Liver transplantation for neonatal-onset citrullinemia

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.

Lethality rescue and long-term amelioration of a citrullinemia type I mouse model by neonatal gene-targeting combined to SaCRISPR-Cas9

Citrullinemia type I is a rare autosomal-recessive disorder caused by deficiency of argininosuccinate synthetase (ASS1). The clinical presentation includes the acute neonatal form, characterized by ammonia and citrulline accumulation in blood, which may lead to encephalopathy, coma, and death, and the milder late-onset form. Current treatments are unsatisfactory, and the only curative treatment is liver transplantation. We permanently modified the hepatocyte genome in lethal citrullinemia mice (Ass1fold/fold) by inserting the ASS1 cDNA into the albumin locus through the delivery of two AAV8 vectors carrying the donor DNA and the CRISPR-Cas9 platform. The neonatal treatment completely rescued mortality ensuring survival up to 5 months of age, with plasma citrulline levels significantly decreased, while plasma ammonia levels remained unchanged. In contrast, neonatal treatment with a liver-directed non-integrative AAV8-AAT-hASS1 vector failed to improve disease parameters. To model late-onset citrullinemia, we dosed postnatal day (P) 30 juvenile animals using the integrative approach, resulting in lifespan improvement and a minor reduction in disease markers. Conversely, treatment with the non-integrative vector completely rescued mortality, reducing plasma ammonia and citrulline to wild-type values. In summary, the integrative approach in neonates is effective, although further improvements are required to fully correct the phenotype. Non-integrative gene therapy application to juvenile mice ensures a stable and very efficient therapeutic effect.

Urea cycle disorders and indications for liver transplantation

Urea cycle disorders (UCD) are inborn errors of metabolism caused by deficiency of enzymes required to convert nitrogen from ammonia into urea. Current paradigms of treatment focus on dietary manipulations, ammonia scavenger drugs, and liver transplantation. The aim of this study was to describe the characteristics and indication of liver transplantation in UCD in a tertiary hospital. We performed a retrospective study of children with UCD seen in the period 2000-2021. Data was collected on clinical onset, hyperammonemia severity, evolution and liver transplantation. There were 33 patients in the study period, whose diagnosis were: ornithine transcarbamylase (OTC, n = 20, 10 females), argininosuccinate synthetase (ASS, n = 6), carbamylphosphate synthetase 1 (CPS1, n = 4), argininosuccinate lyase (ASL, n = 2) and N-acetylglutamate synthetase (NAGS, n = 1) deficiency. Thirty one were detected because of clinical symptoms (45% with neonatal onset). The other 2 were diagnosed being presymptomatic, by neonatal/family screening. Neonatal forms (n = 14) were more severe, all of them presented during the first week of life as severe hyperammonemia (mean peak 1,152 µmol/L). Seven patients died (6 at debut) and all survivors received transplantation. There was no mortality among the late forms. Of the 27 patients who did not die in the neonatal period, 16 (59%) received liver transplantationwith 100% survival, normal protein tolerance and usual need of citrulline supplementation. The transplant's metabolic success was accompanied by neurologic sequelae in 69%, but there was no progression of brain damage. Decision of continuous medical treatment in 11 patients appeared to be related with preserved neurodevelopment and fewer metabolic crises.

Managing recurrent portal steal in auxiliary liver transplantation for non-cirrhotic metabolic liver disease

BACKGROUND

APOLT has been proposed as a treatment modality for certain types of NCMLD. While the short-term outcomes of this operation have been comparable with orthotopic LT, its long-term outcomes have sparsely been reported. We present one such case of Citrullinemia type I who underwent APOLT and developed recurrent PS.

CASE REPORT

A 2-year-old male child with a diagnosis of Citrullinemia type I underwent APOLT with a left lateral segment from a split deceased donor liver, and his postoperative period was unremarkable. Ammonia-lowering agents were stopped 1 week following the operation and the child was discharged home on a normal diet. Four years following APOLT, the child presented with altered sensorium and seizures. A diagnosis of PS was made. Subsequent to an embolization of the native liver's right anterior portal vein his sensorium improved and he remained clinically stable on a normal diet. Six years following the APOLT, the child again presented with features of acute encephalopathy. Imaging was suggestive of PS. A portal vein embolization of the native portal vein was performed and the child's clinical condition improved. At 6 months' follow-up, the child remains well on a normal diet.

CONCLUSIONS

While the early impediments in this technique may have been overcome, in the absence of any realistic clinical application gene therapy, the debate of long-term phenotypic metabolic correction for NCMLD by APOLT needs to be revisited.

Asymptomatic ASS1 carriers with high blood citrulline levels

INTRODUCTION

Citrullinemia Type 1 (CTLN1) is an autosomal recessive disorder caused by variants in the ASS1 gene. This study intends to clarify the etiology of false positives in newborn screening for citrullinemia.

METHOD

Newborns who had elevated dried-blood spot citrulline levels were enrolled, and medical records were reviewed retrospectively. Common ASS1 variants were screened using high-resolution melting analysis.

RESULT

Between 2011 and 2021, 130 newborns received confirmatory testing for citrullinemia, 4 were found to be patients for CTLN1; 11 were patients with citrin deficiency; and 49 newborns were confirmed to be carrying one pathogenic ASS1 variant. The incidence of CTLN1 was 1 in 188,380 (95% confidence interval: 1 in 73,258 to 1 in 484,416). All ASS1 variants studied in this cohort were located in exons 11 to 15, which encode the tetrameric interface regions of the ASS1 protein. Among 10 ASS1 carriers with elevated citrulline levels and complete sequence data, four (40%) revealed additional non-benign ASS1 variants; in contrast, only 2 of the 26 controls (7.7%), with normal citrulline levels, had additional ASS1 variants.

CONCLUSION

Heterozygote ASS1 variants may lead to a mild elevation of blood citrulline levels: about 2-6 times the population mean. Molecular testing and family studies remain critical for precise diagnosis, genetic counseling, and management.

Role of liver transplantation in urea cycle disorders: Report from a nationwide study in Japan

Urea cycle disorders (UCDs) are inherited metabolic diseases causing hyperammonemia by defects in urea cycle enzymes or transporters. Liver transplantation (LT) currently is the only curative treatment option until novel therapies become available. We performed a nationwide questionnaire-based study between January 2000 and March 2018 to investigate the effect of LT in patients with UCDs in Japan. A total of 231 patients with UCDs were enrolled in this study. Of them, a total of 78 patients with UCDs (30 male and 16 female ornithine transcarbamylase deficiency (OTCD), 21 carbamoyl phosphate synthetase 1 deficiency (CPSD), 10 argininosuccinate synthetase deficiency (ASSD) and 1 arginase 1 deficiency (ARGD)) had undergone LT. Concerning the maximum blood ammonia levels at the onset time in the transplanted male OTCD (N = 28), female OTCD (N = 15), CPSD (N = 21) and ASSD (N = 10), those were median 634 (IQR: 277-1172), 268 (211-352), 806 (535-1382), and 628 (425-957) μmol/L, respectively. The maximum blood ammonia levels in female OTCD were thus significantly lower than in the other UCDs (all P < .01). LT was effective for long-term survival, prevented recurrent hyperammonemia attack, and lowered baseline blood ammonia levels in patients with UCDs. LT had limited effect for ameliorating neurodevelopmental outcome in patients with severe disease because hyperammonemia at the onset time already had a significant impact on the brain. Patients with ASSD may be more likely to survive without cognitive impairment by receiving early LT despite severe neonatal hyperammonemia ≥ 360 μmol/L. In patients with neonatal onset OTCD or CPSD, there may be additional factors with adverse effects on the brain that are not improved by LT.

Outcome of Liver Transplantation for Neonatal-onset Citrullinemia Type I

BACKGROUND

We evaluated the outcome of liver transplantation (LT) in neonatal-onset citrullinemia type I patients, especially its impact on neurological deficits and developmental retardation.

METHODS

From October 2006 to October 2019, 5 of the 2003 children who received LT at Ren Ji Hospital had been diagnosed with citrullinemia type I. The primary indication for transplantation was repeated metabolic compensation and developmental retardation in 4 patients and prophylactic transplantation in the other. Among them, 3 patients received living donor LT and 2 received orthotopic LT.

RESULTS

All recipients had successfully recovered within the median follow-up period of 32 months (range, 6-54 mo). Transplantation restored citrulline metabolism and liver function. Plasma ammonia and citrulline concentration decreased to normal levels with no further hyperammonemic episodes being reported, even after normal diet intake began. Meanwhile, uracil-2 and orotic acid were not detected in urinary excretion. Strikingly, patients suffered developmental retardation before LT showed improved psychomotor ability and significant catch-up growth during the follow-up period. Cognitive ability, including language skills and academic performance, also greatly improved. Three patients had sustained brain injuries and exhibited severe neurological deficits before transplantation, especially repeated generalized tonic-clonic seizures. LT halted neurological deterioration and controlled seizure episodes, which further facilitated the intellectual development and improvement of life quality.

CONCLUSIONS

LT is an effective treatment for neonatal-onset citrullinemia type I patients, which reverses metabolism decompensation and improves quality of life. For patients who have suffered severe hyperammonemic insults, LT should be conducted at an early age to avoid further neurological or developmental deficits.

Percutaneous removal of biliary stones post-liver transplant in a pediatric patient: Case report and review of the literature

This case report describes an 8-year-old girl who underwent a segmental LT for a primary diagnosis of citrullinemia at the age of 12 months. She presented with cholangitis secondary to stenosis of the biliary-enteric anastomosis. MRI revealed dilatation of intrahepatic bile ducts associated with multiple stones. An endoscopic approach failed to decompress the bile ducts and remove the stones. A percutaneous approach was then undertaken. After placement of a temporary external biliary drain for 12 days, a 26 French sheath was placed to access the bile ducts. Using a 14Fr flexible cystoscope, 80%-90% of the biliary stones were removed. This was followed by antegrade balloon dilatation of the biliary-enteric anastomosis. Two months later, the procedure was repeated, resulting in complete clearance of the biliary stones. An internal-external biliary drain was maintained in placed for 10 months. The patient has been asymptomatic, with no evidence of stone recurrence for 13 months after drain removal. Percutaneous biliary stone removal is commonly performed in adults with non-transplanted livers, especially in complex cases, and has also been shown to be successful in the pediatric population. However, it is rarely reported in transplanted livers in adults, and to the best of our knowledge, no pediatric cases have been reported. This case illustrates that this technique can be successfully utilized in pediatric LT patients.

Citrullinemia Type 1: Behavioral Improvement with Late Liver Transplantation

Citrullinemia Type 1 (also known as classic citrullinemia) is a rare autosomal recessive urea cycle disorder due to reduced activity of argininosuccinate synthetase 1; characterized by hyperammonemia leading to neurological damage. The authors report a case of an 8-y boy who was diagnosed with Citrullinemia Type 1 at birth which was anticipated prenatally due to family history. His diagnosis was confirmed as a homozygous mutation (Exon 15: c.1168G > A (p.G390R)) of ASS gene. Inspite of being on a protein-free diet and ammonia scavenging treatment; the patient developed recurrent episodes of encephalopathy and seizures; complicated with behavioral issues. The patient underwent living related liver-transplantation from his mother (heterozygous carrier of the same mutation). Peri-transplant management of ammonia and plasma amino acid levels is challenging and has been highlighted. It is important to consider liver transplantation as it corrects the genetic deficiency of ASS resulting in the reversal of neuro-behavioral changes, as was seen in index patient.