A rare interstitial lung disease in children caused by novel mutations of FARSA gene

To the editor, A child born to a non-consanguineous couple was referred to our hospital after their first infant died of multisystem disorders. No family history of genetic disease was recorded. The male infant exhibited congenital hip dislocation and hindfoot valgus. Despite adequate feeding, the infant gained only 160 g in the first month. He was hospitalized at the age of 1.7 months due to severe bilateral edema of the hands and lower limbs (Figure 1A). The infant presented severe hypoproteinemia (14.2 g/L), prominent hypochromic microcytic anemia (56 g/L), cholestasis (89.7 umol/L), leukocytosis (20.26 × 109/L), and increased C-reactive protein (CRP) (18.07 mg/L). Oxygen saturation remained stable at 98%, with no signs of respiratory distress or cough. Hypocalcemia and hypotonia were also noted. Whole-exome sequencing (WES) was performed considering these symptoms, but no causative mutation was identified. Supporting treatment led to the resolution of edema, yet growth was stunted despite the formula containing about 150 calories per kilogram of body weight delivery through a stomach tube. By 3 months, the infant was significantly underweight (2.76 kg; −3SD), short-statured (55 cm; −3SD), with a small head circumference (35 cm), and thoracic circumference (34 cm). Furthermore, the infant suffered persistent inflammation and recurrent infection, with leukocyte counts peaking at 87.43 × 109/L and the level of ferritin escalating from 719 to over 1500 ug/L. Intermittent elevations in IL-6 were also detected, alongside infections with adenoviruses, cytomegalovirus (CMV), Klebsiella pneumoniae (K. pneumoniae), adenoviruses, and Pneumocystis jirovecii. Notably, interstitial pneumonia developed rapidly, as documented by lung X-ray and high-resolution computed tomography (HRCT), showing rapid progression from relatively normal imaging to diffuse interstitial fibrosis (Figure 1B−J). Timely and sufficient antiviral drugs (intravenous ganciclovir followed by oral valganciclovir, sulfamethoxazole), antimycobacterial drugs (piperacillin, meropenem, amoxicillin-clavulanate, cefoperazone-sulbactam), steroids, JAK-inhibitor/Baricitinib, supportive measures (CPAP, finally intubated mechanical ventilation), and anti-reflux treatment failed to improve the poor lung condition of the infant. Repeated alveolar lavage excluded pulmonary alveolar proteinosis, and hemosiderin cells were not detected in gastric aspirates. Anti-histone antibodies were detected by repeated anti-nuclear antibodies (ANA) tests. Congenital heart diseases and pulmonary arterial hypertension (PAH) were ruled out. Elevated liver enzymes (high levels of serum ALT and AST) and nephrolithiasis were also observed. Brain MRI imaging revealed bilateral ventriculomegaly and uneven echo in the choroid plexus (Figure 1K,L). Extremely low levels of transferrin and thyroid-binding globulin were identified. Upon reanalysis of WES data, taking the multisystem disorders dominated by interstitial lung disease (ILD) into consideration, compound variants (c.982A>G, p. T328A and c.1109T>C, p. F370S) of FARSA were identified. Based on DNA analysis, the unaffected mother carried the mutation of c.982A>G, and the unaffected father carried the mutation of c.1109T>C (Supporting Information S1: Figure S1A,1B). Both variants were predicted to be pathogenic according to Polyphen-2, Mutation taster, and Fathmm (Supporting Information S1: Table S1), and their locations were within the important region of FARSA gene (Supporting Information S1: Figure S1C). The infant was diagnosed with Rajab interstitial lung disease [ILD] with brain calcifications 2 (RILDBC2) and he died at 7 months of age due to severe respiratory failure (Figure 2). The use of medical records of this family was approved by the Institutional Review Board of the Women's Hospital, School of Medicine, Zhejiang University (IRB-20220323-R), and the written informed consents were provided by the participants. Interstitial lung disease in children (chILD) presents with a heterogeneous group of respiratory disorders, marked by significant morbidity and mortality, estimated at around 15%.1 Characteristic features of chILD include tachypnea, hypoxemia, and diffuse findings on chest imaging. To date, mutations of several genes have been associated with chILD, such as the well-described variants in SFTPB, SFTPC, and ABCA3, as well as more rare variants, including FARSA. Mutations in FARSA are specifically associated with RILDBC2, a rare and severe subtype of chILD. RILDBC2 is characterized by Rajab ILD with or without cholesterol pneumonitis, growth delay, hypotonia, brain calcifications, and liver dysfunction. In the current investigation, the Chinese infant showed hypoxemia and typical imaging findings consistent with diffuse interstitial fibrosis. c.982A>G and c.1109T>C mutations in FARSA were identified, which was inherited from the unaffected mother and father, respectively. Taking the ILD syndrome and genetic results into consideration, the infant was diagnosed with RILDBC2. To date, only four publications have described RILDBC2, reporting a total of nine patients. The initial case of RILDBC2 was a 15-year-old boy with growth delay in the first month of age. He had experienced various infections from 5 months of age, including CMV infection, pneumonia, and urinary tract infection. Moreover, he was diagnosed with ILD at 13 years old, with calcifications in brain MRI imaging at 15 years old.2 Luise et al. described three patients, with chronic ILD, abnormal muscle histology/respiratory chain function, liver diseases, and hypoalbuminemia. Furthermore, heart defects (cardiovascular system), IgG2 deficiency (immune system), hyperphosphaturia (urinary system), nephrolithiasis (urinary system), poor wound healing (skin), abnormal eye movement (eye), and sensorineural hearing impairment (ear) were also observed.3 Fabienne et al. described four children with RILDBC2, who had inflammatory profiles associated with autoimmunity and interferons, evidenced by chronic elevation of CRP and leukocytosis. There was also evidence of autoimmunity with positive rheumatoid factor, ANA, and anti-neutrophils cytoplasmic antibodies (ANCA). Patients developed recurrent fever, aseptic osteomyelitis or diffuse intra-alveolar hemorrhage (IAH).4 Different from the above cases, Soo et al. not only found two mutations of FARSA in FARSA-deficient patients but also managed to demonstrate the pathogenicity of the biallelic variants in vitro.5 All the previously reported cases with FARSA mutations were listed in Supporting Information S1: Table S2 and Figure S1. All the cases showed multisystem disorders and severe ILD, three of which died at the age of 1.3 years, 28 months, and 12.9 years. The infant we described here, who presented with rapid disease severity and progression, along with persistent hypoproteinemia and repeated infections, was the first case diagnosed as RILDBC2 within 1 year after birth. In summary, we report a case of the exceedingly rare lung disease, RILDBC2, and novel variants of FARSA (c.982A>G and c.1109T>C). Our findings provide an insight into the rare chILD disease. Moreover, our findings underscore the imperative for dynamic reevaluation of genetic diagnostics in tandem with the emergence of novel phenotypic expressions, thereby underscoring the evolving nature of genetic disorders and the necessity for adaptive diagnostic strategies. Minyue Dong conceived of the study and revised the manuscript. Yuqing Xu participated in study design, clinical diagnosis and manuscript writing. Yi Sun collected the clinical data and revised the manuscript. Min Chen extracted the genomic DNA and performed DNA analysis. All authors have read and approved the final manuscript. We thank Dr. Zhen Yang (Clin Lab, BGI Genomics, Shanghai) for help with revising this manuscript. This study was supported by the National Natural Science Foundation of China, Grant number: 82171848; Key Research and Development Program of Zhejiang Province, Grant number: 2019C03025; and the National Natural Science Foundation of China, Grant number: 81901382. The authors declare no conflict of interest. All the data related to the study has been presented in the article. The data are available from the corresponding author upon reasonable request. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.