(2024) 24:539
Dong et al. BMC Pediatrics
https://doi.org/10.1186/s12887-024-05005-5

BMC Pediatrics

RESEARCH

Open Access

Clinical features and CPS1 variants in Chinesepatients with carbamoyl phosphate synthetase
1 deficiency
Hui Dong1†, Tian Sang1†, Xue Ma1†, Jinqing Song1, Zhehui Chen1,3, Huiting Zhang1, Ying Jin1, Mengqiu Li1,
Dingding Dong1, Liying Sun2, Zhijun Zhu2, Yao Zhang1* and Yanling Yang1*

Abstract
Background Carbamoyl phosphate synthetase 1 (CPS1) deficiency (OMIM 237300), an autosomal recessive rare
and severe urea cycle disorder, is associated with hyperammonemia and high mortality.
Methods Herein we present 12 genetic variants identified in seven clinically well-characterized Chinese patientswith CPS1 deficiency who were admitted to the Children’s Medical Center of Peking University First Hospital from September 2014 to August 2023.
Results Seven patients (two male and five female patients including two sisters) experienced symptoms onset
between 2 days and 13 years of age, and they were diagnosed with CPS1 deficiency between 2 months and 20 years.
Peak blood ammonia levels ranged from 160 to 1,000 µmol/L. Three patients showed early-onset CPS1 deficiency,with only one surviving after treatment with sodium phenylbutyrate, N-carbamoyl-L-glutamate, and liver transplantation at 4 months, showing a favorable outcome. The remaining four patients had late-onset CPS1 deficiency, presenting with mental retardation, psychiatric symptoms, and self-selected low-protein diets. Among the 12 CPS1 variants
identified in these patients, 10 were novel, with all patients exhibiting compound heterozygosity for CPS1 mutant
alleles. Seven variants (c.149T > C, c.616 A > T, c.1145 C > T, c.1294G > A, c.3029 C > T, c.3503 A > T, and c.3793 C > T)
resulted in single amino acid substitutions. Three frameshift variations (c.2493del, c.3067dup, and c.3241del) wereidentified, leading to enzyme truncation. One mutation (c.3506_3508del) caused an in-frame single amino acid deletion, while another (c.2895 + 2T > C) resulted in aberrant splicing.
Conclusions Except for two known variants, all other variants were identified as novel. No hotspot variants wereobserved among the patients. Our data contribute to expanding the mutation spectrum of CPS1.
Keywords Hyperammonemia, Carbamoyl phosphate synthetase 1, Urea cycle disorders, Liver transplantation, CPS1
gene†

Hui Dong MD, Tian Sang MD and Xue Ma contributed equally to this work.

*Correspondence:
Yao Zhangzy_tzh@163.com
Yanling Yang
organic.acid@vip.126.com
Full list of author information is available at the end of the article© The Author(s) 2024. Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0
International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as longas you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if
you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article orparts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicatedotherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not
permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To
view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.

Dong et al. BMC Pediatrics(2024) 24:539

Background
Carbamoyl phosphate synthetase 1 (CPS1) deficiency(OMIM 237300), an autosomal recessive inherited disease, is a rare and severe type of urea cycle disorder characterized by hyperammonemia [1–3]. CPS1 acts as therate-limiting enzyme initiating ammonia detoxificationin the urea cycle by synthesizing carbamoyl phosphatefrom bicarbonate, ammonia, and adenosine triphosphate with N-acetylglutamate. Mutations in CPS1 leadto enzyme activity deficiency, severely impeding the conversion of ammonia to carbamoyl phosphate. This resultsin hyperammonemic encephalopathy and liver damage,evident through symptoms such as vomiting, poor feeding, loss of consciousness, seizures, and rapid clinicaldeterioration, often leading to high mortality [4, 5]. The
symptoms of CPS1 deficiency can vary widely, manifesting at any age. Typically, phenotypes are categorized into
neonatal-onset and late-onset forms based on the ageof onset [4]. Neonatal-onset forms are associated with apoorer prognosis and higher mortality rates compared
to late-onset forms, which demonstrate a survival rate of> 90% [6]. The incidence of CPS1 deficiency is 1/62,000 to
1/1,300,000 worldwide [7, 8]. Only a few cases of CPS1
deficiency have been reported in China [9–11].
The severity of CPS1 deficiency, whether early- or lateonset, is influenced by residual enzyme activity related tothe defect and the specific variant site and type. However,there has been limited analysis regarding the correlation between genotypes and phenotypes in patients with
CPS1 deficiency. Our study aims to investigate the clinical features, metabolic profiles, and genotypes of sevencases of CPS1 deficiency, alongside discussing the potential relationship between genotypes and phenotypes.
Methods
Patients

Our study was approved by the Hospital Institution
Committee in accordance with the Declaration of Helsinki. Written informed consent was obtained from theparents of each participant. Seven patients with CPS1
deficiency were from six non-consanguineous Chinesefamilies. They were admitted to Peking University First
Hospital between September 2014 and August 2023.
Routine examination

Clinical and laboratory data at onset and follow-up werecollected. Data from routine physical examination andcomplete blood count; blood ammonia, glucose, lactic
acid, and blood gas; liver and kidney function; and brain
magnetic resonance imaging (MRI) were analyzed.
Blood amino acid and acylcarnitine profiles in dried
blood spots were analyzed by liquid chromatography–
tandem mass spectrometry (API 3200, Triple Quad 4500;

Page 2 of 9

Applied Biosystems, CA, USA). ChemoView software
was used to automatically calculate metabolite concentration. Urine organic acids were determined using gas
chromatography-mass spectrometry (GC-MS, GCMSQP2010plus; Shimadzu, Kyoto, Japan).
Genetic testing

Genomic DNA from peripheral blood samples was
extracted and purified. Whole exon sequencing was conducted for seven patients and their parents. The DNA
was sequenced on Illumina Hiseq2500 (Illumina, San
Diego, USA). Each variant was compared with 1000
Genomics, the ExAC database (http://​exac.​broad​insti​
tute.​org/), and the gnomAD database (http://​gnomad.​broad​insti​tute.​org/). Purified DNA samples were sent toEuler Genomics (Beijing, China), Berry Genomics Corporation (Beijing, China), and Running Gene Inc. (Beijing, China) for whole exon sequencing to screen variants
in patients. Mutation Taster, PolyPhen-2, and SIFT werealso referred to for in silico analysis of the variants to predict pathogenicity. The variants were evaluated according to the HGMD and Clinvar. The pathogenicity of theselected variants was assessed according to the American
College of Medical Genetics and Genomics guidelines[12]. The variants were classified as pathogenic, likely
pathogenic, variants of uncertain significance (VUS),
likely benign, or benign.

Results
Clinical and biochemical features

Seven patients were included in this study, including two(28.6%) male and five (71.4%) female patients (Table 1).
The age of onset ranged from 2 days to 13 years, andthe patients were diagnosed at the age of 2 months to 20
years. Among the patients, three were diagnosed by postmortem examination.
Three patients (Patients 1 to 3) had neonatal-onset
type. They exhibited reluctance to feed, convulsions, andloss of consciousness after breast milk feeding on days 2,
3, and 10 of life, respectively.
Patient 1 was treated with 250 mg/kg/day oral sodium
phenylbutyrate and 130 mg/kg/day N-carbamoyl-L-glutamate intermittently upon the onset of symptoms, anda strict low-protein diet was started after diagnosis. Her
condition stabilized with no vomiting; blood ammonia
levels reduced from 514 µmol/L before treatment to 60µmol/L after treatment, but anorexia and feeding difficulty did not improve. The physical growth and movement development were retarded. The infant underwent
a liver transplant from her father at the age of 4 months.
Subsequently, her blood ammonia levels returned to thenormal range. She was fed with ordinary formula, and her
general condition significantly improved. Her physical

F

M

F

M

F

F

F

1a

2

3

4

5

6

7

a

Underwent liver transplantation

13y

4m

3y

2m

10d

3d

2d

Age of onset

/

20y

6y

1.5y

/

/

2m

Age ofdiagnosis

160

574

/

6.5

3.9

5.3

5.1

489

168

2.3

2.3

>1000

514

Peak ammonia Citrulline

/

2.6

1.6

7.3

2.4

2.6

8.3

Arginine

Blood biochemical markers (µmol/L)

Poor feeding,600
neuropsychiatric symptoms,
headache; vomiting, convulsions and coma
after infections

Developmental
delay, neuropsychiatric
symptoms,
avoiding highprotein foodDevelopmental
delay, irritability, avoiding
high-protein
food, vomiting,convulsion
and coma
after infection

Crying, irritability, developmental delay

Poor feeding,convulsion,coma, reduced
consciousness

Poor feeding,convulsion,coma, respiratory failure,
multiple organ
dysfunction

Poor feeding, vomiting, reduced
consciousness,convulsion

Clinicalfeatures

/

412.3

/

/

606.7

/

503.2

Glutamic acid

OutcomeDied aged 26y
after acute infections

20y now,with developmental delay

Died at 6y
after acute infections

8y now,with developmental delay

Died at 16th day

Died at 5th day

2y9m now,with well development(2024) 24:539

F female, M male, m month, y year

Sex

Patient

Table 1 The clinical and biochemical characteristics of seven cases with CPS1 deficiency

Dong et al. BMC Pediatrics
Page 3 of 9

Dong et al. BMC Pediatrics(2024) 24:539

and psychomotor development gradually reached thoseof healthy infants. The girl, now 3 years old, shows normal physical and mental development.
Patient 2 experienced poor feeding, convulsions, andcoma on the third day of life. His blood ammonia level
was > 1,000 µmol/L. Patient 3 showed similar symptoms
on day 10 of life, with a blood ammonia level of 489µmol/L. Both patients underwent emergency management, including hemodialysis and a low-protein diet.
Despite these interventions, they showed rapid deterioration and severe hyperammonemia and died on days 5
and 16 of life, respectively. Their blood and urine samples
were taken for postmortem metabolic and gene analysis.
Four patients (Patients 4 to 7) were late-onset typewith various non-specific symptoms. Patients 4 and5 presented symptoms at the age of 2 and 4 months,
respectively. Patients 6 and 7 presented with symptoms
aged 3 years and 13 years, respectively. They had diverse
degrees of mental retardation and psychotic behavioral disorders, such as apathy and short temper, andavoided high-protein foods. Patient 4 presented with
non-specific symptoms, including crying, irritability, anddevelopmental delay since 2 months of age, with a highblood ammonia level of 168 µmol/L. Patient 5 showeddevelopmental delay since 4 months of age and later
developed neuropsychiatric symptoms during puberty.
She was diagnosed at the age of 20 years at our hospital.
Patient 6 had recurrent severe symptoms such as vomiting, seizures, loss of consciousness, and coma following
acute infections starting at 3 years of age. The definite
diagnosis of CPS1 deficiency was made at the age of 6
years before death. Patient 5 and Patient 7 were sisters.

Page 4 of 9

Patient 7 had anorexia, altered temperament, and otherneuropsychiatric disorders such as hallucinations since
puberty. She experienced headaches, vomiting, seizures,coma after fever, and acute upper respiratory tract infection at the age of 26 years and died after 5 days. Patient
7 was diagnosed with CPS1 deficiency by postmortem
gene analysis. All four patients received treatment involving intravenous and oral ammonia scavengers, including
250 mg/kg/day sodium phenylbutyrate, 250–300 mg/
kg/day sodium benzoate, 300 mg/kg/day arginine, and
50–200 mg/kg/day levocarnitine.
The blood ammonia of the seven patients was elevated
to 160 to 1,000 µmol/L. Their blood citrulline levels were
either lower than or within the lower end of the normal
range (2.3–6.5 µmol/L, normal range 5–40 µmol/L).
Blood arginine levels were also lower than or within thelower end of the normal range (1.6–8.3 µmol/L, normal
range 5–50 µmol/L). Urine organic acid analysis revealed
normal orotic acid and uracil levels. All patients showedvaried liver dysfunction.
Patients 1 and 6 underwent brain magnetic resonanceimaging during the acute episode. Patient 1 showed short
T1 and long T2 abnormal signals on both globus pallidus
sites, in accordance with hyperammonemic encephalopathy (Fig. 1a and b). Patient 6 showed slight bilateral ventriculomegaly and an enlarged subarachnoid space in thetemporal lobe.
Four patients (Patient 2, 3, 6, and 7) presented withsevere hyperammonemic encephalopathy after acuteinfections or breast milk intake. The patients’ clinicalconditions exacerbated rapidly, and all four patients diedseveral days after symptom onset. Their blood ammonia

Fig. 1 a Brain magnetic resonance imaging (MRI) of Patient 1 at 10 days of age upon initial acceptance into our study before treatment. Brain MRI
was performed at 3.0T at Peking University First Hospital. The axial T1 image revealed symmetrical diffuse high-signal shadows on both globus
pallidus sites (indicated by the red arrow). b Brain MRI of Patient 1 at 10 days of age. The axial T2 image revealed symmetrical diffuse high-signal
shadows on both globus pallidus sites (indicated by the red arrow)Dong et al. BMC Pediatrics(2024) 24:539

level stabilized between 64 and 80 µmol/L with oral
sodium phenylbutyrate and a protein-restricted diet.
However, the psychological and behavioral abnormalities
and mental retardation did not improve.
Gene analysis

Twelve CPS1 variants were identified (NM_001875.4)
from the seven patients included in this study (Table 2).
Only two mutations, c.1145 C > T (p.Pro382Leu) [13]and c.3029 C > T (p.Thr1010Met) [14], have been previously reported to cause CPS1 deficiency. The remaining
10 variants were novel. We assessed the pathogenicity ofthese novel variants using various prediction online tools,
including Mutation Taster [15], PolyPhen-2 [16], and
SIFT [17], and interpreted them according to the standards and guidelines of the American College of Medical
Genetics and Genomics (ACMG) and the Association
for Molecular Pathology [12]. The five novel missense
variations, namely c.149T > C, c.616 A > T, c.1294G > A,
c.3503 A > T, and c.3793 C > T, were all located in thehighly conserved regions of the translated protein.
Three frameshift variations (c.2493del, c.3067dup, andc.3241del), one deletion (c.3506_3508del), and one
splicing variation (c.2895 + 2T > C) were detected. Four(c.2493del, c.3067dup, c.3241del, and c.3506_3508del)were pathogenic variations. Three (c.149T > C,
c.3793 C > T, and c.2895 + 2T > C) were likely pathogenic. Four (c.616 A > T, c.1294G > A, c.3029 C > T, andc.3503 A > T) were VUS. The data have been uploaded
to ClinVar (https://​www.​ncbi.​nlm.​nih.​gov/​clinv​ar, submission ID SUB12523111, ClinVar accession nos.:
SCV003762244 to SCV003762254).
Genotype–phenotype correlations

Three of the 7 patients (Patients 1–3) had neonatal-onset
type, and they carried three missense variants c.149T > C,
c.3503 A > T and c.3793 C > t respectively. Most of thevariants in our study were located in exon 25 (3/14) andexon 29 (2/14) and were in the carbamate phosphorylation domain (6/14). Notably, many of the variants in ourstudy showed substitutions of Leu (2/14), Thr (2/14) andPro (2/14) residues.

Discussion
Herein we provide an account of the clinical presentations, biochemical features, genetic analysis, and outcomes of seven Chinese patients with CPS1 deficiency.
Given the scarcity of research on this topic, our findings
hold significant value for both clinicians and physicians
dealing with such cases.
Our study included seven patients who exhibited arange of manifestations of CPS1 deficiency, spanningfrom the neonatal period to puberty. Among them, three

Page 5 of 9

were categorized as early-onset and four as late-onset
type, each presenting with varied clinical symptoms.
High-protein diets and acute infections emerged as themain triggers for onset in these patients. Notably, theirblood ammonia levels were elevated, and liver dysfunction was evident. Four patients died, while three showed
improvement following metabolic treatment comprisinga low-protein diet, ammonia scavengers, and symptomatic drugs. One patient underwent N-carbamoyl-L-glutamate therapy and liver transplantation as part of theirtreatment regimen.
Patients with CPS1 deficiency usually present with
nonspecific clinical manifestations in childhood. CPS1
deficiency can be divided into two types depending on
the age of onset: the lethal early-onset (onset during thefirst month after birth) and the less severe late-onset(onset after the neonatal period) types [18, 19]. In thisstudy, three cases (42.9%) were identified as having earlyonset CPS1 deficiency. Only one infant recovered, while
two died during the neonatal period. The results indicatethat the prognosis of the early-onset type is extremely
poor. Four cases (57.1%) were late-onset type, presenting symptoms from the age of 2 months to 13 years. The
heterogeneity of the clinical manifestations was moresignificant, including developmental delay, mental andbehavioral abnormalities, and anorexia. Among thesefour patients with late-onset CPS1 deficiency, two developed acute hyperammonemia and encephalopathy after
infection. The disease progressed rapidly, and the patientsdied. These cases suggest that we should pay high attention to hyperammonemia and the underlying etiologicaldisease. For late-onset types, despite stable clinical conditions, there remained a high risk of life-threatening metabolic crisis triggered by infections or high-protein diets.
The primary methods for detecting CPS1 deficiency
include blood ammonia tests and gene analyses. No specific abnormalities are typically observed in blood aminoacid and urine organic acid profiles. Notably, urinary orotic acid test results are negative, which helps distinguish
CPS1 deficiency from other urea cycle disorders [20]. The
definite diagnosis depends on detection of CPS1 pathogenic variants or liver CPS1 enzyme activity assay [1, 21].
In our study, blood ammonia levels of all patients weresignificantly elevated. The peak level of blood ammonia
of Patient 2 was up to 1,000 µmol/L on Day 3, and thepatient died on Day 5. Blood citrulline and arginine levels in all seven patients were below or within the lower
limits of the normal range; however, glutamic acid levelsin three patients were elevated, aligning with findings inexisting literature [22]. These results suggested a definite
diagnosis of CPS1 deficiency.
CPS1 is located on chromosome 2q35, contains 38
exons and 37 introns, and encodes the CPS1 protein of

E11

E26

paternal

maternal

E25

E13paternal

E6maternal

maternal

E25

paternal

E29

E29

paternal

maternal

I23

E2

paternal

maternalc.3241delp.Leu1081Cysfs*19

p.Pro382Leudc.1145 C > ­Td

p.Asp1023Glyfs*3
p.Gly432Ser

c.1294G > A

c.3067dup

p.Thr206Ser

p.Thr1010Metc

c.3029 C > ­Tc

c.616 A > T

p.Lys1168Ile

p.Val1170-

p.Leu50Pro/

p.Pro1265Ser

p.Glu832Asnfs*6

Amino acid s­ ubstitutionsb

c.3503 A > T

c.3506_3508delc.149T > C

c.2895 + 2T > C

c.3793 C > T

c.2493delA

Nucleotide ­changea, b

ACMG/AMP, American College of Medical Genetics and Genomics and the Association for Molecular Pathology

SIFT scores the substitution as ≤ 0.05 = damaging, which means the change is predicted to affect protein function

This study[11]This study

This study

This study[12]This study

This study

This study

This study

This study

This study

References

f

/

/

0.001

/

0.033

/

0.000

/

0.000

/

0.001

/

SIFT

f

Change reported in (1) Häberle et al. Hum Mutat. 2011;32:579; (2) Funghini et al. Gene. 2012;493:228; (3) Liu et al. Hum Mutat. 2021;42:1443; (4) Fan et al. J Clin Lab Anal. 2020;34:e23124

/

/

1.000

/

0.740

/

1.000

/

1.000

/

1.000

/

Poly-Phen2e

Polyphen-2 grades the probability of a damaging effect of an amino acid substitution as 0.85-1.00 = probable damaging, 0.15–0.84 = possibly damaging, and 0-0.14 = benign//

Disease causing/

Disease causing/

Disease causing/

Disease causing/

Disease causing/

Mutation TasterIn silico prediction

e

P

P

VUS

P

VUS

VUS

VUS

P

LP

LP

LP

P

ACMG/
AMP
gradingdUnless indicated with another footnote, this change has been reported first in the present study

Change reported in Rodriguez-Flores et al. Hum Mutat. 2014;35:105c

The reference transcript is NM_001875.4ba

P pathogenic, LP likely pathogenic, VUS a variant of unknown significance6

5 and 7

4

3

2

E20

E32

paternal

maternal

1

Extron (E)/
Intron (I)AllelePatient

Table 2 CPS1 gene variants and pathogenic analysis of seven cases with CPS1 deficiency

SCV003762251/

SCV003762246

SCV003762250

SCV003762245/

SCV003762252

SCV003762253

SCV003762244

SCV003762248

SCV003762254

SCV003762247

ClinVar accession number

Dong et al. BMC Pediatrics(2024) 24:539
Page 6 of 9

Dong et al. BMC Pediatrics(2024) 24:539

1,462 amino acids [23, 24] (Fig. 2). More than 270 mutations have been reported on Human Gene Mutation
Database (HGMD; http://​www.​hgmd.​cf.​ac.​uk/​ac/​index.​php). Up to now, no hot-spot variations of CPS1 has beenreported. In this study, 12 CPS1 variations were detectedamong seven patients, of which only two variations havebeen previously reported [12, 13]. The other ten are
novel. In addition to five missense variations, three wereframeshift variations, one was a deletion, and one was asplicing variation. According to the ACMG pathogenicity
grading, four were pathogenic, three were likely pathogenic, and three were VUS. The novel 10 variants further
enrich the CPS1 pathogenic gene variation database.
The existing literature does not reveal any obvious genotype–phenotype correlations among patients with CPS1
deficiency. As we did not perform enzyme activity analysis in this study, we attempted to analyze genotype–phenotype correlations based on the clinical manifestationsof our patients. Most variants identified in this study
were located in the CPS1 domain (6/14, 42.9%), indicating that the CPS1 domain plays a vital role in enzyme
activity and clinical presentation.
Notably, five of the novel mutations were missensechanges. Among them, c.149T > C and c.616 A > T wereobserved in the N-terminal domain. This domain ishypothesized to activate catalytic activity to stabilize
the enzyme [13]. c.149T > C was found in very severe

Page 7 of 9

neonatal patients, while c.616 A > T was found in lateonset patients, indicating that the variants in the same
domain influence residual enzyme activity differently
in patients. c.2493delA introduces a stop codon in the
integrating domain, which is vital for proper enzyme
folding and regulatory cross-talk between NAG andphosphorylation sites [25]. This may explain the neonatal type observed in Patient 1 in this study. The variantc.3029 C > T, on the other hand, in late-onset patients,
may account for attenuated clinical manifestations andpartial residual enzyme activity. In the third severe neonatal patient, c.3503 A > T was found to coexist with asecond allele where a conserved valine residue is deleted(c.3506_3508del), resulting in severe effects from these
two single amino acid variations.
On the opposite side of the clinical spectrum, data pertaining to late-onset patients also shed light on the lackof severity for the novel missense mutation c.1294G > A,
as it coexists with a null allele in two sisters with lateonset CPS1 deficiency (Patients 5 and 7). In addition, thefrequently reported c.1145 C > T variant was found in alate-onset patient (Patient 6), further supporting that thismissense mutation does not completely abolish CPS1
activity.
At present, promptly reducing blood ammonia production is key to the treatment of CPS1 deficiency, as patient
prognosis is strongly influenced by peak blood ammonia

Fig. 2 Exon and domain structure of CPS1, along with the localization of CPS1 variants from this study. Human CPS1 comprises 1,462 amino acids.
The blue box represents exons, connected by dark blue lines, which represent introns. Colored blocks denote specific protein domains as indicated.
Dashed lines connect reported disease-causing variants with their respective exons and protein domains

Dong et al. BMC Pediatrics(2024) 24:539

levels. Commonly used methods for managing this condition include the administration of phenylbutyric acid,benzoate, L-arginine, and L-citrulline, as well as livertransplantation [26, 27]. L-carnitine was also supplied
to avoid secondary carnitine deficiency. N-carbamoyl-Lglutamate is an analog of N-acetylglutamic acid, which
can activate CPS1 enzyme activity and promote the synthesis of carbamoyl phosphate. The drug is approved
for the treatment of N-acetylglutamic acid synthetase
deficiency. Earlier studies [28–30] have reported goodoutcomes on treating patients with CPS1 deficiency
with N-carbamoyl glutamic acid. In our study, the clinical symptoms of Patient 1 were significantly relieved
after N-carbamoyl glutamic acid was administered withincreased tolerance to natural protein, and the bloodammonia stabilized, which allowed for liver transplantation. The child underwent paternal liver transplantation
at 4 months of age and became the youngest child with
CPS1 deficiency in the world to have successfully undergone liver transplantation.

Conclusions
In conclusion, CPS1 deficiency represents a serious formof urea cycle disorder, with a low incidence, high mortality and disability, and poor prognosis. This condition
manifests as devastating acute attacks with severe consequences impacting multiple organs. Analyzing the genotype–phenotype relationship revealed that the variantsc.149T > C, c.3503 A > T, c.3793 C > T, and c.3506_3508delmarkedly reduce CPS1 protein activity, while c.1294G > A
and c.1145 C > T cause partial deficiency. Notably, no
hotspot variants were identified among the patients inour study. These results further expand the mutation
spectrum of CPS1.
Acknowledgements
We would like to thank all the patients and their families for their participation. We are grateful to the Euler Genomics (Beijing, China), Berry Genomics
Corporation (Beijing, China), and Running Gene Inc. (Beijing, China) for theirprofessional genetic sequencing and analysis services.
Author contributions
HD, TS, and XM wrote the original draft of the manuscript. HD and YY participated in the study design and study conception. YZ, XM, HZ, DD, ZC, LS,
and ZZ collected the clinical data and followed up with the patients. JS, YJ,
and ML performed the metabolic assays. YZ and YY designed the study andsupervised the clinical work. All the authors read and approved of the final
manuscript.
Funding
This work was supported by the National Key Research and Development
Program of China [grant numbers 2021YFC2700903, 2022YFC2703401].
Availability of data and materials
The datasets generated and/or analyzed during the current study are available
in the ClinVar repository（https://www.ncbi.nlm.nih.gov/clinvar）. Submission ID is SUB12523111, and the ClinVar accession numbers are SCV003762244
to SCV003762254.

Page 8 of 9

Declarations
Ethics approval and consent to participate
This study was reviewed and approved by the Institutional Ethics Committeeof Peking University First Hospital and was conducted in accordance with
the Declaration of Helsinki. Written informed consent was obtained from theguardians of all patients in this study.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Author details
1Children’s Medical Center, Peking University First Hospital, Beijing 102600,
China. 2 Department of General Surgery, Beijing Friendship Hospital of Capital
Medical University, Beijing 100050, China. 3 Department of Pediatrics,
Women and Children’s Hospital, School of Medicine, Xiamen University, Xiamen 361003, China.
Received: 28 January 2024 Accepted: 12 August 2024

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4. Isler J, Rüfenacht V, Gemperle C, Allegri G, Haberle J. Improvement of
diagnostic yield in carbamoylphosphate synthetase 1 (CPS1) molecular
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