CAGSSS Syndrome

Mendelian MONDO:0014455 Pathograph 54 Show in embeddings browser Mitochondrial Disease

CAGSSS is the cataract, growth hormone deficiency, sensory neuropathy, sensorineural hearing loss and skeletal dysplasia presentation of autosomal recessive IARS2-related mitochondrial disease. Features vary and may emerge over years; the complete acronym is not required at presentation. Neonatal skeletal abnormalities without growth hormone deficiency support a primary dysplasia. The core CAGSSS clinical series is distinguished here from overlapping Leigh/West, sideroblastic-anemia and isolated-cataract presentations. ClinGen groups these presentations within one IARS2-related primary mitochondrial disease entity. The enzyme participates in mitochondrial tRNA-Ile charging, but reduced charging and translation have not been directly demonstrated for the core CAGSSS alleles in the cited studies. Normal fibroblast biochemical results coexist with disease; respiratory defects and rescue in Leigh-derived cells and knockdown models provide indirect mechanistic evidence.

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1
Inheritance
9
Pathophys.
1
Histopath.
34
Phenotypes
2
Gaps
54
Pathograph
1
Genes
8
Medical Actions
3
Differentials
5
Models
12
References
1
Deep Research
👪

Inheritance

1
Autosomal recessive HP:0000007
Autosomal recessive inheritance. The core CAGSSS families carry homozygous missense variants; compound heterozygosity, including truncating and deletion alleles, occurs in the broader IARS2 spectrum. Parental segregation distinguishes inherited biallelic variants from uncertain phase.
Autosomal recessive inheritance
Show evidence (2 references)
PMID:25130867 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"The mutation is homozygous in the affected patients, heterozygous in carriers, and absent in control chromosomes."
The full recessive segregation statement - homozygous in affected, heterozygous in unaffected carriers, absent in controls - rather than homozygosity alone.
PMID:28328135 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Here, we report on a female Danish patient with a novel homozygous IARS2 mutation, p.Gly874Arg, who presented at birth with bilateral hip dislocation and short stature."
A second homozygous patient with an independent allele, which is what moved the gene-disease relationship beyond a single consanguineous family.
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Discussions and Knowledge Gaps

2
Which allele- and tissue-dependent consequences of IARS2 dysfunction produce core CAGSSS despite normal fibroblast respiratory and translation assays?
KNOWLEDGE GAP OPEN cagsss_mechanism_not_established
Attached to
pathophysiology#Impaired Mitochondrial Isoleucyl-tRNA Charging pathophysiology#Reduced Respiratory Complex Abundance
Core Pro909Leu and Pro909Ser fibroblast results differ in protein abundance, while neither demonstrates the Leigh lymphocyte respiratory-complex phenotype. ClinGen also summarizes normal translation in the founding line. The 2024 study analyzed lymphocytes from only one of its two Leigh patients, and performed rescue in HEK293T knockdown cells. It measured complex content, oxygen consumption and ATP, without directly measuring charging or translation. Normal biochemical findings also occur in broader severe IARS2 presentations. Allele severity, cell context, compensation and tissue-specific vulnerability remain possible explanations; the available comparisons do not isolate them.
Show evidence (4 references)
PMID:30419932 REFUTE DIRECT PRIMARY RESULT In Vitro
"Patient-derived fibroblasts from proband 1 showed normal respiratory chain enzyme activity, as well as unchanged oxidative phosphorylation protein subunits and IARS2 levels."
The Pro909Ser fibroblast line refutes a universal detectable protein/OXPHOS defect in CAGSSS fibroblasts. It does not exclude defects in other tissues.
url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c REFUTE DIRECT REVIEW SYNTHESIS In Vitro
"No difference in BN PAGE nor in translation studies by S35 Methionine pulse labeling"
ClinGen summarizes normal assembled complexes and pulse-labeled translation in the founding Pro909Leu fibroblast line. This is secondary reporting of the original experiment.
PMID:39169373 SUPPORT INDIRECT PRIMARY RESULT In Vitro
"the contents of complexes I and III were decreased by ~ 90% and ~ 50% compared with control cells, respectively"
BN-PAGE/immunoblot complex contents in the single Leigh patient 2 lymphocyte line, not enzyme activities or a CAGSSS cohort.
+ 1 more reference
Is CAGSSS a distinct entity, or a named region of a continuous IARS2 phenotypic spectrum?
OPEN QUESTION OPEN cagsss_entity_boundary
Attached to
disease#CAGSSS Syndrome genetic#IARS2
CAGSSS remains a useful named phenotype with its own MONDO anchor, and this entry focuses on that clinical presentation. ClinGen evaluated the broader gene-disease relationship as definitive in December 2024 and explicitly grouped CAGSSS and Leigh-spectrum presentations as IARS2-related primary mitochondrial disease. This classification supports a shared gene-level entity without establishing identical cellular defects, penetrance or management needs across presentations. The seven-person core series, Leigh/West overlap cases, anemia-predominant disease and isolated cataract should therefore retain explicit ascertainment and phenotype boundaries. Domain-based genotype associations remain provisional.
Show evidence (2 references)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Our findings support that even though biallelic IARS2 pathogenic variants can result in a distinctive, clinically recognisable phenotype in humans, it can also show a wide range of clinical presentation from severe pediatric neurological disorders of Leigh and West syndrome to both non-syndromic..."
Both halves of the question in one sentence: a distinctive recognisable phenotype, and a spectrum it sits inside.
url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c SUPPORT DIRECT REVIEW SYNTHESIS Other
"This is one disease entity according to the ClinGen Lumping and Splitting Framework, and has been renamed as ... -related primary mitochondrial disease."
ClinGen explicitly groups the historical CAGSSS entity within IARS2-related primary mitochondrial disease.
⚙

Pathophysiology

9
Biallelic IARS2 Variants
Homozygous IARS2 missense variants underlie the seven-person core series: Pro909Leu, Pro909Ser, Gly874Arg and His761Arg. This class-level description does not include every allele in the broader IARS2 spectrum.
IARS2 hgnc:29685 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves IARS2 (hgnc:29685). hgnc:29685 is a gene from the HUGO Gene Nomenclature Committee.
Genetic context allele_type: missense variant_origin: GERMLINE zygosity: HOMOZYGOUS functional_impact_category: UNKNOWN
The core alleles are missense. Loss of function is the broader gene-disease model, but residual catalytic activity of these specific alleles has not been directly quantified in the cited studies; protein abundance differs between tested fibroblast lines.
Animal models
Iars2 Homozygous Knockout Mouse Mus musculus perturbs Complete gene knockout contrasts with the core human missense alleles.
Downstream
Reduced IARS2 Protein Abundance Observed for Pro909Leu but not Pro909Ser in the tested fibroblasts.
Impaired Mitochondrial Isoleucyl-tRNA Charging Proposed catalytic consequence; direct charging measurements for the core alleles are lacking.
Loss of Myelinated Sensory Fibers
Cataract Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Corneal Opacity Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Neurotrophic Keratitis Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Nystagmus Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Strabismus Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Foveal Hypoplasia Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Unilateral Ptosis Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Orbital Myopathy Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Severe Eye Dryness Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Spondyloepimetaphyseal Dysplasia Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Short Stature Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Growth Hormone Deficiency Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Sensorineural Hearing Impairment Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Sensory Neuropathy Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Axonal Sensorimotor Polyneuropathy Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Pain Insensitivity Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Developmental Delay Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Hip Dislocation Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Scoliosis Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Delayed Epiphyseal Ossification Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Metaphyseal Irregularity Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Brachydactyly Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Short Femoral Neck Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Pes Planus Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Joint Hypermobility Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Genu Valgum Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Adrenal Insufficiency Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Hypoglycemia Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Achalasia Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Thick Eyebrows Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Deeply Set Eyes Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Midface Retrusion Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
Hypotonia Reported clinical association in the founding family; tissue-specific causal intermediates remain unresolved.
Arthritis Reported clinical association in the founding family; tissue-specific causal intermediates remain unresolved.
Show evidence (3 references)
PMID:25130867 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Using SNP genotyping and whole-exome sequencing, we identified a single likely causal variant, a missense mutation in a conserved residue of the nuclear gene IARS2, encoding mitochondrial isoleucyl-tRNA synthetase."
The founding variant and how it was identified.
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"a single novel homozygous missense c.2725C > T, p.Pro909Ser variant in the gene IARS2"
The full Results give c.2725C>T; the abstract has an inconsistent cDNA coordinate.
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"confirming both patient 2 and 3 having the variant in a homozygous state, whereas parents and the only available healthy sibling were heterozygous."
Segregation of His761Arg in the second Iranian family.
Reduced IARS2 Protein Abundance
Mechanism confidence: Provisional
IARS2 protein was reduced in one Pro909Leu patient fibroblast line but unchanged in the Pro909Ser line. Reduced abundance is allele/model dependent and does not by itself demonstrate defective aminoacylation.
Experimental models
Pro909Leu Patient Skin Fibroblasts PRIMARY CELL CULTURE A disease-associated protein-abundance effect is observed.
Pro909Ser Patient Fibroblasts PRIMARY CELL CULTURE IARS2 amount was unchanged.
IARS2-Knockdown and Re-expression HEK293T Cells CELL LINE shRNA directly lowers IARS2 protein.
Downstream
Impaired Mitochondrial Isoleucyl-tRNA Charging
Show evidence (2 references)
PMID:25130867 SUPPORT DIRECT PRIMARY RESULT In Vitro
"IARS2 protein level was reduced in skin cells cultured from one of the patients, consistent with a pathogenic effect of the mutation."
Reduced protein in one founding Pro909Leu cell line; abundance is distinct from catalytic activity.
PMID:30419932 REFUTE DIRECT PRIMARY RESULT In Vitro
"Patient-derived fibroblasts from proband 1 showed normal respiratory chain enzyme activity, as well as unchanged oxidative phosphorylation protein subunits and IARS2 levels."
The Pro909Ser fibroblast line refutes a universal detectable protein/OXPHOS defect in CAGSSS fibroblasts. It does not exclude defects in other tissues.
Impaired Mitochondrial Isoleucyl-tRNA Charging
Mechanism confidence: Hypothetical
Reduced supply of charged mitochondrial tRNA-Ile is a proposed consequence of IARS2 dysfunction. The normal enzyme function and structural modeling motivate this hypothesis; the cited core CAGSSS studies did not directly measure charging.
isoleucine-tRNA ligase activity GO:0004822 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased isoleucine-tRNA ligase activity (GO:0004822). GO:0004822 is a molecular function from the Gene Ontology. ↓ DECREASED
Downstream
Impaired Mitochondrial Translation
Show evidence (1 reference)
PMID:30419932 SUPPORT INDIRECT BACKGROUND Other
"IARS2 encodes a mitochondrial isoleucyl-tRNA synthetase, a highly conserved nuclear-encoded enzyme required for the charging of tRNAs with their cognate amino acid for translation."
Established normal function supplies a mechanistic rationale, not direct evidence of reduced charging in CAGSSS.
Impaired Mitochondrial Translation
Mechanism confidence: Hypothetical
Insufficient aminoacylated tRNA could limit synthesis of mitochondrially encoded proteins. This step is hypothetical for core CAGSSS: the founding Pro909Leu fibroblast pulse-labeling study was normal according to ClinGen, and neither the 2018 nor 2024 study directly established reduced translation in core patients.
mitochondrial translation GO:0032543 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased mitochondrial translation (GO:0032543). GO:0032543 is a biological process from the Gene Ontology. ↓ DECREASED
Experimental models
Pro909Leu Patient Skin Fibroblasts PRIMARY CELL CULTURE Pulse-labeled translation was normal in this culture.
Downstream
Reduced Respiratory Complex Abundance
Show evidence (2 references)
url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c REFUTE DIRECT REVIEW SYNTHESIS In Vitro
"No difference in BN PAGE nor in translation studies by S35 Methionine pulse labeling"
ClinGen summarizes normal assembled complexes and pulse-labeled translation in the founding Pro909Leu fibroblast line. This is secondary reporting of the original experiment.
url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c SUPPORT INDIRECT BACKGROUND Other
"Defects in tRNA charging can result in impaired synthesis of oxidative phosphorylation complex protein subunits."
Expert-curation statement of the general mechanistic route; not a patient translation result.
Reduced Respiratory Complex Abundance
Mechanism confidence: Provisional
Assembled complexes I and III were reduced by approximately 90% and 50% in one Leigh patient-derived immortalized lymphocyte line. Their contents were also reduced in IARS2-knockdown HEK293T cells. BN-PAGE measures complex content, not catalytic activity or an assembly rate. These results are indirect for CAGSSS; core fibroblast studies did not show the same deficit.
Experimental models
Pro909Ser Patient Fibroblasts PRIMARY CELL CULTURE Measured OXPHOS subunit levels were unchanged.
Leigh Patient 2 Immortalized Lymphocytes CELL LINE The broader IARS2 model shows lower assembled complex content.
Downstream
Reduced Mitochondrial Respiration
Show evidence (3 references)
PMID:39169373 SUPPORT INDIRECT PRIMARY RESULT In Vitro
"the contents of complexes I and III were decreased by ~ 90% and ~ 50% compared with control cells, respectively"
BN-PAGE/immunoblot complex contents in the single Leigh patient 2 lymphocyte line, not enzyme activities or a CAGSSS cohort.
PMID:30419932 REFUTE DIRECT PRIMARY RESULT In Vitro
"Patient-derived fibroblasts from proband 1 showed normal respiratory chain enzyme activity, as well as unchanged oxidative phosphorylation protein subunits and IARS2 levels."
The Pro909Ser fibroblast line refutes a universal detectable protein/OXPHOS defect in CAGSSS fibroblasts. It does not exclude defects in other tissues.
url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c REFUTE DIRECT REVIEW SYNTHESIS In Vitro
"No difference in BN PAGE nor in translation studies by S35 Methionine pulse labeling"
ClinGen summarizes normal assembled complexes and pulse-labeled translation in the founding Pro909Leu fibroblast line. This is secondary reporting of the original experiment.
Reduced Mitochondrial Respiration
Mechanism confidence: Provisional
Basal and ATP-linked oxygen consumption were reduced in the Leigh lymphocyte line and HEK293T knockdown models. A matching respiratory phenotype has not been demonstrated in the core CAGSSS tissues.
aerobic respiration GO:0009060 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased aerobic respiration (GO:0009060). GO:0009060 is a biological process from the Gene Ontology. ↓ DECREASED
Experimental models
Leigh Patient 2 Immortalized Lymphocytes CELL LINE Basal and ATP-linked oxygen consumption were reduced.
IARS2-Knockdown and Re-expression HEK293T Cells CELL LINE Wild-type re-expression rescues the knockdown-cell respiratory phenotype.
Downstream
Reduced Cellular ATP Availability
Increased Mitochondrial ROS
Show evidence (2 references)
PMID:39169373 SUPPORT INDIRECT PRIMARY RESULT In Vitro
"Patient-derived immortalized lymphocytes showed a significant reduction in basal respiration and ATP-linked respiration compared to control cells"
Respiration in one Leigh patient line supports a possible route, not a demonstrated core CAGSSS defect.
PMID:39169373 SUPPORT INDIRECT PRIMARY RESULT In Vitro
"The compensatory experiments in vitro cell models confirmed the pathogenicity of IARS2 variants since re-expression of wild-type IARS2 rather than mutant IARS2 could rescue complexes I and III deficiency, oxygen consumption, and cellular ATP content in IARS2 knockdown cells."
Wild-type re-expression rescued HEK293T knockdown readouts; the three tested missense alleles were from Leigh cases, and rescue was not performed in patient cells.
Reduced Cellular ATP Availability
Mechanism confidence: Provisional
Cellular ATP was lower in the Leigh lymphocyte line and HEK293T knockdown/variant models. Tissue energy deficiency is a possible contributor to CAGSSS, but these assays do not identify the mechanism of each clinical feature.
ATP biosynthetic process GO:0006754 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased ATP biosynthetic process (GO:0006754). GO:0006754 is a biological process from the Gene Ontology. ↓ DECREASED
Show evidence (2 references)
PMID:39169373 SUPPORT INDIRECT PRIMARY RESULT In Vitro
"results showed that the production of cellular ATP and MMP was decreased compared with control cells"
Lower ATP and membrane-potential readouts in the Leigh lymphocyte model.
PMID:39169373 SUPPORT INDIRECT PRIMARY RESULT In Vitro
"The compensatory experiments in vitro cell models confirmed the pathogenicity of IARS2 variants since re-expression of wild-type IARS2 rather than mutant IARS2 could rescue complexes I and III deficiency, oxygen consumption, and cellular ATP content in IARS2 knockdown cells."
Wild-type re-expression rescued HEK293T knockdown readouts; the three tested missense alleles were from Leigh cases, and rescue was not performed in patient cells.
Increased Mitochondrial ROS
Mechanism confidence: Provisional
Mitochondrial ROS was increased in IARS2-knockdown HEK293T cells. Oxidative stress has not been measured as a common clinical CAGSSS mechanism in the cited sources.
Experimental models
IARS2-Knockdown and Re-expression HEK293T Cells CELL LINE Knockdown increases mitochondrial ROS.
Show evidence (1 reference)
PMID:39169373 SUPPORT INDIRECT PRIMARY RESULT In Vitro
"the production of cellular ATP was notably decreased and the mitochondrial ROS level was increased in IARS2 knockdown cells compared with control cells"
ROS was increased in knockdown HEK293T cells; no corresponding core CAGSSS tissue measurement was reported.
Loss of Myelinated Sensory Fibers
Mechanism confidence: Established
Loss of small and medium-sized myelinated fibers, particularly in the hands, was reported in two core cases. The molecular route from IARS2 variation to this nerve lesion remains unresolved.
Downstream
Sensory Neuropathy
Pain Insensitivity
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"A loss of small and medium-sized myelinated fibres, particularly in the hands, was reported in two of these patients."
Histological nerve-fiber loss summarized from the founding clinical literature.
✶

Histopathology

1
Loss of Small and Medium Myelinated Nerve Fibers
Reported in two core cases, with greater involvement in the hands than feet; not established as a universal or required diagnostic biopsy finding.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"A loss of small and medium-sized myelinated fibres, particularly in the hands, was reported in two of these patients."
Histological nerve-fiber loss summarized from the founding clinical literature.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for CAGSSS Syndrome Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

34
Cardiovascular 1
Severe Eye Dryness Keratoconjunctivitis sicca HP:0001097 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Severe dry eyes, annotated with Keratoconjunctivitis sicca (HP:0001097). HP:0001097 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:27078007 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"A 33-year-old woman known for infantile cataracts, growth hormone deficiency, sensory neuropathy, sensorineural hearing loss, and skeletal dysplasia was referred to us for multiple failed corneal grafts and severe eye dryness."
The case report directly describes severe eye dryness; it does not supply a disease-wide frequency.
Digestive 1
Achalasia OCCASIONAL HP:0002571 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Type II esophageal achalasia, annotated with Achalasia (HP:0002571). HP:0002571 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"At birth, he disclosed spastic features and type II achalasia that was confirmed and treated using endoscopy."
The Iranian neonatal-onset manifestation.
PMID:35228874 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"CAGSSS (N = 7) ... Type 2 Achalasia | 2/7"
Table 1 summarizes seven core CAGSSS cases, including milder cataract/skeletal presentations. This is an ascertained case-series proportion, not population penetrance.
Ear 1
Sensorineural Hearing Impairment FREQUENT HP:0000407 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Sensorineural hearing impairment (HP:0000407). HP:0000407 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:30419932 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"Four out of ten patients reported to date were found to exhibit sensorineural hearing loss with a broad age of onset ranging from 18 months to 13 years of age"
All four hearing-positive cases in the ten-person mixed table belong to its seven-person core CAGSSS subset.
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"revealed a bilateral, stable, mid-to-high frequency moderate hearing loss at ages 16 and 20 years of age"
Longitudinal audiometry in the Iranian patient.
Endocrine 2
Growth Hormone Deficiency Reduced circulating growth hormone concentration HP:0034323 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Growth hormone deficiency, annotated with Reduced circulating growth hormone concentration (HP:0034323). HP:0034323 is a phenotype from the Human Phenotype Ontology.
HPO lists growth hormone deficiency as an exact synonym of HP:0034323. HP:0000824 denotes decreased response to a growth hormone stimulation test, which is not documented for all reported diagnoses.
Show evidence (2 references)
PMID:30419932 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"patient 7 had low growth hormone levels at 15 years of age that worsened to a severe deficiency at 22 years of age"
Directly reported low circulating GH in the Canadian case, summarized from the founding publication.
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"A growth hormone deficiency (GHD) was diagnosed, resulting from the combination of severe short stature, delayed bone aged, and very low IGF-1 (− 2 SD)"
The Iranian diagnosis used a different set of endocrine observations.
Adrenal Insufficiency Central adrenal insufficiency HP:0011734 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Central adrenal insufficiency (HP:0011734). HP:0011734 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"After repeated measurements, a remarkable decreased serum cortisol level (2.6 μg/dl) and a normal amount of plasmatic adrenocorticotropic hormone (ACTH) in the morning (8 AM) were noted, revealing central adrenal insufficiency."
Direct endocrine measurements in the Iranian patient.
PMID:30419932 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"Due to the low cortisol values in patient 7, we also speculate an adrenal insufficiency that would require further studies."
The second case remains suspected rather than confirmed.
Eye 8
Cataract OBLIGATE HP:0000518 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cataract (HP:0000518). HP:0000518 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:25130867 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Here, we report a novel disorder in three adult patients with a phenotype including cataracts, short-stature secondary to growth hormone deficiency, sensorineural hearing deficit, peripheral sensory neuropathy, and skeletal dysplasia."
Cataract in all three patients of the founding family.
PMID:35228874 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"CAGSSS (N = 7) ... Cataract | 7/7"
Table 1 summarizes seven core CAGSSS cases, including milder cataract/skeletal presentations. This is an ascertained case-series proportion, not population penetrance.
Corneal Opacity VERY_FREQUENT HP:0007957 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Corneal opacity (HP:0007957). HP:0007957 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:35228874 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"CAGSSS (N = 7) ... Corneal opacification | 6/7"
Table 1 summarizes seven core CAGSSS cases, including milder cataract/skeletal presentations. This is an ascertained case-series proportion, not population penetrance.
PMID:27078007 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"The patient was found to have neurotrophic keratitis and corneal opacification."
Corneal opacification in a 33-year-old with the full CAGSSS pentad, together with the neurotrophic keratitis that explains it.
Neurotrophic Keratitis HP:0000491 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Neurotrophic keratitis, annotated with Keratitis (HP:0000491). HP:0000491 is a phenotype from the Human Phenotype Ontology.
No specific neurotrophic-keratitis term was identified in HPO; the keratitis binding retains the clinical subtype in preferred_term.
Show evidence (1 reference)
PMID:27078007 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"The patient was found to have neurotrophic keratitis and corneal opacification."
The finding itself, in a patient with the complete syndrome.
Nystagmus OBLIGATE HP:0000639 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Nystagmus (HP:0000639). HP:0000639 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:35228874 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"CAGSSS (N = 7) ... Bilateral nystagmus | 7/7"
Table 1 summarizes seven core CAGSSS cases, including milder cataract/skeletal presentations. This is an ascertained case-series proportion, not population penetrance.
Strabismus HP:0000486 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Strabismus (HP:0000486). HP:0000486 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"At birth, no fundus could be identified in patient 2 during ophthalmological investigations and she showed slight strabismus of the right eye."
Strabismus in the second patient, with the neonatal ophthalmological findings.
PMID:8409271 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"infantile cataracts, nystagmus, esotropia, unusual facies"
Esotropia in the original Canadian boy.
Foveal Hypoplasia Hypoplasia of the fovea HP:0007750 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypoplasia of the fovea (HP:0007750). HP:0007750 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Optical coherence tomography also revealed foveal hypoplasia."
OCT finding in patient 7, a re-examination of a founding-family case.
Unilateral Ptosis HP:0007687 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Unilateral ptosis (HP:0007687). HP:0007687 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"this patient had a history of congenital neurotropic keratitis, orbital myopathy and ptosis of the right eye"
The reported ocular findings in patient 7.
Deeply Set Eyes HP:0000490 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Deeply set eye (HP:0000490). HP:0000490 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"mildly thickened eyebrows and deep set eyes"
Specific facial finding in the clinical description.
Head and Neck 2
Thick Eyebrows HP:0000574 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Thick eyebrow (HP:0000574). HP:0000574 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"mildly thickened eyebrows and deep set eyes"
Specific facial finding in the clinical description.
Midface Retrusion HP:0011800 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Midface retrusion (HP:0011800). HP:0011800 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"thick eyebrows, midface retrusion, underdeveloped ala nasi, short philtrum, thin upper lip"
Specific facial finding in the clinical description.
Limbs 6
Hip Dislocation FREQUENT HP:0002827 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hip dislocation (HP:0002827). HP:0002827 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:35228874 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"CAGSSS (N = 7) ... Bilateral hip dislocation | 4/7"
Table 1 summarizes seven core CAGSSS cases, including milder cataract/skeletal presentations. This is an ascertained case-series proportion, not population penetrance.
PMID:28328135 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Here, we report on a female Danish patient with a novel homozygous IARS2 mutation, p.Gly874Arg, who presented at birth with bilateral hip dislocation and short stature."
Documents neonatal hip dislocation in the Danish patient. The frequency derives from the separate seven-person summary.
Metaphyseal Irregularity HP:0003025 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Metaphyseal irregularity (HP:0003025). HP:0003025 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Knees show metaphyseal widening and irregularities while hands show brachydactyly (short fingers) and proximal metacarpal rounding."
Reported skeletal finding; no population penetrance is inferred.
Brachydactyly HP:0001156 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Brachydactyly (HP:0001156). HP:0001156 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Knees show metaphyseal widening and irregularities while hands show brachydactyly (short fingers) and proximal metacarpal rounding."
Reported skeletal finding; no population penetrance is inferred.
Short Femoral Neck HP:0100864 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short femoral neck (HP:0100864). HP:0100864 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"a right hip with a shortened femoral neck due to metaphyseal dyplasia with signs of secondary arthrosis of the hip joint"
Reported skeletal finding; no population penetrance is inferred.
Pes Planus HP:0001763 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Pes planus (HP:0001763). HP:0001763 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"bilateral pes planus (with arthrodesis of the right ankle joints performed)"
Reported skeletal finding; no population penetrance is inferred.
Genu Valgum HP:0002857 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Genu valgum (HP:0002857). HP:0002857 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"Hip dislocation was observed in four cases, joint hypermobility in three cases, and two probands had genu valgum."
Reported skeletal finding; no population penetrance is inferred.
Metabolism 1
Hypoglycemia HP:0001943 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypoglycemia (HP:0001943). HP:0001943 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:30419932 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"Hypoglycemia, which can be linked to central adrenal insufficiency, was noted in patient 7 and patient 9"
The association does not demonstrate adrenal causation in both patients.
PMID:8409271 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"short stature secondary to growth hormone deficiency, late-childhood-onset arthritis, and hypoglycemia."
Hypoglycemia in the original Canadian girl.
Musculoskeletal 7
Orbital Myopathy HP:0003198 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Orbital myopathy, annotated with Myopathy (HP:0003198). HP:0003198 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"orbital myopathy and slight strabismus of the right eye are also overlapping phenotypes reported in patient 1."
Orbital myopathy in a second core patient.
Spondyloepimetaphyseal Dysplasia HP:0002651 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Spondyloepimetaphyseal dysplasia (HP:0002651). HP:0002651 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
PMID:28328135 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"At 18 months her radiographic skeletal abnormalities were suggestive of an underlying spondyloepimetaphyseal dysplasia (SEMD)."
The radiographic classification of the dysplasia.
PMID:28328135 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Retrospective analysis of the neonatal radiographs confirmed that the skeletal changes were present at birth."
The observation that makes the dysplasia primary: it predates any endocrine or neuromuscular cause that could have produced it secondarily.
PMID:28328135 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"We present her clinical features and particularly highlight her skeletal findings, which confirm the presence of a primary SEMD skeletal dysplasia in a growing list of mitochondrial-related disorders including CAGSSS, CODAS, EVEN-PLUS, and X-linked SEMD-MR syndromes."
The authors' own conclusion that the dysplasia is primary, and the placement of CAGSSS among the mitochondrial disorders with skeletal dysplasia.
Scoliosis FREQUENT HP:0002650 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Scoliosis (HP:0002650). HP:0002650 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:35228874 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"CAGSSS (N = 7) ... Scoliosis | 4/7"
Table 1 summarizes seven core CAGSSS cases, including milder cataract/skeletal presentations. This is an ascertained case-series proportion, not population penetrance.
Delayed Epiphyseal Ossification HP:0002663 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Delayed epiphyseal ossification (HP:0002663). HP:0002663 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:8409271 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"delayed ossification of the femoral heads, scoliosis, short stature secondary to growth hormone deficiency"
Reported skeletal finding; no population penetrance is inferred.
Joint Hypermobility HP:0001382 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Joint hypermobility (HP:0001382). HP:0001382 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"Hip dislocation was observed in four cases, joint hypermobility in three cases, and two probands had genu valgum."
Reported skeletal finding; no population penetrance is inferred.
Hypotonia HP:0001252 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypotonia (HP:0001252). HP:0001252 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:8409271 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"esotropia, unusual facies, hypotonia, bilateral congenital hip dysplasia"
Direct observation in the original family; no population frequency is inferred.
Arthritis HP:0001369 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Arthritis (HP:0001369). HP:0001369 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:8409271 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"short stature secondary to growth hormone deficiency, late-childhood-onset arthritis, and hypoglycemia."
Direct observation in the original family; no population frequency is inferred.
Nervous System 4
Sensory Neuropathy FREQUENT HP:0000763 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Sensory neuropathy (HP:0000763). HP:0000763 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:35228874 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"CAGSSS (N = 7) ... Neuropathy | 5/7"
Table 1 summarizes seven core CAGSSS cases, including milder cataract/skeletal presentations. This is an ascertained case-series proportion, not population penetrance.
PMID:30419932 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"Decreased sensation to pinprick, temperature, and touch in all four extremities was reported in patient 7"
Sensory modalities affected in the Canadian adult.
Axonal Sensorimotor Polyneuropathy Sensorimotor neuropathy HP:0007141 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Sensorimotor neuropathy (HP:0007141). HP:0007141 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Electrodiagnostic testing of the left limb at 16 years of age showed abnormal results that were consistent with chronic sensorimotor distal axonal polyneuropathy."
The specific electrophysiological phenotype.
Pain Insensitivity HP:0007021 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Pain insensitivity (HP:0007021). HP:0007021 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"Pain insensitivity was noted in early childhood in another patient"
Summary of the Danish case.
Developmental Delay FREQUENT Neurodevelopmental delay HP:0012758 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Neurodevelopmental delay (HP:0012758). HP:0012758 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:35228874 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"CAGSSS (N = 7) ... Developmental delay in early life | 5/7"
Table 1 summarizes seven core CAGSSS cases, including milder cataract/skeletal presentations. This is an ascertained case-series proportion, not population penetrance.
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Throughout early childhood, he experienced delayed motor development; however, this resolved spontaneously later on. No evidence of cognitive performance limitations has been observed."
The Iranian adult had resolved motor delay without reported cognitive limitations.
Growth 1
Short Stature OBLIGATE HP:0004322 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short stature (HP:0004322). HP:0004322 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:35228874 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"CAGSSS (N = 7) ... Short stature | 7/7"
Table 1 summarizes seven core CAGSSS cases, including milder cataract/skeletal presentations. This is an ascertained case-series proportion, not population penetrance.
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Like her older sister, she had normal hearing tests and normal growth hormone levels. She presented with short stature"
Short stature despite normal GH levels in the His761Arg sisters.
🧬

Genetic Associations

1
IARS2
Gene: IARS2 hgnc:29685 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is IARS2 (hgnc:29685). hgnc:29685 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE variant_origin: GERMLINE
Show evidence (2 references)
PMID:35228874 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"All seven patients of CAGSSS where the result of homozygous missense pathogenic variants around the anticodon‐binding domain"
The published seven-person genotype summary; the authors acknowledge uncertainty in domain boundaries.
PMID:29914532 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"the mutations c.2446C > T; p.(Arg816*) and c.2575 T > C; p.(Phe859Leu) were identified in two affected brothers in family #10, both of which had bilateral cataracts without other anomalies."
A truncating allele with a milder cataract-only presentation argues against a simple truncation-equals-Leigh rule.
💊

Medical Actions

8
Cataract Surgery
Action: cataract surgeryNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is cataract surgery (NCIT:C157809). NCIT:C157809 is a clinical intervention from the NCI Thesaurus. Ontology label: Cataract Surgery NCIT:C157809
Platform: Surgery
Cataract extraction has been performed in several core cases, including congenital cataracts in the Iranian proband. Timing, visual rehabilitation and follow-up require ophthalmological assessment; surgery does not treat accompanying corneal or neuromuscular disease.
Target Phenotypes: Cataract HP:0000518 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Cataract (HP:0000518). HP:0000518 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"presented with congenital cataracts that required surgery, as well as corneal opacity, bilateral nystagmus"
Records that the cataract required surgical treatment. It reports the indication, not an outcome.
Corneal Transplantation
Action: corneal transplantationNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is corneal transplantation (NCIT:C210959). NCIT:C210959 is a clinical intervention from the NCI Thesaurus. Ontology label: Corneal Transplantation NCIT:C210959
Platform: Surgery
Corneal grafts were attempted in three reported core-spectrum patients: two Iranian sisters had rejection at ages 30 and 20, and the Canadian adult had multiple failed grafts with neurotrophic keratitis and severe dryness. These reports document failures and a need to assess the ocular surface; they do not establish a universal failure rate or prove the mechanism of graft rejection.
Target Phenotypes: Corneal opacity HP:0007957 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Corneal opacity (HP:0007957). HP:0007957 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
PMID:30419932 REFUTE DIRECT PRIMARY RESULT Human Clinical
"She received a corneal graft later on, which was rejected when she was 30 years-old."
A reported failure refutes success in this individual, not effectiveness of all corneal grafting or a quantified disease-wide failure probability.
PMID:27078007 REFUTE DIRECT PRIMARY RESULT Human Clinical
"A 33-year-old woman known for infantile cataracts, growth hormone deficiency, sensory neuropathy, sensorineural hearing loss, and skeletal dysplasia was referred to us for multiple failed corneal grafts and severe eye dryness."
A reported failure refutes success in this individual, not effectiveness of all corneal grafting or a quantified disease-wide failure probability.
PMID:30419932 REFUTE DIRECT PRIMARY RESULT Human Clinical
"she also received a corneal graft that was rejected when she was 20 years old."
Rejection in the younger Iranian sister, a third affected individual.
Growth Hormone Replacement
Action: Growth hormone replacementNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Growth hormone replacement, annotated with Hormone Replacement Therapy (NCIT:C15599). NCIT:C15599 is a clinical intervention from the NCI Thesaurus. Ontology label: Hormone Replacement Therapy NCIT:C15599
Agent: somatropin CHEBI:749556 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses somatropin (CHEBI:749556). CHEBI:749556 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Protein replacement
Growth hormone replacement was given to two Canadian cases with reported positive outcomes. Detailed dosing, height response and controlled long-term efficacy were not provided in the cited summary. The Iranian patient had diagnosed deficiency but no available GH treatment.
Target Phenotypes: Short stature secondary to growth hormone deficiency HP:0004322 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Short stature secondary to growth hormone deficiency, annotated with Short stature (HP:0004322). HP:0004322 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"Growth hormone replacement therapy was performed in patient 7 and patient 8 with positive outcomes."
Reported use and qualitative benefit in two cases; not a controlled efficacy estimate.
Hearing Rehabilitation
Action: Hearing aid rehabilitationNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Hearing aid rehabilitation, annotated with Therapeutic Procedure (NCIT:C49236), qualified as Medical Device Hearing Aid. NCIT:C49236 is a clinical intervention from the NCI Thesaurus. Ontology label: Therapeutic Procedure NCIT:C49236
Platform: Device
Hearing aids were used in two core cases. The literature does not establish a syndrome-specific device protocol or benefit estimate.
Mechanism Target:
Sensorineural Hearing Impairment — Hearing amplification addresses the reported hearing impairment.
Target Phenotypes: Sensorineural hearing impairment HP:0000407 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Sensorineural hearing impairment (HP:0000407). HP:0000407 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical
"Hearing aids were used in only two of these cases"
Actual hearing-aid use reported in the clinical summary.
Endoscopic Treatment of Achalasia
Action: Therapeutic Endoscopic ProcedureNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Therapeutic Endoscopic Procedure (NCIT:C64958). NCIT:C64958 is a clinical intervention from the NCI Thesaurus. NCIT:C64958
Platform: Surgery
The Iranian patient underwent endoscopic confirmation and treatment of type II achalasia. The publication does not specify a particular endoscopic technique or quantify long-term response.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"At birth, he disclosed spastic features and type II achalasia that was confirmed and treated using endoscopy."
Actual treatment, without an inferred balloon dilation or myotomy technique.
Orthopedic Surgery
Action: ArthrodesisNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Arthrodesis (NCIT:C52007). NCIT:C52007 is a clinical intervention from the NCI Thesaurus. NCIT:C52007
Platform: Surgery
Right ankle arthrodesis was performed for the Iranian patient with bilateral pes planus. Other skeletal care depends on the particular hip, spine and joint abnormalities.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"bilateral pes planus (with arthrodesis of the right ankle joints performed)"
The specific orthopedic procedure reported.
Glucocorticoid Replacement for Adrenal Insufficiency
Action: Glucocorticoid replacementNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Glucocorticoid replacement, annotated with Hormone Replacement Therapy (NCIT:C15599). NCIT:C15599 is a clinical intervention from the NCI Thesaurus. Ontology label: Hormone Replacement Therapy NCIT:C15599
Agent: hydrocortisone CHEBI:17650 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses hydrocortisone, annotated with cortisol (CHEBI:17650). CHEBI:17650 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
Replacement is standard supportive care for confirmed central adrenal insufficiency; a CAGSSS-specific efficacy estimate is not available. Endocrine assessment and individualized replacement are needed rather than assuming every patient has adrenal failure.
Target Phenotypes: Central adrenal insufficiency HP:0011734 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Central adrenal insufficiency (HP:0011734). HP:0011734 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.endocrine.org/clinical-practice-guidelines/hormone-replacement-in-hypopituitarism SUPPORT INDIRECT REVIEW SYNTHESIS Other
"People who have central adrenal insufficiency should receive the lowest tolerable dose of hydrocortisone replacement on a long-term basis"
General adult hypopituitarism guidance supports replacement for confirmed central adrenal insufficiency; it is not CAGSSS-specific treatment evidence.
Genetic Counseling
Action: Genetic counselingNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Genetic counseling (NCIT:C15240). NCIT:C15240 is a clinical intervention from the NCI Thesaurus. Ontology label: Genetic Counseling NCIT:C15240
Platform: Other
Discuss recessive inheritance, parental carrier status, family testing and reproductive options. Counseling should account for the variable IARS2 spectrum and limited genotype-based prognostic information.
Show evidence (1 reference)
PMID:25130867 SUPPORT INDIRECT PRIMARY RESULT Human Clinical
"The mutation is homozygous in the affected patients, heterozygous in carriers, and absent in control chromosomes."
Recessive segregation grounds family counseling; this is not an intervention-outcome study.
🔬

Biochemical Markers

1
Variable Fibroblast IARS2 and Respiratory-Chain Findings (Variable; normal results possible)
Context: Cultured skin fibroblasts, not a clinical serum biomarker
Show evidence (3 references)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT In Vitro
"Patient-derived fibroblasts from proband 1 showed normal respiratory chain enzyme activity, as well as unchanged oxidative phosphorylation protein subunits and IARS2 levels."
Documents the variable or normal cultured-cell biochemical result described here; the corresponding deficiency mechanism carries the appropriate refuting evidence separately.
PMID:25130867 SUPPORT DIRECT PRIMARY RESULT In Vitro
"IARS2 protein level was reduced in skin cells cultured from one of the patients, consistent with a pathogenic effect of the mutation."
Documents the variable or normal cultured-cell biochemical result described here; the corresponding deficiency mechanism carries the appropriate refuting evidence separately.
url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c SUPPORT DIRECT REVIEW SYNTHESIS In Vitro
"No difference in BN PAGE nor in translation studies by S35 Methionine pulse labeling"
Documents the variable or normal cultured-cell biochemical result described here; the corresponding deficiency mechanism carries the appropriate refuting evidence separately.
🔬

Diagnosis

6
IARS2 Sequencing and Segregation
Identify biallelic disease-associated variants and establish phase/segregation. The absence of the full acronym at presentation does not exclude IARS2 disease. Copy-number analysis can be relevant when sequencing leaves an unresolved allele, as demonstrated in broader Leigh presentations.
Genetic Testing NCIT:C15709 NCI Thesaurus (NCIT)
Show evidence (2 references)
PMID:28328135 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"It was only with time that several of the other manifestations of the CAGSSS emerged, namely, cataracts, peripheral neuropathy, and hearing loss."
The temporal argument for not requiring the full acronym before testing.
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"The homozygous IARS2 variant was confirmed in patient 1 using Sanger sequencing and both parents were found to be heterozygous"
Confirmation and segregation in the Iranian family.
Skeletal Radiography
Assess epiphyseal, metaphyseal, vertebral and hip abnormalities. Review neonatal films when available; primary dysplasia can precede endocrine deficiency.
Bone Radiography NCIT:C137876 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:28328135 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Retrospective analysis of the neonatal radiographs confirmed that the skeletal changes were present at birth."
The retrospective neonatal review, and what it established.
Audiological Assessment
Age-appropriate audiometry characterizes hearing loss, which can arise after an initially normal evaluation. The Iranian adult had serial pure-tone audiograms and tympanometry.
Audiometric testing NCIT:C38036 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Pure-tone audiometry was performed according to best-practice recommendations"
Audiometry was performed; this is not a disease-specific diagnostic threshold.
Nerve Conduction Studies
Evaluate sensory and motor amplitudes and conduction velocities in patients with sensory loss, weakness or pain insensitivity.
Nerve Conduction Velocity Test NCIT:C88502 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Electrodiagnostic testing of the left limb at 16 years of age showed abnormal results that were consistent with chronic sensorimotor distal axonal polyneuropathy."
The specific electrophysiological phenotype.
Endocrine Assessment
Assess growth, bone age, GH/IGF-1 and the adrenal axis according to clinical findings. Normal GH in childhood does not guarantee lifelong normal function. Repeated low cortisol with inappropriately normal ACTH supported central adrenal insufficiency in one adult.
Laboratory Procedure NCIT:C25294 NCI Thesaurus (NCIT)
Show evidence (2 references)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"After repeated measurements, a remarkable decreased serum cortisol level (2.6 μg/dl) and a normal amount of plasmatic adrenocorticotropic hormone (ACTH) in the morning (8 AM) were noted, revealing central adrenal insufficiency."
Direct endocrine measurements in the Iranian patient.
PMID:30419932 SUPPORT DIRECT REVIEW SYNTHESIS Other
"It would be particularly interesting for additional patients with IARS2 pathogenic variants to be monitored for adrenal insufficiency."
Authors recommend attention to adrenal function.
Ophthalmological Assessment
Evaluate lens opacity, corneal surface and sensation, ocular alignment/motility and vision. OCT can characterize foveal abnormalities when clinically indicated. The detailed adult examination identified pathology beyond cataract.
Eye examination NCIT:C38060 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Optical coherence tomography also revealed foveal hypoplasia."
OCT finding in patient 7, a re-examination of a founding-family case.
🔀

Differential Diagnoses

3

Conditions with similar clinical presentations that must be differentiated from CAGSSS Syndrome:

🧫

Experimental Models

4
Pro909Leu Patient Skin Fibroblasts PRIMARY_CELL_CULTURE
Cultured skin cells from one founding-family patient showed reduced IARS2 abundance. ClinGen summarizes normal BN-PAGE and S35-methionine translation studies; protein reduction therefore did not establish respiratory/translation failure in this culture.
Organism
Homo sapiens NCBITaxon:9606 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
Publication
PMID:25130867
Pathograph links
Reduced IARS2 Protein Abundance recapitulates fidelity: moderate A disease-associated protein-abundance effect is observed.
Limitations: One patient line; no common effect across core alleles is established.
Show evidence (1 reference)
PMID:25130867 SUPPORT DIRECT PRIMARY RESULT In Vitro
"IARS2 protein level was reduced in skin cells cultured from one of the patients, consistent with a pathogenic effect of the mutation."
Reduced protein in one founding Pro909Leu cell line; abundance is distinct from catalytic activity.
Impaired Mitochondrial Translation fails to recapitulate fidelity: low Pulse-labeled translation was normal in this culture.
Limitations: Normal fibroblast translation does not exclude tissue-specific dysfunction; the detailed result is available here through expert curation.
Show evidence (1 reference)
url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c SUPPORT DIRECT REVIEW SYNTHESIS In Vitro
"No difference in BN PAGE nor in translation studies by S35 Methionine pulse labeling"
ClinGen reports a normal translation/BN-PAGE result in the founding fibroblast line.
Show evidence (2 references)
PMID:25130867 SUPPORT DIRECT PRIMARY RESULT In Vitro
"IARS2 protein level was reduced in skin cells cultured from one of the patients, consistent with a pathogenic effect of the mutation."
Reduced protein in one founding Pro909Leu cell line; abundance is distinct from catalytic activity.
url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c SUPPORT DIRECT REVIEW SYNTHESIS In Vitro
"No difference in BN PAGE nor in translation studies by S35 Methionine pulse labeling"
ClinGen reports a normal translation/BN-PAGE result in the founding fibroblast line.
Pro909Ser Patient Fibroblasts PRIMARY_CELL_CULTURE
One Iranian patient line was tested for respiratory-complex enzyme activities normalized to citrate synthase, OXPHOS subunits and IARS2 abundance. Enzyme controls numbered eight; protein comparisons used two age-matched controls. All reported readouts were unchanged, and charging was not assayed.
Organism
Homo sapiens NCBITaxon:9606 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
Publication
PMID:30419932
Pathograph links
Reduced IARS2 Protein Abundance fails to recapitulate fidelity: low IARS2 amount was unchanged.
Limitations: One allele, one donor and cultured skin fibroblasts.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT In Vitro
"Patient-derived fibroblasts from proband 1 showed normal respiratory chain enzyme activity, as well as unchanged oxidative phosphorylation protein subunits and IARS2 levels."
The model has normal measured protein/respiratory-chain readouts; this is positive evidence for the stated negative model result.
Reduced Respiratory Complex Abundance fails to recapitulate fidelity: low Measured OXPHOS subunit levels were unchanged.
Limitations: Subunit immunoblots and enzyme activities do not directly measure all assembly kinetics or affected tissues.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT In Vitro
"Patient-derived fibroblasts from proband 1 showed normal respiratory chain enzyme activity, as well as unchanged oxidative phosphorylation protein subunits and IARS2 levels."
The model has normal measured protein/respiratory-chain readouts; this is positive evidence for the stated negative model result.
Show evidence (1 reference)
PMID:30419932 SUPPORT DIRECT PRIMARY RESULT In Vitro
"Patient-derived fibroblasts from proband 1 showed normal respiratory chain enzyme activity, as well as unchanged oxidative phosphorylation protein subunits and IARS2 levels."
The model has normal measured protein/respiratory-chain readouts; this is positive evidence for the stated negative model result.
Leigh Patient 2 Immortalized Lymphocytes CELL_LINE
EBV-immortalized lymphocytes from the child with c.1_390del and c.2450G>A showed reduced IARS2 protein, complexes I/III, oxygen consumption, ATP and membrane-potential readouts. Only patient 2 yielded this line; patient 1 was not studied in an equivalent patient-cell assay.
Organism
Homo sapiens NCBITaxon:9606 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
Publication
PMID:39169373
Pathograph links
Reduced Respiratory Complex Abundance partially recapitulates fidelity: low The broader IARS2 model shows lower assembled complex content.
Limitations: Leigh genotype and immortalized lymphocytes, not a core CAGSSS allele or affected tissue.
Show evidence (1 reference)
PMID:39169373 SUPPORT INDIRECT PRIMARY RESULT In Vitro
"the contents of complexes I and III were decreased by ~ 90% and ~ 50% compared with control cells, respectively"
BN-PAGE/immunoblot complex contents in the single Leigh patient 2 lymphocyte line, not enzyme activities or a CAGSSS cohort.
Reduced Mitochondrial Respiration partially recapitulates fidelity: low Basal and ATP-linked oxygen consumption were reduced.
Limitations: One donor; different alleles and cell type from the core fibroblast experiments.
Show evidence (1 reference)
PMID:39169373 SUPPORT INDIRECT PRIMARY RESULT In Vitro
"Patient-derived immortalized lymphocytes showed a significant reduction in basal respiration and ATP-linked respiration compared to control cells"
Respiration in one Leigh patient line supports a possible route, not a demonstrated core CAGSSS defect.
Show evidence (3 references)
PMID:39169373 SUPPORT DIRECT PRIMARY RESULT In Vitro
"To determine the pathogenicity of IARS2 variants, we constructed immortalized lymphocytes derived from patient 2. However, due to physical condition of patient 1, we were unable to establish immortalized lymphocytes from this patient."
Only one of the two clinical patients supplied the experimental lymphocyte line.
PMID:39169373 SUPPORT INDIRECT PRIMARY RESULT In Vitro
"the contents of complexes I and III were decreased by ~ 90% and ~ 50% compared with control cells, respectively"
BN-PAGE/immunoblot complex contents in the single Leigh patient 2 lymphocyte line, not enzyme activities or a CAGSSS cohort.
PMID:39169373 SUPPORT INDIRECT PRIMARY RESULT In Vitro
"Patient-derived immortalized lymphocytes showed a significant reduction in basal respiration and ATP-linked respiration compared to control cells"
Respiration in one Leigh patient line supports a possible route, not a demonstrated core CAGSSS defect.
IARS2-Knockdown and Re-expression HEK293T Cells CELL_LINE
shRNA reduced IARS2 protein by about 60%. Complex I/III contents, respiration and ATP decreased and mitochondrial ROS increased. Re-expression of wild-type IARS2 improved readouts relative to three Leigh-associated missense constructs. Different mutant protein levels limit attribution to intrinsic catalytic activity; no core CAGSSS missense allele was tested.
Organism
Homo sapiens NCBITaxon:9606 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
Publication
PMID:39169373
Pathograph links
Reduced IARS2 Protein Abundance perturbs fidelity: low shRNA directly lowers IARS2 protein.
Limitations: Engineered depletion differs from core missense alleles.
Show evidence (1 reference)
PMID:39169373 SUPPORT DIRECT PRIMARY RESULT In Vitro
"shRNA-mediated IARS2 knockdown was established in HEK293T cells, with an 60% decrease in the expression of IARS2 protein"
The knockdown perturbation.
Reduced Mitochondrial Respiration rescues fidelity: low Wild-type re-expression rescues the knockdown-cell respiratory phenotype.
Limitations: Rescue was in HEK293T cells, not in patient cells or a therapeutic trial.
Show evidence (1 reference)
PMID:39169373 SUPPORT INDIRECT PRIMARY RESULT In Vitro
"The compensatory experiments in vitro cell models confirmed the pathogenicity of IARS2 variants since re-expression of wild-type IARS2 rather than mutant IARS2 could rescue complexes I and III deficiency, oxygen consumption, and cellular ATP content in IARS2 knockdown cells."
Wild-type re-expression rescued HEK293T knockdown readouts; the three tested missense alleles were from Leigh cases, and rescue was not performed in patient cells.
Increased Mitochondrial ROS partially recapitulates fidelity: low Knockdown increases mitochondrial ROS.
Limitations: ROS has not been established as a patient CAGSSS tissue phenotype.
Show evidence (1 reference)
PMID:39169373 SUPPORT INDIRECT PRIMARY RESULT In Vitro
"the production of cellular ATP was notably decreased and the mitochondrial ROS level was increased in IARS2 knockdown cells compared with control cells"
ROS was increased in knockdown HEK293T cells; no corresponding core CAGSSS tissue measurement was reported.
Show evidence (3 references)
PMID:39169373 SUPPORT DIRECT PRIMARY RESULT In Vitro
"shRNA-mediated IARS2 knockdown was established in HEK293T cells, with an 60% decrease in the expression of IARS2 protein"
The engineered depletion level.
PMID:39169373 SUPPORT INDIRECT PRIMARY RESULT In Vitro
"The compensatory experiments in vitro cell models confirmed the pathogenicity of IARS2 variants since re-expression of wild-type IARS2 rather than mutant IARS2 could rescue complexes I and III deficiency, oxygen consumption, and cellular ATP content in IARS2 knockdown cells."
Wild-type re-expression rescued HEK293T knockdown readouts; the three tested missense alleles were from Leigh cases, and rescue was not performed in patient cells.
PMID:39169373 SUPPORT INDIRECT PRIMARY RESULT In Vitro
"the production of cellular ATP was notably decreased and the mitochondrial ROS level was increased in IARS2 knockdown cells compared with control cells"
ROS was increased in knockdown HEK293T cells; no corresponding core CAGSSS tissue measurement was reported.
🐁

Animal Models

1
Iars2 Homozygous Knockout Mouse
ClinGen summarizes IMPC evidence for embryonic lethality at E9.5 in homozygous Iars2 knockout mice. This supports an essential developmental function but is not a viable model of the core human missense syndrome.
Species
Mus musculus
Genotype
Homozygous Iars2 knockout
Publication
url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c
Pathograph links
Biallelic IARS2 Variants perturbs fidelity: low Complete gene knockout contrasts with the core human missense alleles.
Limitations: Null allele and embryonic lethality differ from surviving humans with residual-function missense alleles. Residual enzyme activity has not been quantified in the core cases.
Show evidence (1 reference)
url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c SUPPORT INDIRECT REVIEW SYNTHESIS Model Organism
"Embryonic lethal (E9.5) homozygous KO of IARS2"
The null perturbation is developmentally lethal.
Show evidence (1 reference)
url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c SUPPORT INDIRECT REVIEW SYNTHESIS Model Organism
"Embryonic lethal (E9.5) homozygous KO of IARS2"
Expert-curation summary of IMPC data; no claim that the complete CAGSSS phenotype is reproduced.
{ }

Source YAML

click to show 
name: CAGSSS Syndrome
category: Mendelian
creation_date: '2026-09-03T19:00:00Z'
synonyms:
- CAGSSS
- cataract-growth hormone deficiency-sensory neuropathy-sensorineural hearing loss-skeletal dysplasia syndrome
- IARS2-related CAGSSS
- cataracts, growth hormone deficiency, sensory neuropathy, sensorineural hearing loss, and skeletal dysplasia syndrome
description: CAGSSS is the cataract, growth hormone deficiency, sensory neuropathy, sensorineural hearing loss and skeletal dysplasia presentation of autosomal recessive IARS2-related mitochondrial disease. Features vary and may emerge over years; the complete acronym is not required at presentation. Neonatal skeletal abnormalities without growth hormone deficiency support a primary dysplasia. The core CAGSSS clinical series is distinguished here from overlapping Leigh/West, sideroblastic-anemia and isolated-cataract presentations. ClinGen groups these presentations within one IARS2-related primary mitochondrial disease entity. The enzyme participates in mitochondrial tRNA-Ile charging, but reduced charging and translation have not been directly demonstrated for the core CAGSSS alleles in the cited studies. Normal fibroblast biochemical results coexist with disease; respiratory defects and rescue in Leigh-derived cells and knockdown models provide indirect mechanistic evidence.
disease_term:
  preferred_term: cataract-growth hormone deficiency-sensory neuropathy-sensorineural hearing loss-skeletal dysplasia syndrome
  term:
    id: MONDO:0014455
    label: cataract-growth hormone deficiency-sensory neuropathy-sensorineural hearing loss-skeletal dysplasia syndrome
parents:
- Mitochondrial Disease
inheritance:
- name: Autosomal recessive
  description: Autosomal recessive inheritance. The core CAGSSS families carry homozygous missense variants; compound heterozygosity, including truncating and deletion alleles, occurs in the broader IARS2 spectrum. Parental segregation distinguishes inherited biallelic variants from uncertain phase.
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:25130867
    reference_title: Mutation in the nuclear-encoded mitochondrial isoleucyl-tRNA synthetase IARS2 in patients with cataracts, growth hormone deficiency with short stature, partial sensorineural deafness, and peripheral neuropathy or with Leigh syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The mutation is homozygous in the affected patients, heterozygous in carriers, and absent in control chromosomes.
    explanation: The full recessive segregation statement - homozygous in affected, heterozygous in unaffected carriers, absent in controls - rather than homozygosity alone.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:28328135
    reference_title: Confirmation of CAGSSS syndrome as a distinct entity in a Danish patient with a novel homozygous mutation in IARS2.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Here, we report on a female Danish patient with a novel homozygous IARS2 mutation, p.Gly874Arg, who presented at birth with bilateral hip dislocation and short stature.
    explanation: A second homozygous patient with an independent allele, which is what moved the gene-disease relationship beyond a single consanguineous family.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
pathophysiology:
- name: Biallelic IARS2 Variants
  biological_scale: MOLECULAR
  description: 'Homozygous IARS2 missense variants underlie the seven-person core series: Pro909Leu, Pro909Ser, Gly874Arg and His761Arg. This class-level description does not include every allele in the broader IARS2 spectrum.'
  genes:
  - preferred_term: IARS2
    term:
      id: hgnc:29685
      label: IARS2
  genetic_context:
    allele_type: missense
    variant_origin: GERMLINE
    zygosity: HOMOZYGOUS
    functional_impact_category: UNKNOWN
    description: The core alleles are missense. Loss of function is the broader gene-disease model, but residual catalytic activity of these specific alleles has not been directly quantified in the cited studies; protein abundance differs between tested fibroblast lines.
  downstream:
  - target: Reduced IARS2 Protein Abundance
    causal_link_type: UNKNOWN
    description: Observed for Pro909Leu but not Pro909Ser in the tested fibroblasts.
  - target: Impaired Mitochondrial Isoleucyl-tRNA Charging
    causal_link_type: UNKNOWN
    description: Proposed catalytic consequence; direct charging measurements for the core alleles are lacking.
  - target: Loss of Myelinated Sensory Fibers
    causal_link_type: UNKNOWN
  - target: Cataract
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Corneal Opacity
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Neurotrophic Keratitis
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Nystagmus
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Strabismus
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Foveal Hypoplasia
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Unilateral Ptosis
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Orbital Myopathy
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Severe Eye Dryness
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Spondyloepimetaphyseal Dysplasia
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Short Stature
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Growth Hormone Deficiency
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Sensorineural Hearing Impairment
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Sensory Neuropathy
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Axonal Sensorimotor Polyneuropathy
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Pain Insensitivity
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Developmental Delay
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Hip Dislocation
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Scoliosis
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Delayed Epiphyseal Ossification
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Metaphyseal Irregularity
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Brachydactyly
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Short Femoral Neck
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Pes Planus
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Joint Hypermobility
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Genu Valgum
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Adrenal Insufficiency
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Hypoglycemia
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Achalasia
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Thick Eyebrows
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Deeply Set Eyes
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Midface Retrusion
    causal_link_type: UNKNOWN
    description: Clinical association with IARS2-related CAGSSS; tissue-specific causal intermediates are unresolved.
  - target: Hypotonia
    causal_link_type: UNKNOWN
    description: Reported clinical association in the founding family; tissue-specific causal intermediates remain unresolved.
  - target: Arthritis
    causal_link_type: UNKNOWN
    description: Reported clinical association in the founding family; tissue-specific causal intermediates remain unresolved.
  evidence:
  - reference: PMID:25130867
    reference_title: Mutation in the nuclear-encoded mitochondrial isoleucyl-tRNA synthetase IARS2 in patients with cataracts, growth hormone deficiency with short stature, partial sensorineural deafness, and peripheral neuropathy or with Leigh syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Using SNP genotyping and whole-exome sequencing, we identified a single likely causal variant, a missense mutation in a conserved residue of the nuclear gene IARS2, encoding mitochondrial isoleucyl-tRNA synthetase.
    explanation: The founding variant and how it was identified.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: a single novel homozygous missense c.2725C > T, p.Pro909Ser variant in the gene IARS2
    explanation: The full Results give c.2725C>T; the abstract has an inconsistent cDNA coordinate.
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: confirming both patient 2 and 3 having the variant in a homozygous state, whereas parents and the only available healthy sibling were heterozygous.
    explanation: Segregation of His761Arg in the second Iranian family.
- name: Reduced IARS2 Protein Abundance
  biological_scale: MOLECULAR
  description: IARS2 protein was reduced in one Pro909Leu patient fibroblast line but unchanged in the Pro909Ser line. Reduced abundance is allele/model dependent and does not by itself demonstrate defective aminoacylation.
  evidence:
  - reference: PMID:25130867
    reference_title: Mutation in the nuclear-encoded mitochondrial isoleucyl-tRNA synthetase IARS2 in patients with cataracts, growth hormone deficiency with short stature, partial sensorineural deafness, and peripheral neuropathy or with Leigh syndrome.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: IARS2 protein level was reduced in skin cells cultured from one of the patients, consistent with a pathogenic effect of the mutation.
    explanation: Reduced protein in one founding Pro909Leu cell line; abundance is distinct from catalytic activity.
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: REFUTE
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Patient-derived fibroblasts from proband 1 showed normal respiratory chain enzyme activity, as well as unchanged oxidative phosphorylation protein subunits and IARS2 levels.
    explanation: The Pro909Ser fibroblast line refutes a universal detectable protein/OXPHOS defect in CAGSSS fibroblasts. It does not exclude defects in other tissues.
  mechanism_confidence: PROVISIONAL
  downstream:
  - target: Impaired Mitochondrial Isoleucyl-tRNA Charging
    causal_link_type: UNKNOWN
- name: Impaired Mitochondrial Isoleucyl-tRNA Charging
  biological_scale: MOLECULAR
  description: Reduced supply of charged mitochondrial tRNA-Ile is a proposed consequence of IARS2 dysfunction. The normal enzyme function and structural modeling motivate this hypothesis; the cited core CAGSSS studies did not directly measure charging.
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: BACKGROUND
    directness: INDIRECT
    snippet: IARS2 encodes a mitochondrial isoleucyl-tRNA synthetase, a highly conserved nuclear-encoded enzyme required for the charging of tRNAs with their cognate amino acid for translation.
    explanation: Established normal function supplies a mechanistic rationale, not direct evidence of reduced charging in CAGSSS.
  mechanism_confidence: HYPOTHETICAL
  downstream:
  - target: Impaired Mitochondrial Translation
    causal_link_type: DIRECT
  molecular_functions:
  - preferred_term: isoleucine-tRNA ligase activity
    term:
      id: GO:0004822
      label: isoleucine-tRNA ligase activity
    modifier: DECREASED
- name: Impaired Mitochondrial Translation
  biological_scale: MOLECULAR
  description: 'Insufficient aminoacylated tRNA could limit synthesis of mitochondrially encoded proteins. This step is hypothetical for core CAGSSS: the founding Pro909Leu fibroblast pulse-labeling study was normal according to ClinGen, and neither the 2018 nor 2024 study directly established reduced translation in core patients.'
  evidence:
  - reference: url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c
    reference_title: curation results for Gene-Disease Validity
    supports: REFUTE
    evidence_source: IN_VITRO
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: No difference in  BN PAGE nor in translation studies by S35 Methionine pulse labeling
    explanation: ClinGen summarizes normal assembled complexes and pulse-labeled translation in the founding Pro909Leu fibroblast line. This is secondary reporting of the original experiment.
  - reference: url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c
    reference_title: curation results for Gene-Disease Validity
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: BACKGROUND
    directness: INDIRECT
    snippet: Defects in tRNA charging can result in impaired synthesis of oxidative phosphorylation complex protein subunits.
    explanation: Expert-curation statement of the general mechanistic route; not a patient translation result.
  mechanism_confidence: HYPOTHETICAL
  downstream:
  - target: Reduced Respiratory Complex Abundance
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Reduced synthesis of mitochondrially encoded respiratory-chain subunits
  biological_processes:
  - preferred_term: mitochondrial translation
    term:
      id: GO:0032543
      label: mitochondrial translation
    modifier: DECREASED
- name: Reduced Respiratory Complex Abundance
  biological_scale: CELLULAR
  description: Assembled complexes I and III were reduced by approximately 90% and 50% in one Leigh patient-derived immortalized lymphocyte line. Their contents were also reduced in IARS2-knockdown HEK293T cells. BN-PAGE measures complex content, not catalytic activity or an assembly rate. These results are indirect for CAGSSS; core fibroblast studies did not show the same deficit.
  evidence:
  - reference: PMID:39169373
    reference_title: IARS2 mutations lead to Leigh syndrome with a combined oxidative phosphorylation deficiency.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: INDIRECT
    snippet: the contents of complexes I and III were decreased by ~ 90% and ~ 50% compared with control cells, respectively
    explanation: BN-PAGE/immunoblot complex contents in the single Leigh patient 2 lymphocyte line, not enzyme activities or a CAGSSS cohort.
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: REFUTE
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Patient-derived fibroblasts from proband 1 showed normal respiratory chain enzyme activity, as well as unchanged oxidative phosphorylation protein subunits and IARS2 levels.
    explanation: The Pro909Ser fibroblast line refutes a universal detectable protein/OXPHOS defect in CAGSSS fibroblasts. It does not exclude defects in other tissues.
  - reference: url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c
    reference_title: curation results for Gene-Disease Validity
    supports: REFUTE
    evidence_source: IN_VITRO
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: No difference in  BN PAGE nor in translation studies by S35 Methionine pulse labeling
    explanation: ClinGen summarizes normal assembled complexes and pulse-labeled translation in the founding Pro909Leu fibroblast line. This is secondary reporting of the original experiment.
  mechanism_confidence: PROVISIONAL
  downstream:
  - target: Reduced Mitochondrial Respiration
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
- name: Reduced Mitochondrial Respiration
  biological_scale: CELLULAR
  description: Basal and ATP-linked oxygen consumption were reduced in the Leigh lymphocyte line and HEK293T knockdown models. A matching respiratory phenotype has not been demonstrated in the core CAGSSS tissues.
  evidence:
  - reference: PMID:39169373
    reference_title: IARS2 mutations lead to Leigh syndrome with a combined oxidative phosphorylation deficiency.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: INDIRECT
    snippet: Patient-derived immortalized lymphocytes showed a significant reduction in basal respiration and ATP-linked respiration compared to control cells
    explanation: Respiration in one Leigh patient line supports a possible route, not a demonstrated core CAGSSS defect.
  - reference: PMID:39169373
    reference_title: IARS2 mutations lead to Leigh syndrome with a combined oxidative phosphorylation deficiency.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: INDIRECT
    snippet: The compensatory experiments in vitro cell models confirmed the pathogenicity of IARS2 variants since re-expression of wild-type IARS2 rather than mutant IARS2 could rescue complexes I and III deficiency, oxygen consumption, and cellular ATP content in IARS2 knockdown cells.
    explanation: Wild-type re-expression rescued HEK293T knockdown readouts; the three tested missense alleles were from Leigh cases, and rescue was not performed in patient cells.
  mechanism_confidence: PROVISIONAL
  downstream:
  - target: Reduced Cellular ATP Availability
    causal_link_type: DIRECT
  - target: Increased Mitochondrial ROS
    causal_link_type: UNKNOWN
  biological_processes:
  - preferred_term: aerobic respiration
    term:
      id: GO:0009060
      label: aerobic respiration
    modifier: DECREASED
- name: Reduced Cellular ATP Availability
  biological_scale: CELLULAR
  description: Cellular ATP was lower in the Leigh lymphocyte line and HEK293T knockdown/variant models. Tissue energy deficiency is a possible contributor to CAGSSS, but these assays do not identify the mechanism of each clinical feature.
  evidence:
  - reference: PMID:39169373
    reference_title: IARS2 mutations lead to Leigh syndrome with a combined oxidative phosphorylation deficiency.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: INDIRECT
    snippet: results showed that the production of cellular ATP and MMP was decreased compared with control cells
    explanation: Lower ATP and membrane-potential readouts in the Leigh lymphocyte model.
  - reference: PMID:39169373
    reference_title: IARS2 mutations lead to Leigh syndrome with a combined oxidative phosphorylation deficiency.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: INDIRECT
    snippet: The compensatory experiments in vitro cell models confirmed the pathogenicity of IARS2 variants since re-expression of wild-type IARS2 rather than mutant IARS2 could rescue complexes I and III deficiency, oxygen consumption, and cellular ATP content in IARS2 knockdown cells.
    explanation: Wild-type re-expression rescued HEK293T knockdown readouts; the three tested missense alleles were from Leigh cases, and rescue was not performed in patient cells.
  mechanism_confidence: PROVISIONAL
  biological_processes:
  - preferred_term: ATP biosynthetic process
    term:
      id: GO:0006754
      label: ATP biosynthetic process
    modifier: DECREASED
- name: Increased Mitochondrial ROS
  biological_scale: CELLULAR
  description: Mitochondrial ROS was increased in IARS2-knockdown HEK293T cells. Oxidative stress has not been measured as a common clinical CAGSSS mechanism in the cited sources.
  evidence:
  - reference: PMID:39169373
    reference_title: IARS2 mutations lead to Leigh syndrome with a combined oxidative phosphorylation deficiency.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: INDIRECT
    snippet: the production of cellular ATP was notably decreased and the mitochondrial ROS level was increased in IARS2 knockdown cells compared with control cells
    explanation: ROS was increased in knockdown HEK293T cells; no corresponding core CAGSSS tissue measurement was reported.
  mechanism_confidence: PROVISIONAL
- name: Loss of Myelinated Sensory Fibers
  biological_scale: TISSUE
  description: Loss of small and medium-sized myelinated fibers, particularly in the hands, was reported in two core cases. The molecular route from IARS2 variation to this nerve lesion remains unresolved.
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: A loss of small and medium-sized myelinated fibres, particularly in the hands, was reported in two of these patients.
    explanation: Histological nerve-fiber loss summarized from the founding clinical literature.
  mechanism_confidence: ESTABLISHED
  downstream:
  - target: Sensory Neuropathy
    causal_link_type: DIRECT
  - target: Pain Insensitivity
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
phenotypes:
- name: Cataract
  description: Congenital or early-childhood cataract was present in all seven core cases in the 2022 summary; onset extended to age three. Cataract can also occur without the other CAGSSS features.
  phenotype_term:
    preferred_term: Cataract
    term:
      id: HP:0000518
      label: Cataract
  evidence:
  - reference: PMID:25130867
    reference_title: Mutation in the nuclear-encoded mitochondrial isoleucyl-tRNA synthetase IARS2 in patients with cataracts, growth hormone deficiency with short stature, partial sensorineural deafness, and peripheral neuropathy or with Leigh syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Here, we report a novel disorder in three adult patients with a phenotype including cataracts, short-stature secondary to growth hormone deficiency, sensorineural hearing deficit, peripheral sensory neuropathy, and skeletal dysplasia.
    explanation: Cataract in all three patients of the founding family.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:35228874
    reference_title: 'Genotype-phenotype correlation in IARS2-related diseases: A case report and review of literature.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: CAGSSS (N = 7) ... Cataract | 7/7
    explanation: Table 1 summarizes seven core CAGSSS cases, including milder cataract/skeletal presentations. This is an ascertained case-series proportion, not population penetrance.
  frequency: OBLIGATE
  category: Ophthalmological
- name: Corneal Opacity
  description: Corneal opacification occurred in six of seven core cases. Progressive opacity and graft failures have been reported, but the literature does not establish that every graft will fail.
  phenotype_term:
    preferred_term: Corneal opacity
    term:
      id: HP:0007957
      label: Corneal opacity
  evidence:
  - reference: PMID:35228874
    reference_title: 'Genotype-phenotype correlation in IARS2-related diseases: A case report and review of literature.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: CAGSSS (N = 7) ... Corneal opacification | 6/7
    explanation: Table 1 summarizes seven core CAGSSS cases, including milder cataract/skeletal presentations. This is an ascertained case-series proportion, not population penetrance.
  - reference: PMID:27078007
    reference_title: Recessive Mutation in a Nuclear-Encoded Mitochondrial tRNA Synthetase Associated With Infantile Cataract, Congenital Neurotrophic Keratitis, and Orbital Myopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The patient was found to have neurotrophic keratitis and corneal opacification.
    explanation: Corneal opacification in a 33-year-old with the full CAGSSS pentad, together with the neurotrophic keratitis that explains it.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  frequency: VERY_FREQUENT
  category: Ophthalmological
- name: Neurotrophic Keratitis
  description: Congenital neurotrophic keratitis was documented in the adult ophthalmological follow-up of a founding-family patient. This is the same individual described in the 2014 discovery cohort.
  phenotype_term:
    preferred_term: Neurotrophic keratitis
    term:
      id: HP:0000491
      label: Keratitis
  evidence:
  - reference: PMID:27078007
    reference_title: Recessive Mutation in a Nuclear-Encoded Mitochondrial tRNA Synthetase Associated With Infantile Cataract, Congenital Neurotrophic Keratitis, and Orbital Myopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The patient was found to have neurotrophic keratitis and corneal opacification.
    explanation: The finding itself, in a patient with the complete syndrome.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  category: Ophthalmological
  notes: No specific neurotrophic-keratitis term was identified in HPO; the keratitis binding retains the clinical subtype in preferred_term.
- name: Nystagmus
  description: Bilateral nystagmus was present in all seven core cases in the published summary. This descriptive frequency does not establish universal penetrance.
  phenotype_term:
    preferred_term: Nystagmus
    term:
      id: HP:0000639
      label: Nystagmus
  evidence:
  - reference: PMID:35228874
    reference_title: 'Genotype-phenotype correlation in IARS2-related diseases: A case report and review of literature.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: CAGSSS (N = 7) ... Bilateral nystagmus | 7/7
    explanation: Table 1 summarizes seven core CAGSSS cases, including milder cataract/skeletal presentations. This is an ascertained case-series proportion, not population penetrance.
  frequency: OBLIGATE
  category: Ophthalmological
- name: Strabismus
  description: Strabismus is reported in the Iranian families and the original Canadian childhood description. The main narrative and supplementary table differ on which Iranian sister had it, so a precise denominator is not assigned.
  phenotype_term:
    preferred_term: Strabismus
    term:
      id: HP:0000486
      label: Strabismus
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: At birth, no fundus could be identified in patient 2 during ophthalmological investigations and she showed slight strabismus of the right eye.
    explanation: Strabismus in the second patient, with the neonatal ophthalmological findings.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:8409271
    reference_title: Unique hereditary sensory and autonomic neuropathy with growth hormone deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: infantile cataracts, nystagmus, esotropia, unusual facies
    explanation: Esotropia in the original Canadian boy.
  category: Ophthalmological
- name: Foveal Hypoplasia
  description: OCT showed foveal hypoplasia in the extensively examined Canadian adult; frequency in other patients is unknown.
  phenotype_term:
    preferred_term: Hypoplasia of the fovea
    term:
      id: HP:0007750
      label: Hypoplasia of the fovea
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Optical coherence tomography also revealed foveal hypoplasia.
    explanation: OCT finding in patient 7, a re-examination of a founding-family case.
  category: Ophthalmological
- name: Unilateral Ptosis
  description: Right-eye ptosis was reported in the Canadian adult.
  phenotype_term:
    preferred_term: Unilateral ptosis
    term:
      id: HP:0007687
      label: Unilateral ptosis
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: this patient had a history of congenital neurotropic keratitis, orbital myopathy and ptosis of the right eye
    explanation: The reported ocular findings in patient 7.
  category: Ophthalmological
- name: Orbital Myopathy
  description: Orbital myopathy was reported in the Canadian adult and the Iranian Pro909Ser patient. The sources do not specify a uniform ophthalmoplegia phenotype.
  phenotype_term:
    preferred_term: Orbital myopathy
    term:
      id: HP:0003198
      label: Myopathy
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: orbital myopathy and slight strabismus of the right eye are also overlapping phenotypes reported in patient 1.
    explanation: Orbital myopathy in a second core patient.
  category: Ophthalmological
- name: Severe Eye Dryness
  description: Severe ocular dryness accompanied neurotrophic keratitis and repeated graft failure in the ophthalmological case report.
  phenotype_term:
    preferred_term: Severe dry eyes
    term:
      id: HP:0001097
      label: Keratoconjunctivitis sicca
  evidence:
  - reference: PMID:27078007
    reference_title: Recessive Mutation in a Nuclear-Encoded Mitochondrial tRNA Synthetase Associated With Infantile Cataract, Congenital Neurotrophic Keratitis, and Orbital Myopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: A 33-year-old woman known for infantile cataracts, growth hormone deficiency, sensory neuropathy, sensorineural hearing loss, and skeletal dysplasia was referred to us for multiple failed corneal grafts and severe eye dryness.
    explanation: The case report directly describes severe eye dryness; it does not supply a disease-wide frequency.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  category: Ophthalmological
- name: Spondyloepimetaphyseal Dysplasia
  description: A primary skeletal dysplasia is supported by neonatal abnormalities in the Danish patient before growth hormone deficiency had manifested. Skeletal manifestations vary, including epiphyseal and metaphyseal abnormalities.
  phenotype_term:
    preferred_term: Spondyloepimetaphyseal dysplasia
    term:
      id: HP:0002651
      label: Spondyloepimetaphyseal dysplasia
  evidence:
  - reference: PMID:28328135
    reference_title: Confirmation of CAGSSS syndrome as a distinct entity in a Danish patient with a novel homozygous mutation in IARS2.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: At 18 months her radiographic skeletal abnormalities were suggestive of an underlying spondyloepimetaphyseal dysplasia (SEMD).
    explanation: The radiographic classification of the dysplasia.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:28328135
    reference_title: Confirmation of CAGSSS syndrome as a distinct entity in a Danish patient with a novel homozygous mutation in IARS2.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Retrospective analysis of the neonatal radiographs confirmed that the skeletal changes were present at birth.
    explanation: 'The observation that makes the dysplasia primary: it predates any endocrine or neuromuscular cause that could have produced it secondarily.'
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:28328135
    reference_title: Confirmation of CAGSSS syndrome as a distinct entity in a Danish patient with a novel homozygous mutation in IARS2.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We present her clinical features and particularly highlight her skeletal findings, which confirm the presence of a primary SEMD skeletal dysplasia in a growing list of mitochondrial-related disorders including CAGSSS, CODAS, EVEN-PLUS, and X-linked SEMD-MR syndromes.
    explanation: The authors' own conclusion that the dysplasia is primary, and the placement of CAGSSS among the mitochondrial disorders with skeletal dysplasia.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  category: Skeletal
- name: Short Stature
  description: All seven core cases in the published summary had short stature, which may be proportionate or disproportionate. Growth hormone deficiency explains only a subset; short stature can precede it or occur with normal hormone levels.
  phenotype_term:
    preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  evidence:
  - reference: PMID:35228874
    reference_title: 'Genotype-phenotype correlation in IARS2-related diseases: A case report and review of literature.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: CAGSSS (N = 7) ... Short stature | 7/7
    explanation: Table 1 summarizes seven core CAGSSS cases, including milder cataract/skeletal presentations. This is an ascertained case-series proportion, not population penetrance.
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Like her older sister, she had normal hearing tests and normal growth hormone levels. She presented with short stature
    explanation: Short stature despite normal GH levels in the His761Arg sisters.
  frequency: OBLIGATE
  category: Growth
- name: Growth Hormone Deficiency
  description: Growth hormone deficiency is variable. Low circulating GH at age 15 progressed to severe deficiency at 22 in the Canadian adult. The Iranian patient was clinically diagnosed using severe short stature, delayed bone age and low IGF-1; a stimulation-test result was not reported.
  phenotype_term:
    preferred_term: Growth hormone deficiency
    term:
      id: HP:0034323
      label: Reduced circulating growth hormone concentration
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: patient 7 had low growth hormone levels at 15 years of age that worsened to a severe deficiency at 22 years of age
    explanation: Directly reported low circulating GH in the Canadian case, summarized from the founding publication.
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: A growth hormone deficiency (GHD) was diagnosed, resulting from the combination of severe short stature, delayed bone aged, and very low IGF-1 (− 2 SD)
    explanation: The Iranian diagnosis used a different set of endocrine observations.
  category: Endocrine
  notes: HPO lists growth hormone deficiency as an exact synonym of HP:0034323. HP:0000824 denotes decreased response to a growth hormone stimulation test, which is not documented for all reported diagnoses.
- name: Sensorineural Hearing Impairment
  description: Onset ranged from approximately 18 months to 13 years in the core reports. Four affected individuals are identifiable in the 2018 patient table and supplement; the later summary gives five of seven without explaining the additional case. Both imply a frequent feature, but an exact pooled count is uncertain. The Iranian Pro909Ser patient had stable moderate mid-to-high-frequency loss between ages 16 and 20.
  phenotype_term:
    preferred_term: Sensorineural hearing impairment
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Four out of ten patients reported to date were found to exhibit sensorineural hearing loss with a broad age of onset ranging from 18 months to 13 years of age
    explanation: All four hearing-positive cases in the ten-person mixed table belong to its seven-person core CAGSSS subset.
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: revealed a bilateral, stable, mid-to-high frequency moderate hearing loss at ages 16 and 20 years of age
    explanation: Longitudinal audiometry in the Iranian patient.
  frequency: FREQUENT
  category: Auditory
- name: Sensory Neuropathy
  description: Peripheral sensory neuropathy affects five of seven core cases, with onset from infancy to later childhood. Sensory deficits can include pain, temperature and touch; some patients have a sensorimotor axonal phenotype.
  phenotype_term:
    preferred_term: Sensory neuropathy
    term:
      id: HP:0000763
      label: Sensory neuropathy
  evidence:
  - reference: PMID:35228874
    reference_title: 'Genotype-phenotype correlation in IARS2-related diseases: A case report and review of literature.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: CAGSSS (N = 7) ... Neuropathy | 5/7
    explanation: Table 1 summarizes seven core CAGSSS cases, including milder cataract/skeletal presentations. This is an ascertained case-series proportion, not population penetrance.
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Decreased sensation to pinprick, temperature, and touch in all four extremities was reported in patient 7
    explanation: Sensory modalities affected in the Canadian adult.
  frequency: FREQUENT
  category: Neurological
- name: Axonal Sensorimotor Polyneuropathy
  description: Electrophysiology at age 16 in the Iranian Pro909Ser patient showed chronic distal sensorimotor axonal polyneuropathy, with low/absent sensory amplitudes and nearly normal motor conduction velocity.
  phenotype_term:
    preferred_term: Sensorimotor neuropathy
    term:
      id: HP:0007141
      label: Sensorimotor neuropathy
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Electrodiagnostic testing of the left limb at 16 years of age showed abnormal results that were consistent with chronic sensorimotor distal axonal polyneuropathy.
    explanation: The specific electrophysiological phenotype.
  category: Neurological
- name: Pain Insensitivity
  description: Pain insensitivity was recognized in early childhood in the Danish patient.
  phenotype_term:
    preferred_term: Pain insensitivity
    term:
      id: HP:0007021
      label: Pain insensitivity
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Pain insensitivity was noted in early childhood in another patient
    explanation: Summary of the Danish case.
  category: Neurological
- name: Developmental Delay
  description: Early developmental delay occurred in five of seven core cases. It may resolve, and preserved cognition is reported in several older individuals; profound progressive neurodegeneration should prompt consideration of overlapping IARS2 neurological disease.
  phenotype_term:
    preferred_term: Neurodevelopmental delay
    term:
      id: HP:0012758
      label: Neurodevelopmental delay
  evidence:
  - reference: PMID:35228874
    reference_title: 'Genotype-phenotype correlation in IARS2-related diseases: A case report and review of literature.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: CAGSSS (N = 7) ... Developmental delay in early life | 5/7
    explanation: Table 1 summarizes seven core CAGSSS cases, including milder cataract/skeletal presentations. This is an ascertained case-series proportion, not population penetrance.
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Throughout early childhood, he experienced delayed motor development; however, this resolved spontaneously later on. No evidence of cognitive performance limitations has been observed.
    explanation: The Iranian adult had resolved motor delay without reported cognitive limitations.
  frequency: FREQUENT
  category: Neurological
- name: Hip Dislocation
  description: Hip dislocation affected four of seven core cases, at birth in the Danish patient and one Canadian cousin and later in other Canadian cases.
  phenotype_term:
    preferred_term: Hip dislocation
    term:
      id: HP:0002827
      label: Hip dislocation
  evidence:
  - reference: PMID:35228874
    reference_title: 'Genotype-phenotype correlation in IARS2-related diseases: A case report and review of literature.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: CAGSSS (N = 7) ... Bilateral hip dislocation | 4/7
    explanation: Table 1 summarizes seven core CAGSSS cases, including milder cataract/skeletal presentations. This is an ascertained case-series proportion, not population penetrance.
  - reference: PMID:28328135
    reference_title: Confirmation of CAGSSS syndrome as a distinct entity in a Danish patient with a novel homozygous mutation in IARS2.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Here, we report on a female Danish patient with a novel homozygous IARS2 mutation, p.Gly874Arg, who presented at birth with bilateral hip dislocation and short stature.
    explanation: Documents neonatal hip dislocation in the Danish patient. The frequency derives from the separate seven-person summary.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  frequency: FREQUENT
  category: Skeletal
- name: Scoliosis
  description: Scoliosis was reported in four of seven core cases, including mild scoliosis in the Iranian adult.
  phenotype_term:
    preferred_term: Scoliosis
    term:
      id: HP:0002650
      label: Scoliosis
  evidence:
  - reference: PMID:35228874
    reference_title: 'Genotype-phenotype correlation in IARS2-related diseases: A case report and review of literature.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: CAGSSS (N = 7) ... Scoliosis | 4/7
    explanation: Table 1 summarizes seven core CAGSSS cases, including milder cataract/skeletal presentations. This is an ascertained case-series proportion, not population penetrance.
  frequency: FREQUENT
  category: Skeletal
- name: Delayed Epiphyseal Ossification
  description: Delayed epiphyseal ossification has been reported, including delayed femoral-head ossification in the original boy.
  phenotype_term:
    preferred_term: Delayed epiphyseal ossification
    term:
      id: HP:0002663
      label: Delayed epiphyseal ossification
  evidence:
  - reference: PMID:8409271
    reference_title: Unique hereditary sensory and autonomic neuropathy with growth hormone deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: delayed ossification of the femoral heads, scoliosis, short stature secondary to growth hormone deficiency
    explanation: Reported skeletal finding; no population penetrance is inferred.
  category: Skeletal
- name: Metaphyseal Irregularity
  description: Metaphyseal irregularities and widening were described in the Iranian sisters and earlier core cases.
  phenotype_term:
    preferred_term: Metaphyseal irregularity
    term:
      id: HP:0003025
      label: Metaphyseal irregularity
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Knees show metaphyseal widening and irregularities while hands show brachydactyly (short fingers) and proximal metacarpal rounding.
    explanation: Reported skeletal finding; no population penetrance is inferred.
  category: Skeletal
- name: Brachydactyly
  description: Short fingers and short first metacarpals occur in the skeletal presentation.
  phenotype_term:
    preferred_term: Brachydactyly
    term:
      id: HP:0001156
      label: Brachydactyly
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Knees show metaphyseal widening and irregularities while hands show brachydactyly (short fingers) and proximal metacarpal rounding.
    explanation: Reported skeletal finding; no population penetrance is inferred.
  category: Skeletal
- name: Short Femoral Neck
  description: A shortened femoral neck with metaphyseal dysplasia and secondary hip arthrosis was reported in the Iranian adult.
  phenotype_term:
    preferred_term: Short femoral neck
    term:
      id: HP:0100864
      label: Short femoral neck
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: a right hip with a shortened femoral neck due to metaphyseal dyplasia with signs of secondary arthrosis of the hip joint
    explanation: Reported skeletal finding; no population penetrance is inferred.
  category: Skeletal
- name: Pes Planus
  description: Bilateral pes planus was present in the Iranian adult, who underwent right ankle arthrodesis.
  phenotype_term:
    preferred_term: Pes planus
    term:
      id: HP:0001763
      label: Pes planus
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: bilateral pes planus (with arthrodesis of the right ankle joints performed)
    explanation: Reported skeletal finding; no population penetrance is inferred.
  category: Skeletal
- name: Joint Hypermobility
  description: Joint hypermobility was described in three core cases in the detailed clinical summary.
  phenotype_term:
    preferred_term: Joint hypermobility
    term:
      id: HP:0001382
      label: Joint hypermobility
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Hip dislocation was observed in four cases, joint hypermobility in three cases, and two probands had genu valgum.
    explanation: Reported skeletal finding; no population penetrance is inferred.
  category: Skeletal
- name: Genu Valgum
  description: Genu valgum was described in two core cases.
  phenotype_term:
    preferred_term: Genu valgum
    term:
      id: HP:0002857
      label: Genu valgum
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Hip dislocation was observed in four cases, joint hypermobility in three cases, and two probands had genu valgum.
    explanation: Reported skeletal finding; no population penetrance is inferred.
  category: Skeletal
- name: Adrenal Insufficiency
  description: Central adrenal insufficiency was confirmed in the Iranian Pro909Ser patient by repeatedly low cortisol with normal morning ACTH. A Canadian Pro909Leu adult had low cortisol suggestive of central insufficiency, but the later authors explicitly considered confirmation incomplete.
  phenotype_term:
    preferred_term: Central adrenal insufficiency
    term:
      id: HP:0011734
      label: Central adrenal insufficiency
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: After repeated measurements, a remarkable decreased serum cortisol level (2.6 μg/dl) and a normal amount of plasmatic adrenocorticotropic hormone (ACTH) in the morning (8 AM) were noted, revealing central adrenal insufficiency.
    explanation: Direct endocrine measurements in the Iranian patient.
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Due to the low cortisol values in patient 7, we also speculate an adrenal insufficiency that would require further studies.
    explanation: The second case remains suspected rather than confirmed.
  category: Endocrine
- name: Hypoglycemia
  description: Hypoglycemia has been reported in two Canadian core cases. Its cause was not established in each patient.
  phenotype_term:
    preferred_term: Hypoglycemia
    term:
      id: HP:0001943
      label: Hypoglycemia
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Hypoglycemia, which can be linked to central adrenal insufficiency, was noted in patient 7 and patient 9
    explanation: The association does not demonstrate adrenal causation in both patients.
  - reference: PMID:8409271
    reference_title: Unique hereditary sensory and autonomic neuropathy with growth hormone deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: short stature secondary to growth hormone deficiency, late-childhood-onset arthritis, and hypoglycemia.
    explanation: Hypoglycemia in the original Canadian girl.
  category: Metabolic
- name: Achalasia
  description: 'Type II esophageal achalasia was reported in two core cases: from birth in the Iranian patient and at age 32 in the Canadian adult. It is not exclusively an adult-onset finding.'
  phenotype_term:
    preferred_term: Type II esophageal achalasia
    term:
      id: HP:0002571
      label: Achalasia
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: At birth, he disclosed spastic features and type II achalasia that was confirmed and treated using endoscopy.
    explanation: The Iranian neonatal-onset manifestation.
  - reference: PMID:35228874
    reference_title: 'Genotype-phenotype correlation in IARS2-related diseases: A case report and review of literature.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: CAGSSS (N = 7) ... Type 2 Achalasia | 2/7
    explanation: Table 1 summarizes seven core CAGSSS cases, including milder cataract/skeletal presentations. This is an ascertained case-series proportion, not population penetrance.
  frequency: OCCASIONAL
  category: Gastrointestinal
- name: Thick Eyebrows
  description: Reported craniofacial feature in the Iranian clinical series; severity and expression vary.
  phenotype_term:
    preferred_term: Thick eyebrow
    term:
      id: HP:0000574
      label: Thick eyebrow
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: mildly thickened eyebrows and deep set eyes
    explanation: Specific facial finding in the clinical description.
  category: Craniofacial
- name: Deeply Set Eyes
  description: Reported craniofacial feature in the Iranian clinical series; severity and expression vary.
  phenotype_term:
    preferred_term: Deeply set eye
    term:
      id: HP:0000490
      label: Deeply set eye
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: mildly thickened eyebrows and deep set eyes
    explanation: Specific facial finding in the clinical description.
  category: Craniofacial
- name: Midface Retrusion
  description: Reported craniofacial feature in the Iranian clinical series; severity and expression vary.
  phenotype_term:
    preferred_term: Midface retrusion
    term:
      id: HP:0011800
      label: Midface retrusion
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: thick eyebrows, midface retrusion, underdeveloped ala nasi, short philtrum, thin upper lip
    explanation: Specific facial finding in the clinical description.
  category: Craniofacial
- name: Hypotonia
  category: Neurological
  description: Hypotonia was described in the boy in the founding Canadian family. A syndrome-wide frequency was not established.
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:8409271
    reference_title: Unique hereditary sensory and autonomic neuropathy with growth hormone deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: esotropia, unusual facies, hypotonia, bilateral congenital hip dysplasia
    explanation: Direct observation in the original family; no population frequency is inferred.
- name: Arthritis
  category: Musculoskeletal
  description: Late-childhood-onset arthritis was described in the female cousin in the founding family; the report did not specify an inflammatory subtype.
  phenotype_term:
    preferred_term: Arthritis
    term:
      id: HP:0001369
      label: Arthritis
  evidence:
  - reference: PMID:8409271
    reference_title: Unique hereditary sensory and autonomic neuropathy with growth hormone deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: short stature secondary to growth hormone deficiency, late-childhood-onset arthritis, and hypoglycemia.
    explanation: Direct observation in the original family; no population frequency is inferred.
genetic:
- name: IARS2
  gene_term:
    preferred_term: IARS2
    term:
      id: hgnc:29685
      label: IARS2
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  features: The core series comprises homozygous Pro909Leu (three relatives), Pro909Ser (one), His761Arg (two sisters) and Gly874Arg (one). Their position near the anticodon-binding region is a small-series association, with domain boundaries varying between annotations. Broader disease includes compound heterozygous missense, nonsense, frameshift and intragenic deletion alleles. A truncating allele can also occur with an isolated-cataract presentation; variant class alone is not a reliable severity rule.
  evidence:
  - reference: PMID:35228874
    reference_title: 'Genotype-phenotype correlation in IARS2-related diseases: A case report and review of literature.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: All seven patients of CAGSSS where the result of homozygous missense pathogenic variants around the anticodon‐binding domain
    explanation: The published seven-person genotype summary; the authors acknowledge uncertainty in domain boundaries.
  - reference: PMID:29914532
    reference_title: Clinical and genetic characteristics of Chinese patients with familial or sporadic pediatric cataract.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: 'the mutations c.2446C > T; p.(Arg816*) and c.2575 T > C; p.(Phe859Leu) were identified in two affected brothers in family #10, both of which had bilateral cataracts without other anomalies.'
    explanation: A truncating allele with a milder cataract-only presentation argues against a simple truncation-equals-Leigh rule.
diagnosis:
- name: IARS2 Sequencing and Segregation
  diagnosis_term:
    preferred_term: Genetic Testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  description: Identify biallelic disease-associated variants and establish phase/segregation. The absence of the full acronym at presentation does not exclude IARS2 disease. Copy-number analysis can be relevant when sequencing leaves an unresolved allele, as demonstrated in broader Leigh presentations.
  evidence:
  - reference: PMID:28328135
    reference_title: Confirmation of CAGSSS syndrome as a distinct entity in a Danish patient with a novel homozygous mutation in IARS2.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: It was only with time that several of the other manifestations of the CAGSSS emerged, namely, cataracts, peripheral neuropathy, and hearing loss.
    explanation: The temporal argument for not requiring the full acronym before testing.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: The homozygous IARS2 variant was confirmed in patient 1 using Sanger sequencing and both parents were found to be heterozygous
    explanation: Confirmation and segregation in the Iranian family.
- name: Skeletal Radiography
  diagnosis_term:
    preferred_term: Bone Radiography
    term:
      id: NCIT:C137876
      label: Bone Radiography
  description: Assess epiphyseal, metaphyseal, vertebral and hip abnormalities. Review neonatal films when available; primary dysplasia can precede endocrine deficiency.
  evidence:
  - reference: PMID:28328135
    reference_title: Confirmation of CAGSSS syndrome as a distinct entity in a Danish patient with a novel homozygous mutation in IARS2.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Retrospective analysis of the neonatal radiographs confirmed that the skeletal changes were present at birth.
    explanation: The retrospective neonatal review, and what it established.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
- name: Audiological Assessment
  diagnosis_term:
    preferred_term: Audiometric testing
    term:
      id: NCIT:C38036
      label: Audiometric Test
  description: Age-appropriate audiometry characterizes hearing loss, which can arise after an initially normal evaluation. The Iranian adult had serial pure-tone audiograms and tympanometry.
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Pure-tone audiometry was performed according to best-practice recommendations
    explanation: Audiometry was performed; this is not a disease-specific diagnostic threshold.
- name: Nerve Conduction Studies
  diagnosis_term:
    preferred_term: Nerve Conduction Velocity Test
    term:
      id: NCIT:C88502
      label: Nerve Conduction Velocity Test
  description: Evaluate sensory and motor amplitudes and conduction velocities in patients with sensory loss, weakness or pain insensitivity.
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Electrodiagnostic testing of the left limb at 16 years of age showed abnormal results that were consistent with chronic sensorimotor distal axonal polyneuropathy.
    explanation: The specific electrophysiological phenotype.
- name: Endocrine Assessment
  diagnosis_term:
    preferred_term: Laboratory Procedure
    term:
      id: NCIT:C25294
      label: Laboratory Procedure
  description: Assess growth, bone age, GH/IGF-1 and the adrenal axis according to clinical findings. Normal GH in childhood does not guarantee lifelong normal function. Repeated low cortisol with inappropriately normal ACTH supported central adrenal insufficiency in one adult.
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: After repeated measurements, a remarkable decreased serum cortisol level (2.6 μg/dl) and a normal amount of plasmatic adrenocorticotropic hormone (ACTH) in the morning (8 AM) were noted, revealing central adrenal insufficiency.
    explanation: Direct endocrine measurements in the Iranian patient.
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: It would be particularly interesting for additional patients with IARS2 pathogenic variants to be monitored for adrenal insufficiency.
    explanation: Authors recommend attention to adrenal function.
- name: Ophthalmological Assessment
  diagnosis_term:
    preferred_term: Eye examination
    term:
      id: NCIT:C38060
      label: Eye Examination
  description: Evaluate lens opacity, corneal surface and sensation, ocular alignment/motility and vision. OCT can characterize foveal abnormalities when clinically indicated. The detailed adult examination identified pathology beyond cataract.
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Optical coherence tomography also revealed foveal hypoplasia.
    explanation: OCT finding in patient 7, a re-examination of a founding-family case.
treatments:
- name: Cataract Surgery
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: cataract surgery
    term:
      id: NCIT:C157809
      label: Cataract Surgery
  description: Cataract extraction has been performed in several core cases, including congenital cataracts in the Iranian proband. Timing, visual rehabilitation and follow-up require ophthalmological assessment; surgery does not treat accompanying corneal or neuromuscular disease.
  target_phenotypes:
  - preferred_term: Cataract
    term:
      id: HP:0000518
      label: Cataract
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: presented with congenital cataracts that required surgery, as well as corneal opacity, bilateral nystagmus
    explanation: Records that the cataract required surgical treatment. It reports the indication, not an outcome.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
- name: Corneal Transplantation
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: corneal transplantation
    term:
      id: NCIT:C210959
      label: Corneal Transplantation
  description: 'Corneal grafts were attempted in three reported core-spectrum patients: two Iranian sisters had rejection at ages 30 and 20, and the Canadian adult had multiple failed grafts with neurotrophic keratitis and severe dryness. These reports document failures and a need to assess the ocular surface; they do not establish a universal failure rate or prove the mechanism of graft rejection.'
  target_phenotypes:
  - preferred_term: Corneal opacity
    term:
      id: HP:0007957
      label: Corneal opacity
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: She received a corneal graft later on, which was rejected when she was 30 years-old.
    explanation: A reported failure refutes success in this individual, not effectiveness of all corneal grafting or a quantified disease-wide failure probability.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:27078007
    reference_title: Recessive Mutation in a Nuclear-Encoded Mitochondrial tRNA Synthetase Associated With Infantile Cataract, Congenital Neurotrophic Keratitis, and Orbital Myopathy.
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: A 33-year-old woman known for infantile cataracts, growth hormone deficiency, sensory neuropathy, sensorineural hearing loss, and skeletal dysplasia was referred to us for multiple failed corneal grafts and severe eye dryness.
    explanation: A reported failure refutes success in this individual, not effectiveness of all corneal grafting or a quantified disease-wide failure probability.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: she also received a corneal graft that was rejected when she was 20 years old.
    explanation: Rejection in the younger Iranian sister, a third affected individual.
- name: Growth Hormone Replacement
  therapeutic_modality: PROTEIN_REPLACEMENT
  treatment_term:
    preferred_term: Growth hormone replacement
    term:
      id: NCIT:C15599
      label: Hormone Replacement Therapy
    therapeutic_agent:
    - preferred_term: somatropin
      term:
        id: CHEBI:749556
        label: somatropin
  description: Growth hormone replacement was given to two Canadian cases with reported positive outcomes. Detailed dosing, height response and controlled long-term efficacy were not provided in the cited summary. The Iranian patient had diagnosed deficiency but no available GH treatment.
  target_phenotypes:
  - preferred_term: Short stature secondary to growth hormone deficiency
    term:
      id: HP:0004322
      label: Short stature
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Growth hormone replacement therapy was performed in patient 7 and patient 8 with positive outcomes.
    explanation: Reported use and qualitative benefit in two cases; not a controlled efficacy estimate.
- name: Hearing Rehabilitation
  treatment_term:
    preferred_term: Hearing aid rehabilitation
    term:
      id: NCIT:C49236
      label: Therapeutic Procedure
    qualifiers:
    - predicate:
        preferred_term: Medical Device
        term:
          id: NCIT:C16830
          label: Medical Device
      value:
        preferred_term: Hearing Aid
        term:
          id: NCIT:C183182
          label: Hearing Aid
  therapeutic_modality: DEVICE
  description: Hearing aids were used in two core cases. The literature does not establish a syndrome-specific device protocol or benefit estimate.
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Hearing aids were used in only two of these cases
    explanation: Actual hearing-aid use reported in the clinical summary.
  target_phenotypes:
  - preferred_term: Sensorineural hearing impairment
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
  target_mechanisms:
  - target: Sensorineural Hearing Impairment
    description: Hearing amplification addresses the reported hearing impairment.
- name: Endoscopic Treatment of Achalasia
  treatment_term:
    preferred_term: Therapeutic Endoscopic Procedure
    term:
      id: NCIT:C64958
      label: Therapeutic Endoscopic Procedure
  therapeutic_modality: SURGERY
  description: The Iranian patient underwent endoscopic confirmation and treatment of type II achalasia. The publication does not specify a particular endoscopic technique or quantify long-term response.
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: At birth, he disclosed spastic features and type II achalasia that was confirmed and treated using endoscopy.
    explanation: Actual treatment, without an inferred balloon dilation or myotomy technique.
- name: Orthopedic Surgery
  treatment_term:
    preferred_term: Arthrodesis
    term:
      id: NCIT:C52007
      label: Arthrodesis
  therapeutic_modality: SURGERY
  description: Right ankle arthrodesis was performed for the Iranian patient with bilateral pes planus. Other skeletal care depends on the particular hip, spine and joint abnormalities.
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: bilateral pes planus (with arthrodesis of the right ankle joints performed)
    explanation: The specific orthopedic procedure reported.
- name: Glucocorticoid Replacement for Adrenal Insufficiency
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Glucocorticoid replacement
    term:
      id: NCIT:C15599
      label: Hormone Replacement Therapy
    therapeutic_agent:
    - preferred_term: hydrocortisone
      term:
        id: CHEBI:17650
        label: cortisol
  target_phenotypes:
  - preferred_term: Central adrenal insufficiency
    term:
      id: HP:0011734
      label: Central adrenal insufficiency
  description: Replacement is standard supportive care for confirmed central adrenal insufficiency; a CAGSSS-specific efficacy estimate is not available. Endocrine assessment and individualized replacement are needed rather than assuming every patient has adrenal failure.
  evidence:
  - reference: url:https://www.endocrine.org/clinical-practice-guidelines/hormone-replacement-in-hypopituitarism
    reference_title: Hormone Replacement in Hypopituitarism Guideline Resources | Endocrine Society
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: INDIRECT
    snippet: People who have central adrenal insufficiency should receive the lowest tolerable dose of hydrocortisone replacement on a long-term basis
    explanation: General adult hypopituitarism guidance supports replacement for confirmed central adrenal insufficiency; it is not CAGSSS-specific treatment evidence.
- name: Genetic Counseling
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  description: Discuss recessive inheritance, parental carrier status, family testing and reproductive options. Counseling should account for the variable IARS2 spectrum and limited genotype-based prognostic information.
  evidence:
  - reference: PMID:25130867
    reference_title: Mutation in the nuclear-encoded mitochondrial isoleucyl-tRNA synthetase IARS2 in patients with cataracts, growth hormone deficiency with short stature, partial sensorineural deafness, and peripheral neuropathy or with Leigh syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The mutation is homozygous in the affected patients, heterozygous in carriers, and absent in control chromosomes.
    explanation: Recessive segregation grounds family counseling; this is not an intervention-outcome study.
    quote_role: PRIMARY_RESULT
    directness: INDIRECT
discussions:
- discussion_id: cagsss_mechanism_not_established
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: Which allele- and tissue-dependent consequences of IARS2 dysfunction produce core CAGSSS despite normal fibroblast respiratory and translation assays?
  attaches_to:
  - pathophysiology#Impaired Mitochondrial Isoleucyl-tRNA Charging
  - pathophysiology#Reduced Respiratory Complex Abundance
  rationale: Core Pro909Leu and Pro909Ser fibroblast results differ in protein abundance, while neither demonstrates the Leigh lymphocyte respiratory-complex phenotype. ClinGen also summarizes normal translation in the founding line. The 2024 study analyzed lymphocytes from only one of its two Leigh patients, and performed rescue in HEK293T knockdown cells. It measured complex content, oxygen consumption and ATP, without directly measuring charging or translation. Normal biochemical findings also occur in broader severe IARS2 presentations. Allele severity, cell context, compensation and tissue-specific vulnerability remain possible explanations; the available comparisons do not isolate them.
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: REFUTE
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Patient-derived fibroblasts from proband 1 showed normal respiratory chain enzyme activity, as well as unchanged oxidative phosphorylation protein subunits and IARS2 levels.
    explanation: The Pro909Ser fibroblast line refutes a universal detectable protein/OXPHOS defect in CAGSSS fibroblasts. It does not exclude defects in other tissues.
  - reference: url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c
    reference_title: curation results for Gene-Disease Validity
    supports: REFUTE
    evidence_source: IN_VITRO
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: No difference in  BN PAGE nor in translation studies by S35 Methionine pulse labeling
    explanation: ClinGen summarizes normal assembled complexes and pulse-labeled translation in the founding Pro909Leu fibroblast line. This is secondary reporting of the original experiment.
  - reference: PMID:39169373
    reference_title: IARS2 mutations lead to Leigh syndrome with a combined oxidative phosphorylation deficiency.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: INDIRECT
    snippet: the contents of complexes I and III were decreased by ~ 90% and ~ 50% compared with control cells, respectively
    explanation: BN-PAGE/immunoblot complex contents in the single Leigh patient 2 lymphocyte line, not enzyme activities or a CAGSSS cohort.
  - reference: PMID:33327715
    reference_title: Biallelic IARS2 mutations presenting as sideroblastic anemia.
    supports: REFUTE
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: INDIRECT
    snippet: Respiratory chain enzyme activities were normal in the liver, skeletal muscle or lymphocytes of patients 1 and 3
    explanation: Normal enzymology also occurs in severe non-core IARS2 presentations.
- discussion_id: cagsss_entity_boundary
  kind: OPEN_QUESTION
  status: OPEN
  prompt: Is CAGSSS a distinct entity, or a named region of a continuous IARS2 phenotypic spectrum?
  attaches_to:
  - disease#CAGSSS Syndrome
  - genetic#IARS2
  rationale: CAGSSS remains a useful named phenotype with its own MONDO anchor, and this entry focuses on that clinical presentation. ClinGen evaluated the broader gene-disease relationship as definitive in December 2024 and explicitly grouped CAGSSS and Leigh-spectrum presentations as IARS2-related primary mitochondrial disease. This classification supports a shared gene-level entity without establishing identical cellular defects, penetrance or management needs across presentations. The seven-person core series, Leigh/West overlap cases, anemia-predominant disease and isolated cataract should therefore retain explicit ascertainment and phenotype boundaries. Domain-based genotype associations remain provisional.
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Our findings support that even though biallelic IARS2 pathogenic variants can result in a distinctive, clinically recognisable phenotype in humans, it can also show a wide range of clinical presentation from severe pediatric neurological disorders of Leigh and West syndrome to both non-syndromic cataract and cataract accompanied by skeletal dysplasia.
    explanation: 'Both halves of the question in one sentence: a distinctive recognisable phenotype, and a spectrum it sits inside.'
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c
    reference_title: curation results for Gene-Disease Validity
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: This is one disease entity according to the ClinGen Lumping and Splitting Framework, and has been renamed as ... -related primary mitochondrial disease.
    explanation: ClinGen explicitly groups the historical CAGSSS entity within IARS2-related primary mitochondrial disease.
notes: Frequency bands describe small published core CAGSSS series, not population penetrance. The 2018 ten-person table includes Leigh/West presentations; the 2022 summary separates seven core cases. Repeated reports of the Canadian family are not independent patients. The original skeletal-dysplasia correspondence (PMID:25771764 and PMID:25771765) has no retrievable quotable text; the neonatal skeletal evidence is supplied by the subsequent Danish report.
histopathology:
- name: Loss of Small and Medium Myelinated Nerve Fibers
  description: Reported in two core cases, with greater involvement in the hands than feet; not established as a universal or required diagnostic biopsy finding.
  diagnostic: false
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: A loss of small and medium-sized myelinated fibres, particularly in the hands, was reported in two of these patients.
    explanation: Histological nerve-fiber loss summarized from the founding clinical literature.
biochemical:
- name: Variable Fibroblast IARS2 and Respiratory-Chain Findings
  presence: Variable; normal results possible
  context: Cultured skin fibroblasts, not a clinical serum biomarker
  notes: Pro909Ser fibroblasts had normal respiratory enzyme activities, OXPHOS subunits and IARS2 protein. Pro909Leu fibroblasts had lower IARS2 protein, but normal BN-PAGE and translation were summarized by ClinGen. Normal cultured-cell results do not exclude IARS2-related disease.
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Patient-derived fibroblasts from proband 1 showed normal respiratory chain enzyme activity, as well as unchanged oxidative phosphorylation protein subunits and IARS2 levels.
    explanation: Documents the variable or normal cultured-cell biochemical result described here; the corresponding deficiency mechanism carries the appropriate refuting evidence separately.
  - reference: PMID:25130867
    reference_title: Mutation in the nuclear-encoded mitochondrial isoleucyl-tRNA synthetase IARS2 in patients with cataracts, growth hormone deficiency with short stature, partial sensorineural deafness, and peripheral neuropathy or with Leigh syndrome.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: IARS2 protein level was reduced in skin cells cultured from one of the patients, consistent with a pathogenic effect of the mutation.
    explanation: Documents the variable or normal cultured-cell biochemical result described here; the corresponding deficiency mechanism carries the appropriate refuting evidence separately.
  - reference: url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c
    reference_title: curation results for Gene-Disease Validity
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: No difference in  BN PAGE nor in translation studies by S35 Methionine pulse labeling
    explanation: Documents the variable or normal cultured-cell biochemical result described here; the corresponding deficiency mechanism carries the appropriate refuting evidence separately.
experimental_models:
- name: Pro909Leu Patient Skin Fibroblasts
  experimental_model_type: PRIMARY_CELL_CULTURE
  organism:
    preferred_term: Homo sapiens
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  publication: PMID:25130867
  description: Cultured skin cells from one founding-family patient showed reduced IARS2 abundance. ClinGen summarizes normal BN-PAGE and S35-methionine translation studies; protein reduction therefore did not establish respiratory/translation failure in this culture.
  evidence:
  - reference: PMID:25130867
    reference_title: Mutation in the nuclear-encoded mitochondrial isoleucyl-tRNA synthetase IARS2 in patients with cataracts, growth hormone deficiency with short stature, partial sensorineural deafness, and peripheral neuropathy or with Leigh syndrome.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: IARS2 protein level was reduced in skin cells cultured from one of the patients, consistent with a pathogenic effect of the mutation.
    explanation: Reduced protein in one founding Pro909Leu cell line; abundance is distinct from catalytic activity.
  - reference: url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c
    reference_title: curation results for Gene-Disease Validity
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: No difference in  BN PAGE nor in translation studies by S35 Methionine pulse labeling
    explanation: ClinGen reports a normal translation/BN-PAGE result in the founding fibroblast line.
  modeled_mechanisms:
  - target: Reduced IARS2 Protein Abundance
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: A disease-associated protein-abundance effect is observed.
    evidence:
    - reference: PMID:25130867
      reference_title: Mutation in the nuclear-encoded mitochondrial isoleucyl-tRNA synthetase IARS2 in patients with cataracts, growth hormone deficiency with short stature, partial sensorineural deafness, and peripheral neuropathy or with Leigh syndrome.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: IARS2 protein level was reduced in skin cells cultured from one of the patients, consistent with a pathogenic effect of the mutation.
      explanation: Reduced protein in one founding Pro909Leu cell line; abundance is distinct from catalytic activity.
    limitations: One patient line; no common effect across core alleles is established.
  - target: Impaired Mitochondrial Translation
    relationship: FAILS_TO_RECAPITULATE
    fidelity: LOW
    description: Pulse-labeled translation was normal in this culture.
    evidence:
    - reference: url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c
      reference_title: curation results for Gene-Disease Validity
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: REVIEW_SYNTHESIS
      directness: DIRECT
      snippet: No difference in  BN PAGE nor in translation studies by S35 Methionine pulse labeling
      explanation: ClinGen reports a normal translation/BN-PAGE result in the founding fibroblast line.
    limitations: Normal fibroblast translation does not exclude tissue-specific dysfunction; the detailed result is available here through expert curation.
- name: Pro909Ser Patient Fibroblasts
  experimental_model_type: PRIMARY_CELL_CULTURE
  organism:
    preferred_term: Homo sapiens
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  publication: PMID:30419932
  description: One Iranian patient line was tested for respiratory-complex enzyme activities normalized to citrate synthase, OXPHOS subunits and IARS2 abundance. Enzyme controls numbered eight; protein comparisons used two age-matched controls. All reported readouts were unchanged, and charging was not assayed.
  evidence:
  - reference: PMID:30419932
    reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Patient-derived fibroblasts from proband 1 showed normal respiratory chain enzyme activity, as well as unchanged oxidative phosphorylation protein subunits and IARS2 levels.
    explanation: The model has normal measured protein/respiratory-chain readouts; this is positive evidence for the stated negative model result.
  modeled_mechanisms:
  - target: Reduced IARS2 Protein Abundance
    relationship: FAILS_TO_RECAPITULATE
    fidelity: LOW
    description: IARS2 amount was unchanged.
    evidence:
    - reference: PMID:30419932
      reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Patient-derived fibroblasts from proband 1 showed normal respiratory chain enzyme activity, as well as unchanged oxidative phosphorylation protein subunits and IARS2 levels.
      explanation: The model has normal measured protein/respiratory-chain readouts; this is positive evidence for the stated negative model result.
    limitations: One allele, one donor and cultured skin fibroblasts.
  - target: Reduced Respiratory Complex Abundance
    relationship: FAILS_TO_RECAPITULATE
    fidelity: LOW
    description: Measured OXPHOS subunit levels were unchanged.
    evidence:
    - reference: PMID:30419932
      reference_title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Patient-derived fibroblasts from proband 1 showed normal respiratory chain enzyme activity, as well as unchanged oxidative phosphorylation protein subunits and IARS2 levels.
      explanation: The model has normal measured protein/respiratory-chain readouts; this is positive evidence for the stated negative model result.
    limitations: Subunit immunoblots and enzyme activities do not directly measure all assembly kinetics or affected tissues.
- name: Leigh Patient 2 Immortalized Lymphocytes
  experimental_model_type: CELL_LINE
  organism:
    preferred_term: Homo sapiens
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  publication: PMID:39169373
  description: EBV-immortalized lymphocytes from the child with c.1_390del and c.2450G>A showed reduced IARS2 protein, complexes I/III, oxygen consumption, ATP and membrane-potential readouts. Only patient 2 yielded this line; patient 1 was not studied in an equivalent patient-cell assay.
  evidence:
  - reference: PMID:39169373
    reference_title: IARS2 mutations lead to Leigh syndrome with a combined oxidative phosphorylation deficiency.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: To determine the pathogenicity of IARS2 variants, we constructed immortalized lymphocytes derived from patient 2. However, due to physical condition of patient 1, we were unable to establish immortalized lymphocytes from this patient.
    explanation: Only one of the two clinical patients supplied the experimental lymphocyte line.
  - reference: PMID:39169373
    reference_title: IARS2 mutations lead to Leigh syndrome with a combined oxidative phosphorylation deficiency.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: INDIRECT
    snippet: the contents of complexes I and III were decreased by ~ 90% and ~ 50% compared with control cells, respectively
    explanation: BN-PAGE/immunoblot complex contents in the single Leigh patient 2 lymphocyte line, not enzyme activities or a CAGSSS cohort.
  - reference: PMID:39169373
    reference_title: IARS2 mutations lead to Leigh syndrome with a combined oxidative phosphorylation deficiency.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: INDIRECT
    snippet: Patient-derived immortalized lymphocytes showed a significant reduction in basal respiration and ATP-linked respiration compared to control cells
    explanation: Respiration in one Leigh patient line supports a possible route, not a demonstrated core CAGSSS defect.
  modeled_mechanisms:
  - target: Reduced Respiratory Complex Abundance
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    description: The broader IARS2 model shows lower assembled complex content.
    evidence:
    - reference: PMID:39169373
      reference_title: IARS2 mutations lead to Leigh syndrome with a combined oxidative phosphorylation deficiency.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: INDIRECT
      snippet: the contents of complexes I and III were decreased by ~ 90% and ~ 50% compared with control cells, respectively
      explanation: BN-PAGE/immunoblot complex contents in the single Leigh patient 2 lymphocyte line, not enzyme activities or a CAGSSS cohort.
    limitations: Leigh genotype and immortalized lymphocytes, not a core CAGSSS allele or affected tissue.
  - target: Reduced Mitochondrial Respiration
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    description: Basal and ATP-linked oxygen consumption were reduced.
    evidence:
    - reference: PMID:39169373
      reference_title: IARS2 mutations lead to Leigh syndrome with a combined oxidative phosphorylation deficiency.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: INDIRECT
      snippet: Patient-derived immortalized lymphocytes showed a significant reduction in basal respiration and ATP-linked respiration compared to control cells
      explanation: Respiration in one Leigh patient line supports a possible route, not a demonstrated core CAGSSS defect.
    limitations: One donor; different alleles and cell type from the core fibroblast experiments.
- name: IARS2-Knockdown and Re-expression HEK293T Cells
  experimental_model_type: CELL_LINE
  organism:
    preferred_term: Homo sapiens
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  publication: PMID:39169373
  description: shRNA reduced IARS2 protein by about 60%. Complex I/III contents, respiration and ATP decreased and mitochondrial ROS increased. Re-expression of wild-type IARS2 improved readouts relative to three Leigh-associated missense constructs. Different mutant protein levels limit attribution to intrinsic catalytic activity; no core CAGSSS missense allele was tested.
  evidence:
  - reference: PMID:39169373
    reference_title: IARS2 mutations lead to Leigh syndrome with a combined oxidative phosphorylation deficiency.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: shRNA-mediated IARS2 knockdown was established in HEK293T cells, with an 60% decrease in the expression of IARS2 protein
    explanation: The engineered depletion level.
  - reference: PMID:39169373
    reference_title: IARS2 mutations lead to Leigh syndrome with a combined oxidative phosphorylation deficiency.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: INDIRECT
    snippet: The compensatory experiments in vitro cell models confirmed the pathogenicity of IARS2 variants since re-expression of wild-type IARS2 rather than mutant IARS2 could rescue complexes I and III deficiency, oxygen consumption, and cellular ATP content in IARS2 knockdown cells.
    explanation: Wild-type re-expression rescued HEK293T knockdown readouts; the three tested missense alleles were from Leigh cases, and rescue was not performed in patient cells.
  - reference: PMID:39169373
    reference_title: IARS2 mutations lead to Leigh syndrome with a combined oxidative phosphorylation deficiency.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: INDIRECT
    snippet: the production of cellular ATP was notably decreased and the mitochondrial ROS level was increased in IARS2 knockdown cells compared with control cells
    explanation: ROS was increased in knockdown HEK293T cells; no corresponding core CAGSSS tissue measurement was reported.
  modeled_mechanisms:
  - target: Reduced IARS2 Protein Abundance
    relationship: PERTURBS
    fidelity: LOW
    description: shRNA directly lowers IARS2 protein.
    evidence:
    - reference: PMID:39169373
      reference_title: IARS2 mutations lead to Leigh syndrome with a combined oxidative phosphorylation deficiency.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: shRNA-mediated IARS2 knockdown was established in HEK293T cells, with an 60% decrease in the expression of IARS2 protein
      explanation: The knockdown perturbation.
    limitations: Engineered depletion differs from core missense alleles.
  - target: Reduced Mitochondrial Respiration
    relationship: RESCUES
    fidelity: LOW
    description: Wild-type re-expression rescues the knockdown-cell respiratory phenotype.
    evidence:
    - reference: PMID:39169373
      reference_title: IARS2 mutations lead to Leigh syndrome with a combined oxidative phosphorylation deficiency.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: INDIRECT
      snippet: The compensatory experiments in vitro cell models confirmed the pathogenicity of IARS2 variants since re-expression of wild-type IARS2 rather than mutant IARS2 could rescue complexes I and III deficiency, oxygen consumption, and cellular ATP content in IARS2 knockdown cells.
      explanation: Wild-type re-expression rescued HEK293T knockdown readouts; the three tested missense alleles were from Leigh cases, and rescue was not performed in patient cells.
    limitations: Rescue was in HEK293T cells, not in patient cells or a therapeutic trial.
  - target: Increased Mitochondrial ROS
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    description: Knockdown increases mitochondrial ROS.
    evidence:
    - reference: PMID:39169373
      reference_title: IARS2 mutations lead to Leigh syndrome with a combined oxidative phosphorylation deficiency.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: INDIRECT
      snippet: the production of cellular ATP was notably decreased and the mitochondrial ROS level was increased in IARS2 knockdown cells compared with control cells
      explanation: ROS was increased in knockdown HEK293T cells; no corresponding core CAGSSS tissue measurement was reported.
    limitations: ROS has not been established as a patient CAGSSS tissue phenotype.
animal_models:
- name: Iars2 Homozygous Knockout Mouse
  species: Mus musculus
  genotype: Homozygous Iars2 knockout
  description: ClinGen summarizes IMPC evidence for embryonic lethality at E9.5 in homozygous Iars2 knockout mice. This supports an essential developmental function but is not a viable model of the core human missense syndrome.
  publication: url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c
  evidence:
  - reference: url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c
    reference_title: curation results for Gene-Disease Validity
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: REVIEW_SYNTHESIS
    directness: INDIRECT
    snippet: Embryonic lethal (E9.5) homozygous KO of IARS2
    explanation: Expert-curation summary of IMPC data; no claim that the complete CAGSSS phenotype is reproduced.
  modeled_mechanisms:
  - target: Biallelic IARS2 Variants
    relationship: PERTURBS
    fidelity: LOW
    description: Complete gene knockout contrasts with the core human missense alleles.
    evidence:
    - reference: url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c
      reference_title: curation results for Gene-Disease Validity
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: REVIEW_SYNTHESIS
      directness: INDIRECT
      snippet: Embryonic lethal (E9.5) homozygous KO of IARS2
      explanation: The null perturbation is developmentally lethal.
    limitations: Null allele and embryonic lethality differ from surviving humans with residual-function missense alleles. Residual enzyme activity has not been quantified in the core cases.
differential_diagnoses:
- name: IARS2-Related Leigh and West Syndrome Presentations
  description: Overlapping IARS2 disease may present with early spasms, developmental regression and characteristic basal-ganglia lesions. These cases share the gene but do not define the clinical frequencies in the core CAGSSS series.
  evidence:
  - reference: PMID:30041933
    reference_title: Novel IARS2 mutations in Japanese siblings with CAGSSS, Leigh, and West syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Here we report a case of two Japanese siblings with Leigh syndrome, some features of CAGSSS, and West syndrome that are found to have compound heterozygous novel IARS2 mutations.
    explanation: Primary description of overlap, not a sharp mutually exclusive subtype boundary.
- name: IARS2-Related Sideroblastic Anemia
  description: Early anemia, hypoparathyroidism, pancreatic dysfunction, cardiomyopathy or severe neurological disease can dominate broader IARS2 presentations. Normal respiratory enzymology does not exclude these phenotypes either. Their disease course and treatment observations are not automatically transferred to core CAGSSS.
  evidence:
  - reference: PMID:33327715
    reference_title: Biallelic IARS2 mutations presenting as sideroblastic anemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Our report expands the clinical spectrum of IARS2- related disorders to early-onset sideroblastic anemia mimicking Pearson syndrome.
    explanation: The anemia-predominant allelic presentation.
- name: IARS2-Related Isolated Pediatric Cataract
  description: Three affected children in two 2018 families had cataracts without other anomalies at ascertainment. They warrant follow-up for emerging systemic features but are not counted as core multisystem CAGSSS cases.
  evidence:
  - reference: PMID:29914532
    reference_title: Clinical and genetic characteristics of Chinese patients with familial or sporadic pediatric cataract.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: these patients did not present with additional anomalies besides the cataract. Thus, growth hormone levels, neurotrophic keratitis, orbital myopathy, and skeletal dysplasia should be monitored through later follow-ups.
    explanation: The source recommends longitudinal assessment rather than assuming a permanently isolated phenotype.
references:
- reference: PMID:25130867
  title: Mutation in the nuclear-encoded mitochondrial isoleucyl-tRNA synthetase IARS2 in patients with cataracts, growth hormone deficiency with short stature, partial sensorineural deafness, and peripheral neuropathy or with Leigh syndrome.
- reference: PMID:27078007
  title: Recessive Mutation in a Nuclear-Encoded Mitochondrial tRNA Synthetase Associated With Infantile Cataract, Congenital Neurotrophic Keratitis, and Orbital Myopathy.
- reference: PMID:28328135
  title: Confirmation of CAGSSS syndrome as a distinct entity in a Danish patient with a novel homozygous mutation in IARS2.
- reference: PMID:29914532
  title: Clinical and genetic characteristics of Chinese patients with familial or sporadic pediatric cataract.
- reference: PMID:30041933
  title: Novel IARS2 mutations in Japanese siblings with CAGSSS, Leigh, and West syndrome.
- reference: PMID:30419932
  title: Expanding the clinical phenotype of IARS2-related mitochondrial disease.
- reference: PMID:33327715
  title: Biallelic IARS2 mutations presenting as sideroblastic anemia.
- reference: PMID:35228874
  title: 'Genotype-phenotype correlation in IARS2-related diseases: A case report and review of literature.'
- reference: PMID:39169373
  title: IARS2 mutations lead to Leigh syndrome with a combined oxidative phosphorylation deficiency.
- reference: PMID:8409271
  title: Unique hereditary sensory and autonomic neuropathy with growth hormone deficiency.
- reference: url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_4cfed420-da98-46fb-a9fd-9cd9f6e83d6c
  title: curation results for Gene-Disease Validity
- reference: url:https://www.endocrine.org/clinical-practice-guidelines/hormone-replacement-in-hypopituitarism
  title: Hormone Replacement in Hypopituitarism Guideline Resources | Endocrine Society
📚

References & Deep Research

References

12
PMID:25130867
Mutation in the nuclear-encoded mitochondrial isoleucyl-tRNA synthetase IARS2 in patients with cataracts, growth hormone deficiency with short stature, partial sensorineural deafness, and peripheral neuropathy or with Leigh syndrome.
No top-level findings curated for this source.
PMID:27078007
Recessive Mutation in a Nuclear-Encoded Mitochondrial tRNA Synthetase Associated With Infantile Cataract, Congenital Neurotrophic Keratitis, and Orbital Myopathy.
No top-level findings curated for this source.
PMID:28328135
Confirmation of CAGSSS syndrome as a distinct entity in a Danish patient with a novel homozygous mutation in IARS2.
No top-level findings curated for this source.
PMID:29914532
Clinical and genetic characteristics of Chinese patients with familial or sporadic pediatric cataract.
No top-level findings curated for this source.
PMID:30041933
Novel IARS2 mutations in Japanese siblings with CAGSSS, Leigh, and West syndrome.
No top-level findings curated for this source.
PMID:30419932
Expanding the clinical phenotype of IARS2-related mitochondrial disease.
No top-level findings curated for this source.
PMID:33327715
Biallelic IARS2 mutations presenting as sideroblastic anemia.
No top-level findings curated for this source.
PMID:35228874
Genotype-phenotype correlation in IARS2-related diseases: A case report and review of literature.
No top-level findings curated for this source.
PMID:39169373
IARS2 mutations lead to Leigh syndrome with a combined oxidative phosphorylation deficiency.
No top-level findings curated for this source.
PMID:8409271
Unique hereditary sensory and autonomic neuropathy with growth hormone deficiency.
No top-level findings curated for this source.
No top-level findings curated for this source.
url:https://www.endocrine.org/clinical-practice-guidelines/hormone-replacement-in-hypopituitarism
Hormone Replacement in Hypopituitarism Guideline Resources | Endocrine Society
No top-level findings curated for this source.

Deep Research

1

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (1)

Create: CAGSSS Syndrome (IARS2) · 2026-09-03T19:35:00Z · View source

De novo curation of IARS2-related CAGSSS from primary literature plus one openscientist deep-research run. Three judgement calls are recorded structurally rather than in prose: the skeletal dysplasia is curated as primary on the neonatal-radiograph evidence that answers a published letter exchange; functional_impact_category is UNKNOWN rather than LOSS_OF_FUNCTION because no aminoacylation assay on any patient allele has been reported; and the respiratory-chain mechanism is carried as a node whose every evidence item is INDIRECT, because the demonstration used Leigh-syndrome alleles while the only CAGSSS-range measurement was negative. The deep-research run supplied PMID:39169373, which changed that discussion from an unexplained contradiction into a testable allele-severity question. Two cached letters are deliberately uncited because PubMed carries no abstract for either and a title is not a finding. Validated: schema, terms, 34/34 snippets, entity refs, causal targets, duplicate keys, enum values, qualifier terms.

OpenScientist ▸
CAGSSS Syndrome (IARS2-related): Comprehensive Disease Characteristics Report
openscientist-autonomous 8 citations 2026-09-03T19:24:28.131369

CAGSSS Syndrome (IARS2-related): Comprehensive Disease Characteristics Report

Disease: CAGSSS syndrome — Cataract, growth hormone deficiency (G), Sensory neuropathy, Sensorineural hearing loss, and Skeletal dysplasia MONDO ID: MONDO:0014455 · OMIM: 616007 · Orphanet: ORPHA:436174 · Category: Mendelian (autosomal recessive mitochondrial disorder) Causal gene: IARS2 (HGNC:29685; NCBI Gene 55699; UniProt Q9NSE4; chr 1q41; OMIM 612801)

Summary

CAGSSS syndrome is an ultra-rare autosomal-recessive multisystem mitochondrial disorder caused by biallelic (predominantly missense) variants in IARS2, the nuclear gene encoding mitochondrial isoleucyl-tRNA synthetase. It was first delineated in 2014 by Schwartzentruber and colleagues in three adult patients from a French-Canadian family, who presented with the constellation of cataracts, short stature secondary to growth-hormone deficiency, sensorineural hearing loss, peripheral sensory neuropathy, and skeletal dysplasia — the five features that give the syndrome its acronym (PMID: 25130867). The gene, its protein product, and the biochemical logic of the disease place it firmly within the family of mitochondrial aminoacyl-tRNA synthetase (mt-ARS) disorders.

Mechanistically, loss of IARS2 function impairs the aminoacylation (charging) of mitochondrial tRNA-Ile with isoleucine, which is required for translation of the 13 mtDNA-encoded subunits of the oxidative-phosphorylation (OXPHOS) machinery. The downstream result is a combined respiratory-chain deficiency with reduced ATP synthesis, lowered oxygen consumption and mitochondrial membrane potential, and increased mitochondrial reactive oxygen species — an energy-failure phenotype that most severely affects high-demand, post-mitotic tissues (lens, cochlea, sensory neurons, pituitary somatotrophs, growth-plate chondrocytes, and, at the severe end of the spectrum, the basal ganglia) (PMID: 39169373). Importantly, IARS2 variants produce a broad clinical continuum: from isolated cataract and adult-onset CAGSSS at the mild end to infantile Leigh syndrome and West syndrome at the severe end (PMID: 30419932).

Diagnosis rests on whole-exome or whole-genome sequencing (historically combined with SNP genotyping / homozygosity mapping in consanguineous families), because standard respiratory-chain biochemistry is unreliable — combined OXPHOS deficiency is demonstrable in patient lymphocytes and knockdown cell models but can be normal in patient fibroblasts. No disease-modifying therapy exists; management is entirely supportive and multidisciplinary (cataract surgery, recombinant growth-hormone replacement, hearing rehabilitation, orthopedic and neuropathy care, corneal protection, and genetic counseling with cascade/prenatal testing). Fewer than a handful of families have been reported worldwide, and consanguinity/founder homozygosity is a key risk factor.

1. Disease Information

CAGSSS syndrome is a Mendelian, autosomal-recessive, mitochondrial multisystem disorder defined by five core features encoded in its acronym: Cataract, growth-hormone deficiency, Sensory neuropathy, Sensorineural hearing loss, and Skeletal dysplasia. The disorder was newly delineated in 2014 in three adult patients and is caused by biallelic variants in IARS2 (PMID: 25130867): "we report a novel disorder in three adult patients with a phenotype including cataracts, short-stature secondary to growth hormone deficiency, sensorineural hearing deficit, peripheral sensory neuropathy, and skeletal dysplasia."

Key identifiers (verified via EBI OLS4 cross-references to MONDO:0014455; Finding F008):

Resource Identifier
MONDO MONDO:0014455
OMIM 616007
Orphanet ORPHA:436174
GARD 0017727
MedGen 863379
UMLS C4014942
Gene (OMIM) IARS2 612801

Synonyms / alternative names: "cataract–growth hormone deficiency–sensory neuropathy–sensorineural hearing loss–skeletal dysplasia syndrome"; CAGSSS; IARS2-related mitochondrial disease (as part of a broader phenotypic spectrum). Note: an earlier working note listing the Orphanet ID as ~468631 was corrected — the verified Orphanet ID is ORPHA:436174.

Source of information: Aggregated from individual clinical case reports and small family series (French-Canadian, Danish, Iranian, Japanese, and Chinese ancestry) combined with disease-level ontology resources (OMIM, Orphanet, MONDO, HPO). There is no EHR-scale or registry-scale dataset for this ultra-rare disorder.

2. Etiology

Primary cause — genetic. CAGSSS is caused by biallelic (homozygous or compound-heterozygous) variants in IARS2, a nuclear gene encoding mitochondrial isoleucyl-tRNA synthetase. In the founding cohort the causal variant was "homozygous in the affected patients, heterozygous in carriers, and absent in control chromosomes" — the classic signature of autosomal-recessive inheritance (PMID: 25130867). IARS2 protein level was reduced in patient-derived skin cells, providing functional support for pathogenicity: "IARS2 protein level was reduced in skin cells cultured from one of the patients, consistent with a pathogenic effect of the mutation" (Finding F001).

Genetic risk factors. The disease requires two pathogenic IARS2 alleles. Consanguinity and founder homozygosity are the dominant risk mechanisms: homozygous variants in reported families arise within large runs of homozygosity (e.g., a 14.3 Mb and an ~8 Mb ROH in two consanguineous probands) (PMID: 30419932, Finding F006). Population constraint metrics (pLI ≈ 0.0018) indicate IARS2 is not haploinsufficient, consistent with a recessive loss-of-function mechanism (Finding F011).

Environmental risk factors. None established. As a fully penetrant Mendelian disorder, there are no known toxin, lifestyle, occupational, or infectious contributors. Age and sex are not risk factors (autosomal recessive; no sex predilection expected). Family history / consanguinity is the only meaningful non-molecular risk indicator.

Protective factors. None identified — no protective IARS2 alleles or modifier alleles have been described, and no dietary or lifestyle protective exposures are known. This is expected for a rare monogenic disorder.

Gene–environment interactions. No specific G×E interaction has been documented. On mechanistic grounds, tissue energy demand and metabolic stress could theoretically modulate the phenotype (energy-failure disorders often worsen under catabolic stress), but this is inferred, not demonstrated, for CAGSSS.

3. Phenotypes

The five acronymic features are consistent core phenotypes, but the official HPO annotation for OMIM:616007 comprises 69 terms, showing the phenotype extends well beyond the acronym (Finding F009). Observed frequencies below are drawn from the HPO/OMIM annotation, derived from PMID: 25130867 and PMID: 28328135.

Phenotype HPO term Type Observed frequency Onset / course
Cataract HP:0000518 Physical/ocular sign 4/4 Congenital/infantile; often earliest; progressive
Sensorineural hearing impairment HP:0000407 Clinical sign 4/4 Childhood; progressive
Distal sensory impairment HP:0002936 Clinical sign 3/3 Childhood/adult; progressive
Growth delay / short stature HP:0001510 Physical 3/3 Childhood
Decreased response to GH stimulation HP:0000824 Lab abnormality 3/3 Childhood (endocrine)
Hypoglycemia HP:0001943 Lab abnormality 3/3 Childhood
Scoliosis HP:0002650 Skeletal sign 3/3 Childhood; progressive
Hip dislocation HP:0002827 Skeletal sign 2/2 Congenital (present at birth)
Genu valgum HP:0002857 Skeletal sign 2/4 Childhood
Achalasia HP:0002571 Clinical sign 1/3 Variable
Spondyloepimetaphyseal dysplasia HP:0002651 Skeletal — Congenital
Keratoconjunctivitis sicca (dry eye) HP:0001097 Ocular sign — Variable
Central adrenal insufficiency HP:0011734 Endocrine — Variable

Additional HPO-annotated features include skeletal (coronal cleft vertebrae, delayed epiphyseal ossification, odontoid hypoplasia, cervical spinal canal stenosis, osteopenia), neurologic (cerebral cortical atrophy, global developmental delay, hyporeflexia, hypsarrhythmia — the latter at the severe/West-syndrome end), and dysmorphic facial features.

Expanded ocular phenotype. Beyond cataract, a 33-year-old CAGSSS woman developed neurotrophic keratitis, corneal opacification, multiple failed corneal grafts, severe dry eye, and orbital myopathy (PMID: 27078007, Finding F004): "Patients with this very rare mutation present with a myriad of ocular findings, including infantile cataract, neurotrophic keratitis, corneal opacification, and orbital myopathy."

Severity and progression. Highly variable and largely progressive. The acronymic features tend to accumulate and worsen over time. At the severe extreme, the phenotype becomes an early-onset, life-threatening encephalopathy (Leigh/West syndrome).

Quality-of-life impact. No formal EQ-5D/SF-36/PROMIS data exist for this ultra-rare disease. Qualitatively, the combination of visual impairment (cataract/keratitis), deafness, sensory neuropathy, short stature, and skeletal deformity implies substantial multisystem disability affecting mobility, communication, and independent function; the severe Leigh/West end carries profound neurodevelopmental disability.

4. Genetic / Molecular Information

Causal gene: IARS2 — HGNC:29685; NCBI Gene 55699; UniProt Q9NSE4; Ensembl ENSG00000067704; chromosome 1q41; OMIM 612801. Encodes isoleucine–tRNA ligase, mitochondrial, a class-I aminoacyl-tRNA synthetase.

Protein architecture (UniProt Q9NSE4; Finding F010): 1012 amino acids; N-terminal mitochondrial transit peptide (residues 1–48); class-I aaRS Rossmann-fold catalytic core with the signature HIGH motif (residues 116–126) and KMSKS motif (residues 664–668, ATP-contacting binding-site residues at 664 and 667); localizes to the mitochondrial matrix.

Reported pathogenic / likely-pathogenic variants (NM_018060.3; Finding F003):

Variant (protein) cDNA Zygosity Ancestry Phenotype Reference
p.Pro909Ser c.2625C>T Homozygous Iranian CAGSSS PMID: 30419932
p.His761Arg c.2282A>G Homozygous Iranian CAGSSS PMID: 30419932
p.Gly874Arg — Homozygous Danish CAGSSS / SEMD PMID: 28328135
p.Phe227Ser; p.Arg817His — Compound het Japanese CAGSSS/Leigh/West overlap PMID: 30041933
c.1_390del; c.2090G>A; c.2450G>A; c.2122G>A multiple Biallelic Chinese Leigh syndrome PMID: 39169373

The Danish patient "presented at birth with bilateral hip dislocation and short stature" and "her radiographic skeletal abnormalities were suggestive of an underlying spondyloepimetaphyseal dysplasia (SEMD)" (PMID: 28328135). The Japanese siblings carried "compound heterozygous missense mutations in IARS2, p.[(Phe227Ser)];[(Arg817His)]" (PMID: 30041933).

Variant classification & type. Predominantly missense (with at least one deletion, c.1_390del). Reported pathogenic missense changes map C-terminal to the catalytic core (e.g., p.His761Arg, p.Arg817His, p.Gly874Arg, p.Pro909Ser in the C-terminal/anticodon-binding region; p.Phe227Ser near the catalytic domain), consistent with destabilizing/hypomorphic effects rather than complete null (Finding F010).

ClinVar / population landscape (Finding F011): ClinVar lists ~688 IARS2 variant records — approximately 121 pathogenic and 21 likely pathogenic, alongside a large VUS burden (~635 records) and many benign/likely-benign entries. gnomAD constraint: pLI = 0.0018 (not haploinsufficient), LoF observed/expected = 0.44 (90% CI 0.36–0.55; 56 observed vs 126 expected), missense Z = 1.44, LoF Z = 5.31. These metrics indicate IARS2 tolerates heterozygous LoF (consistent with recessive disease) while being under moderate selection against biallelic loss.

Functional consequence: Loss of function / hypomorphic. IARS2 protein was reduced in patient skin cells (PMID: 25130867); knockdown reproduces the OXPHOS defect (PMID: 39169373).

Modifier genes / epigenetics / chromosomal abnormalities: None identified. No large-scale chromosomal abnormalities are associated with CAGSSS (Finding F011). No epigenetic mechanism has been described.

5. Environmental Information

CAGSSS is a monogenic disorder with no established environmental, lifestyle, or infectious contribution. No toxin, radiation, pollution, occupational exposure, dietary, or behavioral factor has been linked to disease onset or severity. There are no infectious agents involved. The only relevant "environmental" consideration is consanguinity/population structure, which increases the probability of biallelic IARS2 variants (a genetic-demographic, not toxicologic, factor).

6. Mechanism / Pathophysiology

Ordered causal chain

  1. A biallelic hypomorphic IARS2 variant (most often missense) results in a destabilized or partially inactive mitochondrial isoleucyl-tRNA synthetase, with reduced steady-state IARS2 protein in some tissues (demonstrated in patient skin cells, PMID: 25130867).
  2. Reduced IARS2 aminoacylation activity leads to impaired charging of mitochondrial tRNA-Ile with isoleucine (inferred from the enzyme's known function — "ARSs attach amino acids to their cognate tRNA molecules in the cytoplasm and mitochondria", PMID: 18767960; direct patient aminoacylation assays not reported).
  3. Deficient charged mt-tRNA-Ile leads to defective mitochondrial translation of the 13 mtDNA-encoded OXPHOS subunits (inferred mechanistically; supported by downstream OXPHOS readouts).
  4. Impaired synthesis of OXPHOS subunits results in combined respiratory-chain (complex I/III/IV) deficiency, with reduced oxygen consumption rate, reduced complex activity, decreased ATP production, decreased mitochondrial membrane potential, and increased mitochondrial ROS (demonstrated in patient lymphocytes and IARS2-knockdown HEK293T cells, PMID: 39169373).
  5. Bioenergetic failure plus oxidative stress leads to dysfunction/degeneration of high-demand, post-mitotic tissues — and here the mechanism branches by tissue:
  6. Lens epithelium → cataract
  7. Cochlear hair / spiral-ganglion cells → sensorineural hearing loss
  8. Peripheral sensory neurons → sensory neuropathy
  9. Pituitary somatotrophs / GH axis → growth-hormone deficiency, short stature, hypoglycemia
  10. Growth-plate chondrocytes / bone → spondyloepimetaphyseal skeletal dysplasia
  11. (Severe end) Basal ganglia and brainstem neurons → Leigh/West syndrome with bilateral basal-ganglia lesions and diffuse brain atrophy
  12. Accumulated multisystem tissue injury results in the clinical CAGSSS phenotype (or the more severe encephalopathic phenotypes).

Threshold / tissue-specificity caveat (branch qualifier): The biochemical defect is not uniform. Patient fibroblasts from one proband showed "normal respiratory chain enzyme activity, as well as unchanged oxidative phosphorylation protein subunits and IARS2 levels" (PMID: 30419932), whereas lymphocytes/knockdown cells show clear deficits (PMID: 39169373). This indicates a tissue-specific / threshold effect: cells with high mitochondrial demand cross the pathogenic threshold while others compensate (Finding F005).

Mechanistic detail

  • Molecular pathway: Mitochondrial gene expression / mitochondrial translation (aminoacyl-tRNA biosynthesis → OXPHOS).
  • Cellular processes: Energy failure, oxidative stress, and (inferred) apoptosis/degeneration of post-mitotic cells.
  • Protein dysfunction: Loss-of-function/hypomorphic destabilization of a class-I aaRS; missense variants cluster C-terminal to the catalytic core.
  • Metabolic changes: Impaired oxidative phosphorylation / ATP synthesis; combined complex I/III/IV deficiency; elevated mitochondrial ROS.
  • Tissue-damage mechanism: Oxidative stress + chronic bioenergetic insufficiency in neurons, sensory epithelia, endocrine cells, and chondrocytes.
  • Immune involvement: None described.

Suggested ontology terms: GO:0032543 (mitochondrial translation), GO:0006428 (isoleucyl-tRNA aminoacylation), GO:0006119 (oxidative phosphorylation), GO:0006979 (response to oxidative stress); GO cellular component GO:0005759 (mitochondrial matrix), GO:0005743 (inner mitochondrial membrane). Cell types (CL): CL:0000540 (neuron), CL:0000101 (sensory neuron), CL:0000138 (chondrocyte), lens fiber cell, cochlear hair cell, somatotroph.

7. Anatomical Structures Affected

Organ level (primary): eye/lens (UBERON:0000965 lens; UBERON:0000970 eye), inner ear/cochlea (UBERON:0001844), peripheral nerves (UBERON:0000010 peripheral nervous system), pituitary gland (UBERON:0000007), skeletal system/vertebrae/long bones (UBERON:0004288 skeleton; UBERON:0001130 vertebral column). Severe end: brain — basal ganglia (UBERON:0002420) and cerebral cortex (UBERON:0000956).

Secondary organ involvement: cornea (neurotrophic keratitis, opacification), lacrimal function (dry eye), esophagus (achalasia), adrenal axis (central adrenal insufficiency), cervical spinal cord (canal stenosis / odontoid hypoplasia risk).

Body systems: ocular/visual, auditory, peripheral nervous, central nervous, endocrine (GH/adrenal axes), musculoskeletal, and (occasionally) gastrointestinal (achalasia).

Tissue / cell level: lens epithelial and fiber cells; cochlear sensory epithelium and spiral-ganglion neurons; peripheral sensory neurons (large-fiber sensory loss); pituitary somatotrophs; growth-plate chondrocytes; central neurons of basal ganglia (severe phenotypes).

Subcellular level: the mitochondrion, specifically the mitochondrial matrix (GO:0005759) where IARS2 charges mt-tRNA-Ile, and the inner mitochondrial membrane OXPHOS complexes (GO:0005743). This is a canonical mitochondrial-matrix / respiratory-chain disorder.

Localization / laterality: manifestations are characteristically bilateral (cataracts, hearing loss, symmetric distal sensory neuropathy, bilateral hip dislocation, and — when present — bilateral basal-ganglia signal abnormality).

8. Temporal Development

Onset: Ranges from congenital (bilateral hip dislocation and skeletal dysplasia present at birth; congenital/infantile cataract) through childhood (hearing loss, short stature/GH deficiency, sensory neuropathy) to adult recognition of the full syndrome. The Danish patient presented at birth with bilateral hip dislocation and short stature, with cataracts, neuropathy, and hearing loss emerging over time (PMID: 28328135, Finding F003). At the severe end, infantile onset produces Leigh/West syndrome.

Onset pattern: Chronic/insidious and cumulative for CAGSSS; more acute/subacute neurodegenerative decline in infantile Leigh/West presentations.

Progression: Progressive across the spectrum. Individual features (cataract, hearing loss, neuropathy, scoliosis) accumulate and worsen. Disease course is chronic and lifelong. There is no known remission (spontaneous or treatment-induced).

Critical periods / windows for intervention: early infancy/childhood for cataract surgery (visual development), GH replacement (linear growth), and hearing rehabilitation (language acquisition) — these are the practical windows in which supportive care most alters outcomes.

9. Inheritance and Population

Inheritance: Autosomal recessive — biallelic IARS2 variants; homozygous in affected, heterozygous in carriers, absent in controls (PMID: 25130867).

Epidemiology: Ultra-rare. Fewer than a handful of families reported worldwide; as of 2018 only ~3 families with IARS2-related disease had been described — "IARS2 mutations and diseases related to it have only been reported in three families" (PMID: 30041933, Finding F006). Precise prevalence/incidence figures are not established (too few cases). Orphanet lists it under ORPHA:436174.

Penetrance / expressivity: Penetrance appears complete for biallelic pathogenic genotypes, but expressivity is highly variable — the same gene yields anything from isolated cataract to full CAGSSS to Leigh/West syndrome, and even siblings can differ.

Genetic anticipation: Not applicable (no repeat-expansion mechanism). Germline mosaicism: not reported.

Founder effects / consanguinity: Consanguinity and founder homozygosity are prominent. Homozygous variants sit "within a 14.3 Mb run of homozygosity in proband 1" and an ~8 Mb ROH in a second proband in consanguineous Iranian families (PMID: 30419932). No broad founder haplotype in an outbred population is documented.

Carrier frequency: Not formally established; given ultra-rarity, carrier frequency is very low in the general population but elevated within affected consanguineous kindreds.

Population demographics: Reported ancestries span French-Canadian, Danish, Iranian, Japanese, and Chinese — i.e., no single ethnic clustering beyond the enrichment expected in consanguineous populations. Sex ratio: ~1:1 (autosomal recessive; no sex predilection expected). Age distribution: birth through adulthood, depending on severity.

IARS2 is one of 19 identified mt-ARS genes strongly associated with mitochondrial disorders, 7 of which cause hereditary sensorineural hearing loss — "To date, 19 mt-ARS genes have been identified and found to be strongly associated with the development of mitochondrial disorders" (PMID: 41059449, Finding F006).

10. Diagnostics

Molecular diagnosis is definitive. CAGSSS was discovered — and is diagnosed — via whole-exome sequencing, historically combined with SNP genotyping / homozygosity mapping in consanguineous families: "Using SNP genotyping and whole-exome sequencing, we identified a single likely causal variant" (PMID: 25130867, Finding F007).

Recommended genetic testing approach: - WES or WGS — first-line and highest yield for this multisystem, phenotypically variable disorder. - Multigene mitochondrial-disease / mt-ARS panels including IARS2. - Targeted single-gene / variant testing for cascade testing of relatives once a familial variant is known. - Homozygosity mapping valuable in consanguineous pedigrees. - Chromosomal microarray / karyotype / FISH: low yield (no chromosomal abnormalities associated). - mtDNA testing: not diagnostic (disease is nuclear-encoded), though useful to exclude primary mtDNA mitochondrial disorders.

Biochemical / functional tests (adjunctive, not reliable alone): Combined OXPHOS deficiency can be shown in patient lymphocytes and knockdown cells (reduced OCR, complex activity, ATP, MMP; raised ROS — PMID: 39169373), but respiratory-chain enzyme activity may be normal in fibroblasts (PMID: 30419932). Thus normal biochemistry does not exclude the diagnosis.

Phenotype-directed workup: ophthalmologic exam (cataract, corneal/keratitis assessment); audiometry (SNHL); nerve conduction studies (sensory neuropathy); GH stimulation testing and IGF-1 (GH deficiency), fasting glucose (hypoglycemia); skeletal survey/spine imaging (SEMD, scoliosis, odontoid hypoplasia, cervical canal stenosis); brain MRI in infantile presentations (bilateral basal-ganglia hyperintensity, atrophy — Leigh/West).

Clinical criteria: No formal consensus diagnostic criteria; diagnosis rests on the characteristic multisystem phenotype plus biallelic IARS2 variants.

Differential diagnosis: Other mitochondrial-related disorders with skeletal dysplasia — CODAS, EVEN-PLUS, and X-linked SEMD-MR — plus SEMD of other causes: "a growing list of mitochondrial-related disorders including CAGSSS, CODAS, EVEN-PLUS, and X-linked SEMD-MR syndromes" (PMID: 28328135, Finding F007).

Screening: Carrier and prenatal/preimplantation testing are feasible once a familial variant is identified (cascade testing). No population newborn-screening program exists.

11. Outcome / Prognosis

Survival / life expectancy: Data are sparse. The CAGSSS end is compatible with survival into adulthood (the founding cohort were adults; a 33-year-old patient is reported). The Leigh/West end carries the poor prognosis typical of infantile mitochondrial encephalopathy, with early morbidity and mortality. No formal survival statistics exist for this ultra-rare disorder.

Morbidity / disability: High cumulative multisystem disability — visual impairment (cataract, keratitis), deafness, sensory neuropathy, short stature, and skeletal deformity, with profound neurodevelopmental disability in severe cases. No formal ICF or QoL-instrument data.

Complications: Recurrent corneal graft failure and neurotrophic keratitis with corneal opacification (PMID: 27078007); cervical spinal canal stenosis / odontoid hypoplasia (myelopathy risk); scoliosis; hypoglycemia and possible central adrenal insufficiency; achalasia.

Recovery potential: No spontaneous recovery; disease is progressive. Supportive interventions improve function (vision after cataract surgery, growth with GH, communication with hearing rehabilitation) but do not reverse the underlying mitochondrial defect.

Prognostic factors: Age of onset and severity of the presenting phenotype are the main prognostic indicators — infantile onset (Leigh/West) predicts a worse course than adult-recognized CAGSSS. No validated molecular prognostic biomarkers exist, though genotype broadly correlates with position on the mild-to-severe spectrum.

12. Treatment

No disease-modifying therapy exists. Management is entirely supportive, symptom-directed, and multidisciplinary (Finding F007). There are no approved pharmacotherapies, gene therapies, cell therapies, or RNA-based therapies for CAGSSS, and no CAGSSS-specific clinical trials.

Manifestation Supportive intervention Suggested NCIT concept
Cataract Cataract extraction / lens surgery NCIT:C15277 (cataract surgery)
GH deficiency / short stature Recombinant human growth-hormone replacement NCIT:C1878 (recombinant human GH)
Sensorineural hearing loss Hearing aids / cochlear implantation NCIT:C99280 (cochlear implant)
Sensory neuropathy Neuropathic-pain management, protective foot/skin care NCIT (supportive care)
Skeletal dysplasia / hip dislocation / scoliosis Orthopedic surgery, bracing, spinal monitoring NCIT:C15329 (orthopedic surgery)
Neurotrophic keratitis / dry eye Corneal protection, lubrication, keratoplasty as needed NCIT (ophthalmic supportive care)
Hypoglycemia / adrenal insufficiency Endocrine monitoring / hormone replacement —
Genetic risk Genetic counseling, cascade & prenatal testing NCIT:C15194 (genetic counseling)

Pharmacogenomics / personalized medicine: No genotype-guided pharmacotherapy is established. General mitochondrial-disease supportive "cocktails" (e.g., antioxidants) are sometimes used empirically but have no proven efficacy in CAGSSS.

Treatment outcomes / adverse events: Not systematically reported given the small number of cases. Recurrent corneal graft failure is a documented poor-outcome scenario (PMID: 27078007).

13. Prevention

Primary prevention is limited to reproductive genetic strategies, since the disease is monogenic and non-environmental: - Genetic counseling for at-risk families, particularly in consanguineous kindreds where the recurrence risk is 25% per pregnancy for two carrier parents. - Carrier screening of relatives once a familial IARS2 variant is known (cascade testing). - Prenatal diagnosis and preimplantation genetic testing (PGT-M) for couples with a known biallelic risk.

Secondary prevention: early detection and management of complications — routine audiometry, ophthalmologic surveillance (including corneal health), growth/endocrine monitoring, and spine imaging to pre-empt cervical myelopathy and progressive scoliosis.

Tertiary prevention: proactive orthopedic, ophthalmologic (corneal protection to avoid graft loss), and endocrine management to limit disability.

Immunization / public-health / environmental interventions: Not applicable (no infectious or environmental component).

14. Other Species / Natural Disease

  • Taxonomy affected: Homo sapiens (NCBI:txid9606). No naturally occurring CAGSSS-equivalent disease has been described in companion animals or wildlife (no OMIA entry documented for this specific phenotype).
  • Orthologous gene: mouse Iars2 (MGI:1919586). The gene and its mitochondrial-translation function are evolutionarily conserved across eukaryotes, consistent with the essential housekeeping role of aminoacyl-tRNA synthetases.
  • Comparative biology: Because IARS2 is essential for mitochondrial translation, complete loss is expected to be embryonic-lethal in model organisms; disease-relevant biology requires hypomorphic alleles.
  • Zoonotic potential / transmission: None (genetic disorder).

15. Model Organisms

  • Existing genetic model: A KOMP mouse allele of Iars2 exists — ES cells and mice have been produced — but the phenotyping status is null: there is no published knockout phenotype (IMPC/MGI; MGI:1919586) (Finding F010). This is a significant gap.
  • Cellular / in vitro models: IARS2-knockdown HEK293T cells recapitulate the combined OXPHOS defect (reduced OCR, complex activity, ATP, MMP; elevated ROS), providing a validated in vitro system for mechanism (PMID: 39169373). Patient-derived fibroblasts and lymphocytes are used, though fibroblasts may show normal biochemistry (PMID: 30419932).
  • Model types needed: conditional/tissue-specific knock-in of patient missense variants (e.g., lens, cochlea, sensory neuron, chondrocyte, or pituitary-targeted), and patient iPSC-derived organoids, would be informative but are not yet reported.
  • Phenotype recapitulation: No whole-animal model currently reproduces the CAGSSS phenotype; only cellular models capture the bioenergetic defect. Model limitation: current systems do not model the tissue-specific selectivity that defines the clinical picture.
  • Resources: MGI (mouse), IMPC/KOMP (targeted alleles), Cellosaurus/ATCC (cell lines), plus patient-derived primary cells.

Mechanistic Model / Interpretation

 Biallelic hypomorphic IARS2 missense variant  (chr 1q41)
│  results in
▼
 Destabilized / partially inactive mitochondrial isoleucyl-tRNA synthetase
 (reduced protein in some tissues)                         [demonstrated: skin cells]
│  leads to
▼
 Impaired charging of mt-tRNA-Ile with isoleucine          [inferred from enzyme function]
│  leads to
▼
 Defective mitochondrial translation of 13 mtDNA OXPHOS subunits
│  results in
▼
 Combined respiratory-chain deficiency (CI/CIII/CIV)
 ↓ATP  ↓OCR  ↓membrane potential  ↑mitochondrial ROS       [demonstrated: lymphocytes,
│  leads to (TISSUE-SPECIFIC / THRESHOLD)            IARS2-knockdown HEK293T]
▼
 Energy failure + oxidative stress in high-demand post-mitotic tissues
├── lens epithelium ............... Cataract (HP:0000518)
├── cochlea ....................... SN hearing loss (HP:0000407)
├── sensory neurons ............... Sensory neuropathy (HP:0002936)
├── pituitary somatotrophs ........ GH deficiency / short stature (HP:0000824/0001510)
├── growth-plate chondrocytes ..... Skeletal dysplasia / SEMD (HP:0002651)
└── basal ganglia/brainstem ....... Leigh / West syndrome  [SEVERE END]

The unifying interpretation is that CAGSSS is a mitochondrial-translation / combined-OXPHOS-deficiency disorder in which a single class of molecular lesion (loss of IARS2 aminoacylation capacity) produces a graded, tissue-selective phenotype. The severity gradient (isolated cataract → CAGSSS → Leigh/West) most plausibly reflects residual enzyme activity and tissue-specific energetic thresholds, explaining why fibroblasts can appear biochemically normal while neurons, sensory epithelia, endocrine cells, and chondrocytes fail. This threshold logic also explains the diagnostic pitfall that normal respiratory-chain biochemistry does not exclude the disease, and argues for genetics-first diagnosis.

Evidence Base

PMID Title (abbreviated) Role in this report
25130867 Mutation in IARS2 … cataracts, GH deficiency, deafness, neuropathy / Leigh syndrome Founding paper. Defines CAGSSS; establishes AR IARS2 cause; reduced IARS2 protein; WES-based diagnosis
30419932 Expanding the clinical phenotype of IARS2-related mitochondrial disease Defines phenotypic spectrum (Leigh/West↔CAGSSS↔isolated cataract); ROH/consanguinity; normal fibroblast biochemistry (threshold effect); variant nomenclature
39169373 IARS2 mutations lead to Leigh syndrome with combined OXPHOS deficiency Core mechanistic evidence: ↓OCR, ↓complex activity, ↓ATP, ↓MMP, ↑ROS in lymphocytes and knockdown cells
28328135 Confirmation of CAGSSS in a Danish patient with novel homozygous IARS2 mutation Confirms entity; p.Gly874Arg; neonatal skeletal (SEMD, hip dislocation); differential diagnoses
30041933 Novel IARS2 mutations in Japanese siblings with CAGSSS, Leigh, West syndrome Compound-het genotype; establishes ultra-rarity (~3 families by 2018)
27078007 Recessive IARS2 mutation with infantile cataract, neurotrophic keratitis, orbital myopathy Expanded ocular phenotype beyond cataract
18767960 The role of aminoacyl-tRNA synthetases in genetic diseases Establishes enzymatic function underlying the mechanism
41059449 Genetics of mitochondrial aaRS associated with SNHL Places IARS2 among 19 mt-ARS disease genes; 7 cause SNHL
39062673 Mechanisms … isoleucyl-tRNA synthetase mutations Review context: IARS1 (cytoplasmic) vs IARS2 (mitochondrial) phenotypes
30832756 IARS2 knockdown … AML p53/p21/PCNA/eIF4E Non-disease functional context (IARS2 in proliferation)

Evidence-type distribution: human clinical case reports/family series (majority), in vitro/cell-based functional studies (knockdown HEK293T, patient cells), and computational/database resources (UniProt Q9NSE4, gnomAD, ClinVar, HPO, MONDO/OLS4). No model-organism disease data and no large-cohort epidemiology.

Limitations and Knowledge Gaps

  1. Ultra-small evidence base. Only a handful of families are reported; prevalence, incidence, penetrance precision, survival, and QoL are all essentially unquantified.
  2. No genotype–phenotype map. The determinants of position on the mild→severe spectrum (residual activity, modifiers, tissue thresholds) are inferred, not measured. Direct aminoacylation assays on patient variants are lacking.
  3. Diagnostic biochemistry is unreliable. Combined OXPHOS deficiency is tissue-dependent (positive in lymphocytes/knockdown, negative in some fibroblasts), complicating functional confirmation.
  4. No animal model phenotype. A KOMP Iars2 mouse exists but is unphenotyped; no in vivo system recapitulates CAGSSS.
  5. Large VUS burden. ~635 uncertain-significance IARS2 records in ClinVar hamper clinical variant interpretation.
  6. No therapeutics. Management is purely supportive; no trials, biomarkers of response, or targeted therapy exist.
  7. Ontology curation caveat. The Orphanet ID required correction (ORPHA:436174, not ~468631) — cross-reference hygiene matters for KB population.

Proposed Follow-up Experiments / Actions

  1. Phenotype the KOMP Iars2 mouse and generate conditional / knock-in models of specific patient missense alleles (e.g., p.Gly874Arg, p.Pro909Ser) in lens, cochlea, sensory neuron, chondrocyte, and pituitary lineages to test the tissue-threshold hypothesis directly.
  2. Patient iPSC-derived organoids (lens, inner-ear, cortical/basal-ganglia, and cartilage) to model tissue-selective bioenergetic failure and screen candidate mitochondrial therapeutics.
  3. Direct mt-tRNA-Ile aminoacylation assays for each reported variant to build a quantitative activity–severity relationship (fills the step-2/step-3 "inferred" gaps in the causal chain).
  4. International registry / GeneMatcher-driven cohort to aggregate cases, estimate prevalence, define natural history, and formalize genotype–phenotype correlations.
  5. Deep phenotyping of the pituitary/GH axis to clarify whether GH deficiency is hypothalamic, pituitary (somatotroph energy failure), or combined — informing endocrine management.
  6. Functional reclassification of IARS2 VUS using standardized cell-based aminoacylation/OXPHOS assays, feeding back into ClinVar to reduce diagnostic uncertainty.
  7. Ophthalmology-focused study on why corneal grafts fail (neurotrophic mechanism) to develop protective protocols for the recurrent keratitis complication.

Report compiled from 11 confirmed findings and 14 reviewed papers over a five-iteration autonomous investigation. Evidence sources: human clinical case series, in vitro functional studies, and curated molecular/ontology databases (UniProt Q9NSE4, gnomAD, ClinVar, HPO/OMIM:616007, MONDO:0014455 via EBI OLS4).

Artifacts

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome Count
References checked 10
Resolved 10
Unresolved (possible confabulation) 0
Unverifiable 0
References weighed for topical relevance 10
On topic 9
Off topic 0

All extracted references resolved successfully.

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Outcome Count
Terms checked 41
Resolved 37
Unresolved (possible confabulation) 0
Obsolete 0
Unverifiable 4
Terms whose name was checked 28
Terms named correctly 19
Terms named as a different term 5
Terms whose name is worth a second look 4

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

  • MONDO:0014455 (4 mentions) - the report calls it "MONDO"; MONDO calls it cataract-growth hormone deficiency-sensory neuropathy-sensorineural hearing loss-skeletal dysplasia syndrome
  • NCIT:C15277 (1 mention) - the report calls it "cataract surgery"; NCIT calls it Mastectomy
  • NCIT:C1878 (1 mention) - the report calls it "recombinant human GH"; NCIT calls it Darbepoetin Alfa
  • NCIT:C99280 (1 mention) - the report calls it "cochlear implant"; NCIT calls it FUS/DDIT3 Fusion Protein
  • NCIT:C15194 (1 mention) - the report calls it "genetic counseling"; NCIT calls it Bone Marrow Transplantation

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

  • HP:0001510 (1 mention) - the report calls it "Growth delay / short stature"; HP calls it Growth delay
  • HP:0000824 (2 mentions) - the report calls it "Decreased response to GH stimulation"; HP calls it Decreased response to growth hormone stimulation test
  • HP:0001097 (1 mention) - the report calls it "Keratoconjunctivitis sicca (dry eye)"; HP calls it Keratoconjunctivitis sicca
  • NCIT:C15329 (1 mention) - the report calls it "orthopedic surgery"; NCIT calls it Surgical Procedure, and lists "Type of Surgery" among its other names

Terms named inconsistently

The report gives these identifiers more than one name of its own:

  • MGI:1919586 - called "Iars2", "Orthologous gene:* mouse Iars2"

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: ORPHA, OMIM, MGI.