis in both patients, who successfully underwent LDLT using liver segments from donor siblings with confirmed heterozygous gene expression. Case 2 also underwent conservative therapy with arginine and a high-fat, carbohydrate-restricted diet prior to LDLT. Postoperative recovery was uneventful and food was unrestricted in both patients. We also identified 77 cases of CTLN2 in the literature and reviewed them in terms of outcome of both liver transplantation and conservative therapy. The survival rate in patients treated by liver transplantation was 100%, whereas that in patients treated by conservative treatment showed improvement from 39.5% to 76.5% over the years. Liver transplantation is a practical treatment that fundamentally improves patient quality of life after transplantation. However, recent studies have suggested that arginine and sodium pyruvate administration combined with intensive nutritional support is also an effective therapy for CTLN2. Further development of conservative therapy may provide a safer, more affordable alternative to liver transplantation in the near future.

Three cases of adult-onset type II citrullinemia treated with different therapies: Efficacy of sodium pyruvate and low-carbohydrate diet

We report three cases of adult-onset type II citrullinemia (CTLN2) treated with different therapies including one case successfully treated with p.o. administration of sodium pyruvate and low-carbohydrate diet. Although recent advances in liver transplantation have enabled successful treatment of patients with CTLN2, several issues concerning liver transplantation remain. Further, there is still an urgent need for therapies that do not rely on liver transplantation. The first case was a 41-year-old man who developed impaired consciousness in 1992. The patient was treated with conventional therapy for hepatic encephalopathy and died of severe brain edema. The second case was a 31-year-old man who suddenly presented a syncope-like attack with hyperammonemia. He was treated with carbohydrate-restricted diet but the encephalopathy could not be controlled, and he received emergency living donor liver transplantation. The third patient was a 67-year-old man who developed abnormal behavior with hyperammonemia. He has remained well with oral sodium pyruvate and a low-carbohydrate diet without receiving liver transplantation.

Patient with adult-onset type II citrullinemia beginning 2 years after operation for duodenal malignant somatostatinoma: Indication for liver transplantation

We report a 51-year-old female patient with adult-onset type II citrullinemia (CTLN2) who had a history of pancreatoduodenectomy for duodenal somatostatinoma with metastases to regional lymph nodes at age 49 years, paying special attention to indications for liver transplantation. At age 50 years, she developed hepatic encephalopathy with elevation of plasma ammonia and citrulline levels. A diagnosis of CTLN2 was made by DNA analysis of the SLC25A13 gene and treatment with conservative therapies was begun, including a low-carbohydrate diet and supplementation with arginine and sodium pyruvate. However, despite these treatments, frequent attacks of encephalopathy occurred with markedly elevated plasma ammonia levels. While we were apprehensive regarding the risk of recurrence of somatostatinoma due to immunosuppressive therapy after liver transplantation, the patient was in a critical condition with CTLN2 and it was decided to perform living-donor liver transplantation using a graft obtained from her son. Her postoperative clinical course was uneventful and she has had an active life without recurrence of somatostatinoma for 2 years. This is the first case of CTLN2 with somatostatinoma. As the condition of CTLN2 patients with rapidly progressive courses is often intractable by conservative therapies alone, liver transplantation should be considered even after surgery for malignant tumors in cases with neither metastasis nor recurrence.

Hyperammonemia in children: on the crossroad of different disorders

BACKGROUND

Symptoms of hyperammonemia occur in patients irrespective of the kind of metabolic diseases. Age, metabolic and nutritional status, and decompensation factors such as infections influence clinical manifestations. Prolonged, untreated hyperammonemia leads to brain injury and intellectual disability. Treatment is directed at lowering plasma ammonia. Brain ammonium concentrations are 1.5 to 3.0 times higher than that in blood.

REVIEW SUMMARY

The authors discuss the pathophysiology of the symptoms and consequences of hyperammonemia in children, focusing on the metabolic disorders leading to an increased level of ammonia.

CONCLUSIONS

Ammonia toxicity has been investigated for a long time. According to the main hypotheses, the neurological alterations are connected to alterations in glutamatergic neurotransmission.

First two cases of adult-onset type II citrullinemia successfully treated by deceased-donor liver transplantation in Japan

We report the first two cases of adult-onset type II citrullinemia (CTLN2) successfully treated by liver transplantation from deceased donors in Japan. One patient was a 34-year-old female, who had suffered from depression since the age of 28 years and developed consciousness disturbance at 34 years old. The other patient was a 41-year-old man who began to experience consciousness disturbance with abnormal behavior at 37 years old. Both patients were first treated with non-surgical therapies, including low-carbohydrate diet, arginine granules and sodium pyruvate. However, their therapeutic efficacy was limited and attacks of encephalopathy occurred frequently with elevation of plasma ammonia despite treatment. While both patients and their families desired liver transplantation, no candidate donors for live-donor liver transplantation were available. Fortunately, within a relatively short period after enrollment for liver transplant from deceased donors in Japan (13 and 43 days, respectively), they underwent cadaveric liver transplantation. The clinical courses after the operation were uneventful in both cases and no attacks of hepatic encephalopathy have occurred. Although there have been no reports of good therapies for CTLN2 patients with resistance to non-surgical therapies and no live-donor candidates, our observations indicate that cadaveric liver transplantation can be a promising therapeutic option for CTLN2 patients.

The role of amino acid transporters in inherited and acquired diseases

Amino acids are essential building blocks of all mammalian cells. In addition to their role in protein synthesis, amino acids play an important role as energy fuels, precursors for a variety of metabolites and as signalling molecules. Disorders associated with the malfunction of amino acid transporters reflect the variety of roles that they fulfil in human physiology. Mutations of brain amino acid transporters affect neuronal excitability. Mutations of renal and intestinal amino acid transporters affect whole-body homoeostasis, resulting in malabsorption and renal problems. Amino acid transporters that are integral parts of metabolic pathways reduce the function of these pathways. Finally, amino acid uptake is essential for cell growth, thereby explaining their role in tumour progression. The present review summarizes the involvement of amino acid transporters in these roles as illustrated by diseases resulting from transporter malfunction.

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.

[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.

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.