Let me get the primary papers' details.

Research report: cerebellar ataxia, brain abnormalities, and cardiac conduction defects (CABAC)

Evidence status. This report rests on a limited number of fetched sources: the Calame 2021 full text (PMC8382094), part of the Slavotinek 2020 full text, and secondary aggregators (MedGen, MalaCards, KEGG, GenCC, PanelApp, GeneCards). I did not confirm OMIM, Orphanet, MONDO or MeSH identifiers directly, because OMIM, PubMed and MalaCards blocked fetches. Items marked [unverified] come from aggregator summaries or my own recall, and need a lookup before they go into the KB. All ontology IDs below are suggestions and must be looked up with runoak or OLS before binding.

The literature is small: about 10 reported patients, and the recurrent variant p.Thr114Ile accounts for most conduction disease.

1. Disease information

• Overview. CABAC is a rare autosomal recessive neurodevelopmental disorder caused by biallelic variants in EXOSC5, which encodes a structural subunit of the RNA exosome. It features hypotonia, developmental delay, ataxic gait, cerebellar hypoplasia or atrophy, and progressive cardiac conduction disease with arrhythmia.
• Identifiers. OMIM #619576 (per MedGen and GenCC summaries). Other identifiers I did not retrieve: MONDO (unknown), Orphanet, ICD-10/11, MeSH. KEGG has an entry, H02549.
• Synonyms. CABAC; EXOSC5-related disease; EXOSC5-related neurodevelopmental disorder.
• Related earlier description. Zaki et al. 2011 described a family with bradycardia and second-degree heart block ("Zaki-Gleeson syndrome"). Calame 2021 lists it as a possibly related family with unknown locus.
• Data source. The data come from individual patient case reports and small series, not from EHR or population resources.

2. Etiology

• Cause. Biallelic loss or hypomorphic variants in EXOSC5. GenCC lists the gene-disease relationship as "Strong" and autosomal recessive (GenCC SGC-178553.1). Genomics England PanelApp notes a caveat: all of the first three families shared p.Thr114Ile (PanelApp EXOSC5).
• Risk factors. Consanguinity (see Section 9). No environmental risk factors, protective factors or gene-environment interactions are reported. The report does not state this; it is an absence of data.
• Modifier genes. None reported.

3. Phenotypes

Sources: Slavotinek 2020 (HMG 29:2218, DOI 10.1093/hmg/ddaa108, PMID 32504085 per GenCC) and Calame 2021 (PMC8382094, PMID 34089229). Frequencies are not computable from about 10 patients. Counts below are per reported patients.

• Variable or single-patient findings. Hypospadias, tethered cord, metopic craniosynostosis, OCD and coronary fistula appear in single Slavotinek patients and may not be core features.
• Onset and progression. Neurological features start in infancy. Cardiac conduction disease appears in infancy to adolescence and is progressive. Calame reports that both siblings showed intermittent complete heart block and profound sinus node dysfunction at ICD implantation. Brain MRI shows progressive cerebellar and cerebral atrophy over time.
• Quality of life. No data are available.

4. Genetic and molecular information

• Gene. EXOSC5 (hgnc ID not verified; look it up with runoak or HGNC). Transcript NM_020158.4.
• Variants reported.

• Functional consequence. Most variants are hypomorphic missense. The abstract of Slavotinek 2020 concludes that "different EXOSC5 variants may act through different disease mechanisms" (paraphrased by the fetch tool, not a verified verbatim quote). Allele frequencies in gnomAD were not retrieved. Calame 2021 calls both missense alleles ultra-rare.
• Genotype-phenotype pattern. Calame 2021 states that six of ten reported patients have conduction abnormalities, and that all six carry p.Thr114Ile. The paper's introduction gives a different count (four of eight) and the article does not reconcile the two. The Slavotinek P2 (p.Leu206His) and P3 (p.Met148Thr) patients, with homozygous alleles that are not p.Thr114Ile, had no documented conduction disease, though their cardiac work-up was limited. Treat this pattern as suggestive.
• Epigenetic or chromosomal. Segmental uniparental disomy (chr19 isodisomy) is documented in one patient. No other epigenetic data are available.

5. Environmental information

None reported. No infectious, toxic or lifestyle contribution is documented.

6. Mechanism and pathophysiology

Causal chain (steps 1–3 are demonstrated or inferred from the molecular data. Steps 4–6 are inferred, not demonstrated):

1. Biallelic EXOSC5 variants (mostly hypomorphic missense, plus rare null alleles) alter the Rrp46 subunit (EXOSC5) of the RNA exosome. Demonstrated by genetics.
2. This impairs RNA exosome function. In yeast, the allele equivalent to p.Leu206His (rrp46-L191H) caused growth defects at 30°C and 37°C. The equivalents of p.Thr114Ile and p.Met148Thr (rrp46-Q86I, L127T) showed no growth defect in the fetched content. The Thr114 equivalent was not clearly identified in the text I read, so I do not link the yeast result to that variant.
3. This leads to reduced exosome-mediated 3'→5' RNA processing and decay. The specific RNA targets in affected cells are not identified in the sources read. Inferred from exosome biology.
4. Neural tissue is selectively vulnerable. This is inferred from the pattern in other exosomopathies (EXOSC3, 8, 9: pontocerebellar hypoplasia, motor neuronopathy), and the mechanism of selectivity is unknown.
5. This leads to cerebellar and brainstem hypoplasia or atrophy, hypomyelination and ventriculomegaly, causing hypotonia, ataxia and developmental delay.

6. In the heart, the mechanism is unknown. Conduction tissue (sinus node, AV node, His-Purkinje) appears vulnerable, leading to AV block, bundle branch block, VT and a risk of sudden cardiac death. Inferred from phenotype only.

7. Branch. Missense alleles may differ in mechanism. Slavotinek 2020 reports that mutant EXOSC5 protein levels were not significantly altered in mammalian cells, while neuronal cells showed differences in interactions with other exosome subunits. This part was truncated in the fetched text.

8. Suggested terms. GO: RNA catabolic process (GO:0006401 lead); nuclear RNA surveillance; exosome (RNase complex) (GO:0000178 lead). CL: Purkinje cell (CL:0000121), cardiac muscle cell, cardiac pacemaker cell (verify). All to be looked up.
9. Not available. Transcriptomics, proteomics, single-cell data and CRISPR screens for CABAC were not found.

7. Anatomical structures affected

• Primary. Cerebellum, brainstem and pons, cerebral white matter, corpus callosum, and the cardiac conduction system (sinus node, AV node, His-Purkinje) (UBERON: cerebellum UBERON:0002037; pons; corpus callosum; heart; verify).
• Secondary. Eye (retina, extraocular muscles, optic nerve), skeletal system (short stature, scoliosis), and swallowing function.
• Subcellular. The RNA exosome in nucleus and cytoplasm.
• Lateralization. Bilateral.

8. Temporal development

• Onset. Congenital or infantile for neurological features. Cardiac onset ranges from age 2 (syncope, complete heart block) to adolescence (RBBB, bradycardia). One patient died at 11 months of respiratory disease (Slavotinek P2).
• Progression. Progressive cerebellar atrophy on serial MRI, and progressive conduction disease.
• Critical period. Cardiac surveillance before and through adolescence.

9. Inheritance and population

• Inheritance. Autosomal recessive (HP:0000007).
• Parents. Obligate carriers are unaffected. Calame's family had unrelated parents and three unaffected siblings.
• Consanguinity. Present in some families (first-cousin parents in Slavotinek P2; the Iranian siblings).
• Founder effect. p.Thr114Ile is recurrent across different populations. Founder status is not established.
• Prevalence, incidence, carrier frequency, sex ratio. Not available. Ten or fewer reported patients.

10. Diagnostics

• Genetic testing. Exome or genome sequencing, or a panel (EXOSC5 is on the Genomics England ataxia and cerebellar anomalies panel). Include copy-number analysis, because a 1,023 bp intragenic deletion was found. Consider UPD when a homozygous variant is found with a single carrier parent (Slavotinek P3).
• Imaging. Brain MRI: cerebellar hypoplasia or atrophy, small brainstem or pons, ventriculomegaly, hypomyelination, thin corpus callosum.
• Electrophysiology and cardiac. ECG and Holter. Calame found the Holter showed bradycardia, AV block and monomorphic VT. Echocardiograms were normal in both siblings, so a normal echocardiogram does not exclude conduction disease.
• Differential diagnosis. Pontocerebellar hypoplasia types due to EXOSC3, EXOSC8, EXOSC9 and EXOSC1, and other recessive cerebellar ataxias with cardiac involvement.
• Screening. No established program. Calame recommends proactive cardiac screening.

11. Outcome and prognosis

• Survival. Not systematically characterized. Early death (11 months) was reported in one patient. Sudden cardiac death has been reported in this and other exosome disorders in secondary sources [unverified in primary papers]. Calame notes sudden unexplained death in a 10-year-old with EXOSC9 disease.
• Morbidity. Developmental disability ranges from mild to profound; the severe brother in Calame had no walking or speech, epilepsy and spasticity.
• Prognostic factors. The p.Thr114Ile allele is associated with conduction disease in reported cases. No validated prognostic model exists.

12. Treatment

No disease-specific therapy exists. Management is supportive and cardiac.

• Cardiac devices. Pacemaker (Slavotinek P1; Iranian siblings). Dual-chamber ICD in both Calame siblings (NCIT: Cardiac Pacemaker Implantation / Implantable Cardioverter Defibrillator Placement, to be looked up). Calame recommends considering a pacemaker or ICD when conduction disease or arrhythmia is found.
• Supportive. Physical, occupational and speech therapy, feeding support (gastrostomy), antiseizure treatment and ophthalmologic care. Suggested NCIT: Physical Therapy NCIT:C15302; Supportive Care NCIT:C15747; Genetic Counseling NCIT:C15240.
• Experimental. No trials, gene therapy, RNA therapy or pharmacogenomic data were found. I did not search ClinicalTrials.gov.

13. Prevention

• Genetic counseling and carrier testing for at-risk relatives. Prenatal or preimplantation diagnosis is possible for known familial variants.
• Cascade testing of siblings.
• Calame recommends periodic ECG and Holter surveillance for conduction defects and arrhythmias, and suggests that cardiac evaluation may also be prudent for people with variants in other exosome genes.

14. Other species and natural disease

No naturally occurring disease in other species was found. I did not check OMIA, so this is an absence of retrieved data, not a confirmed negative.

15. Model organisms

• Zebrafish. Slavotinek 2020 made exosc5 crispants, which showed shortened and curved tails and bodies, reduced eye and head size, edema, fin defects, increased ventricle size and reduced brain size. Reporter lines (mnx1:EGFP motor neuron, NBT:dsRed pan-neuronal) showed reduced fluorescence and abnormal brain morphology in severe larvae. qRT-PCR showed reduced exosc5 expression in abnormal larvae. This is partial, crispant-level evidence, and cardiac phenotypes were not reported in the text I read.
• Budding yeast. Rrp46 variants modeling patient alleles. Only the p.Leu206His equivalent caused a growth defect (doubling time about 64–69% longer).
• Mouse. A mouse knockout resource appeared in search results for a different gene (a mousephenotype.org page); I did not verify an Exosc5 mouse model.
• Limitations. Crispants are mosaic and acute. Yeast has no heart or cerebellum, so the cardiac phenotype is not modeled by any retrieved system.

Open items before curation

1. Look up the MONDO ID, Orphanet and ICD entries, and confirm OMIM #619576 and its clinical synopsis.
2. Confirm PMIDs. Slavotinek 2020 = 32504085 (from GenCC, not independently confirmed) and Calame 2021 = 34089229 (from search result). The Beheshtian 2019 PMID is unknown. GenCC lists PMID 29302074 as "Hu et al., 2019", which I could not tie to Beheshtian, so do not use it for that paper without checking.
3. Run just fetch-reference for each PMID before quoting snippets. All snippets must be copied from the cached text; I have not supplied verbatim quotes.
4. Check for newer EXOSC5 cases after 2021. The search returned none, but it was not exhaustive.

Sources

• GenCC submission SGC-178553.1
• Slavotinek et al. 2020, Hum Mol Genet
• Calame et al. 2021, Am J Med Genet A (PMC8382094)
• Genomics England PanelApp, EXOSC5
• NCBI MedGen 1794215
• MalaCards CABAC
• KEGG H02549
• GeneCards EXOSC5

Reference Validation

Checked with linkml-reference-validator 0.3.0.

All extracted references resolved successfully.

Term Validation

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

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:

• HP:0001252 (1 mention) - the report calls it "Infantile onset (Slavotinek P2; GeneCards summary)"; HP calls it Hypotonia
• HP:0007366 (1 mention) - the report calls it "lead; check the exact brainstem term"; HP calls it Atrophy/Degeneration affecting the brainstem
• HP:0002119 (1 mention) - the report calls it "Slavotinek P2, P3, P4"; HP calls it Ventriculomegaly
• HP:0003429 (1 mention) - the report calls it "lead"; HP calls it CNS hypomyelination
• HP:0033725 (1 mention) - the report calls it "lead"; HP calls it Thin corpus callosum
• HP:0000252 (1 mention) - the report calls it "Calame P1 (OFC Z −2.77)"; HP calls it Microcephaly
• HP:0011968 (1 mention) - the report calls it "Slavotinek P2 (gastrostomy)"; HP calls it Feeding difficulties
• HP:0000548 (1 mention) - the report calls it "Slavotinek P1 only"; HP calls it Cone/cone-rod dystrophy
• HP:0000648 (1 mention) - the report calls it "Calame P2"; HP calls it Optic atrophy
• HP:0001678 (1 mention) - the report calls it "Slavotinek P1 (syncope at age 2, pacemaker)"; HP calls it Atrioventricular block
• HP:0011704 (1 mention) - the report calls it "Calame P1 and P2"; HP calls it Sick sinus syndrome
• HP:0004756 (1 mention) - the report calls it "Calame P1 and P2"; HP calls it Ventricular tachycardia