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

Biochemical characteristics, genetic variants and treatment outcomes of 55 Chinese cases with neonatal intrahepatic cholestasis caused by citrin deficiency

Background

The diagnostic criteria of neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) have not been established due to non-specific clinical manifestations, and our understanding on the treatment outcome is still limited. We aim to investigate the biochemical characteristics, genetic variants, and treatment outcome of NICCD patients.

Methods

We compared the nutritional status and biochemical characteristics of 55 NICCD infants and 27 idiopathic neonatal cholestasis (INC) infants. SLC25A13 gene variant analysis was performed for definitive diagnosis of NICCD. NICCD infants received 12 months of lactose-free and/or medium-chain triglyceride-enriched (LF/MCT) formula treatment. The treatment efficacy was evaluated by comparing the outcome of NICCD with the 24 healthy infants that were selected as normal controls. All NICCD patients were followed up until death or at least 1 year of age.

Results

Compared to INC group, significant increase was found in levels of total bilirubin, indirect bilirubin, total bile acid, gamma-glutamyl transpeptidase, alkaline phosphatase, prothrombin time, thrombin time, international normalized ratio, alpha-fetoprotein (AFP), Vitamin D, and Vitamin E of NICCD group, while alanine aminotransferase, albumin, fibrinogen, glucose, and Vitamin A levels showed significant decrease in the NICCD group (P < 0.05). There were 7 novel variants among 19 SLC25A13 variant types. No significant differences were found between NICCD patients treated for 12 months and normal controls. In long term follow-up, 2 cases developed FTTDCD, 8 cases had special dietary habits, and 1 case died from cirrhosis.

Conclusions

NICCD showed more severe impairments in liver, coagulation, and metabolic function than INC. Significantly increased AFP levels could provide reference for the differential diagnosis of NICCD. The newly discovered variants may be meaningful for the individualized treatment of NICCD patients. LF/MCT formula was recommended for NICCD patients.

Citrin deficiency-The East-side story

Citrin deficiency (CD) is a complex metabolic condition due to defects in SLC25A13 encoding citrin, an aspartate/glutamate carrier located in the mitochondrial inner membrane. The condition was first described in Japan and other East Asian countries in patients who were thought to suffer from classical citrullinemia type 1, and was therefore classified as a urea cycle disorder. With an improved understanding of its molecular basis, it became apparent that a defect of citrin is primarily affecting the malate-aspartate shuttle with however multiple secondary effects on many central metabolic pathways including glycolysis, gluconeogenesis, de novo lipogenesis and ureagenesis. In the meantime, it became also clear that CD must be considered as a global disease with patients identified in many parts of the world and affected by SLC25A13 genotypes different from those known in East Asian populations. The present short review summarizes the (hi)story of this complex metabolic condition and tries to explain the relevance of including CD as a differential diagnosis in neonates and infants with cholestasis and in (not only adult) patients with hyperammonemia of unknown origin with subsequent impact on the emergency management.

Citrin-deficient patient-derived induced pluripotent stem cells as a pathological liver model for congenital urea cycle disorders

Citrin deficiency is a congenital secondary urea cycle disorder lacking useful disease models for effective treatment development. In this study, human induced pluripotent stem cells (iPSCs) were generated from two patients with citrin deficiency and differentiated into hepatocyte-like cells (HLCs). Citrin-deficient HLCs produced albumin and liver-specific markers but completely lacked citrin protein and expressed argininosuccinate synthase only weakly. In addition, ammonia concentrations in a medium cultured with citrin-deficient HLCs were higher than with control HLCs. Sodium pyruvate administration significantly reduced ammonia concentrations in the medium of citrin-deficient HLCs and slightly reduced ammonia in HLCs differentiated from control iPSCs, though this change was not significant. Our results suggest that sodium pyruvate may be an efficient treatment for patients with citrin deficiency. Citrin-deficient iPSCs are a pathological liver model for congenital urea cycle disorders to clarify pathogenesis and develop novel therapies.

Genetic aetiologies of acute liver failure

Acute liver failure (ALF) is a rare, rapidly evolving, clinical syndrome with devastating consequences where definitive treatment is by emergency liver transplantation. Establishing a diagnosis can be challenging and, historically, the cause of ALF was unidentified in up to half of children. However, recent technological and clinical advances in genomic medicine have led to an increasing proportion being diagnosed with monogenic aetiologies of ALF. The conditions encountered include a diverse group of inherited metabolic disorders each with prognostic and treatment implications. Often these disorders are clinically indistinguishable and may even mimic disorders of immune regulation or red cell disorders. Rapid genomic sequencing for children with ALF is, therefore, a key component in the diagnostic work up today. This review focuses on the monogenic aetiologies of ALF.

Update on the diagnosis and management of neonatal intrahepatic cholestasis caused by citrin deficiency: Expert review on behalf of the Asian Pan-Pacific Society for Pediatric Gastroenterology, Hepatology, and Nutrition

Citrin deficiency is an autosomal recessive metabolic liver disease caused by mutations in the SLC25A13 gene. The disease typically presents with cholestasis, elevated liver enzymes, hyperammonemia, hypercitrullinemia, and fatty liver in young infants, resulting in a phenotype known as "neonatal intrahepatic cholestasis caused by citrin deficiency" (NICCD). The diagnosis relies on clinical manifestation, biochemical evidence of hypercitrullinemia, and identifying mutations in the SLC25A13 gene. Several common mutations have been found in patients of East Asian background. The mainstay treatment is nutritional therapy in early infancy utilizing a lactose-free and medium-chain triglyceride formula. This approach leads to the majority of patients recovering liver function by 1 year of age. Some patients may remain asymptomatic or undiagnosed, but a small proportion of cases can progress to cirrhosis and liver failure, necessitating liver transplantation. Recently, advancements in newborn screening methods have improved the age of diagnosis. Early diagnosis and timely management improve patient outcomes. Further studies are needed to elucidate the long-term follow-up of NICCD patients into adolescence and adulthood.

Features of liver injury in 138 Chinese patients with NICCD

OBJECTIVES

To find biochemical and molecular markers can assist in identifying serious liver damage of neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) patients.

METHODS

138 patients under 13 days to 1.1 year old diagnosed of NICCD in our center from 2004 to 2020. Base on the abnormal liver laboratory tests, we divided 138 patients into three groups: acute liver failure (ALF), liver dysfunction, and non-liver dysfunction groups, then compared their clinical, biochemical and, molecular data.

RESULTS

96 % of 138 patients had high levels of citrulline and high ratio of threonine to serine, which is the distinctive feature of plasma amino acid profile for NICCD. A total of 18.1 % of 138 patients had evidence of ALF who presented the most severity hepatic damage, 51.5 % had liver dysfunction, and the remaining 30.4 % presented mild clinical symptoms (non-liver dysfunction). In ALF group, the levels of citrulline, tyrosine, TBIL, ALP, and γ-GT was significantly elevated, and the level of ALB and Fisher ratio was pronounced low. Homozygous mutations of 1,638_1660dup, IVS6+5G.A, or IVS16ins3kb in SLC25A13 gene were only found in ALF and liver dysfunction groups. Supportive treatment including medium-chain triglyceride supplemented diet and fresh frozen plasma could be life-saving and might reverse ALF.

CONCLUSIONS

High level of citrulline, tyrosine, TBIL, ALP, γ-GT, and ammonia, low level of albumin, and low Fisher ratio were predictors to suggest severe liver damage in NICCD patients who may go on to develop fatal metabolic disorder. Early identification and proper therapy is particularly important for these patients.

The prognosis of citrin deficiency differs between early-identified newborn and later-onset symptomatic infants

BACKGROUND

The prognosis for patients with citrin deficiency is not always benign. This study examined the differences between patients identified early by newborn screening and patients identified later with cholestasis/hepatitis.

MATERIALS AND METHODS

This retrospective study included 42 patients with genetically confirmed SLC25A13 mutations who were born between May 1996 and August 2019. Fifteen patients were identified during newborn screening (NBS group) and 27 patients were identified through the onset of cholestasis/hepatitis in infancy (clinical group).

RESULTS

Overall, 90% of the patients presented with cholestasis, among whom 86% (31/36) recovered at a median age of 174 days. Compared with patients in the clinical group, patients in the NBS group were significantly younger at diagnosis and at cholestasis-free achievement; they also had significantly lower levels of peak direct bilirubin and liver enzymes. At the median follow-up age of 11.8 years, 21% of the patients had dyslipidemia, whereas 36% of the patients had failure to thrive. The overall mortality rate was 2.4%. Variant c.851_854del was the most frequent, constituting 44% of the mutant alleles.

CONCLUSION

Patients identified early by NBS had a better prognosis, demonstrating the importance of a timely diagnosis of NICCD and the need for careful follow-up.

IMPACT

Some cases of neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) are not benign. Compared with patients identified later based on the presence of cholestasis/hepatitis, patients identified early by newborn screening have less severe cholestasis and are cholestasis-free at a significantly younger age. A timely diagnosis is needed, along with follow-up examinations that assess metabolic profile and body weight, to improve the long-term prognosis of NICCD patients.

Multiple pneumatoceles and lung abscesses caused by early-onset E. coli sepsis in a preterm neonate

Early-onset sepsis (EOS) is a serious and fatal illness in neonates, Group B Streptococcus and Escherichia coli are major causative pathogens. We report a case of EOS and pneumonia caused by E. coli in a preterm neonate with multiple pneumatoceles and lung abscesses. A male neonate weighing 1670g was delivered at 33 6/7 weeks' gestation by a mother with clinical chorioamnionitis. He showed respiratory distress soon after birth and developed septic shock. He was intubated and mechanical ventilation was started. E.coli was detected in blood culture obtained from both the patient and his mother. He developed multiple pneumatoceles and lung abscesses. Surgical drainage was complicated, cefotaxime was thus continued until day 74. Pneumatoceles and lung abscesses are complications of neonatal pneumonia, rarely reported by E. coli. Multiple lung abscesses in our patient are distinct from single abscesses in previous case studies of neonatal lung abscesses. We speculate that bacteremia along with pneumatoceles led to multiple lung abscesses in our patient. These complications require long-term antibiotic therapy, to minimize morbidity and mortality, and should thus be considered when managing EOS caused by E. coli.

[Jaundice in Young Children]

Jaundice in children have various etiologies. Among them, physiological jaundice is a very common disease observed in more than half of full-term neonates. When jaundice persists or develops after 2 weeks of age, the total/direct bilirubin is measured in consideration of the possibility of cholestasis. In case of cholestasis, imaging studies differentiate biliary atresia and other disorders of the extrahepatic bile ducts. In this review, we briefly presented the major differential diseases of cholestasis in children and introduced diagnostic imaging techniques, including normal findings.

Dynamic changes of metabolic characteristics in neonatal intrahepatic cholestasis caused by citrin deficiency

Introduction: Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) is a pan-ethnic complicated inborn error of metabolism but the specific mechanism is not fully understood.

Methods: A total of 169 patients with NICCD who have biallelic pathogenic SLC25A13 variants detected by targeted next-generation sequencing were collected. They were divided into the “Newborn-screen Group” and “Clinical diagnosed Group” depending on the newborn screening results. Amino acid and acylcarnitine profiles were measured by MS/MS. The total bile acids, blood amino acids and acylcarnitines, general biochemistry, blood count, and coagulation parameters were monitored every 2–3 months. We compared the differences in metabolic indices and their dynamic changes between these two groups. The Mann–Whitney test and orthogonal partial least squares discrimination analysis (OPLS-DA) were used for statistical analysis.

Results: At the onset of NICCD, we found that the “Clinical diagnosed Group” had higher levels of intermediate products of the urea cycle, free carnitine, and short-chain and long-chain acylcarnitines than those in the “Newborn-screen Group,” but the levels of ketogenic/glucogenic amino acids and several medium-chain acylcarnitines were lower. Furthermore, concentrations of direct bilirubin, total bile acid, lactate, prothrombin time, and several liver enzymes were significantly higher while total protein, amylase, and hemoglobin were lower in the “Clinical diagnosed Group” than in the “Newborn-screen Group.” Dynamic change analysis showed that direct bilirubin, albumin, arginine, and citrulline were the earliest metabolic derangements to reach peak levels in NICCD groups, followed by acylcarnitine profiles, and finally with the elevation of liver enzymes. All abnormal characteristic metabolic indicators in the “Newborn-screen Group” came back to normal levels at earlier ages than the “Clinical diagnosed Group.” c.852_855del (41.2%), IVS16ins3kb (17.6%), c.615 + 5G&gt;A (9.6%), 1638_1660dup (4.4%), and c.1177 + 1G&gt;A (3.7%) accounted for 76.5% of all the mutated SLC25A13 alleles in our population.

Conclusion: Argininosuccinate synthesis, gluconeogenesis, ketogenesis, fatty acid oxidation, liver function, and cholestasis were more severely affected in the “Clinical diagnosed Group.” The “Newborn-screen Group” had a better prognosis which highlighted the importance of newborn screening of NICCD.

Obstacles to home-based dietary management for caregivers of children with citrin deficiency: a qualitative study

Background

Dietary management is the most important and effective treatment for citrin deficiency, as well as a decisive factor in the clinical outcome of patients. However, the dietary management ability of caregivers of children with citrin deficiency is generally poor, especially in East Asia where carbohydrate-based diets are predominant. The aim of this study was to identify the difficulties that caregivers encounter in the process of home-based dietary management, and the reasons responsible for these challenges.

Results

A total of 26 caregivers of children with citrin deficiency were recruited, including 24 mothers, one father, and one grandmother. Grounded theory was employed to identify three themes (covering 12 sub-themes) related to the dilemma of dietary management: dietary management that is difficult to implement; conflicts with traditional concepts; and the notion that children are only a part of family life. The first theme describes the objective difficulties that caregivers encounter in the process of dietary management; the second theme describes the underlying reasons responsible for the non-adherent behavior of caregivers; the third theme further reveals the self-compromise by caregivers in the face of multiple difficulties.

Conclusions

This study reflects the adverse effects of multi-dimensional contradictions on the adherence of caregivers to dietary management. These findings reveal that the dietary management of citrin deficiency is not only a rational process, rather it is deeply embedded in family, social, and dietary traditions.

Hemostatic rebalance in neonatal intrahepatic cholestasis with citrin deficiency

BACKGROUND

Neonatal intrahepatic cholestasis with citrin deficiency (NICCD) results in coagulopathy due to decreased levels of vitamin (V)K-dependent clotting factors, similar to biliary atresia (BA). However, the involvement of VK-independent coagulant and anticoagulant factor(s) remains unknown. We examined relationships between coagulant and anticoagulant potential before and after nutritional treatment in NICCD.

METHODS

Three cases (aged 12, 21, and 45 days) with NICCD-associated coagulopathy were evaluated with standard coagulation/anticoagulation tests and comprehensive coagulation assays, rotational thromboelastometry, and protein C/protein S (PC/PS) pathway function assay (ThromboPath^® ), before and after nutritional treatment.

RESULTS

In all cases, activated partial thromboplastin time and prothrombin time were significantly prolonged, which is associated with very low levels of VK-independent fibrinogen and antithrombin. The initiation of nutritional treatment of medium-chain triglycerides oil improved these levels within the normal range, although low levels of other clotting factors were modestly increased. Whole blood- rotational thromboelastometry analysis revealed near-normal coagulation potential, even before treatment, comparable to healthy adults, and supportive of their non-bleeding symptoms. The introduction of nutritional treatment had further improved comprehensive coagulation potential. The global PC/PS-pathway function assay demonstrated the absence of the features of this function associated with the pathogenesis of NICCD. Compared to BA, the plasma levels of fibrinogen and antithrombin in all cases were markedly low, whilst those after treatment improved, especially to similar level of BA.

CONCLUSIONS

Neonatal intrahepatic cholestasis with citrin deficiency has the characteristic of rebalancing hemostatic mechanisms associated with coagulant and anticoagulant potential involving low levels of fibrinogen and antithrombin, suggesting a pathophysiological coagulopathy distinct from BA.

Validation of amplicon-based next generation sequencing panel for second-tier test in newborn screening for inborn errors of metabolism

Objectives

Next generation sequencing (NGS) technology has allowed cost-effective massive parallel DNA sequencing. To evaluate the utility of NGS for newborn screening (NBS) of inborn errors of metabolism (IEM), a custom panel was designed to target 87 disease-related genes. The pilot study was primarily proposed for second-tier testing under the NBSIEM program in Hong Kong.

Methods

The validation of the panel was performed with two reference genomes and an external quality assurance (EQA) sample. Sequencing libraries were synthesized with amplicon-based approach. The libraries were pooled, spiked-in with 2% PhiX DNA as technical control, for 16-plex sequencing runs. Sequenced reads were analyzed using a commercially available pipeline.

Results

The average target region coverage was 208× and the fraction of region with target depth ≥20× was 95.7%, with a sensitivity of 91.2%. There were 85 out of 87 genes with acceptable coverage, and EQA result was satisfactory. The turnaround time from DNA extraction to completion of variant calling and quality control (QC) procedures was 2.5 days.

Conclusions

The NGS approach with the amplicon-based panel has been validated for analytical performance and is suitable for second-tier NBSIEM test.

Food Preferences of Patients with Citrin Deficiency

Citrin deficiency is characterized by a wide range of symptoms from infancy through adulthood and presents a distinct preference for a diet composed of high protein, high fat, and low carbohydrate. The present study elucidates the important criteria by patients with citrin deficiency for food selection through detailed analysis of their food preferences. The survey was conducted in 70 citrin-deficient patients aged 2–63 years and 55 control subjects aged 2–74 years and inquired about their preference for 435 food items using a scale of 1–4 (the higher, the more favored). The results showed that the foods marked as “dislike” accounted for 36.5% in the patient group, significantly higher than the 16.0% in the controls. The results also showed that patients clearly disliked foods with 20–24 (% of energy) or less protein, 45–54% (of energy) or less fat, and 30–39% (of energy) or more carbohydrate. Multiple regression analysis showed carbohydrates had the strongest influence on patients’ food preference (β = −0.503). It also showed female patients had a stronger aversion to foods with high carbohydrates than males. The protein, fat, and carbohydrate energy ratio (PFC) of highly favored foods among patients was almost the same as the average PFC ratio of their daily diet (protein 20–22: fat 47–51: carbohydrates 28–32). The data strongly suggest that from early infancy, patients start aspiring to a nutritional balance that can compensate for the metabolism dissonance caused by citrin deficiency in every food.

Hypoglycemic attacks and growth failure are the most common manifestations of citrin deficiency after 1 year of age

Citrin deficiency develops in different symptomatic periods from the neonatal period to adulthood. Some infantile patients are diagnosed by newborn mass screening or symptoms of neonatal intrahepatic cholestasis caused by citrin deficiency, some patients in childhood may develop hepatopathy or dyslipidemia as failure to thrive and dyslipidemia caused by citrin deficiency, and some adults are diagnosed after developing adult-onset type 2 citrullinemia (CTLN2) with hyperammonemia or encephalopathy. A diagnosis is needed before the development of severe phenotypic CTLN2 but is often difficult to obtain because newborn mass screening cannot detect all patients with citrin deficiency, and undiagnosed patients often appear healthy in childhood. There are only a few reports that have described patients in childhood. To explore the clinical features of undiagnosed patients with citrin deficiency in childhood, we studied 20 patients who were diagnosed after the first year of life. Of these patients, 45% experienced hypoglycemic attacks in childhood. The acetoacetic acid level during hypoglycemic attacks was lower than expected. Growth failure at diagnosis (45%) was also noted. From the patients' history, fat- and protein-rich food preferences (80%), a low birth weight (70%), and prolonged jaundice or infantile hepatopathy (40%) were identified. To diagnose citrin deficiency in childhood, we should ask about food preferences and a history of infantile hepatopathy for all children with severe hypoglycemia or growth failure and consider the genetic test for citrin deficiency if the patient has characteristic food preferences or a history of infantile hepatopathy.

Hyperammonemic Encephalopathy in an Adolescent Patient of Citrullinemia Type 1 With an Atypical Presentation

Citrullinemia refers to a family of autosomal recessive disorders involving the urea cycle. Three forms exist, which have different implications. Type I citrullinemia exists in both mild and severe forms. It arises due to mutations with argininosuccinate synthase leading to accumulation of ammonia and producing symptoms of lethargy, poor feeding, and seizures. Type II citrullinemia occurs due to citrin mutations involved in the urea cycle transport or during neonatal cholestasis. Management of both conditions requires low-protein diets along with arginine, sodium benzoate, and sodium phenylacetate. While traditional treatment shows improved outcomes, modifications may be necessary depending on a patient’s presentation.

We present a unique case of a 19-year-old wheelchair-bound female with a past medical history of heterozygous type I citrullinemia, seizures, and chronic encephalopathy presented to a local children’s hospital for evaluation of altered mental status with a lethargic mental state. She was initially found to have an ammonia level of 329 µmol/L and choledocholithiasis on admission. Dietary modification with intravenous dextrose and intralipids with oral lactulose saw improvement in her labs. However, her ammonia level increased to 381 µmol/L despite such interventions. Intensive care was required to normalize her serum ammonia level and clear her for a magnetic resonance cholangiopancreatography (MRCP).

We present a unique case of heterozygous type I citrullinemia with some overlap with type II citrullinemia features. Further studies are needed to understand better the observed unique presentation and long-term clinical implications associated with the disease.

Neonatal intrahepatic cholestasis caused by citrin deficiency with no hepatic steatosis: a case report

Background

Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) is a common form of neonatal jaundice. Histopathological examination of the liver in patients with NICCD typically shows fatty liver, steatohepatitis, and liver fibrosis. Jaundice and fatty liver often improve by 1 year of age. We herein describe a girl who was diagnosed with NICCD based on an SLC25A13 mutation, although no fatty deposits were found on pathologic examination of the liver.

Case presentation

The patient in this case was a 3-month-old girl. At 2 months of age, she presented with jaundice, discolored stools, and poor weight gain and was found to have hyperbilirubinemia. Cholangiography revealed that she did not have biliary atresia. A laparoscopic liver biopsy was performed, and liver histopathology showed no fatty deposits. Genetic analysis revealed a compound heterozygous mutation in SLC25A13, and she was diagnosed with NICCD. She was given medium-chain triglyceride milk and gained weight. She resumed consumption of normal milk and breast milk, and her stool color improved. She was discharged at 4 months of age with adequate weight gain and a lower total bilirubin concentration. She was in good condition after discharge and showed normal development at the time of outpatient follow-up.

Conclusions

We experienced a case of NICCD in a patient without fatty liver. This case illustrates that the absence of hepatic steatosis in neonatal cholestasis does not rule out NICCD.

Analysis of daily energy, protein, fat, and carbohydrate intake in citrin-deficient patients: Towards prevention of adult-onset type II citrullinemia

Patients with citrin deficiency during the adaptation/compensation period exhibit diverse clinical features and have characteristic diet of high protein, high fat, and low carbohydrate. Japanese cuisine typically contains high carbohydrate but evaluation of diet of citrin-deficient patients in 2008 showed a low energy intake and a protein:fat:carbohydrate (PFC) ratio of 19:44:37, which indicates low carbohydrate consumption rate. These findings prompted the need for diet intervention to prevent the adult onset of type II citrullinemia (CTLN2). Since the publication of the report about 10 years ago, patients are generally advised to eat what they wish under active dietary consultation and intervention. In this study, citrin-deficient patients and control subjects living in the same household provided answers to a questionnaire, filled-up a maximum 6-day food diary, and supplied physical data and information on medications if any. To study the effects of the current diet, the survey collected data from 62 patients and 45 controls comparing daily intakes of energy, protein, fat, and carbohydrate. Food analysis showed that patient's energy intake was 115% compared to the Japanese standard. The confidence interval of the PFC ratio of patients was 20-22:47-51:28-32, indicating higher protein, higher fat and lower carbohydrate relative to previous reports. The mean PFC ratio of female patients (22:53:25) was significantly different from that of male patients (20:46:34), which may explain the lower frequency of CTLN2 in females. Comparison of the present data to those published 10 years ago, energy, protein, and fat intakes were significantly higher but the amount of carbohydrate consumption remained the same. Regardless of age, most patients (except for adolescents) consumed 100-200 g/day of carbohydrates, which met the estimated average requirement of 100 g/day for healthy individuals. Finally, patients were generally not overweight and some CTLN2 patients were underweight although their energy intake was higher compared with the control subjects. We speculate that high-energy of a low carbohydrate diet under dietary intervention may help citrin-deficient patients attain normal growth and prevent the onset of CTLN2.

Rapid Genetic Diagnosis of Citrin Deficiency by Multicolor Melting Curve Analysis

Citrin deficiency caused by SLC25A13 genetic mutations is an autosomal recessive disease, and four prevalent mutations including c.851_854del, c.1638_1660dup, IVS6+5G>A, and IVS16ins3kb make up >80% of total pathogenic mutations within the Chinese population. However, suitable assays for detection of these mutations have not yet been developed for use in routine clinical practice. In the current study, a real-time PCR-based multicolor melting curve analysis (MMCA) was developed to detect the four prevalent mutations in one closed-tube reaction. The analytical and clinical performances were evaluated using artificial templates and clinical samples. All four mutations in the test samples were accurately genotyped via their labeling fluorophores and Tm values, and the standard deviations of Tm values were indicated to be <0.2°C. The limit of detection was estimated to be 500 diploid human genomes per reaction. The MMCA assay of 5,332 healthy newborns from southern China identified a total of 107 SLC25A13-mutation carriers, indicating a carrier rate of 2%. The genotypes of 107 carriers and 112 random non-carriers were validated using direct sequencing and Long-range PCR with 100% concordance. In conclusion, the assay developed in this study may potentially serve as a rapid genetic diagnostic tool for citrin deficiency.

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.

Combined primary carnitine deficiency with neonatal intrahepatic cholestasis caused by citrin deficiency in a Chinese newborn

Background

Primary carnitine deficiency (PCD) is an autosomal recessive disorder affecting the carnitine cycle and resulting in defective fatty acid oxidation. Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) is an autosomal recessive disorder and one of the main causes of inherited neonatal cholestasis. Both PCD and NICCD are included in the current expanded newborn screening (NBS) targets.

Case presentation

Targeted exome sequencing was performed on a Chinese proband, and Sanger sequencing was utilised to validate the detected mutations. The patient who was initially suspected to have PCD based on the NBS results presented with neonatal intrahepatic cholestasis and ventricular septal defect. Further investigations not only confirmed PCD but also revealed the presence of NICCD. Four distinct mutations were detected, including c.51C > G (p.F17L) and c.760C > T (p.R254X) in SLC22A5 as well as c.615 + 5G > A and IVS16ins3kb in SLC25A13.

Conclusions

This is the first reported case of PCD and NICCD occurring in the same patient. The dual disorders in a newborn broaden our understanding of inherited metabolic diseases. Thus, this study highlighted the importance of further genetic testing in patients presenting with unusual metabolic screening findings.

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.

Combining newborn metabolic and genetic screening for neonatal intrahepatic cholestasis caused by citrin deficiency

To evaluate the feasibility of incorporating genetic screening for neonatal intrahepatic cholestasis, caused by citrin deficiency (NICCD), into the current newborn screening (NBS) program. We designed a high-throughput iPLEX genotyping assay to detect 28 SLC25A13 mutations in the Chinese population. From March 2018 to June 2018, 237 630 newborns were screened by tandem mass spectrometry at six hospitals. Newborns with citrulline levels between ^1/2 cutoff and cutoff values of the upper limit were recruited for genetic screening using the newly developed assay. The sensitivity and specificity of the iPLEX genotyping assay both reached 100% in clinical practice. Overall, 29 364 (12.4%) newborns received further genetic screening. Five patients with conclusive genotypes were successfully identified. The most common SLC25A13 mutation was c.851_854del, with an allele frequency of 60%. In total, 658 individuals with one mutant allele were identified as carriers. Eighteen different mutations were observed, yielding a carrier rate of 1/45. Notably, Quanzhou in southern China had a carrier rate of up to 1/28, whereas Jining in northern China had a carrier rate higher than that of other southern and border cities. The high throughput iPLEX genotyping assay is an effective and reliable approach for NICCD genotyping. The combined genetic screening could identify an additional subgroup of patients with NICCD, undetectable by conventional NBS. Therefore, this study demonstrates the viability of incorporating genetic screening for NICCD into the current NBS program.

Amino Acid Transport Defects in Human Inherited Metabolic Disorders

Amino acid transporters play very important roles in nutrient uptake, neurotransmitter recycling, protein synthesis, gene expression, cell redox balance, cell signaling, and regulation of cell volume. With regard to transporters that are closely connected to metabolism, amino acid transporter-associated diseases are linked to metabolic disorders, particularly when they involve different organs, cell types, or cell compartments. To date, 65 different human solute carrier (SLC) families and more than 400 transporter genes have been identified, including 11 that are known to include amino acid transporters. This review intends to summarize and update all the conditions in which a strong association has been found between an amino acid transporter and an inherited metabolic disorder. Many of these inherited disorders have been identified in recent years. In this work, the physiological functions of amino acid transporters will be described by the inherited diseases that arise from transporter impairment. The pathogenesis, clinical phenotype, laboratory findings, diagnosis, genetics, and treatment of these disorders are also briefly described. Appropriate clinical and diagnostic characterization of the underlying molecular defect may give patients the opportunity to avail themselves of appropriate therapeutic options in the future.

Neonatal cholestasis: recent insights

Background

Neonatal physiological jaundice is a common benign condition that rarely extends behind the second week of life; however, it may interfere with the diagnosis of a pathological condition termed neonatal cholestasis (NC). The latter is a critical, uncommon problem characterized by conjugated hyperbilirubinaemia. This review aims to highlight the differences between physiological and pathological jaundice, identify different causes of NC, and provide a recent approach to diagnosis and management of this serious condition.

Main text

NC affects 1/2500 live births, resulting in life-threatening complications due to associated hepatobiliary or metabolic abnormalities. NC is rarely benign and indicates the presence of severe underlying disease. If jaundice extends more than 14 days in full-term infants or 21 days in preterm infants, the serum bilirubin level fractionated into conjugated (direct) and unconjugated (indirect) bilirubin should be measured. A stepwise diagnostic approach starts with obtaining a complete history, and a physical examination which are valuable for the rapid diagnosis of the underlying disease. The most frequently diagnosed causes of NC are biliary atresia (BA) and idiopathic neonatal hepatitis (INH). The early diagnosis of NC ensures more accurate management and better prognosis. Despite the unavailability of any specific treatments for some causes of NC, the patient can benefit from nutritional management and early medical intervention. Future research should attempt to shed light on methods of screening for NC, especially for causes that can be effectively treated either through proper nutritional support, appropriate chemotherapeutic management, or timely surgical intervention.

Conclusion

Further attention should be paid for diagnosis and treatment of NC as it may be misdiagnosed as physiological jaundice; this may delay the proper management of the underlying diseases and aggravates its complications.

Sodium Taurocholate Cotransporting Polypeptide (NTCP) Deficiency Hidden Behind Citrin Deficiency in Early Infancy: A Report of Three Cases

Sodium taurocholate cotransporting polypeptide (NTCP), a carrier protein encoded by the gene SLC10A1, is expressed in the basolateral membrane of the hepatocyte to uptake bile acids from plasma. As a new inborn error of bile acid metabolism, NTCP deficiency remains far from being well understood in terms of the clinical and molecular features. Citrin deficiency is a well-known autosomal recessive disease arising from SLC25A13 mutations, and in neonates or infants, this condition presents as transient intrahepatic cholestasis which usually resolves before 1 year of age. All the three patients in this paper exhibited cholestatic jaundice and elevated total bile acids in their early infancy, which were attributed to citrin deficiency by SLC25A13 genetic analysis. In response to feeding with lactose-free and medium-chain triglycerides-enrich formula, their clinical and laboratory presentations disappeared gradually while the hypercholanemia persisted, even beyond 1 year of age. On subsequent SLC10A1 analysis, they were all homozygous for the well-known pathogenic variant c.800C > T (p.Ser267Phe), and NTCP deficiency was thus definitely diagnosed. The findings in this paper indicated that NTCP deficiency could be covered up by citrin deficiency during early infancy; however, in citrin-deficient patients with intractable hypercholanemia following resolved cholestatic jaundice, NTCP deficiency should be taken into consideration.

Identification of a novel splicing mutation in the SLC25A13 gene from a patient with NICCD: a case report

Background

Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) is an autosomal recessive disorder and one of the most common inherent causes of cholestatic jaundice in Asian infants. Mutations in the SLC25A13 gene, which encodes citrin protein expressed in the liver, have been identified as the genetic cause for NICCD.

Case presentation

Here, we report a 4-month-old female with clinical features including jaundice, hyperbilirubinemia, hyperlactacidemia, and abnormal liver function. The patient was diagnosed with NICCD by differential diagnosis using genetic analysis. Mutations in 60 jaundice-related genes were tested by using amplicon sequencing, which was performed on an Ion S5XL genetic analyzer. A compound heterozygous mutation in the SLC25A13 gene was identified, consisting of a known deletion SLC25A13:c.852_855delTATG and a novel splicing mutation SLC25A13:c.1841 + 3_1841 + 4delAA. Sanger sequencing for the proband and her parents was performed to validate the result and reveal the source of mutations.

Conclusion

A compound heterozygous mutation in the SLC25A13 gene was identified in a 4-month-old female patient with NICCD. Our data suggest that amplicon sequencing is a helpful tool for the differential diagnosis of inherited diseases with similar symptoms. Further studies of the mutation spectrum of neonatal jaundice in China are warranted.

Current treatment for citrin deficiency during NICCD and adaptation/compensation stages: Strategy to prevent CTLN2

Identification of the genes responsible for adult-onset type II citrullinemia (CTLN2) and citrin protein function have enhanced our understanding of citrin deficiency. Citrin deficiency is characterized by 1) neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD); 2) adaptation/compensation stage with unique food preference from childhood to adulthood; and 3) CTLN2. The treatment of NICCD aims to prevent the progression of cholestasis, and it includes medium chain triglycerides (MCT) milk and lactose-free milk, in addition to medications (e.g., vitamin K₂, lipid-soluble vitamins and ursodeoxycholic acid). Spontaneous remission around the age of one is common in NICCD, though prolonged cholestasis can lead to irreversible liver failure and may require liver transplantation. The adaptation/compensation stage (after one year of age) is characterized by the various signs and symptoms such as hypoglycemia, fatty liver, easy fatigability, weight loss, and neuropsychiatric symptoms. Some poorly-controlled patients show failure to thrive and dyslipidemia caused by citrin deficiency (FTTDCD). Diet therapy is the key in the adaptation/compensation stage. Protein- and fat-rich diet with a protein: fat: carbohydrate ratio being 15-25%: 40-50%: 30-40% along with the appropriate energy intake is recommended. The use of MCT oil and sodium pyruvate is also effective. The toxicity of carbohydrate is well known in the progression to CTLN2 if the consumption is over a long term or intense. Alcohol can also trigger CTLN2. Continuous intravenous hyperalimentation with high glucose concentration needs to be avoided. Administration of Glyceol® (an osmotic agent containing glycerol and fructose) is contraindicated. Because the intense treatment such as liver transplantation may become necessary to cure CTLN2, the effective preventative treatment during the adaptation/compensation stage is very important. At present, there is no report of a case with patients reported having the onset of CTLN2 who are on the diet therapy and under the appropriate medical support during the adaptation/compensation stage.

Bioinformatic and functional analysis of promoter region of human SLC25A13 gene

The human SLC25A13 gene encodes the liver type aspartate/glutamate carrier isoform 2 (AGC2, commonly named as citrin), which plays a key role in the main NADH-shuttle of human hepatocyte. Biallelic SLC25A13 mutations result in Citrin deficiency (CD). In order to identify the important regulatory region of SLC25A13 gene and elucidate the way how potential promoter mutations affect the citrin expression, we performed promoter deletion analysis and established the reporter constructs of luciferase gene-carrying SLC25A13 promoter containing several mutations located in putative transcription factor-binding sites. The luciferase activities of all promoter constructs were measured using a Dual-Luciferase Reporter Assay System. Bioinformatic analysis showed that the promoter of SLC25A13 gene lacks TATA box and obviously typical initiator element, but contains a CCAAT box and two GC box. Promoter deletion analysis confirmed the region from -221 to -1 upstream ATG was essential for SLC25A13 to maintain the promoter activity. We utilized dual-luciferase reporter system as function analytical model to tentatively assess the effect of artificially constructed promoter mutations on citrin expression, and our analysis revealed that mutated putative CCAAT box and GC box could significantly affect the citrin expression. Our study confirmed the important SLC25A13 promoter regions that influenced citrin expression in HL7702 cells, and constructed a function analytical model. This work may be useful to further identify the pathogenic mutations leading to CD in the promoter region.

Risk factors associated with mortality in neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) and clinical implications

Background

Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) has high prevalence in East Asia, and has been reported in other parts of the world. NICCD is also the most common form of genetic cholestasis among East Asians. There has been reports of mortalities or liver transplants associated with NICCD, but risk factors associated with poor outcome were unknown. Our objective is to report NICCD mortalities in a tertiary pediatric hepatology center, and to explore associated risk factors along with implications to clinical practice.

Method

This is a retrospective analysis of NICCD cases collected from June 2003 until January 2017 in the Children’s Hospital of Fudan University. Clinical, biochemical, and genetic data were compared between deceased cases and survivors without liver transplant.

Results

Sixty-one confirmed NICCD cases, including 52 cases in the survival group, and 9 cases in the mortality group, were included in the analysis. Mean age at referral in the mortality group was significantly higher when compared to the survival group (9.58 ± 5.03 VS 3.96 ± 3.13 months, p < 0.000). The proportion with infection in the mortality group was significantly higher than the survival group (p = 0.023). 44.4% of patients in the mortality group did not receive lactose-free and/or medium chain triglycerides enriched (LF/MCT) formula, and this percentage was significantly higher than the survival group (9.6%, p = 0.021). Mean platelet (PLT) count in the mortality group was significantly lower than the survival group (p = 0.010). Mean serum gamma-glutamyl transpeptidase (GGT), and total cholesterol (TCH) levels were significantly lower in the mortality group when compared to the survival group with p values of 0.001, and 0.019, respectively. Those who died had higher serum ammonium levels than survivors (p = 0.016). Mean level of citrulline was significantly lower in the mortality group compared to the survival group (p = 0.010). On the other hand, mean level of tyrosine was significantly higher in the mortality group than that of the survival group (p = 0.015).

Conclusion

Late referral, presence of infection, delayed treatment with LF/MCT formula, lower platelet count, lower levels of GGT, total cholesterol, blood citrulline, and higher level of blood ammonia and tyrosine, were associated with poor prognosis in NICCD.

Electronic supplementary material

The online version of this article (10.1186/s12887-018-1383-5) contains supplementary material, which is available to authorized users.

A Case Report: Can Citrin Deficiency Lead to Hepatocellular Carcinoma in Children?

Citrin deficiency initially presents as neonatal intrahepatic cholestasis (NICCD) and often resolves within first year of infancy. Failure to thrive and dyslipidemia caused by citrin deficiency (FTTDCD) has been recently proposed as a novel post-NICCD phenotype and its clinical features are still being established. Herein, we encountered a 2-year-old girl who was hospitalized for intermittent fever lasting 10 days. Besides pneumonia, we observed an NICCD-like phenotype with the presence of liver dysfunction, dyslipidemia, aminoacidemia, organic academia, and extremely high levels of alpha-fetoprotein (AFP). Genetic testing confirmed the diagnosis of citrin deficiency and, liver histology revealed she had already developed cirrhosis. Although, improvement of biochemical parameters and liver histology were observed after treatment that included dietary restrictions and symptomatic treatments, AFP levels remained elevated (>400 ng/ml) during a 3-year follow-up period. Moreover, liver magnetic resonance imaging (MRI) examination performed on the patient at age 5 revealed the development of multiple liver nodules with diffusion restriction on diffusion-weighted imaging (DWI). These observations highly indicate the possibility of hepatocellular carcinoma (HCC). Thus, this case reveals that an NICCD-like phenotype complicated with cirrhosis can exist during FTTDCD stage without any prior signs. It also emphasizes the necessity of monitoring AFP levels during follow-up for citrin deficiency patients with persistently high AFP level after treatment as FTTDCD may progress to HCC. Individualized treatment strategy for patients with FTTDCD also need to be explored.

A 6-Year-Old Child With Citrin Deficiency and Advanced Hepatocellular Carcinoma

We report the case of a 6-year-old boy with citrin deficiency and advanced hepatocellular carcinoma diagnosed by using imaging. He exhibited intrahepatic cholestasis 2 days after his birth and was misdiagnosed with inspissated bile syndrome at that time. The symptoms of jaundice spontaneously resolved when he was 5 months old. However, his transaminase levels remained elevated for ∼6 years, for which he received no treatment. He preferred a high-protein, high-fat, low-carbohydrate diet, which has been observed in many patients with citrin deficiency, but no clinical features of adult-onset type II citrullinemia were observed. At the age of 6 years, he was admitted to our hospital with a nonviral infection and high α-fetoprotein level; results from an abdominal MRI and computed tomography revealed multiple tumors in the liver. Because of his history of intrahepatic cholestasis in the neonatal period, he was suspected to have citrin deficiency. A genetic analysis of solute carrier family 25, member 13 revealed the presence of a homozygous 851del4 mutation, and a diagnosis of citrin deficiency was made. The patient did not qualify for liver transplantation and died 2 months later, after discharge from our hospital. Thus, this case reveals that not all patients with neonatal intrahepatic cholestasis spontaneously and totally improve, and this case is used to emphasize that patients with neonatal intrahepatic cholestasis should be managed carefully, especially in the stage of failure to thrive and dyslipidemia caused by citrin deficiency, which may lead to advanced hepatocellular carcinoma.

Jaundice revisited: recent advances in the diagnosis and treatment of inherited cholestatic liver diseases

Background

Jaundice is a common symptom of inherited or acquired liver diseases or a manifestation of diseases involving red blood cell metabolism. Recent progress has elucidated the molecular mechanisms of bile metabolism, hepatocellular transport, bile ductular development, intestinal bile salt reabsorption, and the regulation of bile acids homeostasis.

Main body

The major genetic diseases causing jaundice involve disturbances of bile flow. The insufficiency of bile salts in the intestines leads to fat malabsorption and fat-soluble vitamin deficiencies. Accumulation of excessive bile acids and aberrant metabolites results in hepatocellular injury and biliary cirrhosis. Progressive familial intrahepatic cholestasis (PFIC) is the prototype of genetic liver diseases manifesting jaundice in early childhood, progressive liver fibrosis/cirrhosis, and failure to thrive. The first three types of PFICs identified (PFIC1, PFIC2, and PFIC3) represent defects in FIC1 (ATP8B1), BSEP (ABCB11), or MDR3 (ABCB4). In the last 5 years, new genetic disorders, such as TJP2, FXR, and MYO5B defects, have been demonstrated to cause a similar PFIC phenotype. Inborn errors of bile acid metabolism also cause progressive cholestatic liver injuries. Prompt differential diagnosis is important because oral primary bile acid replacement may effectively reverse liver failure and restore liver functions. DCDC2 is a newly identified genetic disorder causing neonatal sclerosing cholangitis. Other cholestatic genetic disorders may have extra-hepatic manifestations, such as developmental disorders causing ductal plate malformation (Alagille syndrome, polycystic liver/kidney diseases), mitochondrial hepatopathy, and endocrine or chromosomal disorders. The diagnosis of genetic liver diseases has evolved from direct sequencing of a single gene to panel-based next generation sequencing. Whole exome sequencing and whole genome sequencing have been actively investigated in research and clinical studies. Current treatment modalities include medical treatment (ursodeoxycholic acid, cholic acid or chenodeoxycholic acid), surgery (partial biliary diversion and liver transplantation), symptomatic treatment for pruritus, and nutritional therapy. New drug development based on gene-specific treatments, such as apical sodium-dependent bile acid transporter (ASBT) inhibitor, for BSEP defects are underway.

Short conclusion

Understanding the complex pathways of jaundice and cholestasis not only enhance insights into liver pathophysiology but also elucidate many causes of genetic liver diseases and promote the development of novel treatments.

Molecular and clinical characterization of citrin deficiency in a cohort of Chinese patients in Hong Kong

Background and objectives: This retrospective study analysed a case series of subjects with citrin deficiency, and aims to present the molecular and clinical characterization of this disease in the Hong Kong Chinese population for the first time. Patients and Methods: Data from medical records of eighteen patients with citrin deficiency (years 2006–2015) were retrieved. Demographic data, biochemical parameters, radiological results, genetic testing results, management, and clinical outcome were collected and analysed. Results: Eighteen patients with diagnosis of citrin deficiency were recruited. All 18 patients carried at least one common pathogenic variant c.852_855delTATG in SLC25A13. Prolonged jaundice (neonatal intrahepatic cholestasis caused by citrin deficiency, NICCD) was the most common presenting symptom, in conjunction with elevated plasma citrulline, threonine, alkaline phosphatase, and alpha-fetoprotein levels. The abnormal biochemical parameters including liver derangement returned to normal range in most of the cases by 6 months of age after the introduction of a lactose-free formula. There were a few cases with atypical presentations. Two subjects did not present with NICCD, and were subsequently diagnosed later in life after their siblings presented with symptoms of citrin deficiency at one month of age and subsequently received a molecular diagnosis. One patient with citrin deficiency also exhibited multiple liver hemangioendotheliomas, which subsided gradually after introduction of a lactose-free formula. Only one patient from this cohort was offered expanded metabolic screening at birth. She was not ascertained by conducted newborn screening and was diagnosed upon presentation with cholestatic jaundice by 1 month of age. Conclusion: This is the first report of the clinical and molecular characterization of a large cohort of patients with citrin deficiency in Hong Kong. The presentation of this cohort of patients expands the clinical phenotypic spectrum of NICCD. Benign liver tumors such as hemangioendotheliomas may be associated with citrin deficiency in addition to the well-known association with hepatocellular carcinoma. Citrin deficiency may manifest in later infancy period with an NICCD-like phenotype. Furthermore, this condition is not always ascertained by expanded newborn metabolic screening testing.

Cholesterol Metabolism Is Enhanced in the Liver and Brain of Children With Citrin Deficiency

CONTEXT

Citrin-deficient infants present neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD), which resolves at 12 months. Thereafter, they have normal liver function associated with hypercholesterolemia, and a preference for lipid-rich carbohydrate-restricted diets. However, some develop adult-onset type II citrullinemia, which is associated with metabolic abnormalities.

OBJECTIVES

To identify the causes of hypercholesterolemia in citrin-deficient children post-NICCD.

DESIGN AND SETTING

We determined the concentrations of sterol markers of cholesterol synthesis, absorption, and catabolism by liquid chromatography-electrospray ionization-tandem mass spectrometry and evaluated serum lipoprotein profiles.

SUBJECTS

Twenty citrin-deficient children aged 5 to 13 years and 37 age-matched healthy children.

INTERVENTION

None.

MAIN OUTCOME MEASURES

Relationship between serum lipoproteins and sterol markers of cholesterol metabolism.

RESULTS

The citrin-deficient group had a significantly higher high-density lipoprotein cholesterol (HDL-C) concentration than did the control group (78 ± 11 mg/dL vs 62 ± 14 mg/dL, P < 0.001), whereas the two groups had similar low-density lipoprotein cholesterol and triglyceride concentrations. The concentrations of markers of cholesterol synthesis (lathosterol and 7-dehydrocholesterol) and bile acids synthesis (7α-hydroxycholesterol and 27-hydroxycholesterol) were 1.5- to 2.8-fold and 1.5- to 3.9-fold, respectively, higher in the citrin-deficient group than in the control group. The concentration of 24S-hydroxycholesterol, a marker of cholesterol catabolism in the brain, was 2.5-fold higher in the citrin-deficient group. In both groups, the HDL-C concentration was significantly positively correlated with that of 27-hydroxycholesterol, the first product of the alternative bile acid synthesis pathway.

CONCLUSIONS

HDL-C and sterol marker concentrations are elevated in citrin-deficient children post-NICCD. Moreover, cholesterol synthesis and elimination are markedly enhanced in the liver and brain of citrin-deficient children.

Early Detection and Diagnosis of Neonatal Intrahepatic Cholestasis Caused by Citrin Deficiency Missed by Newborn Screening Using Tandem Mass Spectrometry

Citrullinemia is the earliest identifiable biochemical abnormality in neonates with intrahepatic cholestasis due to a citrin deficiency (NICCD) and it has been included in newborn screening panels using tandem mass spectrometry. However, only one neonate was positive among 600,000 infants born in Sapporo city and Hokkaido, Japan between 2006 and 2017. We investigated 12 neonates with NICCD who were initially considered normal in newborn mass screening (NBS) by tandem mass spectrometry, but were later diagnosed with NICCD by DNA tests. Using their initial NBS data, we examined citrulline concentrations and ratios of citrulline to total amino acids. Although their citrulline values exceeded the mean of the normal neonates and 80% of them surpassed +3 SD (standard deviation), all were below the cutoff of 40 nmol/mL. The ratios of citrulline to total amino acids significantly elevated in patients with NICCD compared to the control. By evaluating two indicators simultaneously, we could select about 80% of patients with missed NICCD. Introducing an estimated index comprising citrulline values and citrulline to total amino acid ratios could assure NICCD detection by NBS.

Analysis of islet beta cell functions and their correlations with liver dysfunction in patients with neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD)

Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) primarily manifests in neonates or infants with hepatomegaly, liver dysfunction, and hypoglycemia. This study investigated the functions of islet beta cells and their correlations with liver dysfunction in NICCD patients.We retrospectively analyzed clinical data on liver function and islet beta cell functions for 36 patients diagnosed with NICCD and 50 subjects as the control group. The NICCD group had significantly higher total bilirubin (TBIL), direct bilirubin (DBIL), alanine aminotransferase (ALT), aspartate amino transferase (AST), gamma-glutamyl transpeptidase (GGT), alkaline phosphatase (ALP) and alpha-fetoprotein (AFP) levels and albumin/globulin ratio (A/G) (P < .05), and lower ALB and GLB levels than the control group (P < .05). The differences in fasting blood glucose (FBG), fasting insulin, C-peptide (C-P), the homeostasis model of assessment for the insulin resistance index (HOMA-IR), fasting beta cell function (FBCI), and the HOMA beta cell function index (HBCI) between the NICCD and control groups were not significant (P > .05). A linear correlation was found between FBG and fasting insulin (P < .001) and between FBG and C-P in the NICCD patients (P = .001). Fasting insulin (P = .023), HOMA-IR (P = .023), FBCI (P = .049), and HBCI (P = .048) were positively correlated with increases in the ALT level. There was no difference in islet beta cell functions between the NICCD and control groups. The liver dysfunction may be correlated with islet beta cell functions in NICCD patients.

Liver involvement in urea cycle disorders: a review of the literature

Urea cycle disorders (UCDs) are inborn errors of metabolism of the nitrogen detoxification pathway and encompass six principal enzymatic deficiencies. The aging of UCD patients leads to a better knowledge of the long-term natural history of the condition and to the reporting of previously unnoticed manifestations. Despite historical evidence of liver involvement in UCDs, little attention has been paid to this organ until recently. Hence, we reviewed the available scientific evidence on acute and chronic liver dysfunction and liver carcinogenesis in UCDs and discuss their pathophysiology. Overall, liver involvement, such as acute liver failure or steatotic-like disease, which may evolve toward cirrhosis, has been reported in all six main UCDs. Excessive glycogen storage is also a prominent histologic feature, and hypoglycemia has been reported in citrin deficiency. Hepatocarcinomas seem frequent in some UCDs, such as in citrin deficiency, and can sometimes occur in non-cirrhotic patients. UCDs may differ in liver involvement according to the enzymatic deficiency. Ornithine transcarbamylase deficiency may be associated more with acute liver failure and argininosuccinic aciduria with chronic liver failure and cirrhosis. Direct toxicity of metabolites, downstream metabolic deficiencies, impaired tricarboxylic acid cycle, oxidative stress, mitochondrial dysfunction, energy deficit, and putative toxicity of therapies combine in various ways to cause the different liver diseases reported.

Molecular diagnosis of citrin deficiency in an infant with intrahepatic cholestasis: identification of a 21.7kb gross deletion that completely silences the transcriptional and translational expression of the affected SLC25A13 allele

Neonatal Intrahepatic Cholestasis caused by Citrin Deficiency (NICCD) arises from biallelic SLC25A13 mutations, and SLC25A13 analysis provides reliable evidences for NICCD definite diagnosis. However, novel large insertions/deletions in this gene could not be detected just by conventional DNA analysis. This study aimed to explore definite diagnostic evidences for an infant highly-suspected to have NICCD. Prevalent mutation screening and Sanger sequencing of SLC25A13 gene just revealed a paternally-inherited mutation c.851_854del4. Nevertheless, neither citrin protein nor SLC25A13 transcripts of maternal origin could be detected on Western blotting and cDNA cloning analysis, respectively. On this basis, the hidden maternal mutation was precisely positioned using SNP analysis and semi-quantitative PCR, and finally identified as a novel large deletion c.-3251_c.15+18443del21709bp, which involved the SLC25A13 promoter region and the entire exon 1 where locates the translation initiation codon. Hence, NICCD was definitely diagnosed in the infant. To the best of our knowledge, the novel gross deletion, which silenced the transcriptional and translational expression of the affected SLC25A13 allele, is the hitherto largest deletion in SLC25A13 mutation spectrum. The Western blotting approach using mitochondrial protein extracted from expanded peripheral blood lymphocytes, of particular note, might be a new minimally-invasive and more-feasible molecular tool for NICCD diagnosis.

Blood glucose and insulin and correlation of SLC25A13 mutations with biochemical changes in NICCD patients

Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) is a hereditary metabolic disease arising from biallelic mutations of SLC25A13. This study aimed to explore the characteristics of fasting blood glucose (FBG), fasting insulin (FINS) and C-peptide (C-P) levels in NICCD infants, analyze their SLC25A13 genetic mutations and further discuss the correlation between SLC25A13 genetic mutations and biochemical changes. Seventy-two cases of infants with cholestasis disease were gathered. Among them, 36 cases with NICCD diagnosis were case group. Meanwhile, 36 cases with unknown etiology but excluded NICCD were control group. FBG, FINS, C-P, ALT, AST, GGT, ALP, TG, HDL-C, LDL-C and Non-HDL-C were collected from all subjects, and DNA was extracted from venous blood for SLC25A13 mutations detection. The incidence of hypoglycemia was 3% in NICCD group. There were no significant statistical difference of FBG, FINS and C-P between NICCD and INC groups ( P > 0.05). ALT, LDL-C and Non-HDL-C levels in NICCD group were lower than the INC group, while SLC25A13 mutations were associated with the level of GGT ( P < 0.05). Ten different SLC25A13 genetic mutations were detected, among which, 851del4, IVS16ins3kb, IVS6+5 G > A and 1638ins23 mutations made up 82% of all mutations. The incidence of hypoglycemia may be higher in small gestational age infants with NICCD. Low LDL-C may be one of the characteristics of dyslipidemia in NICCD infants. There was a correlation between SLC25A13 gene mutations distribution and the GGT level, but the meaning of this finding remains to be further in-depth study. Impact statement This study aims to compare FBG, FINS, C-P, other biochemical and clinical manifestations between NICCD and non-NICCD infants, and discuss differential diagnosis of NICCD and INC beyond the genetic analysis. And investigate the correlation between SLC25A13 genetic mutations and biochemical changes. This work presented that incidence of hypoglycemia may be higher in small gestational age infants with NICCD. Low LDL-C may be one of the characteristics of dyslipidemia in NICCD infants. There was a correlation between SLC25A13 gene mutations distribution and the GGT level.

[Current status of research on infantile cholestatic liver disease in China: a visualization analysis]

OBJECTIVE

To investigate the current status of research on infantile cholestatic liver disease in China and future research trends.

METHODS

A co-word analysis was performed in October 2016. Document retrieval and screening were performed in the Chinese databases CNKI and Wanfang Data using "cholestasis" and "infant" as key words. Excel 2010 was used to establish a co-occurrence matrix of high-frequency key words, and Ucinet 6.0 and Netdraw were used to develop a visualized network of these high-frequency key words.

RESULTS

A total of 383 articles were included. The co-occurrence analysis showed that "infant" and "cholestasis" were the core of research in this field, and "infantile hepatitis syndrome", "neonate", "intrahepatic", "biliary atresia", "heredity and metabolism", "hepatitis", "cytomegalovirus", "jaundice", and "conjugated bilirubin" were main research topics. Most of the other articles focused on "parenteral nutrition", "hepatobiliary imaging", "gene mutation", and "liver biopsy". There were relatively few articles on surgical diagnostic techniques and treatment for this disease.

CONCLUSIONS

The research on infantile cholestatic liver disease in China focuses on etiology and differential diagnosis, and genetic diagnosis has become a hot topic in recent years. The research on treatment should be enhanced, and new diagnostic techniques are the research interest in future.

Circulating tricarboxylic acid cycle metabolite levels in citrin-deficient children with metabolic adaptation, with and without sodium pyruvate treatment

Citrin deficiency causes adult-onset type II citrullinemia (CTLN-2), which later manifests as severe liver steatosis and life-threatening encephalopathy. Long-standing energy deficit of the liver and brain may predispose ones to CTLN-2. Here, we compared the energy-driving tricarboxylic acid (TCA) cycle and fatty acid β-oxidation cycle between 22 citrin-deficient children (age, 3-13years) with normal liver functions and 37 healthy controls (age, 5-13years). TCA cycle analysis showed that basal plasma citrate and α-ketoglutarate levels were significantly higher in the affected than the control group (p<0.01). Conversely, basal plasma fumarate and malate levels were significantly lower than those for the control (p<0.001). The plasma level of 3-OH-butyrate derived from fatty acid β-oxidation was significantly higher in the affected group (p<0.01). Ten patients underwent sodium pyruvate therapy. However, this therapy did not correct or attenuate such deviations in both cycles. Sodium pyruvate therapy significantly increased fasting insulin secretion (p<0.01); the fasting sugar level remained unchanged. Our results suggest that citrin-deficient children show considerable deviations of TCA cycle metabolite profiles that are resistant to sodium pyruvate treatment. Thus, long-standing and considerable TCA cycle dysfunction might be a pivotal metabolic background of CTLN-2 development.

SLC25A13 cDNA cloning analysis using peripheral blood lymphocytes facilitates the identification of a large deletion mutation: Molecular diagnosis of an infant with neonatal intrahepatic cholestasis caused by citrin deficiency

Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) is an autosomal recessive disorder resulting from biallelic mutations of the SLC25A13 gene. Due to the lack of well‑recognized clinical or biochemical diagnostic criteria, the definitive diagnosis of this disease relies on the genetic analysis of SLC25A13 at present. As novel large deletion/insertion mutations of the SLC25A13 gene are difficult to detect using routine DNA analytic approaches, the timely diagnosis of patients with these types of mutations remains a challenge. The present study aimed to examine SLC25A13 mutations in an infant with a suspected diagnosis of NICCD. DNA was extracted from blood samples, and SLC25A13 mutations were examined by screening for high‑frequency mutations and Sanger sequencing. Reverse transcription-polymerase chain reaction and cDNA cloning analyses were then performed using peripheral blood lymphocytes (PBLs) to identify the obscure mutation. The results demonstrated that the infant was heterozygous for a paternally‑inherited mutation, c.851_854del4, and a maternally‑inherited large deletion, c.1019_1177+893del, which has not been reported previously. A positive diagnosis of NICCD was made, and the infant responded favorably to a galactose‑free and medium‑chain triglyceride‑enriched formula. The present study confirmed the effectiveness of this formula in NICCD therapy, enriched the SLC25A13 mutational spectrum and supported the feasibility of cDNA cloning analysis using PBLs as a molecular tool for facilitating the identification of large SLC25A13 deletions.