Rajab Interstitial Lung Disease with Brain Calcifications 1 (RILDBC1) — Comprehensive Research Report

MONDO:0100215 | OMIM #613658 | Orphanet ORPHA:178506 | Gene: FARSB (OMIM *609690, HGNC:17800, chr2q36.1)

1. Disease Information

Overview. Rajab interstitial lung disease with brain calcifications 1 (RILDBC1) is a rare, autosomal recessive, multisystem disorder of highly variable severity — ranging from a relatively mild neurodevelopmental phenotype to a lethal infantile multi-organ disease. It is caused by biallelic (homozygous or compound heterozygous) loss-of-function variants in FARSB, which encodes the beta subunit of cytoplasmic phenylalanyl-tRNA synthetase (FARS1/PheRS). The disease is one of two genetically distinct forms of "Rajab interstitial lung disease with brain calcifications": RILDBC1 (FARSB, OMIM #613658) and RILDBC2 (FARSA, OMIM #619013), which together with related reports form the broader "FARS1-related disorder" spectrum (Schuch et al., 2021, Clin Genet 99:789–801, DOI:10.1111/cge.13943, ResearchGate PDF).

Most affected individuals present in infancy or early childhood with intrauterine growth restriction (IUGR), poor growth/failure to thrive, and progressive, sometimes fatal, interstitial lung disease (ILD). Additional features include developmental delay, hypotonia, liver dysfunction, and — in a subset — skeletal, renal, and vascular (cerebral aneurysm) abnormalities. Neuroimaging in nearly all reported patients shows characteristic bilateral, symmetric intracranial calcifications (basal ganglia, subcortical white matter, cerebellum, cortex), often with preserved myelination and normal-to-mildly-impaired cognition despite motor delay (OMIM #613658; MedGen C3150910).

Key identifiers:

Synonyms/alternative names: RILDBC1; Rajab syndrome; brain calcification, Rajab type; FARS1-related disorder (FARSB-related); phenylalanyl-tRNA synthetase-related disease of growth restriction, brain calcification, and interstitial lung disease; recessive aminoacyl-tRNA synthetase (ARS1)-related disease.

Data provenance. Nearly all current knowledge derives from aggregated case series and family reports in the medical literature (not large EHR cohorts): the original clinical/linkage description of two consanguineous Omani kindreds (Rajab et al., 2009, Am J Med Genet A 149A:129–137, PMID:19161147, PMC2800951), the gene-identification papers (Zadjali et al. 2018; Antonellis et al. 2018; Xu/Ling et al. 2018 — see §4), subsequent case reports/series (Karimzadeh et al. 2022; others), and a systematic literature-review/phenotype paper (Schuch et al. 2021; Hoytema van Konijnenburg et al. 2025, J Inherit Metab Dis, DOI:10.1002/jimd.70017). As of 2026, media coverage of a newly diagnosed U.S. toddler (Wrenley Lantaff, diagnosed October 2025) reiterates that only "about 10" cases have been formally reported worldwide (Respiratory Therapy, 2026; 14 News, July 2026) — this figure should be treated as an approximate, informally tracked count rather than a registry-verified prevalence estimate.

2. Etiology

Disease causal factors — genetic/mechanistic, monogenic. RILDBC1 is caused by biallelic (homozygous or compound heterozygous) pathogenic variants in FARSB, which reduce or abolish function of cytoplasmic phenylalanyl-tRNA synthetase (FARS1/PheRS), the enzyme that charges tRNA^Phe with phenylalanine during protein translation and additionally appears to have non-canonical/non-translational roles important to vascular and pulmonary tissue homeostasis (Xu et al., 2018, AJHG 103:100–114, PMID:29979980, PMC6035289). There is no known infectious, toxic, or purely environmental cause; RILDBC1 is a purely Mendelian (single-gene) disorder.

Genetic risk factors: - Causal biallelic variants in FARSB (2q36.1) — see §4 for specific alleles. - Consanguinity is a strong risk factor for homozygosity at this rare recessive locus: essentially all reported kindreds are from consanguineous unions (Omani, Iranian, and other Middle Eastern families are over-represented in the literature). - Founder variant: c.853G>A (p.Glu285Lys) segregates as a founder allele in an extended Omani kindred (8 affected individuals; Zadjali et al., 2018, Hum Mutat 39:1355–1359, PMID:30014610) — this variant is absent from gnomAD, ExAC, 1000 Genomes, and Iranome, consistent with a rare, population-restricted allele rather than a common polymorphism. - Modifier/severity factors: Genotype (null/loss-of-function vs. hypomorphic missense; homozygous vs. compound heterozygous) appears to correlate with phenotypic severity across the FARS1-related-disorder spectrum, per the pooled genotype–phenotype analysis in Schuch et al. (2021) and Hoytema van Konijnenburg et al. (2025) — patients with near-complete loss of FARSB/FARS1 activity (e.g., the compound-heterozygous T256M + frameshift patient of Antonellis et al. 2018, with 97% reduction of FARSB protein) tend toward the most severe, early-lethal end of the spectrum.

Environmental risk factors: None have been identified as causal. Given the pulmonary phenotype, it is plausible (but not established in the literature reviewed here) that intercurrent respiratory infections or environmental lung insults could exacerbate the interstitial lung disease course, analogous to other genetic pediatric ILDs — this should be treated as an inference, not a documented finding for RILDBC1 specifically.

Protective factors: None reported. No protective genetic variants, modifier alleles, or environmental/lifestyle protective factors are described in the literature identified.

Gene–environment interactions: Not established for this monogenic disorder; no GxE studies were identified.

3. Phenotypes

RILDBC1 is multisystemic. Frequencies below are qualitative ("most," "some," "occasional") as reported by OMIM's clinical synopsis aggregation and the case series/reviews cited, since no large denominator cohort exists to generate precise percentages.

Pulmonary

Neurological / CNS

Hepatic

Skeletal / Renal / Other

Phenotype characteristics: - Onset: Most patients present in infancy/early childhood; some features (IUGR) are prenatal. - Severity/progression: Highly variable — from a milder, largely neurodevelopmental/skeletal phenotype without early lethality (original Omani kindreds, Rajab et al. 2009) to a rapidly progressive, fatal multisystem disease in infancy (Antonellis et al. 2018 patient died at 32 months; the 2025–2026 U.S. patient developed liver failure awaiting transplant). - Neurological course: A notable feature emphasized by Rajab et al. (2009) is the absence of progressive neurological deterioration despite static brain calcifications — this distinguishes RILDBC from progressive leukoencephalopathies. - Quality-of-life impact: Not formally studied with standardized instruments (no EQ-5D/SF-36/PedsQL data identified). Qualitatively, disease burden is driven by respiratory insufficiency, growth failure, and (when present) liver failure requiring transplantation; developmental/cognitive impact is comparatively mild in most reported patients.

HP term IDs above are best-effort suggestions based on standard HPO nomenclature for these clinical concepts; exact CURIEs should be verified against the HPO browser/OAK before curation*, per this KB's ontology-term contract — some (e.g., the specific basal-ganglia-calcification and cerebral-volume-loss terms) were not independently confirmed via a live HPO lookup in this research session.

4. Genetic / Molecular Information

Gene: FARSB — Phenylalanyl-tRNA synthetase subunit beta (aliases: FARSLB, FRSB, PheHB, PheRS-beta). HGNC:17800; NCBI Gene ID 10056; OMIM 609690; located at chromosome 2q36.1* (GRCh38: chr2:222,566,899–222,656,092). Encodes a 589-amino-acid, ~66 kDa protein.

Function: Cytoplasmic phenylalanyl-tRNA synthetase (FARS1/PheRS) is a heterotetramer (α2β2): two catalytic alpha subunits (FARSA, OMIM 602918) and two regulatory beta subunits (FARSB). In the presence of ATP, the enzyme charges tRNA^Phe with L-phenylalanine, an essential step in cytoplasmic mRNA translation. Beyond canonical aminoacylation, evidence supports non-canonical (non-translational) functions* of FARS1 relevant to vascular and pulmonary development/homeostasis (Xu et al., 2018, PMID:29979980).

Causal variants reported to date (biallelic in all cases; autosomal recessive):

Functional consequences: Western blot in the Antonellis et al. (2018) patient's fibroblasts showed a 97% reduction in FARSB protein and a 66% reduction in FARSA protein relative to controls, indicating that loss of the beta (regulatory) subunit destabilizes the catalytic alpha subunit and severely impairs holoenzyme (FARS1) activity — consistent with a loss-of-function mechanism. The c.848+1G>A splice variant similarly produces decreased transcript/protein levels, again consistent with loss-of-function.

Variant classification: Reported variants are classified pathogenic/likely pathogenic under ACMG/AMP criteria based on segregation with disease, absence/extreme rarity in population databases (gnomAD, ExAC, 1000 Genomes, Iranome all show zero frequency for the E285K founder allele), and functional/protein-level evidence of loss-of-function.

Allele frequency: All reported pathogenic FARSB variants are private or population-restricted (e.g., the Omani founder E285K allele) and are essentially absent from gnomAD — consistent with the disease's extreme rarity.

Somatic vs. germline: Exclusively germline (constitutional), autosomal recessive.

Modifier genes: None specifically identified for FARSB-related disease; genotype (allele severity, e.g., null vs. hypomorphic) itself functions as the principal determinant of phenotypic severity across the FARS1-related-disorder spectrum (Schuch et al. 2021; Hoytema van Konijnenburg et al. 2025).

Epigenetic information / chromosomal abnormalities: None reported specific to RILDBC1; this is a classic monogenic sequence-variant disorder, not a copy-number or epigenetic condition.

Related gene — FARSA: Biallelic FARSA variants cause the phenotypically overlapping but genetically distinct RILDBC2 (OMIM #619013), and a growing, partially overlapping literature on "FARSA deficiency" describes neonatal cholestasis progressing to multisystem disease with liver cirrhosis (Aelvoet et al. 2025, JIMD Reports), systemic inflammatory syndrome (PMC9303323), and fatal systemic disease (PMC9344665) — useful comparator literature for curating the FARSB entry's "related disorders" context.

5. Environmental Information

No environmental, occupational, toxic, or lifestyle causal or contributory factors have been identified for RILDBC1 in the literature reviewed — it is a purely monogenic autosomal recessive disorder. No infectious agents are implicated (notably, the brain-calcification phenotype must be actively distinguished from congenital TORCH infections, which are a key differential diagnosis rather than a cause — see §10 differential diagnosis). No CTD/TOXNET/EPA entries or infectious-agent associations were found.

6. Mechanism / Pathophysiology

Causal chain (numbered, from molecular lesion to clinical phenotype)

1. Biallelic loss-of-function variants in FARSB (missense in the editing/catalytic-interface domain, frameshift, or splice-donor variants) lead to markedly reduced steady-state FARSB protein (up to ~97% reduction demonstrated by Western blot in patient fibroblasts).
2. Reduced FARSB leads to destabilization/co-depletion of its obligate heterotetramer partner, the FARSA catalytic subunit (a ~66% reduction in FARSA protein was demonstrated in the same patient), because FARS1 (α2β2 PheRS) assembly requires stoichiometric beta subunit.
3. Loss of holoenzyme (FARS1) abundance/activity results in impaired charging of tRNA^Phe with phenylalanine — impairing canonical cytoplasmic mRNA translation capacity, particularly in tissues with high translational/proteostatic demand.
4. In parallel — and this is an inferred, not fully demonstrated, branch — evidence from Xu et al. (2018) supports a non-canonical, non-translational function of FARS1 that is specifically required for normal pulmonary and vascular tissue integrity; disruption of this non-translational role is proposed (rather than conclusively proven) to contribute independently to the lung and vascular phenotypes, distinguishing this disease's pathogenesis from a "simple" translation-insufficiency model common to other aminoacyl-tRNA synthetase disorders.
5. Combined translational impairment and disrupted non-canonical FARS1 function in the lung lead to alveolar/interstitial injury with a distinctive histologic response: cholesterol pneumonitis (intra-alveolar and interstitial cholesterol granulomas), which results in progressive interstitial lung disease, impaired gas exchange, and — in severe cases — respiratory failure and death.
6. In the developing brain, disrupted FARS1 function is hypothesized (mechanism not fully elucidated) to cause a static, non-progressive process of basal ganglia/subcortical calcification, accompanied in some patients by developmental delay, hypotonia, and microcephaly, but — notably — without progressive neurodegeneration, distinguishing it mechanistically/clinically from progressive interferonopathies such as Aicardi–Goutières syndrome.
7. In the liver, impaired FARS1 function leads to hepatocellular dysfunction, manifesting as hepatomegaly/hepatosplenomegaly, cholestasis, and — in severe cases — progression to cirrhosis and liver failure requiring transplantation (as in the 2025–2026 U.S. index case).
8. In blood vessels and connective tissue, disrupted FARS1 function (again, an area where non-canonical function is implicated) is associated in a subset of patients with cerebral/intracranial aneurysm formation and skeletal connective-tissue features (scoliosis, pectus deformity), suggesting a vascular/connective-tissue mechanistic branch parallel to the pulmonary and neurological ones.
9. Growth failure (IUGR, failure to thrive, short stature, osteopenia) is best understood as a systemic consequence of chronic translational insufficiency and multi-organ disease burden rather than a single localized lesion.

Detail by mechanistic category

• Molecular pathways: Aminoacyl-tRNA synthetase (aaRS) charging step of cytoplasmic mRNA translation (not a classical signaling cascade like Wnt/MAPK/mTOR); secondary proteostatic stress. GO term suggestions: GO:0004826 (phenylalanine-tRNA ligase activity), GO:0006432 (phenylalanyl-tRNA aminoacylation), GO:0006418 (tRNA aminoacylation for protein translation).
• Cellular processes: Impaired protein synthesis; possible proteotoxic/proteostatic stress in high-translation-demand tissues (lung epithelium, hepatocytes, neurons); no direct evidence reviewed here for classical apoptosis/autophagy dysregulation specific to this disease, though such mechanisms are plausible extrapolations from general aaRS-disease biology.
• Protein dysfunction: Loss-of-function via (a) destabilizing missense substitutions in conserved domains (e.g., T256M in the "editing domain," E285K), (b) frameshift/premature truncation (His496LysfsTer14), and (c) splice-site disruption (c.848+1G>A) — all converging on reduced FARSB protein abundance and secondary FARSA co-depletion, i.e., loss of holoenzyme rather than a dominant-negative or gain-of-function mechanism.
• Metabolic changes: Not specifically characterized (no dedicated metabolomics studies identified); the primary metabolic lesion is at the level of amino-acid-charging of tRNA rather than a classical small-molecule metabolic pathway.
• Immune system involvement: Not a primary feature of RILDBC1 per se, though the related FARSA-deficiency literature describes a "systemic inflammatory syndrome" phenotype (PMC9303323) — raising the possibility of an inflammatory/immune contribution to the FARS1-disease spectrum broadly, not conclusively established for FARSB specifically.
• Tissue damage mechanisms: Cholesterol pneumonitis/granulomatous lung injury (lung); calcific deposition (brain); fibrosis/cirrhosis (liver) — the lung and liver findings both reflect a chronic injury-and-remodeling pattern; the exact cellular trigger for cholesterol accumulation in alveolar macrophages/interstitium is not fully elucidated in the literature reviewed.
• Biochemical abnormalities: Reduced/absent phenylalanyl-tRNA synthetase (FARS1) enzymatic activity, demonstrable by reduced FARSA/FARSB protein on Western blot in patient-derived fibroblasts (direct evidence, IN_VITRO, Antonellis et al. 2018).
• Epigenetic changes: None reported.
• Molecular profiling: No transcriptomic, proteomic, metabolomic, or single-cell/spatial datasets specific to RILDBC1/FARSB patient tissue were identified in this search; this remains an open evidence gap.
• Cell types involved (suggested CL terms):
• Type II pneumocyte (CL:0002063) — alveolar epithelium, relevant to ILD.
• Alveolar macrophage (CL:0000583) — likely relevant to cholesterol granuloma formation (inferred).
• Hepatocyte (CL:0000182) — liver dysfunction/cirrhosis.
• Neuron (CL:0000540) / astrocyte (CL:0000127) — relevant to CNS calcification context (by analogy to other brain-calcification disorders; not directly demonstrated for FARSB).

Upstream vs. downstream: The FARSB loss-of-function lesion and consequent FARS1 holoenzyme deficiency are clearly upstream/initiating; the pulmonary (cholesterol pneumonitis/ILD), hepatic (cirrhosis), neurological (calcification, developmental delay), skeletal (osteopenia), and vascular (aneurysm) manifestations are downstream, organ-specific consequences that appear to arise largely in parallel rather than in a strict linear cascade from one another — i.e., this is best modeled as one causal trigger with several parallel downstream organ-specific branches, rather than a single linear chain (the ordered list above reflects that branching explicitly at steps 4–8).

7. Anatomical Structures Affected

Organ level: - Primary: Lungs (interstitial lung disease, cholesterol pneumonitis), brain (calcifications), liver (dysfunction/cirrhosis). - Secondary: Skeleton (osteopenia, scoliosis, pectus deformity), kidneys (nonspecific renal abnormalities), cerebral vasculature (aneurysms), gastrointestinal tract (intestinal malrotation in some), craniofacial structures (dysmorphism in some). - Body systems: Respiratory, nervous, hepatobiliary, skeletal, renal, cardiovascular (cerebrovascular).

Suggested UBERON terms: - UBERON:0002048 (lung) - UBERON:0000955 (brain) / UBERON:0002420 (basal ganglion) - UBERON:0002107 (liver) - UBERON:0001474 (bone element) — for skeletal involvement - UBERON:0002113 (kidney) - UBERON:0002049 (vasculature) / cerebral artery structures — for aneurysms

Tissue/cell level: Alveolar epithelium and interstitium (pulmonary), hepatocytes, basal ganglia/subcortical neural tissue and its vasculature (site of calcification), osteoblast/osteoclast-mediated bone tissue (osteopenia). Specific single-cell profiling of affected tissue was not identified.

Subcellular level: No cellular-compartment-specific pathology (e.g., mitochondrial, ER) is specifically implicated beyond the cytoplasmic localization of FARS1 itself (GO Cellular Component: GO:0017101, aminoacyl-tRNA synthetase multienzyme complex, or GO:0005737 cytoplasm) — this is distinct from the mitochondrial FARS2-related disease (see §10 differential diagnosis), a common point of confusion given the similarly named gene.

Localization/lateralization: Brain calcifications are characteristically bilateral and symmetric (a distinguishing feature from many acquired/vascular calcification patterns).

8. Temporal Development

• Onset: Prenatal (IUGR) through infancy/early childhood for most features; the pulmonary and hepatic manifestations are typically first recognized in infancy or toddlerhood (e.g., the 2025–2026 U.S. index case first showed feeding difficulty, vomiting, and poor weight gain, with abdominal distension noted in toddlerhood).
• Onset pattern: Generally insidious/subacute for growth failure and neurodevelopmental features; can be more acute for pulmonary decompensation or liver failure.
• Progression: Highly variable across reported patients — from a comparatively stable, non-progressive course dominated by static brain findings and mild developmental delay (original Omani kindreds) to rapid, fatal multisystem progression in infancy (death at 32 months in the Antonellis et al. patient; the current U.S. patient in liver failure awaiting transplant). A key emphasized feature (Rajab et al. 2009) is that neurological findings, despite radiographically striking calcifications, generally do not show progressive deterioration — differentiating the neurological course from progressive interferonopathies.
• Disease course pattern: Chronic; can be stable (neurological) while progressive in other organs (lung, liver) within the same patient.
• Duration: Lifelong for survivors; disease can be fatal in infancy/early childhood in severe cases.
• Remission: Not described — this is not a relapsing-remitting condition.
• Critical periods: Infancy/early childhood is the critical period both for diagnosis (symptom onset) and for the highest mortality risk (progressive ILD, liver failure).

9. Inheritance and Population

Epidemiology: - Prevalence: Orphanet lists ORPHA:178506 ("Interstitial lung disease-brain calcification syndrome") prevalence as <1/1,000,000. - Approximately 10 or fewer molecularly confirmed cases have been reported in the literature/media as of 2026, spanning the original Omani kindred (8 individuals), the Antonellis et al. 2018 patient, the Xu et al. 2018 cohort (5 individuals/4 families), the Karimzadeh et al. 2022 Iranian siblings, and the 2025-diagnosed U.S. toddler — noting overlap/possible double-counting across these reports is plausible and a rigorous unique-patient census was not attempted here. - No incidence estimates, sex-ratio data, or age-distribution statistics were identified — consistent with the disease's extreme rarity and absence of large-scale registries.

Inheritance pattern: Autosomal recessive.

Penetrance: Presumed complete for the reported biallelic loss-of-function genotypes, though this has not been formally studied given the small number of cases; phenotypic expressivity is markedly variable (see §8).

Expressivity: Markedly variable — from a relatively mild neurodevelopmental/skeletal phenotype to fatal infantile multisystem disease, apparently correlating in part with the severity of the underlying variant(s) (null/loss-of-function vs. partial hypomorph) per the pooled analysis in Schuch et al. (2021) and Hoytema van Konijnenburg et al. (2025).

Genetic anticipation: Not applicable/not reported (not a repeat-expansion disorder).

Germline mosaicism: Not specifically reported for FARSB.

Founder effects: A founder allele, c.853G>A (p.Glu285Lys), segregates in an extended consanguineous Omani kindred (Zadjali et al. 2018) — the clearest documented founder effect for this gene.

Consanguinity: A major contributing factor — the majority of reported families (Omani, Iranian) are consanguineous, consistent with autosomal recessive inheritance of a very rare allele.

Carrier frequency: Not established in population databases; the causal alleles are essentially absent from gnomAD, ExAC, 1000 Genomes, and Iranome.

Population demographics: Reported cases cluster in Middle Eastern populations (Oman, Iran) with documented consanguinity, plus at least one North American (U.S.) case (2025–2026, ancestry not specified in available reporting) and cases reported from other unspecified families in the Xu et al. 2018 cohort. No robust geographic-distribution or ethnic-prevalence data exist beyond these case reports.

10. Diagnostics

Clinical tests: - Chest imaging (CT): identifies interstitial lung disease pattern. - Lung biopsy/histopathology: characteristic finding is cholesterol pneumonitis — intra-alveolar and interstitial cholesterol granulomas — described as an early, distinguishing histologic feature across the FARS1-related-disorder spectrum (Schuch et al. 2021). - Brain imaging (CT/MRI): bilateral, symmetric calcifications of basal ganglia, subcortical white matter, cerebellum, and cortex; periventricular cysts (more typical of RILDBC2); preserved myelination; incomplete Sylvian fissure closure; cerebral volume loss. - Liver function tests / liver biopsy: assess for cholestasis, coagulopathy, cirrhosis. - Skeletal survey: for osteopenia, scoliosis, pectus deformity. - Functional/biochemical assay: FARS1 (PheRS) enzymatic activity or FARSA/FARSB protein levels can be assessed in patient-derived fibroblasts by Western blot, as demonstrated in Antonellis et al. (2018) — a research-grade rather than routine clinical assay.

Genetic testing: - Recommended approach: Given the extreme rarity and phenotypic overlap with other genetic ILD/brain-calcification syndromes, whole-exome sequencing (WES) is the diagnostic modality used in essentially all published cases (Zadjali et al. 2018; Antonellis et al. 2018; Xu et al. 2018), often following genome-wide linkage analysis in consanguineous families. Whole-genome sequencing (WGS) would be expected to have similar or greater utility, particularly for detecting the reported splice-region variants, but was not the primary method used historically for this gene. - Gene panels: A FARSB single-gene test or a targeted panel for genetic pediatric interstitial lung disease (chILD) / aminoacyl-tRNA synthetase-related disease panels would be expected to include FARSB and FARSA; specific commercial panel names were not catalogued in this search. - Single-gene testing: Feasible once a specific familial variant or strong phenotypic suspicion exists (e.g., in a consanguineous family from a population with a known founder allele). - Chromosomal microarray/karyotype/FISH: Not informative — this is a sequence-variant (not copy-number or structural chromosomal) disorder. - Mitochondrial DNA testing: Not relevant to FARSB (cytoplasmic enzyme) — important differential-diagnostic caveat: do not confuse with FARS2 (mitochondrial phenylalanyl-tRNA synthetase), which causes a clinically distinct, unrelated mitochondrial disease ("FARS2 deficiency," covered by its own GeneReviews chapter, NCBI Bookshelf NBK538658) with combined oxidative phosphorylation deficiency and epilepsy — a naming-based confusion risk worth flagging explicitly during curation.

Clinical criteria: No formal consensus diagnostic criteria (e.g., DSM/ICD-style) exist for this ultra-rare disorder; diagnosis rests on the combination of characteristic multisystem phenotype (ILD + brain calcification + growth failure ± liver/skeletal/renal findings) plus molecular confirmation of biallelic FARSB variants.

Differential diagnosis (as explicitly discussed by Rajab et al. 2009 and general brain-calcification-syndrome literature): - Aicardi–Goutières syndrome (AGS) — considered and explicitly distinguished by Rajab et al. (2009); AGS typically shows progressive neurological deterioration, elevated CSF interferon-alpha/CSF lymphocytosis, and leukodystrophy, which are not features of RILDBC1. - Coats plus syndrome — also explicitly considered and excluded by Rajab et al. (2009) based on divergent clinical features. - Congenital TORCH infections (CMV, toxoplasmosis, etc.) — can produce intracranial calcifications and hepatosplenomegaly; excluded by negative infectious serologies/PCR. - FARSA-related disease (RILDBC2) — clinically overlapping (ILD, liver disease, brain calcifications/periventricular cysts) but genetically distinct; distinguished by molecular testing. - FARS2 deficiency (mitochondrial PheRS) — a different, unrelated disease despite the similar gene name; distinguished by molecular testing and by its distinct clinical/biochemical (mitochondrial) profile. - Other genetic pediatric interstitial lung diseases (e.g., surfactant protein gene disorders — SFTPC, ABCA3) — distinguished by the combination of brain calcification and multisystem (hepatic/skeletal) involvement, which is atypical for isolated surfactant dysfunction disorders. - Primary familial brain calcification (PFBC) — typically adult-onset and without the pulmonary/hepatic phenotype; distinguished on clinical grounds and by molecular testing (PFBC genes: SLC20A2, PDGFB, PDGFRB, XPR1, MYORG).

Screening: No population or newborn screening program exists for this ultra-rare condition; case-finding is clinical (presentation with ILD/growth failure/brain calcification) followed by genetic confirmation. Carrier screening could theoretically be offered in populations with a known founder allele (e.g., the Omani E285K allele) for at-risk consanguineous families, though this was not explicitly documented as an established practice in the sources reviewed.

11. Outcome / Prognosis

• Survival/mortality: Highly variable. Some reported patients (original Omani kindred) survived into childhood with relatively stable neurological status; others died in infancy/early childhood from progressive respiratory failure (e.g., death at 32 months, Antonellis et al. 2018). No formal survival curves, 5-/10-year survival rates, or standardized mortality statistics exist given the very small number of published cases.
• Life expectancy: Not quantifiable from available data; ranges from early childhood death (severe genotype/phenotype) to survival into later childhood/beyond with chronic multisystem morbidity (milder genotype/phenotype).
• Morbidity/function: Chronic respiratory insufficiency, growth failure/short stature, variable developmental/motor impairment (cognition often relatively spared), and — in severe cases — progressive liver disease culminating in liver failure requiring transplantation (illustrated by the 2025–2026 U.S. case).
• Complications: Progressive interstitial lung disease/respiratory failure; hepatic cirrhosis/liver failure; cerebral aneurysm (vascular complication risk in a subset of patients, per Xu et al. 2018); recurrent infections; skeletal deformity (scoliosis).
• Recovery potential: No curative treatment exists; clinical course is managed supportively. In the FARS1-disease spectrum broadly, amino-acid supplementation has shown benefit for some organ systems in some patients (see §12) but does not reliably prevent the most severe phenotypes.
• Prognostic factors: Genotype severity (null/loss-of-function vs. partial-function alleles) appears to be the principal prognostic determinant identified in the pooled literature (Schuch et al. 2021; Hoytema van Konijnenburg et al. 2025), though formal statistical genotype–phenotype correlation studies with adequate sample size do not exist given the rarity of the disease.
• Prognostic biomarkers: None validated; residual FARS1 enzymatic activity/protein level (measured in patient fibroblasts) is a research-level correlate of severity rather than a clinically validated prognostic biomarker.

12. Treatment

There is no disease-specific approved therapy for RILDBC1; management is supportive and organ-directed, informed by the broader FARS1-related-disorder / aminoacyl-tRNA synthetase (ARS1)-deficiency literature.

Pharmacotherapy / experimental disease-modifying approach: - Cognate amino acid supplementation (i.e., supplementation with phenylalanine, the amino acid product of the deficient enzyme's charging reaction, by analogy with strategies used in other aaRS deficiencies) has been described across the pooled FARS1-related-disorder literature: Hoytema van Konijnenburg et al. (2025, J Inherit Metab Dis, DOI:10.1002/jimd.70017) report that amino-acid supplementation was attempted in a substantial number of patients (reported in the broader FARS1-deficiency literature as having been tried in roughly two dozen patients across the FARSA/FARSB spectrum) with beneficial effects on growth, development, and liver/lung disease in the majority, but with poor response in the most severely affected patients, and with difficulty distinguishing true treatment effect from natural disease history given the absence of controlled trials. This should be treated as a general FARS1-related-disorder therapeutic strategy, not a treatment specifically validated in a controlled trial for FARSB/RILDBC1 alone. Suggested NCIT term: NCIT:C15447 (Dietary Intervention) or NCIT:C15433 (Nutritional Support), used cautiously per this KB's guidance that supplement-type interventions frequently name a specific compound rather than a behavioral/dietary pattern. - No small-molecule, enzyme-replacement, gene-therapy, or RNA-based therapy specific to FARSB/RILDBC1 was identified in the literature reviewed.

Advanced therapeutics: None reported — no gene therapy, cell therapy, or targeted molecular therapy specific to this disease has reached even early clinical description.

Surgical/interventional: - Liver transplantation — required in the most severe hepatic phenotype (the 2025–2026 U.S. index case was reported awaiting liver transplant for progressive liver failure). Suggested NCIT term: NCIT:C15289 (Organ Transplantation). - Management of cerebral aneurysms, where present, would follow standard neurovascular/neurosurgical practice (not specifically described for this disease in the literature reviewed). - Orthopedic management (e.g., for scoliosis) as clinically indicated — NCIT:C16186 (Orthopedic Surgical Procedure).

Supportive and rehabilitative care: - Nutritional support for growth failure/failure to thrive (NCIT:C15447 Dietary Intervention). - Respiratory supportive care (supplemental oxygen, management of infections, and — in end-stage disease — consideration of lung transplantation, though no specific report of lung transplantation for RILDBC1 was identified in this search) — NCIT:C15747 (Supportive Care). - Physical/occupational therapy for hypotonia and motor delay (NCIT:C15302 Physical Therapy). - Immunomodulatory therapy for interstitial lung disease is used empirically in genetic pediatric ILDs generally (corticosteroids, hydroxychloroquine), but no report specifically documenting these agents' use or efficacy in RILDBC1/FARSB-confirmed patients was identified in this search — this should be flagged as an evidence gap rather than asserted as an established RILDBC1 treatment.

Genetic counseling — recommended for families given the autosomal recessive inheritance pattern and elevated recurrence risk (25% per pregnancy for carrier couples), particularly relevant in consanguineous families and populations carrying the Omani founder allele. NCIT:C15240 (Genetic Counseling).

Treatment outcomes: No systematic response-rate or adverse-event data exist. The overarching message from the most recent pooled review (Hoytema van Konijnenburg et al. 2025) is that current therapies (chiefly amino acid supplementation and organ-directed supportive/transplant care) have not eliminated the most severe phenotypes, and international collaboration/longitudinal natural-history data are explicitly called for to refine genotype–phenotype correlation and develop better treatments.

Experimental treatments in clinical trials: No disease-specific registered clinical trial (ClinicalTrials.gov) for FARSB/RILDBC1 was identified in this search.

13. Prevention

• Primary prevention: Not applicable in the traditional sense (no modifiable environmental cause); the only actionable primary-prevention lever is genetic counseling and reproductive planning in known carrier couples or high-risk (consanguineous, founder-allele) populations, including consideration of preimplantation genetic diagnosis or prenatal diagnosis where a familial variant is known.
• Secondary prevention: Early clinical recognition (growth failure + ILD + brain calcification triad) followed by prompt genetic testing could, in principle, expedite supportive management, though no formal early-detection/screening program exists.
• Tertiary prevention: Organ-directed supportive care (nutritional support, pulmonary care, monitoring for and managing hepatic and vascular complications) aims to reduce complication burden and prolong function, though it is not curative.
• Immunization: No disease-specific immunization strategy; standard-of-care vaccination (including against respiratory pathogens, e.g., RSV prophylaxis where age-appropriate, influenza, pneumococcal vaccination) would be a reasonable general supportive measure for a child with chronic ILD, though this is inferred general pediatric-ILD practice rather than a documented RILDBC1-specific recommendation.
• Screening/genetic counseling: Carrier screening is feasible in principle for populations with a known founder allele (e.g., Omani p.Glu285Lys) but was not documented as an established program in the sources reviewed. Cascade testing of at-risk relatives following an index diagnosis is the standard approach for ultra-rare autosomal recessive disorders.
• Public health/environmental interventions: Not applicable — no environmental risk factor to mitigate.
• Prophylaxis: None specific; amino acid supplementation (see §12) has been framed in the broader FARS1-disorder literature as potentially disease-modifying rather than strictly prophylactic, and is not curative.

14. Other Species / Natural Disease

No naturally occurring veterinary or wildlife disease attributable to FARSB loss-of-function was identified in this search (no OMIA entries or veterinary case reports were found). FARSB orthologs exist across mammals (mouse, and others) and more distantly across vertebrates, consistent with the gene's essential, highly conserved role in cytoplasmic translation, but no spontaneous animal disease model analogous to RILDBC1 has been reported in the literature reviewed. Given that complete loss of an essential translation-machinery gene would be expected to be embryonic lethal in most vertebrate models (see §15), it is plausible that no viable naturally occurring null animal phenotype exists — this is an inference, not a documented finding.

• Taxonomy: Human disease-relevant ortholog searches identified only the human FARSB gene page and general cross-species conservation notes (GeneCards); NCBI Taxon-level comparative data specific to disease modeling were not identified.
• Zoonotic potential: Not applicable (genetic, non-infectious disease).

15. Model Organisms

No dedicated, published animal or cellular disease model specifically engineered to recapitulate FARSB-related RILDBC1 was identified in this search (no zebrafish, mouse conditional-knockout, or patient-iPSC-derived organoid model of FARSB loss-of-function was found in the literature reviewed).

• Patient-derived fibroblasts: The principal "model system" used to date is patient-derived dermal fibroblasts, in which Western blot demonstrated the ~97%/66% reduction in FARSB/FARSA protein (Antonellis et al. 2018) — this is an in vitro, patient-cell-based functional confirmation rather than an engineered model organism, and is the strongest direct functional evidence available for the loss-of-function mechanism.
• Related-gene models (context, not RILDBC1-specific): A zebrafish morpholino knockdown model of fars2 (the distinct, mitochondrial paralog) has been used to study developmental angiogenesis requirements for mitochondrial phenylalanyl-tRNA synthetase (PMID:34540921, Front Cardiovasc Med 2021) — this is informative for the general biology of Phe-tRNA synthetases in vascular development (relevant context given the cerebral-aneurysm phenotype seen in some FARSB patients) but is not a direct model of the cytoplasmic FARSB gene or of RILDBC1, and should not be conflated with it during curation.
• Essential-gene consideration: Because FARSB encodes a core, ubiquitously required subunit of the cytoplasmic protein-synthesis machinery, a complete germline knockout would be expected on general principle to be embryonic lethal in mouse or other standard model systems (as is typical for aminoacyl-tRNA synthetase genes generally) — no MGI record of a Farsb knockout mouse phenotype was retrieved in this search, and this point should be verified directly against IMPC/MGI (https://www.informatics.jax.org, MGI:1346035) before being asserted as an established finding in a curated entry.
• Research applications / resources: Given the absence of an established animal model, functional studies of FARSB variants to date rely on (a) patient fibroblasts for protein-level/functional assays and (b) presumably (though not directly confirmed in this search) in vitro aminoacylation assays with recombinant/purified FARS1 complex — both are reasonable candidate approaches for future model-development work, representing a clear research gap: no organism-level model exists to study the tissue-specific (lung/brain/liver/vascular) pathophysiology of FARSB loss-of-function in vivo.

Summary of Key Evidence Gaps (for curation awareness)

1. No large cohort/registry — all data derive from fewer than ~20 published patients across 4–5 kindreds/case series; percentage-based phenotype frequencies should not be over-stated.
2. No animal or iPSC/organoid model of FARSB loss-of-function has been published; mechanistic claims about non-canonical FARS1 function in lung/vascular tissue rest on human genetic/histologic correlation (Xu et al. 2018) rather than direct experimental perturbation in a model system.
3. No controlled treatment trial; amino acid supplementation evidence is retrospective/observational and pooled across the FARSA+FARSB spectrum, not RILDBC1-specific.
4. HPO term IDs given above are best-effort suggestions and should be verified against a live HPO/OAK lookup before being bound in a curated entry, consistent with this knowledge base's anti-hallucination term-validation policy.
5. This session's WebFetch tool was unavailable (proxy connection refused) for the full duration of research, so OMIM, Orphanet, and PubMed full-text/abstract pages could not be directly fetched and parsed; all information above was synthesized from WebSearch result snippets, which sometimes provide only excerpted or aggregated text rather than verbatim primary-source quotations. Direct fetches of OMIM #613658, OMIM *609690, Orphanet ORPHA:178506, and the primary PMIDs cited (19161147, 29573043, 29979980, 30014610) are recommended as a follow-up verification step before finalizing any curated entry, to obtain exact verbatim abstract quotations for evidence snippet: fields.

Sources

• Entry - #613658 - RAJAB INTERSTITIAL LUNG DISEASE WITH BRAIN CALCIFICATIONS 1; RILDBC1 - OMIM
• Entry - #619013 - RAJAB INTERSTITIAL LUNG DISEASE WITH BRAIN CALCIFICATIONS 2; RILDBC2 - OMIM
• Entry - *609690 - PHENYLALANINE-tRNA SYNTHETASE, BETA SUBUNIT; FARSB - OMIM
• Orphanet: Interstitial lung disease-brain calcification syndrome (ORPHA:178506)
• Rajab interstitial lung disease with brain calcifications 1 - NORD
• MedGen C3150910 / MedGen C5436603 (RILDBC2)
• Recessive developmental delay, small stature, microcephaly and brain calcifications with locus on chromosome 2 — Rajab et al. 2009, PMID:19161147 / PMC2800951
• Homozygosity for FARSB mutation leads to Phe-tRNA synthetase-related disease of growth restriction, brain calcification, and interstitial lung disease — Zadjali et al. 2018, PMID:30014610
• Compound heterozygosity for loss-of-function FARSB variants in a patient with classic features of recessive aminoacyl-tRNA synthetase-related disease — Antonellis et al. 2018, PMID:29573043
• Bi-allelic Mutations in Phe-tRNA Synthetase Associated with a Multi-system Pulmonary Disease Support Non-translational Function — Xu et al. 2018, PMID:29979980, PMC6035289
• FARS1-related disorders caused by bi-allelic mutations in cytosolic phenylalanyl-tRNA synthetase genes: Look beyond the lungs! — Schuch et al. 2021, Clin Genet
• Neurodegenerative disorder and diffuse brain calcifications due to FARSB mutation in two siblings — Karimzadeh et al. 2022, PMC9347330
• Setting the Stage for Treatment of Aminoacyl-tRNA Synthetase (ARS)1-Deficiencies — Hoytema van Konijnenburg et al. 2025, J Inherit Metab Dis
• FARSB Gene - GeneCards
• NM_005687.5(FARSB):c.1618+17G>A AND Rajab interstitial lung disease with brain calcifications 1 - ClinVar
• Developmental Angiogenesis Requires the Mitochondrial Phenylalanyl-tRNA Synthetase (FARS2 zebrafish model, context only) — PMID:34540921
• First US Toddler Diagnosed With Rare Lung Disease - Respiratory Therapy, 2026
• Pike County toddler is first U.S. child diagnosed with rare lung disease - 14 News, July 2026
• FARS2 Deficiency - GeneReviews - NCBI Bookshelf NBK538658 (differential-diagnosis context)