ABCA3 Gene Mutations in Late Preterm and Term Infants With Fatal Unexplained Respiratory Distress Syndrome
Conditions: Respiratory Distress Syndrome, Newborn
Sponsor: Children's Hospital of Chongqing Medical University

Title: ABCA3 gene and RDS in late preterm and term infants 
NCT number: NCT04137783 
Date of document: March 16, 2021 
 
 
 

Neonatal respiratory distress syndrome (RDS) is caused by the deficiency 
or inactivation of pulmonary surfactant, and is commonly seen in early 
preterm infants due to their immature lung development. However, some 
maternal and neonatal characteristics in late preterm and term infants such 
as maternal diabetes, meconium aspirated pneumonia, neonatal sepsis, and 
severe intrapartum asphyxia, could also contribute to RDS. Existing 
evidence has demonstrated that RDS in late preterm and term infants is a 
somewhat distinct disease entity, with risk factors and clinical profiles that 
differ from those in early preterm infants [1-3]. In a neonatal unit, some late 
preterm or term infants experience RDS; however, the etiology has not 
been well defined after a routine workup. This unique RDS entity was 
referred to as unexplained respiratory distress syndrome (URDS) by 
numerous previous studies, as well as our study [4-7].  
Given that a large body of literature has demonstrated the essential role 
genetic mechanism play in the pathogenesis of most URDS cases, 
numerous medical facilities have carried out clinical exome sequencing to 
identify the underlying genetic cause of URDS [8-10]. Among all of the 
genetic factors that contribute to the RDS, the most common is ABCA3 
gene mutation, which involves the assembly of pulmonary surfactant in the 
lamellar body of pneumocyte II [11]. Existing evidence indicated that 
patients with homozygous or compound heterozygous ABCA3 gene 
mutations were commonly in critically ill conditions [12]. A single ABCA3 
mutation was also likely to increase the risk and severity of RDS [4, 13].  
Unfortunately, in a considerable proportion of neonatal URDS patients, 
genetic testing fails to yield any abnormal findings, making these patients 
the “true URDS” patients. Currently, whether the ABCA3-mutated URDS 
patients have similar or more challenging clinical profiles to those without 
any genetic abnormalities continues to confound most neonatologists. An 
answer to this question would help to guide the management and predict 

the clinical outcomes of neonatal URDS patients. The present study aimed 
to address this by comparing the clinical characteristics of late preterm and 
term infants with severe URDS with homozygous or compound 
heterozygous ABCA3 mutations, a single ABCA3 mutation, or no defined 
genetic abnormalities.  
 
Patient selection 
This single-center retrospective cohort study involved infants ≥34 weeks' 
gestation with severe URDS who were admitted to Children's Hospital of 
Chongqing Medical University between January 2013 and December 2019. 
In this study, severe RDS was mainly defined according to the consensus 
of the Pediatric Acute Lung Injury Consensus Conference [14], and 
Montreux definition 
[15]: (1) manifestations and chest radiograph 
compatible with RDS; (2) on invasive mechanical ventilation with 
oxygenation index ≥16, which was calculated based on the daily blood 
gas, or as an alternative measurement, on the subcutaneous oxygen tension 
[16, 17].  
Almost all infants with severe RDS had undergone a comprehensive 
workup, 
including 
serial 
infection 
markers, 
chest 
radiograph, 
echocardiography, and blood and sputum pathogen testing. For all patients 
with severe RDS who responded inadequately to interventions and had 
unremarkable workup findings,  trio exome sequencing on samples from 
patients and their parents were usually recommended. All URDS patients 
who underwent genetic testing were enrolled in this study. Those whose 
parents rejected genetic testing, or who had cardiopulmonary 
malformations, pulmonary hypoplasia, culture-positive sepsis, or known 
respiratory disease-associated gene mutations (such as SFTPA1, SFTPA2, 
SFTPB, SFTPC, CHPT1, LPCAT1, PCYT1B, NKX2, CFTR, and FOXF1) 

were excluded. This study was approved by the Institutional Review Board 
of Children's Hospital of the Chongqing Medical University (No.2018-158) 
and was registered on clinicaltrials.gov (NCT04137783).   
 
Exome sequencing and gene mutation detection 
All infants in this study underwent trio exome sequencing after written 
consent had been obtained from their parents. A gene company (Chigene, 
Beijing) offered the sequencing as a clinical laboratory service. Sequence 
analysis of coding exons and flanking introns were performed as 
previously described [18, 19]. All samples were analyzed to detect frame-shift 
mutations, nonsense mutations, missense mutations, splicing site 
mutations, and in-frame indel mutations. Assessment of copy number 
variation was also performed from exome sequencing data using 
computational tools. A variant was strictly defined as a mutation if it had 
been previously described to cause disease with a presentation consistent 
with these patients, or resulted in an amino acid change or protein structure 
alteration to disrupt protein function that was predicted by both SIFT and 
PolyPhen for missense mutations [20, 21], and MaxEntScan and dbscSNV for 
splicing site mutations[22]. In the case of a novel mutation, phastCons and 
phyloP were used to determine the evolutionary conservation of the region 
where the mutation was located [23]. The American College of Medical 
Genetics and Genomics/Association for Molecular Pathology (ACMG-
AMP) criteria were applied to interpret the mutations [24]. The subjects in 
this study were categorized into three groups: homozygous or compound 
heterozygous ABCA3 mutations, a single ABCA3 mutation, and no defined 
genetic abnormalities. 
 
Clinical profiles data  
All relevant clinical data were extracted from a hospital information system. 

All antepartum and postpartum data were collected and included: maternal 
age, parity, and pregnancy-related complications; mode of birth, amniotic 
fluid condition, and history of asphyxia and resuscitation; postnatal age of 
respiratory symptom onset, modalities of respiratory support, and the daily 
record of blood gas and subcutaneous oxygen tension; laboratory data 
including complete blood count, C-reactive protein, procalcitonin, blood 
and sputum culture, respiratory viral detection test, and genetic testing; 
radiographic examination including chest X-ray and echocardiogram; 
medications taken during the hospital stay.  
 
Radiological scoring 
All chest X-rays were reviewed on a hospital information system by one 
radiologist. The most severe images were scored according to the 
Fleischner Society criteria[25]. The chest X-ray was rated in three sections 
on both sides of the lung: apex to the carina, carina to the lower pulmonary 
vein, and lower pulmonary vein to the diaphragm. The incidence of 
radiological features, including ground-glass opacity, reticular pattern, air 
bronchogram, atelectasis, and air leak, were evaluated for each lung section. 
Each finding was scored as 0 = none, 1 = discrete,2=diffuse, or 3 = strong 
at each section. An overall cumulative score was calculated by adding the 
individual section scores together, with a maximum score of 18 for each 
patient.  
 
Statistical Analysis 
Analysis of variance (ANOVA) and the Chi-square or Fisher's exact tests 
were used to compare clinical characteristics and radiographic scores 
between different groups of patients. Tests for the differences in the age of 
symptom onset and the age of development of severe RDS between the 
groups were carried out using the log-rank test. A two-tailed p-value of 

<0.05 was considered statistically significant. 
 
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