Outcome of Liver Transplantation for Neonatal-onset Citrullinemia Type I

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.

A glance at transient hyperammonemia of the newborn: Pathophysiology, diagnosis, and treatment: A review

Hyperammonemia is the excessive accumulation of ammonia in the blood, and is usually defined as a plasma level above 100 µmol/L in neonates or above 50 µmol/L in term infants, children, and adolescents. Patients with hyperammonemia usually experience life-threatening neuropsychiatric symptoms, especially newborns. It is routinely caused by inherited metabolic diseases and also by acquired disorders, such as liver failure, portosystemic shunting, gastrointestinal hemorrhage, ureterosigmoidostomy, renal tubular acidosis, hypoxic ischemic encephalopathy, infections with urea-metabolizing organisms, and some drugs. Transient hyperammonemia of the newborn (THAN) is a special type of hyperammonemia acknowledged in the field of metabolic disease as an inwell-defined or well-understood entity, which can be diagnosed only after the exclusion of genetic and acquired causes of hyperammonemia. Although the prognosis for THAN is good, timely identification and treatment are essential. Currently, THAN is underdiagnosed and much less is mentioned for early diagnosis and vigorous treatment. Herein, we present common themes that emerge from the pathogenesis, diagnosis, and management of THAN, based on current evidence. When a newborn presents with sepsis, intracranial hemorrhage, or asphyxia that cannot explain coma and seizures, doctors should always keep this disease in mind.

Novel Gene-Correction-Based Therapeutic Modalities for Monogenic Liver Disorders

The majority of monogenic liver diseases are autosomal recessive disorders, with few being sex-related or co-dominant. Although orthotopic liver transplantation (LT) is currently the sole therapeutic option for end-stage patients, such an invasive surgical approach is severely restricted by the lack of donors and post-transplant complications, mainly associated with life-long immunosuppressive regimens. Therefore, the last decade has witnessed efforts for innovative cellular or gene-based therapeutic strategies. Gene therapy is a promising approach for treatment of many hereditary disorders, such as monogenic inborn errors. The liver is an organ characterized by unique features, making it an attractive target for in vivo and ex vivo gene transfer. The current genetic approaches for hereditary liver diseases are mediated by viral or non-viral vectors, with promising results generated by gene-editing tools, such as CRISPR-Cas9 technology. Despite massive progress in experimental gene-correction technologies, limitations in validated approaches for monogenic liver disorders have encouraged researchers to refine promising gene therapy protocols. Herein, we highlighted the most common monogenetic liver disorders, followed by proposed genetic engineering approaches, offered as promising therapeutic modalities.

Long-Term Results of Pediatric Liver Transplantation for Progressive Familial Intrahepatic Cholestasis

We analyzed the long-term survival rate and development of progressive familial intrahepatic cholestasis (PFIC) patients after liver transplantation (LT). From October 2007 to May 2019, 41 patients were diagnosed as PFIC (type I-III) and received LT in Ren Ji Hospital due to end-stage liver diseases. The median age at LT was 2.93 years, with 75.6% of patients receiving living donor liver transplantation (LDLT). The 5- and 10-year patient survival rates after LT were 92.7% and 92.7%, respectively, and no difference was found among the three subtypes of PFIC. Two PFIC type II patients received re-transplantation due to vascular complications. Liver function and bile acid metabolism returned to normal levels in all living recipients. Catch-up growth was recorded as the height and weight Z scores increased from −2.53 and −1.54 to −0.55 and −0.27 with a median follow-up time of 5.55 years. Improved psychomotor ability and age-appropriate study ability was also observed. A total of 72.4% of school-aged recipients exhibited average academic performance. Diarrhea was reported in all PFIC type I recipients but resolved after resin absorptive treatment. However, allograft steatosis occurred in one PFIC type I patient and exhibited a “remission–relapse circle” under the treatment of cholestyramine. In conclusion, LT is an effective treatment for end-stage PFIC patients with encouraging long-term survival rate and development. However, allograft steatosis should be closely monitored in PFIC type I patients even if diarrhea has been well treated.

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.

Citrullinemia type I in Chinese children: Identification of two novel argininosuccinate synthetase gene mutations

BACKGROUND

In this study, we evaluated the clinical characteristics, prognosis, and gene mutations of five children with citrullinemia type I (CTLN1) diagnosed in our department and identified two novel ASS1 gene mutations.

METHODS

We examined the clinical characteristics, prognosis, and gene mutations of the five children through data collection, tandem mass spectrometry, and whole-exon sequencing. MutationTaster, regSNP-intron, and SWISS-MODEL were used for bioinformatic analysis to evaluate the two novel gene mutations. We analyzed differences in blood ammonia and citrulline levels based on clinical phenotypes. Finally, we reviewed the medical literature describing Chinese children with CTLN1.

RESULTS

ASS1 C773 + 6T > G and c.848 delA as well as c.952_953 del insTT and c.133G > A have not been previously reported in the Human Gene Mutation Database. Using MutationTaster and regSNP-intron, we predicted that these mutations affected protein function. The 3D structure obtained using SWISS-MODEL supported this prediction. Through comparative analysis showed that the ammonia level of the neonatal type was markedly higher than that of other types, whereas citrulline levels did not differ between groups.

CONCLUSION

We identified two novel mutations that cause disease. The blood ammonia level of neonatal form citrullinemia was markedly higher than that of other types. The genotype-phenotype association in Chinese patients remains unclear and should be further evaluated in genetic studies of larger sample sizes.