Patient 1 was a Han boy born at 32 + 2 weeks of gestation and with a weight of 1150 g at birth. He is the first child of a Chinese couple. His mother was 28 years old during pregnancy and had no history of spontaneous abortion or any genetic diseases. She has received progesterone treatment for one month due to low levels of human chorionic gonadotropin and progesterone during the first trimester. The boy was admitted to the neonatal care unit due to his premature delivery and shortness of breath. He was also observed to have jaundice on the second day after birth. Irreversible severe hypoalbuminemia (minimum 23 g/L) and anemia (minimum 52 g/L) were observed as well after repeated infusion of red cell suspension and albumin (Table 1). Jaundice continued to be present despite receiving treatments including nutrition support, continuous positive airway pressure, antibiotics, ursodeoxycholic acid, and fat-soluble vitamin supplementation. The boy was admitted to the local centre because he was experiencing persistent jaundice and failure to thrive. When he was sent to us, he was 5 months and 12 days old with the corrected gestational age being 3 months and 18 days. The boy had a circumference of the head 37 cm (< percentile (P) 1), length 49 cm (< P1), weight 4.0 kg (< P1). He fell behind in the development of the nervous system as the boy could only raise his head for 1 min, but couldn’t turn over. The physical examination indicated a chubby face (Supplement Fig. 1.A&B) with moderate to severe jaundice. Abdominal distension was noticed with hepatosplenomegaly (liver edge 4 cm and spleen tip 2 cm below costal margin). No abnormality was identified on specialist neurological examination.

The laboratory examination revealed severe microcytic hypochromic anemia (minimum 52 g/L, mean corpuscular volume of 65-87fL, mean corpuscular hemoglobin of 18.5-30pg, Mean corpuscular hemoglobin concentration 285–346 g/L, reticulocyte 1-6.9%) after bone marrow cytology. No abnormalities were observed in serum iron, unsaturated iron binding capacity, total iron binding capacity, transferrin saturation, thalassemia gene, G6PD enzyme activity, folic acid, and Vitamin B12 levels. and Coombs test, except for ferritin at 1328ng/ml (normal reference range, NRM: 26-287ng/mL). Hepatobiliary-system biomarker values included total bilirubin (TB) 21.7-187.3umol/L, direct bilirubin (DB) 7.8-122.2umol/L, alanine aminotransferase (ALT) 3-196.9U/L, aspartate aminotransferase (AST) 22-441.9U/L, total bile acids (TBA) 92.1-278.4umol/L, progressive declined gamma-glutamyl transferase (GGT) level (185-42U/L) with low albumin (a minimum of 18.3 g/L), coagulation abnormality (international normalized ratio, INR 2.1–2.4, after vitamin K1 injection), with normal ammonia. The level of alpha-fetoprotein was 19665ng/mL (NRM: <28ng/mL). Blood analysis by tandem mass spectrometry showed elevated levels of tyrosine, methionine, and arginine during liver failure. No abnormalities were observed on TORCH or hepatitis-virus serologic studies, on blood and urine culture, or in values for fasting cortisol and adrenocorticotropic-hormone levels, biomarkers of thyroid function, immunoglobulins, autoantibodies, lymphocyte subsets, urinary organic acids, fasting blood glucose, blood ketones, and lipids.

Computerised tomograms of the thorax (Supplement Fig. 1. C-F) showed exudation in both lungs with decreased thoracic bone density. Findings on brain magnetic-resonance imaging suggested myelination less than in full-term children of the same postnatal age. Whole exome sequencing indicated biallelic variation in LARS1 [c.1284G > A (p.Pro428Pro); c.3379 C > T (p.Arg1127Ter)]. The patient’s clinical signs improved, with resolution of liver failure, after infusion of red blood cell suspension, albumin, immunoglobulin, and cefepime as well as with nutritional support, ursodeoxycholic acid (UDCA), and fat-soluble vitamins. However, after discharge from hospital at 6.5 months, the boy’s liver function deteriorated sharply with severe hypoproteinemia and severe anemia after development of fever and cough. He died in multiple organ failure aged 8.4 month.

Patient 2 was a boy, the second child of a non-consanguineous couple who had no remarkable medical history. He was born full-term, at 39 weeks and 2 days with a normal birth weight (3700 g). He developed diarrhea shortly after birth and was transferred to our center because of aggravated cholestasis. At 34 days of age, laparoscopic biliary exploration was performed to exclude biliary atresia due to the presence of alcoholic stools. The liver function progressively worsened, with coagulopathy (INR 2.62), anemia (minimum 82 g/L), hypoalbuminemia (minimum 18 g/L), and hypoglycemia (2.4mmol/L). Whole exome sequencing indicated biallelic variation in the LARS1 gene [c.1321 C > T (p.Arg441Ter); c.149 C > G (p.Ala50Gly)]. Nutrition supplement support and UDCA treatment. The boy died at home (at parental request) in liver failure, with unresolved diarrhea, aged 2 month.

Patient 3 is a female. She was born prematurely at 35 weeks and 2 days of gestation to a non-consanguineous couple with a low birth weight of 1400 g (< P3). Her mother experienced gestational hypertension during pregnancy, and following birth, the patient experienced asphyxia and rescue. The patient was noted to have jaundice on the second day after birth. Increased levels of direct bilirubin were observed on the ninth day after birth. An increase in transaminase levels was noted until one month of age. The child was diagnosed with anemia (minimum 77 g/L), hypoalbuminemia (minimum 20 g/L), coagulopathy (INR = 2.62) and hyperammonemia (111umol/L). Physical examination found hepatomegaly. Elevated citrulline was found by blood analysis using tandem mass spectrometry. Whole exome sequencing indicated biallelic variation in the LARS1 gene [c.497T > C (p.Leu166Pro); c.2806T > C (p.Cys936Arg)]. The patient’s condition greatly improved and she had been discharged from the hospital after receiving anti-infection treatment, infusion of red blood cell suspension, albumin, immunoglobulin, and nutritional support. Additionally, UDCA and fat-soluble vitamins were also administered during the hospital stay. However, the girl died at age of 6 month in acute liver failure associated with fever.

The algorithm employed is schematized in Fig. 1. PubMed (https://pubmed.ncbi.nlm.nih.gov/) was searched for the terms “leucyl-tRNA synthetase 1”, “LARS1”, “infantile liver failure syndrome type 1”, and “ILFS1”. Descriptions of patients with confirmed LARS1 variants were collected. In all, 33 [1, 4, 6,7,8,9,10,11,12,13,14,15,16] cases from 14 publications were identified. Clinical manifestations, laboratory values, histopathologic findings in liver, and LARS1 status were reviewed.

Diagram of screening and selection of included cases

Among the 36 patients enrolled, 22 were male and 13 were female; gender in one was not specified (Table 2). IUGR was noted in 31 patients (31/32). 14 of 23 patients were reported to have had premature delivery. The ages of disease onset ranged from 0 day after birth to 23 years, with a median age of 2 months. 31 of 32 patients had been diagnosed with IUGR.

The main clinical signs presented by the patients included failure to thrive (30/31), anaemia (32/33), and hypoalbuminemia (32/32). Furthermore, 34 out of 36 patients had liver involvement, including 3 out of 34 with coagulation abnormalities, 17 out of 34 with acute liver failure, 7 out of 34 with recurrent liver failure, 9 out of 12 with jaundice, and 32 out of 34 with elevated enzymes. Additionally, 28 out of 35 patients exhibited nervous system involvement, including 25 out of 30 with mental retardation, 9 out of 18 with encephalopathy, and 22 out of 29 with seizures. Fifteen out of 18 patients experienced hepatomegaly and/or splenomegaly, while 7 out of 34 patients had renal involvement, with 1 patient having renal calculus, 5 having kidney failure, and 1 having renal tubular injury. Muscle involvement was also present in 15 out of 31 patients, with 13 out of 27 having hypotonia and 2 out of 4 having skeletal muscle abnormalities. Hypoglycemia was reported in 12 out of 27 patients, and hyperammonemia was reported in 6 out of 28 patients. Finally, a chubby face was observed in 2 out of 4 patients. These findings are summarized in Table 2 and Table S1.

There were 11 cases that died between the ages of 2 months and 8 years. One patient survived at 3 years during last follow-up after undergone liver transplantation for acute liver failure at the age of 4 months. Seven cases died due to multiple organ failure induced by liver failure before reaching the age of 1 year. Three cases died due to infection-related or associated encephalopathy at the ages of 20 months, 4 years, and 8 years respectively. Among the 24 children whom survived with their own native liver at the last follow-up, 18 had a follow-up age larger than 3 years, but another 6 children had no follow-up information at the age of 3 years. In addition, it is interesting to note that cases older than 2 years exhibited repeated elevations of transaminase, but no cases of liver failure were observed.

Whole exon sequencing indicated biallelic variation in the LARS1 gene was observed in the three cases identified in our medical center, i.e., Case1: c.1284G > A (p.Pro428Pro) / c.3379 C > T (p.Arg1127Ter); Case 2: c.497T > C (p.Leu166Pro) / c.2806T > C (p.Cys936Arg); Case 3: c.1321 C > T (p.Arg441Ter) / c.149 C > G (p.Ala50Gly)]. Six novel variants were identified in the three new patients, including two nonsense variants, three missense variants and one synonymous variant. The pathogenicity of the newly discovered missense LARS1 variants were assessed using in silico tools (Tables 3 and 4). Of the reported cases, 32 had complete genetic data and 34 variants, including frameshift variants, nonsense variants, splice site variants, and missense variants, were identified. The genetic mutations of c.1118 A > G (p.Tyr373Cys), c.245 A > G (p.Lys82Arg), c.1292T > A (p.Val431Asp) and c.3313 C > T (p.Arg1105Ter) were identified in thirteen, nine, eight and four alleles, respectively. The mutation of c.3420del (p.Ile1141PhefsTer12) was found in three alleles, while the mutations of c.1283 C > T (p.Pro428Leu), c.1838_1843del (p.Gly613_Leu615delinsVal), c.2445G > T (p.Met815Ile), and c.587G > C (p.Gly196Ala) each occurred two times (Table 4). However, no significant correlations were observed between the type of variants and the presence of liver failure or the severity of diseases among reviewed patients (Supplementary Material 1, Supplementary Table S1).

Out of the three new cases, liver biopsy specimens were obtained from case 3 by needle biopsy. The biopsy of this case showed hepatocyte diffuse steatosis, cholestasis, fibrosis, and regional iron deposition, as displayed in Fig. 2. No liver biopsies were performed for case 1 and case 2 due to liver failure that occurred during hospitalization. Out of the 33 reported cases, 14 showed pathological findings and the common manifestations included steatosis (7/14) with mixed bulla and vesicles in some of these cases, liver fibrosis (10/14) and cirrhosis (6/14) (See Table 3).

Histopathologic features, liver biopsy specimen, Patient 3. Ballooning and steatosis characterize hepatocytes, with focal rosetting. Flecks of bile pigment are seen in hepatocyte cytoplasm, as are occasional canalicular bile plugs. Stainable iron is present in Kupffer cells. Portal-tract fibrosis is mild to moderate, with perisinusoidal extension, spurring, and suggestions of early portal – portal bridging. A – E, respectively hematoxylin and eosin; periodic acid – Schiff technique; Perls’ stain for iron; Masson’s trichrome stain; and reticulin stain. For original magnifications, see individual images

Kaplan-Meier plotter analysis indicated that early age of onset and occurrence of liver failure were the main factors associated with the prognosis of patients. We used the Kaplan-Meier method to perform survival analysis and assessed the association between patients’ demographic data, such as the child’s gender and age of onset (before or after 3 months), and the main clinical manifestations. The primary clinical manifestations that were considered included liver failure, premature delivery, failure to thrive, anemia, hypoalbuminemia, nervous system involvement, hepatomegaly and/or splenomegaly, renal involvement, muscle involvement, hypoglycemia, and hyperammonemia. We also analyzed patients’ follow-up information, such as age at death or liver transplantation, censoring during follow-up, or their last clinical contact as recorded. As a result, no significant correlation between the prognosis of patients and the clinical curse of patients was found except for the age of onset (P = 0.0015, Hazard ratio = 12.29, 95% CI = 3.74–40.3) and the occurrence of liver failure (P = 0.0343, Hazard ratio = 6.57, 95% CI = 1.96-22.0) (Fig. 3, other data were not shown).

Kaplan-Meier plotter analyse: A the early age of onset (less than 3 months) and B the occurrence of liver failure was associated with poor prognosis (died or underwent liver transplantation)