Citrin deficiency (CD), caused by mutations in the SLC25A13 gene, is a rare autosomal recessive urea cycle disorder with variable clinical presentations depending on age. These include neonatal intrahepatic cholestasis (NICCD), failure to thrive with dyslipidemia, and adult-onset type II citrullinemia. Patients with NICCD typically present with transient intrahepatic cholestasis in infancy, which often resolves spontaneously by one year of age; however, some may progress to severe complications later in life. Four cases diagnosed with NICCD phenotype are presented. All patients presented with neonatal cholestasis, hypertransaminasemia, galactosuria, and elevated citrulline levels. Molecular analysis identified three disease-causing variants: two previously reported variants, c.955C>T (p.Arg319*) and c.74C>A (p.Ala25Glu), and a novel variant, c.1359G>T (p.Lys453Asn). Treatment included a galactose-free formula, medium-chain triglycerides, and nutritional supplementation, resulting in biochemical and clinical improvement. All patients in our series exhibited a milder clinical course, with no episodes of hyperammonemia or hypoglycemia, no progression to liver failure, and favorable long-term outcomes with dietary management. During a long-term follow-up period ranging from 7 to 11 years, no severe complications were observed. Notably, one patient developed a recurrence of cataract, emphasizing the importance of lifelong dietary adherence and regular eye examinations. The findings in this paper further expand the genotypic spectrum and genotype-phenotype correlations of CD. Lifelong follow-up is recommended, including ocular examination.

Elevated blood ammonia concentration, resulting from various hereditary and acquired conditions, can cause severe damage to the central nervous system, leading to increased rates of disability and infant mortality. In newborns, hyperammonemia is etiologically classified into two main categories: congenital, associated with inborn errors of the urea cycle or organic acidemias, and acquired, which arises secondary to other pathological conditions such as severe perinatal hypoxia, renal or hepatic failure, or intrauterine infections. Despite the differing etiologies, the clinical presentation is often non-specific and may include lethargy, hypotonia, feeding difficulties, respiratory distress, and seizures. This non-specificity frequently leads to initial misdiagnosis. Consequently, a thorough understanding of the pathogenesis, clinical features, and differential diagnosis of congenital versus acquired hyperammonemia is critical for pediatricians, neonatologists, and intensive care specialists. Timely initiation of treatment is paramount, as it directly impacts patient survival and long-term neurological outcomes. Our findings underscore the utility of machine learning in the early differential diagnosis of neonatal hyperammonemia, identifying key predictors that can guide clinical decision-making.

Hyperekplexia is a rare non-epileptic paroxysmal disorder characterized by a marked startle response and hypertonia to auditory, tactile, or visual sudden external stimuli. GLRA1, SLC6A5, GLRB, and ATAD1 gene pathogenic variants have been identified in these patients. The girl was born 39+1 weeks and admitted to the neonatal intensive care unit with spasm-like contractions and followed by breath holding. Except for transient hyperammonemia, neurologic and metabolic tests were normal, and there was no seizure-like movement during hospitalization. In the 4th month of her life, the patient had spasm-like findings with stimulation, and the symptoms were controlled with clonazepam, considering hyperekplexia. Clinical exome sequencing revealed a previously undescribed homozygous variant [c.748T>C; p.(Ser250Pro) in exon 4] in the SLC6A5 (NM_004211.5) gene. Sanger sequencing confirmed the c.748T>C variant in the family: both parents were heterozygous carriers, while the brother was homozygous. Her sibling also had stimulus-induced crying and stiffness in infancy, but these resolved within months without treatment, and his developmental milestones have been age-appropriate. This case highlights the importance of recognizing hereditary hyperekplexia in the differential diagnosis of neonatal seizures and supports the potential pathogenic relevance of the SLC6A5 c.748T>C (p.Ser250Pro) variant, particularly in benign, nonrecurrent cases with transient hyperammonemia from catabolic stress and glycine transporter dysfunction.

Transient hyperammonemia of the newborn is a rare form of hyperammonemia with an unclear, likely nongenetic etiology, primarily affecting larger preterm infants. However, lower birth weight and gestational age are associated with higher ammonia levels, increasing the risk of neurotoxicity and hepatotoxicity. Transient hyperammonemia of the newborn typically manifests as respiratory distress within the first 24 h post-birth, progressing to seizures and coma within 48 h. Continuous renal replacement therapy has demonstrated considerable efficacy in managing severe transient hyperammonemia of the newborn due to its high ammonia clearance rate; however, its application remains limited in very low birth weight preterm infants. Herein, we report the case of a male infant born at 28+2 weeks gestation, weighing 1120 g, who developed transient hyperammonemia of the newborn 22 h post-birth. Despite initial pharmacotherapy and peritoneal dialysis, his ammonia levels continued to rise, necessitating continuous renal replacement therapy. After 42 h of continuous renal replacement therapy, his ammonia levels decreased significantly and he recovered fully, eventually being discharged in good health. This case highlights continuous renal replacement therapy as a viable, life-saving intervention for severe transient hyperammonemia of the newborn, even in very low birth weight preterm infants. Citrin deficiency can manifest in newborns or infants as neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD), in older children as failure to thrive and dyslipidemia caused by citrin deficiency (FTTDCD), and in adults as recurrent hyperammonemia with neuropsychiatric symptoms in citrullinemia type II (CTLN2). Often citrin deficiency is characterized by strong preference for protein-rich and/or lipid-rich foods and aversion to carbohydrate-rich foods. NICCD: Children younger than age one year have a history of low birth weight with growth restriction and transient intrahepatic cholestasis, hepatomegaly, diffuse fatty liver, and parenchymal cellular infiltration associated with hepatic fibrosis, variable liver dysfunction, hypoproteinemia, decreased coagulation factors, anemia, and/or hypoglycemia. NICCD is generally not severe, and clinical manifestations are often resolved by age one year with appropriate treatment, although liver failure may still occur; liver transplantation has been required in rare instances. FTTDCD: Beyond age one year, many children with citrin deficiency develop a protein-rich and/or lipid-rich food preference and aversion to carbohydrate-rich foods. Clinical abnormalities may include poor weight gain, growth deficiency, severe fatigue, anorexia, and impaired quality of life. Laboratory changes are dyslipidemia, recurrent hypoglycemia, increased lactate-to-pyruvate ratio, higher levels of urinary oxidative stress markers, and considerable deviation in tricarboxylic acid cycle metabolites. One or more decades later, some adults with NICCD or FTTDCD may progress and develop features of CTLN2. CTLN2: Presentation is sudden and usually between ages 20 and 50 years. Clinical manifestations include recurrent hyperammonemia with neuropsychiatric (aggression, irritability, restlessness, hyperactivity, delusions, nocturnal delirium) and neurologic manifestations (flapping tremors, memory loss, disorientation, drowsiness, convulsive seizures, coma). Clinical manifestations are often caused by alcohol and sugar intake, medication, and/or surgery. Complications include severe liver steatosis and pancreatitis. Affected individuals may or may not have a prior history of NICCD or FTTDCD. The diagnosis of citrin deficiency is established in an individual with characteristic biochemical analytes (increased blood or plasma concentration of ammonia, plasma or serum concentration of citrulline and arginine, plasma or serum threonine-to-serine ratio) and biallelic pathogenic variants in SLC25A13 identified by molecular genetic testing. Treatment of manifestations: NICCD: lactose-free and medium-chain triglyceride (MCT)-enriched formula supplemented with fat-soluble vitamins. FTTDCD: protein- and lipid-rich, low-carbohydrate diet; in addition to dietary treatment, administration of sodium pyruvate and MCT oil may improve growth. CTLN2: reduced calorie/carbohydrate intake and increased protein intake lessens hypertriglyceridemia. Sodium pyruvate can increase weight and decrease frequency of hyperammonemia; arginine administration decreases blood ammonia concentration; MCT oil can decrease frequency of hyperammonemia; use of arginine, sodium pyruvate, and MCT oil may delay the need for liver transplantation; liver transplantation prevents hyperammonemic crises, corrects metabolic disturbances, and eliminates preferences for protein-rich foods. Surveillance: Periodic measurement of plasma concentration of ammonia and citrulline for all phenotypes associated with citrin deficiency. Assess growth and development throughout childhood; assessment of liver and pancreatic function as clinically indicated; neuropsychologic testing and quality of life assessment as clinically indicated; complete blood count and ferritin as clinically indicated. Agents/circumstances to avoid: Low-protein and high-carbohydrate diets; glycerol, fructose, and glucose infusions due to risk of brain edema; alcohol. Evaluation of relatives at risk: It is appropriate to identify affected sibs of a proband so that appropriate dietary management can be instituted before symptoms occur. Citrin deficiency is inherited in an autosomal recessive manner. If both parents are known to be heterozygous for an SLC25A13 pathogenic variant, each sib of an affected individual has at conception a 25% chance of inheriting biallelic pathogenic variants, a 50% chance of inheriting one pathogenic variant and being a carrier, and a 25% chance of inheriting neither of the familial SLC25A13 pathogenic variants. If one parent is known to be heterozygous for an SLC25A13 pathogenic variant and the other parent is known to have biallelic SLC25A13 pathogenic variants, each sib of an affected individual has at conception a 50% chance of inheriting biallelic SLC25A13 pathogenic variants and a 50% chance of inheriting one SLC25A13 pathogenic variant. In general, sibs who inherit biallelic SLC25A13 pathogenic variants will be affected and have clinical manifestations of citrin deficiency similar to those of the proband in the family. Once the SLC25A13 pathogenic variants have been identified in an affected family member, carrier testing for at-risk relatives and prenatal/preimplantation genetic testing are possible. Individuals with clinical manifestations of isovaleric acidemia (IVA) have either classic IVA identified on newborn screening or classic IVA with a later diagnosis due to a missed diagnosis or later onset of clinical manifestations. Classic IVA is characterized by acute metabolic decompensations (vomiting, poor feeding, lethargy, hypotonia, seizures, and a distinct odor of sweaty feet). Acute metabolic decompensations are typically triggered by fasting, (febrile) illness (especially gastroenteritis), or increased protein intake. Clinical deterioration often occurs within hours to days after birth. Additional manifestations of classic IVA include developmental delay, intellectual disability and/or impaired cognition, epilepsy, and movement disorder (tremor, dysmetria, extrapyramidal movements). Early treatment in those identified by newborn screening can significantly reduce morbidity and mortality in individuals with classic IVA. The diagnosis of classic IVA is established in a proband by identification of C5-carnitine metabolites by tandem mass spectrometry and isovalerylglycine (IVG) and 3-hydroxyisovaleric acid (3-HIVA) on analysis of urinary organic acids by gas chromatography-mass spectrometry, or identification of biallelic pathogenic variants in IVD by molecular genetic testing. Targeted therapy: Low-leucine/protein-reduced diet and the supplementation of a leucine-free formula in infants or leucine-free amino acid mixture in older children; carnitine and/or glycine supplementation. Supportive care: Routine daily treatment includes education of affected individuals and caregivers about the natural history, maintenance and emergency treatment, prognosis, and risks of acute encephalopathic crises; emergency treatment letter and MedicAlert®; management of movement disorder per neurologist; physical therapy and aggressive rehabilitation therapy for gross motor delay; notify metabolic center prior to planned surgeries; consult metabolic disease specialist with any emergency surgery/procedure. Emergency outpatient treatment includes carbohydrate supplementation orally or via tube feeding, transient reduction of natural protein intake, elevation of carnitine supplementation, and glycine; antipyretics for fever; antiemetics for vomiting. Acute inpatient treatment includes stopping protein intake, intravenous glucose, and hydration with normal saline; adjusting treatments for new or evolving neurologic manifestations; consider buffers as needed for life-threatening metabolic acidosis; nitrogen scavengers for hyperammonemia. Surveillance: Quantitative analysis of plasma amino acids at least every three months until age one year, every six months from age one to six years, and annually in those age six years and older; blood gases, albumin, calcium, phosphate, parathyroid hormone, complete blood count, and vitamin B12 at least annually in those on a protein-restricted diet; measurement of growth and head circumference at each visit throughout childhood; monitor weight throughout adulthood; monitor developmental milestones at each visit; neuropsychological testing and standardized quality-of-life assessments as needed; assessment of movement disorder at each visit. Agents/circumstances to avoid: Excess of dietary protein or protein malnutrition inducing catabolic state; prolonged fasting; catabolism during illness. Evaluation of relatives at risk: Biochemical or molecular genetic testing of all at-risk sibs of any age is warranted to allow for early diagnosis and treatment of classic IVA. Classic IVA is inherited in an autosomal recessive manner. If both parents are known to be heterozygous for an IVD pathogenic variant, each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Once the IVD pathogenic variants have been identified in an affected family member, carrier testing for at-risk relatives and prenatal and preimplantation genetic testing are possible.

To investigate genotype-phenotype characteristics and long-term prognosis of neonatal carbamoyl phosphate synthetase 1 (CPS1) deficiency among children through newborn screening in Zhejiang province. The clinical and follow-up data of children with CPS1 deficiency detected through neonatal screening and confirmed by tandem mass spectrometry and genetic testing in Zhejiang Province Newborn Disease Screening Center from September 2013 to August 2023 were retrospectively analyzed. A total of 4 056 755 newborns were screened and 6 cases of CPS1 deficiency were diagnosed through phenotypic and genetic testing. Ten different variations of CPS1 genewere identified in genetic testing, including 2 known pathogenic variations (c.2359C>T and c.1549+1G>T) and 8 unreported variations (c.3405-1G>T, c.2372C>T, c.1436C>T, c.2228T>C, c.2441G>A, c.3031G>A, c.3075T>C and c.390-403del). All patients had decreased citrulline levels (2.72-6.21 μmol/L), and varying degrees of elevated blood ammonia. The patients received restricted natural protein intake (special formula), arginine and supportive therapy after diagnosis, and were followed-up for a period ranging from 9 months to 10 years. Three patients experienced hyperammonemia, and one patient each had attention deficit hyperactivity disorder, transient facial twitching and increased muscle tone. One patient died, while the other five surviving patients had normal scores of the Ages & Stages Questionnaires (ASQ) and Griffiths Development Scales up to the present time; 4 cases had combined height or weight lag and one case was normal in height and weight. Low citrulline levels and hyperammonemia are common in CPS1 deficiency patients in Zhejiang. Most gene variants identified were specific to individual families, and no hotspot mutations were found. Early diagnosis through newborn screening and following standardized treatment can significantly improve the prognosis of the patients. 目的: 研究浙江省新生儿筛查发现的氨甲酰磷酸合成酶1（CPS1）缺乏症患儿的基因型和表型特点及长期预后。方法: 回顾性分析2013年9月至2023年8月浙江省新生儿疾病筛查中心采用干血斑串联质谱法筛查并联合基因检测诊断的CPS1缺乏症患者的所有筛查及临床随访资料。结果: 共筛查新生儿4 056 755名，联合表型及基因检测诊断CPS1缺乏症6例；基因检测结果发现CPS1 10种变异，包括2种已知致病性变异（c.2359C>T、c.1549+1G>T）及8种未报道变异（c.3405-1G>T、c.2372C>T、c.1436C>T、c.2228T>C、c.2441G>A、c.3031G>A、c.3075T>C、c.390-403del）。患儿初筛血瓜氨酸值均有下降（2.72~6.21 μmol/L），伴有血氨不同程度升高；诊断后给予限制天然蛋白摄入（特殊奶粉）、精氨酸及支持治疗，分别随访至9个月~10岁，有高氨血症发作3例，注意力缺陷多动、一过性口角抽动、肌张力增高各1例；除1例死亡，5例存活患儿的年龄与发育进程问卷及格里菲斯发育评估量表评分均正常，但合并身高或体重发育落后4例。结论: 浙江省CPS1缺乏症患儿表现为典型血瓜氨酸低、高氨血症生化改变；基因变异多数为家族特有，未发现热点突变。新生儿筛查早期诊断规范治疗患儿预后较好。. To investigate genotype-phenotype characteristics and long-term prognosis of neonatal carbamoyl phosphate synthetase 1 (CPS1) deficiency among children through newborn screening in Zhejiang province. The clinical and follow-up data of children with CPS1 deficiency detected through neonatal screening and confirmed by tandem mass spectrometry and genetic testing in Zhejiang Province Newborn Disease Screening Center from September 2013 to August 2023 were retrospectively analyzed. A total of 4 056 755 newborns were screened and 6 cases of CPS1 deficiency were diagnosed through phenotypic and genetic testing. Ten different variations of CPS1 genewere identified in genetic testing, including 2 known pathogenic variations (c.2359C>T and c.1549+1G>T) and 8 unreported variations (c.3405-1G>T, c.2372C>T, c.1436C>T, c.2228T>C, c.2441G>A, c.3031G>A, c.3075T>C and c.390-403del). All patients had decreased citrulline levels (2.72-6.21 μmol/L), and varying degrees of elevated blood ammonia. The patients received restricted natural protein intake (special formula), arginine and supportive therapy after diagnosis, and were followed-up for a period ranging from 9 months to 10 years. Three patients experienced hyperammonemia, and one patient each had attention deficit hyperactivity disorder, transient facial twitching and increased muscle tone. One patient died, while the other five surviving patients had normal scores of the Ages & Stages Questionnaires (ASQ) and Griffiths Development Scales up to the present time; 4 cases had combined height or weight lag and one case was normal in height and weight. Low citrulline levels and hyperammonemia are common in CPS1 deficiency patients in Zhejiang. Most gene variants identified were specific to individual families, and no hotspot mutations were found. Early diagnosis through newborn screening and following standardized treatment can significantly improve the prognosis of the patients. Infants with untreated TRMU deficiency, a mitochondrial disorder, typically become symptomatic between ages two and four months with transient acute liver dysfunction (including elevated transaminases, abnormal synthetic functions, and/or hepatomegaly), metabolic derangements (severe persistent lactic acidosis, hypoglycemia, hyperammonemia), and poor weight gain. With proper supportive treatment (but not disease-targeted therapy), abnormal liver findings (including coagulopathy) improve or normalize. Likewise, metabolic derangements improve. However, other manifestations typical of a mitochondrial disorder such as persistent lactic acidosis, neurologic dysfunction (including developmental delay / intellectual disability and seizures), cardiomyopathy, and respiratory failure may persist or develop or over time. The diagnosis of TRMU deficiency is established in a proband with suggestive findings and biallelic pathogenic (or likely pathogenic) variants in TRMU identified by molecular genetic testing. Targeted therapies: L-cysteine, with or without N-acetylcysteine (NAC), should be initiated as soon as a diagnosis of TRMU deficiency is suspected. Because the endogenous supply of cysteine is normally low in the first few months of life and because the enzyme TRMU requires adequate amounts of cysteine to enable the essential function of thiolating mitochondrial transfer RNAs, the initial manifestations of TRMU deficiency (primarily hepatopathy) may be reversed, ameliorated, or in some cases prevented by exogenous oral cysteine supplementation in infants with TRMU deficiency. To date, two infants treated presymptomatically overall had a milder clinical course than their affected relatives. Liver transplantation: Liver transplantation is indicated when hepatopathy does not respond to medical interventions. Supportive care: Supportive care by a multidisciplinary team of clinicians, including a hepatologist, neurologist, and medical geneticist, is recommended to manage the commonly reported complications of developmental delay / intellectual disability, cardiomyopathy, seizures, and/or respiratory failure. Surveillance: Routine follow up is recommended to monitor response to L-cysteine and NAC supplementation, to evaluate response to supportive interventions, and to identify emergence of new findings or concerns regarding developmental/educational progress such as persistent neurodevelopmental delay or new onset of seizures that may develop over time. Agents/circumstances to avoid: Avoid medications that increase metabolic demand (such as corticosteroids) or inhibit mitochondrial activity (such as valproic acid and prolonged propofol infusion) and fasting, as it increases metabolic demand and may exacerbate hypoglycemia. Consider avoiding acetaminophen (paracetamol) during episodes of liver dysfunction based on theoretical concerns for oxidative stress. Evaluation of relatives at risk: Molecular genetic prenatal testing of fetuses at risk may be performed via amniocentesis or chorionic villus sampling to inform maternal cysteine supplementation (reported in one pregnancy) and to facilitate institution of exogenous cysteine supplementation (as L-cysteine, N-acetylcysteine, or both) at birth. If prenatal testing has not been performed on a pregnancy at risk, supplementation with L-cysteine (and possibly N-acetylcysteine) of an at-risk newborn sib should be offered until molecular genetic testing for the family-specific TRMU pathogenic variants has been completed. TRMU deficiency is inherited in an autosomal recessive manner. If both parents are known to be heterozygous for a TRMU pathogenic variant, each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of inheriting neither of the familial TRMU pathogenic variants. Once the TRMU pathogenic variants have been identified in an affected family member, molecular genetic carrier testing and prenatal/preimplantation genetic testing are possible.