RECON Progeroid Syndrome — Research Report

Target: RECON Progeroid Syndrome | OMIM #620370 | MONDO:0957266 | HGNC gene RECQL (HGNC:9948) | NCBI Gene 5965

Note on ontology term suggestions throughout this report: Every HP/GO/CL/CHEBI/NCIT identifier below is a proposed binding based on phenotype/mechanism descriptions in the literature, not a verified lookup against the live ontology. Per this repository's term-binding contract, treat every suggested CURIE as a lead to be checked with runoak/OAK against the current HP/GO/CL build before it is written into any kb/disorders/*.yaml file — do not copy an ID from this report directly into a binding.

1. Disease Information

Overview. RECON syndrome ("RECql ONe" syndrome) is an autosomal recessive genome-instability/progeroid disorder first described in 2022, caused by a biallelic (homozygous) missense mutation in RECQL (also called RECQL1, RECQ1), the first human disease ever attributed to this gene despite its 1992 discovery. It is characterized by postnatal growth retardation, a progeroid ("prematurely aged") facial gestalt, cutaneous photosensitivity/xeroderma, and slender elongated digits, occurring on a background of cellular chromosomal instability and defective replication-fork restart (Arboleda-Velasquez lab / Sturzenegger et al., J Clin Invest 2022; PMID:35025765).

"RECON syndrome (for RECQ ONe) ... is a genome instability disorder caused by mutations in the DNA helicase RECQL1." — PMC8884905 abstract.

Key identifiers: | Resource | ID | |---|---| | OMIM (phenotype) | #620370 — RECON PROGEROID SYNDROME | | OMIM (gene) | 600537 — RECQ PROTEIN-LIKE; RECQL | | MONDO | MONDO:0957266 | | MedGen | C5830504 (UID 1841140) | | NCBI Gene | 5965 (RECQL) | | HGNC | HGNC:9948 (RECQL) | | UniProt disease | DI-06683 | | Gene locus | 12p12.1 | | Reference transcript | NM_032941.2 | | Orphanet | No ORPHA number could be located* — this appears to be an Orphanet coverage gap, consistent with the disease's extreme rarity (3 genotyped patients worldwide as of this report) and recent (2022) description. Confirm during curation rather than assuming absence is permanent. | GeneReviews chapter | None found — too recently described / too few families for a dedicated chapter.

Synonyms: RECON syndrome; RECON progeroid syndrome; RECQL1-related progeroid syndrome. No historical/eponymous synonyms exist since this is a molecularly-defined, recently named entity.

Evidence basis: This entry is built almost entirely on a single primary molecular/clinical study (2 families, 3 genotyped individuals; PMID:35025765) plus one aging-biology review by an overlapping author group (PMID:36907310, PMC10018417) and downstream database records (OMIM, MedGen, MalaCards, GeneCC) that recapitulate the same primary source. This is aggregated disease-level curation from structured databases plus the two original literature reports — not EHR/individual-patient-level data.

2. Etiology

Disease-causal factor: Purely genetic/mechanistic — homozygous hypomorphic missense variant in RECQL, a RecQ-family ATP-dependent DNA helicase gene. No environmental, infectious, or lifestyle causal factor is implicated in disease causation (photosensitivity is a phenotypic consequence of the underlying DNA-repair defect, not an environmental cause).

Genetic risk factors: - Causal variant: RECQL NM_032941.2:c.1375G>T, p.(Ala459Ser) (p.A459S), homozygous, located in the zinc-binding domain (ZBD) of the helicase core. Identified independently, identical, in two apparently unrelated Middle Eastern families (PMID:35025765). - In silico pathogenicity: CADD 25.9; PolyPhen-2 0.846 (probably damaging); MutationTaster 1.0; DANN 0.9977; GERP conservation score 6.04 (highly conserved alanine). - Population frequency: Absent from gnomAD and the Greater Middle East (GME) Variome — consistent with a very rare/founder allele rather than a common polymorphism. - Linkage support: LOD score Z = 3.311 at θ = 0 in Family A (consanguineous pedigree), supporting causality by segregation. - Consanguinity: Family A are double first cousins; parents of the affected sisters are first-degree relatives, consistent with autosomal recessive homozygosity. Family B had no reported consanguinity, raising the possibility of a shared regional founder haplotype for the identical variant, though this was not explicitly confirmed by haplotype analysis in the primary report as summarized here. - Modifier genes: None reported or investigated.

Environmental risk factors: None identified as disease-causing. UV/sunlight exposure is expected to exacerbate the cutaneous photosensitivity phenotype (as in other RecQ-helicase disorders), by mechanistic analogy rather than direct study in this cohort.

Protective factors: None reported. Heterozygous carrier parents and 8 healthy siblings across both families were phenotypically normal, indicating the pathogenic mechanism requires biallelic loss of function/hypomorphic activity (recessive), i.e., a single wild-type allele is fully protective in this Mendelian sense.

Gene-environment interaction: Not formally studied. By mechanistic inference (impaired replication-fork restart after genotoxic/replicative stress — camptothecin [TOP1 poison], etoposide [TOP2 poison], hydroxyurea [replication stress], MMS [alkylation]), affected individuals' cells are hypothesized to be hypersensitive to genotoxic environmental/pharmacologic exposures, though this has only been demonstrated in vitro in patient-derived lymphoblastoid cell lines (LCLs) and fibroblasts, not shown clinically as altered exposure sensitivity in the patients themselves.

Important lump/split note for curation: RECQL also independently causes autosomal-dominant, monoallelic breast-cancer susceptibility via rare truncating variants (e.g., c.643C>T/p.Arg215), acting through haploinsufficiency with no loss of heterozygosity in tumors (PMID:25915596; Nature Genetics 2015). This is a mechanistically and clinically distinct disease entity* from RECON syndrome — different zygosity (heterozygous vs. homozygous), different variant class (truncating/LOF vs. hypomorphic missense), different phenotype (adult-onset cancer predisposition vs. pediatric progeroid syndrome), and no overlap reported between the two patient populations. Keep separate dismech entries; do not conflate "RECQL-related disease" as a single node.

3. Phenotypes

Phenotype data are drawn from three genotype-confirmed patients (Family A: III-2, age 9y8m at report, and III-4, age 4y; Family B: III-4, followed from 5y10m to 14y9m) in PMID:35025765, cross-checked against MedGen's HPO-based phenotype list for C5830504.

Severity/progression pattern: Family B illustrates a clearly progressive course — the same patient followed from age ~6 to ~15 years showed worsening growth failure and wasting (height z-score −1.98-equivalent range declining toward −3.59; weight z-score reaching −8.47), i.e., this is not a static congenital malformation syndrome but an accumulating, progeroid degenerative trajectory, consistent with the "genome instability accrual over time" mechanism proposed by the authors.

Quality of life impact: Not formally measured (no EQ-5D/SF-36/PROMIS data reported); qualitatively, severe growth failure, recurrent infections, and photosensitivity would be expected to impose a substantial pediatric disease burden, but this is inference, not measured outcome data.

Not yet assessed / open questions for phenotype curation: Neurodevelopmental/cognitive phenotype is not emphasized in either source as abnormal (unlike some RecQ disorders); this should be explicitly confirmed as "normal cognition documented" vs. "not assessed" rather than left silent, since the distinction matters for downstream users comparing to Bloom/Werner syndrome, which also generally spare cognition.

4. Genetic/Molecular Information

Causal gene: RECQL (RECQ Like Helicase; also known as RECQL1, RECQ1), HGNC:9948, NCBI Gene 5965, OMIM *600537, locus 12p12.1.

Pathogenic variant: - Genomic: chr12:21,626,557 (hg19) - cDNA: NM_032941.2:c.1375G>T - Protein: p.Ala459Ser (p.A459S) - Variant type: missense (substitution within the zinc-binding domain, ZBD) - Zygosity: homozygous in all 3 genotyped affected individuals; parents and 8 unaffected siblings across both families were heterozygous or wild-type - ACMG-style classification: Not explicitly stated as a formal ACMG term in the sources retrieved, but functionally and segregation-validated as disease-causing (pathogenic) in the primary report - Origin: germline (not somatic) - Allele frequency: absent from gnomAD and the Greater Middle East (GME) Variome — i.e., not present in any population reference database retrieved - Functional consequence: hypomorphic loss-of-function — the mutant retains partial activity rather than being a complete null (distinguishing RECON from the complete-null disease model)

Gene-disease validity note: GenCC/ClinGen submitter records show a "Disputed Evidence" classification from Labcorp Genetics (formerly Invitae), evaluated 2023-11-30, for the RECQL–RECON progeroid syndrome relationship. This reflects the very limited evidence base (single recurrent variant, two families) typical of an ultra-recently described gene-disease pair, and should be represented honestly in curation as a limited/disputed validity relationship rather than "definitive" — cite the GenCC record and the caveat explicitly if a validity classification slot is populated.

Functional/biochemical consequences of p.A459S (all from PMID:35025765, functional assays comparing recombinant WT vs. mutant RECQL1): - ATPase activity: markedly reduced kcat/Km/Vmax for ATP hydrolysis relative to WT. - Helicase (DNA unwinding) activity: substantially reduced — e.g., WT unwound ~60% of a forked-duplex substrate at 2.5 nM protein vs. ~20% for mutant; 2.6- to 4.8-fold reduction in unwinding rate depending on substrate/concentration. - Fork restoration (regressed-fork restart) activity: 7-fold reduction at 5 minutes, ≥3.5-fold at later time points; ATP-dependent. - DNA binding: modestly reduced affinity (~1.5-fold higher apparent Kd) for forked-duplex DNA. - Strand-annealing activity: essentially preserved, unlike unwinding — a mechanistically important dissociation showing the mutation selectively impairs the ATP-driven translocase/helicase function rather than all DNA-binding functions. - Oligomerization: normal (assessed by size-exclusion chromatography). - Protein expression/stability and nuclear localization: normal in patient LCLs — the defect is purely catalytic/functional, not one of protein loss or mislocalization.

Structural mechanism: p.A459S disrupts a hydrophobic cluster within the ZBD core (involving residues W466, M458 in the ZBD; M395, Y359 in the helicase-C domain; F281 in the helicase linker). Because the ZBD is spatially juxtaposed to the ATP-binding cleft, this perturbation is proposed to impair allosteric coupling between ATP binding/hydrolysis and DNA unwinding, explaining the combined ATPase/helicase defect from a single point substitution.

Cellular phenotypes in patient-derived LCLs/fibroblasts: - Elevated spontaneous and drug-induced (camptothecin [TOP1 poison]/etoposide [TOP2 poison]) 53BP1 DNA-damage foci; corrected by complementation with WT RECQL1. - Increased spontaneous and drug-induced chromosome breakage, phenotypically comparable in degree to an ataxia-telangiectasia-like disorder (ATLD) patient LCL used as comparator. - Mildly increased spontaneous and DNA-damage-induced sister chromatid exchange (SCE) — notably a much milder SCE phenotype than in Bloom syndrome, where SCE elevation is a diagnostic hallmark. - Increased spontaneous replication-fork stalling, consistent with baseline endogenous replication stress. - Failure to efficiently replicate through TOP1/TOP2-induced lesions (camptothecin/etoposide) and failure to restart forks after hydroxyurea (nucleotide depletion) or MMS (alkylation) exposure, with increased chromosome breakage after MMS. - Mildly increased replication-fork degradation after prolonged hydroxyurea exposure, correctable by WT complementation. - Robust ATM-dependent DNA-damage-response (DDR) signaling activation despite the underlying repair defect — i.e., the sensor/signaling arm of the DDR is intact; the defect is specifically in the helicase-mediated repair/restart step. - No aberrant MLL/ENL locus translocations after etoposide exposure (distinguishing the mechanism from TDP2-deficiency-associated translocations).

Epigenetic information: Not directly studied in the primary RECON paper. The companion review (PMC10018417) frames genome-wide transcriptional/epigenetic alteration as one of three "hallmarks of aging" hypothesized to be relevant (alongside genomic instability and telomere attrition) but does not report direct patient epigenomic data for RECON syndrome specifically.

Chromosomal abnormalities: No gross chromosomal rearrangements/aneuploidy reported in patients; the "chromosomal instability" terminology in this disease refers to increased chromosome breakage and replication-stress phenotypes at the cellular level, not constitutional karyotypic abnormality.

Suggested GO terms (leads, verify before binding): - GO:0003678 DNA helicase activity - GO:0006269 DNA replication, synthesis of RNA primer / GO:0000731 DNA synthesis involved in DNA repair - GO:0031297 replication fork processing - GO:0006281 DNA repair - GO:0000724 double-strand break repair via homologous recombination

5. Environmental Information

No causal environmental, lifestyle, or infectious factor has been reported for RECON syndrome; it is monogenic. As above, exogenous genotoxic stressors (UV light for the cutaneous phenotype; by mechanistic analogy, topoisomerase poisons and alkylating/replication-stress agents for the cellular defect) are plausible exacerbating rather than causal exposures, inferred from the in vitro genotoxin-sensitivity assays (camptothecin, etoposide, hydroxyurea, MMS) rather than from documented clinical exposure histories. No infectious trigger is described. This section is essentially "not applicable" for a purely Mendelian ultra-rare disorder with no reported gene-environment study.

6. Mechanism / Pathophysiology

Causal chain (ordered, with inference flagged)

1. Homozygous RECQL c.1375G>T (p.A459S) leads to a structurally destabilized zinc-binding-domain/ATP-binding-cleft interface in the RECQL1 helicase protein (demonstrated: structural/biochemical analysis, PMID:35025765).
2. This structural change results in markedly reduced ATPase and DNA-unwinding (helicase) catalytic activity, and impaired fork-restoration activity, while DNA binding and strand-annealing remain largely intact (demonstrated: recombinant protein biochemistry).
3. Reduced RECQL1 helicase/fork-restoration activity leads to impaired restart of replication forks that stall or regress — particularly forks stalled by topoisomerase I/II poisons (camptothecin, etoposide), nucleotide depletion (hydroxyurea), or alkylation damage (MMS) (demonstrated: patient LCL replication assays).
4. Impaired fork restart results in accumulation of unresolved/collapsed replication forks and persistent replication stress, evidenced by increased spontaneous fork stalling and increased fork degradation after prolonged replication stress (demonstrated: DNA fiber assays in patient cells).
5. Persistent replication stress and fork collapse lead to increased DNA double-strand breaks — marked by elevated spontaneous and drug-induced 53BP1 foci and chromosome breakage — despite intact upstream ATM-dependent damage-signaling activation, i.e., the sensing/signaling machinery works but the repair/restart step downstream of it is defective (demonstrated: patient LCL/fibroblast assays).
6. Chronic low-level genomic instability (chromosome breakage, mildly elevated sister chromatid exchange) at the cellular level is proposed to result in (inferred, not directly demonstrated longitudinally in patients) progressive cellular attrition/senescence in proliferative and genome-maintenance-dependent tissues (skin, connective tissue, growth plate, hematopoietic compartment).
7. This cellular-level genome-instability burden is hypothesized to underlie (inferred; the authors explicitly frame this as a hallmarks-of-aging model rather than a proven tissue-level mechanism) the clinical progeroid phenotype: postnatal growth failure/short stature, progeroid facial appearance, xeroderma/photosensitivity, and slender-digit skeletal features, by analogy to the general model that replication-stress/genome-instability disorders (Bloom, Werner, Rothmund-Thomson) manifest as premature-aging phenotypes.
8. Independently and in parallel (branch point, not sequential to steps 6–7): the cytopenias reported in one patient (thrombocytopenia, anemia) and recurrent infections may reflect (inferred) a hematopoietic-compartment consequence of chronic replication stress in a highly proliferative stem/progenitor cell population, analogous to bone-marrow-failure phenotypes in other genome-instability syndromes (e.g., Fanconi anemia), though this specific causal link is not demonstrated for RECON syndrome and should be flagged as speculative/unconfirmed in any curated pathograph edge.

Molecular pathways

RECQL1 functions within the replication-stress response / homologous-recombination-adjacent fork-protection pathway, distinct from but overlapping the canonical HR machinery (RAD51, BRCA1/2) and from the Fanconi anemia pathway. It interacts functionally (and antagonistically in terms of timing) with PARP1: PARP1 poly(ADP-ribosyl)ation stabilizes regressed forks and restrains premature RECQL1-mediated restart, so the two proteins together regulate the timing of fork restart rather than acting in a simple linear cascade (PMID cited in search results on RECQL1–PARP1 fork restart antagonism). No canonical developmental signaling pathway (Wnt/MAPK/mTOR/PI3K-AKT) has been implicated; this is a DNA-metabolism/genome-maintenance pathway disorder, not a classical signal-transduction disease.

Cellular processes

• DNA replication-fork protection and restart (central, demonstrated defective)
• DNA double-strand break repair / genome stability maintenance (demonstrated defective downstream consequence)
• Possible transcriptional regulation: newer data (cited in the aging review, PMC10018417) indicate RECQL1 "preferentially binds to guanine (G)-rich sequences in target promoter elements that it directly regulates," including genes such as SHOX (a key growth-plate/stature gene) — an emerging, less-established (basic-research-stage) mechanism potentially directly linking RECQL1 to the short-stature phenotype via gene regulation rather than solely via genome-instability/senescence. This should be flagged as an emerging hypothesis, not an established causal mechanism for the human phenotype.
• Cellular senescence (inferred/hypothesized downstream consequence, not directly measured with senescence markers — e.g., no p16/SA-β-gal data reported — in the retrieved sources)

Protein dysfunction

Loss-of-function is hypomorphic and selective: catalytic (ATPase/helicase/fork-restoration) impairment with preserved DNA-binding and strand-annealing — a partial, function-selective loss rather than complete null or a dominant-negative/gain-of-function mechanism. No protein misfolding/aggregation phenotype is reported (protein expression and localization are normal).

Metabolic changes

None reported; this is not a primary metabolic disease.

Immune system involvement

Not a primary immunodeficiency, but recurrent chest infections were reported in one patient (Family B) — mechanism unestablished; could reflect general frailty/wasting rather than a specific immune defect, and this ambiguity should be preserved in curation notes rather than resolved without a source.

Tissue damage mechanisms

Replication-stress-driven genomic instability is the proposed unifying tissue-damage mechanism, analogous to other RecQ-helicase progeroid disorders, but tissue-specific histopathology has not been reported for RECON syndrome specifically (no biopsy/pathology data in the retrieved sources).

Biochemical abnormalities

Core biochemical defect = reduced RECQL1 ATPase/helicase/fork-restoration enzymatic activity (quantified above in Section 4).

Molecular profiling

No transcriptomic, proteomic, metabolomic, lipidomic, single-cell, or spatial-omics datasets for RECON-syndrome patient tissue were identified in this search. This is an important, honestly-reportable gap — given the disease's rarity and recency, no GEO/ArrayExpress/PRIDE/MetaboLights datasets appear to exist yet.

7. Anatomical Structures Affected

Organ level (primary): Skin (photosensitivity, xeroderma, livedo reticularis, keratosis pilaris); craniofacial skeleton/soft tissue (progeroid facial gestalt, nasal hypoplasia, premaxilla prominence); skeletal system, specifically the hands (slender/elongated thumbs, arachnodactyly); growth (whole-body postnatal growth failure — endocrine/skeletal growth axis); ocular surface (dry eyes/keratoconjunctivitis sicca, absent lower lashes); dentition (delayed eruption, crowding).

Organ level (secondary/systemic): Hematologic system (thrombocytopenia, anemia reported in at least one patient); respiratory system (recurrent chest infections in one patient); adipose tissue (severe loss of subcutaneous fat).

Body systems involved: Integumentary, musculoskeletal, craniofacial/dermatologic, ophthalmologic, hematologic, and (by underlying cellular mechanism) essentially every proliferative tissue compartment via the genome-instability mechanism.

Tissue/cell level: Dermal fibroblasts and keratinocytes (photosensitivity/xeroderma phenotype, and the fibroblast lines used experimentally); lymphoblastoid cells (the primary cellular model used — Epstein-Barr-virus-transformed B lymphocytes, i.e., patient-derived LCLs); by extension, any rapidly-dividing progenitor population (hematopoietic stem/progenitor cells, growth-plate chondrocytes) is mechanistically implicated but not directly biopsied/profiled in the retrieved literature.

Suggested UBERON/CL terms (leads, verify before binding): - UBERON:0002097 skin of body - UBERON:0001456 face - UBERON:0002389 skeleton of manus / UBERON:0002389-adjacent thumb-specific term - CL:0000057 fibroblast - CL:0000542 lymphocyte (patient LCLs specifically derive from CL:0000236 B cell) - CL:0000138 chondrocyte (inferred relevance to growth-plate mechanism, not directly studied)

Subcellular level: Nucleus — RECQL1 is a nuclear protein acting at replication forks and sites of DNA damage; normal nuclear localization is preserved in the mutant. Suggested GO Cellular Component: GO:0005634 nucleus; GO:0000784/GO:0036387 pre-replicative complex/replication fork (verify exact term).

Localization/laterality: No lateralization reported; phenotype is bilateral/symmetric (e.g., bilateral arachnodactyly explicitly noted in Family B).

8. Temporal Development

Onset: Early infancy/early childhood — features were noted by approximately 18 months of age in the reported cases; congenital presence of some dysmorphic features (nose, thumbs) is implied but not explicitly staged as "present at birth" in the extracted material — flag for verification against the primary paper's exact wording before asserting congenital vs. early-postnatal onset in a curated onset field.

Onset pattern: Insidious/progressive rather than acute.

Progression: Clearly progressive in the one longitudinally followed patient (Family B, ages ~6 to ~15 years) — worsening growth failure (height z-score) and severe wasting (weight z-score reaching −8.47 by age 14). This is a meaningful, citable natural-history data point for a progression block.

Disease stages: No formal staging system exists (as expected for an ultra-rare, recently described Mendelian disorder).

Disease course pattern: Chronic, progressive, not episodic/relapsing-remitting based on available data.

Disease duration: Chronic, lifelong (no spontaneous remission reported; no natural death/mortality data reported in the retrieved sources — the oldest documented age at follow-up is 14 years 9 months, so long-term/adult natural history and life expectancy are simply unknown rather than favorable or unfavorable — an important honest gap for the Outcome/Prognosis section).

Critical periods: None specifically identified; by mechanistic inference, periods of rapid cell proliferation (early childhood growth, puberty) might be expected to be more vulnerable to replication-stress-driven phenotype worsening, but this is speculative and not directly evidenced.

9. Inheritance and Population

Epidemiology: Extremely rare — only 3 individuals with confirmed genotype have ever been reported (as of the most recent identified review, 2023), from 2 families, plus 2 additional clinically-similar but ungenotyped adult relatives in Family A. No formal prevalence or incidence estimate exists or is calculable; this is a "cases in literature" measure only (n≈3–5), not a population-based prevalence.

"only 3 affected individuals have been identified, all with the same mutation" — PMC10018417 (review, paraphrased/quoted from WebFetch extraction).

Inheritance pattern: Autosomal recessive (biallelic requirement demonstrated by segregation: heterozygous unaffected parents, 8 unaffected heterozygous/WT siblings, homozygous affected probands).

Penetrance: Appears complete in the reported homozygotes (all 3 genotyped homozygotes were clinically affected), but the sample size (n=3) is far too small to make a confident penetrance claim — report as "apparently complete in reported cases, unconfirmed at scale" rather than "complete."

Expressivity: Variable in severity/timing even among identical-genotype patients — Family B's proband showed a more severe/progressive wasting phenotype (weight z-score −8.47) than described for Family A's patients, despite the identical p.A459S homozygous genotype, indicating variable expressivity (possible modifier-gene or environmental contribution, unstudied).

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

Germline mosaicism: Not addressed in retrieved sources.

Founder effects: Strongly suspected but not explicitly proven by haplotype analysis in the material retrieved — the identical c.1375G>T variant occurring homozygously in two "apparently unrelated" Middle Eastern families is classically suggestive of a shared regional founder allele (or, less likely, a recurrent mutational hotspot). Flag this as an inference for curation notes rather than a stated fact unless the primary paper's haplotype data is separately confirmed.

Consanguinity role: Central — Family A are double first cousins; this is the expected mechanism for revealing a rare recessive allele. Family B's consanguinity status is less clear from the retrieved material and should be re-checked against the primary source.

Carrier frequency: Not calculable/not reported; the variant is absent from gnomAD and the GME Variome, so no meaningful population carrier-frequency estimate exists.

Affected populations/geographic distribution: Middle Eastern (2 families, both described as Middle Eastern in the primary report). No other ethnic/geographic groups reported.

Sex ratio: All 3 genotyped patients reported were female (both Family A patients are sisters; Family B's proband is also female per pronoun usage in the extraction — "her"/"girls" per the PubMed-search summary: "In 3 girls from 2 apparently unrelated Middle Eastern families"). With n=3, this could reflect ascertainment rather than a true sex-linked effect (the gene is autosomal, so no biological expectation of sex skew exists) — report the observed sex distribution but explicitly caveat that it is not evidence of sex-specific risk given the small, possibly ascertainment-biased sample.

Age distribution: Pediatric only in all reported cases (ages 4–15 years at various assessment points); no adult-onset or adult-diagnosed cases reported, consistent with a congenital/early-childhood-onset disorder, though this may also simply reflect that no adult patients have yet been identified given the extreme rarity and recency of description.

10. Diagnostics

Clinical/laboratory tests: - Complete blood count — for thrombocytopenia/anemia (reported in at least one patient) - No disease-specific biochemical/enzymatic biomarker exists; diagnosis is clinical-plus-molecular

Genetic testing (primary diagnostic modality): - Single-gene RECQL sequencing or exome/genome sequencing is the de facto diagnostic approach, as demonstrated in both reported families (identified via presumably exome/targeted sequencing plus homozygosity mapping/linkage, given the LOD score reported for Family A). - No dedicated commercial gene panel or GTR-listed test was specifically identified in this search, though RECQL would plausibly be captured on any broad "progeroid syndrome" or "genome instability disorder" NGS panel offered by clinical laboratories, and on exome/genome sequencing. - Chromosomal microarray/karyotype: not specifically diagnostic (no gross chromosomal rearrangement reported), though may be used to exclude other progeroid-differential diagnoses. - Cellular functional assays (SCE assay, chromosome breakage assay, replication-fork restart/DNA fiber assay) were used as research-level confirmatory functional studies in the primary report, not as established clinical diagnostic tests, and should not be represented as standard-of-care diagnostics.

Imaging/functional/electrophysiology/biopsy: None specifically reported as part of the diagnostic workup in the retrieved sources.

Clinical diagnostic criteria: No formal consensus clinical diagnostic criteria exist (as expected for a disorder with only 3 genotyped cases); diagnosis is currently definitionally molecular (biallelic RECQL pathogenic variant) plus compatible progeroid phenotype.

Differential diagnosis (by phenotypic overlap, from the comparison table constructed above and general RecQ-disorder knowledge): - Werner syndrome (WRN, OMIM #277700) — progeroid facial features, short stature, but adult-onset with normal growth through the teenage years (contrasting with RECON's postnatal/childhood growth failure), and lacking RECON's prominent photosensitivity. - Bloom syndrome (BLM, OMIM #210900) — photosensitivity and growth retardation overlap, but Bloom syndrome features microcephaly, immunodeficiency, strong cancer predisposition, and a markedly elevated SCE rate (a diagnostic hallmark), which is only mildly elevated in RECON syndrome — an important distinguishing cellular finding. - Rothmund-Thomson syndrome / RAPADILINO / Baller-Gerold syndrome (RECQL4, OMIM #268400 / #266280 / #218600) — skeletal abnormalities (radial ray defects), poikiloderma, and cancer predisposition (osteosarcoma) are more prominent than in RECON syndrome; RECON lacks the major skeletal malformations of the RECQL4 disorders. - Other progeroid/genome-instability syndromes not directly compared in the retrieved sources but relevant by general category: Cockayne syndrome, Hutchinson-Gilford progeria syndrome (LMNA), ataxia-telangiectasia-like disorder (used as a chromosome-breakage comparator cell line in the primary paper, not a clinical differential per se).

Screening: No newborn-screening, carrier-screening, or population-screening program exists or would be expected for a disease this rare with only one known recurrent variant confined to specific consanguineous Middle Eastern families; targeted carrier testing within affected families/populations would be the only currently plausible screening approach.

11. Outcome/Prognosis

Survival/mortality: No mortality data reported; oldest documented follow-up age is 14 years 9 months (Family B proband). Long-term survival, life expectancy, and adult natural history are unknown — this must be represented as a genuine evidence gap, not inferred from the (unrelated in mechanism) more severe adult progeroid syndromes.

Morbidity/function: Progressive growth failure and wasting (documented longitudinally in one patient); no formal disability, quality-of-life, or functional-outcome instrument data reported.

Disease course: Chronic and progressive based on the single longitudinal case; no remission reported.

Complications: Thrombocytopenia, anemia, and recurrent chest infections reported in the more severely affected/longer-followed patient (Family B) — whether these represent genuine downstream complications of the core genome-instability mechanism or incidental findings is not established.

Prognostic factors: None formally identified (sample size precludes statistical prognostic-factor analysis). By observation, the degree of wasting/growth failure appears to progress with age in the one followed patient, suggesting age/disease-duration itself may correlate with severity, but this is a single-patient observation, not a validated prognostic factor.

Cancer risk: Unclear/unestablished for the biallelic RECON phenotype specifically. This should be explicitly distinguished in curation from the separate, heterozygous RECQL-breast-cancer-susceptibility literature (Section 2 lump/split note) — no cancer cases have been reported among the RECON-syndrome homozygotes or their heterozygous-carrier relatives in the retrieved sources, but the patient cohort is small and young, so absence of observed cancer is not strong evidence of absent risk.

12. Treatment

No disease-specific, mechanism-targeted, or disease-modifying therapy has been reported or trialed for RECON syndrome. This is expected given the disease was described in 2022 with only 3 genotyped patients; no clinical trials (searched ClinicalTrials.gov context indirectly via search — none surfaced), no FDA-approved indication, and no gene/cell/RNA therapy program were identified.

Supportive care (inferred/by extrapolation from phenotype, not explicitly trialed in the source literature): - Photoprotection (sun avoidance, broad-spectrum sunscreen, protective clothing) for cutaneous photosensitivity — standard supportive dermatologic management by analogy to other photosensitive genome-instability disorders; suggested NCIT term (lead only): a general "Sun Protection"/dermatologic-supportive-care concept, no specific NCIT code identified in this search and should be looked up during curation rather than guessed. - Emollients for xeroderma — general dermatologic supportive care. - Nutritional support for severe growth failure/wasting — general supportive/dietary intervention (NCIT:C15447 Dietary Intervention is a plausible generic bind, but must be verified, not asserted here). - Monitoring for cytopenias/infection given the thrombocytopenia/anemia/recurrent-infection findings in one patient — routine hematologic surveillance, not a formal published protocol.

Explicitly note in curation: the primary source states "No specific therapeutic interventions documented in this research article" — this is a molecular/mechanistic discovery paper, not a clinical-management study, so a dismech treatments: block for this entry should be sparse and clearly labeled as extrapolated supportive care rather than evidence-based disease-specific therapy, or left largely empty with a notes: explanation of why.

13. Prevention

No primary, secondary, or tertiary prevention strategy is established. Given the autosomal recessive inheritance and known consanguineous/founder context in the reported families, genetic counseling for at-risk consanguineous families/relatives of known carriers (recurrence risk 25% for full siblings of an affected homozygote, given two heterozygous-carrier parents) is the only currently applicable prevention-adjacent intervention, plus carrier testing and reproductive options (e.g., preimplantation genetic testing) within already-identified affected families — none of this is explicitly documented as having been offered/performed in the retrieved sources, so it should be framed as a generically applicable Mendelian-recessive-disease counseling principle rather than a reported, disease-specific intervention. No population screening program, vaccine, or public-health intervention applies to this ultra-rare monogenic disorder.

14. Other Species / Natural Disease

Naturally occurring RECON-syndrome-equivalent disease in animals: None reported. No OMIA entry or veterinary case series was identified for a naturally occurring RECQL-associated progeroid phenotype in any non-human species.

Orthologous gene: Mouse Recql (NCBI Gene; human-mouse orthology is well established for RecQ helicase family genes), rat Recql, and orthologs are present across vertebrates as expected for a conserved genome-maintenance gene family.

Comparative biology: The RecQ helicase family (BLM, WRN, RECQL, RECQL4, RECQL5) and its disease associations are evolutionarily conserved in function (E. coli RecQ, yeast Sgs1, etc., are the ancestral homologs referenced in the general RecQ-family literature retrieved above), but human disease phenotypes for the RECQL1/RECON-specific homozygous hypomorphic-missense mechanism have not been shown to have a natural veterinary or wildlife counterpart.

15. Model Organisms

Mouse: Recql-knockout mice are reported as phenotypically grossly normal at the whole-organism level — a notable and important contrast to the human progeroid phenotype:

"Mice devoid of this enzyme are phenotypically normal" (as extracted from PMC8884905), despite showing clear cellular abnormalities.

At the cellular level, however, primary embryonic fibroblasts from Recql-knockdown/knockout mice do show relevant genome-instability phenotypes: aneuploidy, spontaneous chromosomal breakage, translocations, elevated spontaneous sister chromatid exchange, increased ionizing-radiation sensitivity, and elevated double-strand-break burden — i.e., the mouse null recapitulates the cellular genome-instability signature reasonably well but fails to recapitulate the organismal progeroid phenotype seen in humans with the homozygous hypomorphic p.A459S variant.

Human-model mismatch — important curation flag: This is a textbook case for a HUMAN_MODEL_MISMATCH framing (per this repository's schema for model-to-mechanism links) rather than ordinary model recapitulation. Two non-mutually-exclusive explanations are offered in the literature: (1) the human disease variant is a hypomorphic partial-function allele, not a null, and may produce a qualitatively different (potentially more severe, or differently distributed) cellular phenotype than complete genetic ablation; and (2) as the authors state, RECQL1 may have functions in human development that are not shared with, or not essential in, mouse — i.e., a species-specific requirement, with the review explicitly noting that despite cellular redundancy expectations, "RECQL1 is not redundant with WRN, BLM, or RECQL4 and has unique functions during human development" based on the human clinical phenotype. Any model-mechanism link from a mouse Recql-null study to the RECON pathograph should therefore be recorded with relationship: PARTIALLY_RECAPITULATES or FAILS_TO_RECAPITULATE at the organismal-phenotype level (short stature, progeroid facial features are not observed in the null mouse) while potentially RECAPITULATES at the cellular genome-instability level, with model_scale distinguishing the two, and divergences typed as likely SPECIES_MISMATCH and/or a hypomorphic-vs-null PROXY_QUANTITY-type divergence — this should be worked out carefully against the primary mouse-knockout paper (not directly retrieved in full text here) before being written into a KB entry.

Cellular/in vitro models used in the primary human study (not "model organisms" in the strict sense, but the disease's actual experimental evidence base): - Patient-derived lymphoblastoid cell lines (LCLs) — the principal cellular disease model, used for chromosome-breakage, SCE, replication-fork-restart, and DDR-signaling assays. - Patient-derived dermal fibroblasts — used for 53BP1 foci/DNA-damage-response assays. - Recombinant purified WT and mutant RECQL1 protein — used for all biochemical (ATPase, helicase, fork-restoration, strand-annealing, DNA-binding, oligomerization) assays. - Complementation experiments (re-expressing WT RECQL1 in patient LCLs/fibroblasts) — used to confirm that observed cellular defects are attributable specifically to RECQL1 dysfunction and are correctable, supporting causality beyond genetic association alone.

No zebrafish, Drosophila, C. elegans, yeast, iPSC, or organoid model of RECON syndrome specifically was identified in this search — the yeast/invertebrate RecQ-helicase literature retrieved (Sgs1 in yeast, Rqh1 in fission yeast, Drosophila BLM ortholog studies) pertains to general RecQ-family biology, not to a RECQL1/RECON-specific disease model.

Summary of Key Evidence Gaps for Curation

1. No ORPHA code located — confirm this is a genuine coverage gap rather than a search miss before curating mappings.mondo_mappings/cross-references.
2. GenCC/ClinGen "Disputed Evidence" classification exists — represent gene-disease validity honestly as limited, not definitive.
3. No long-term natural history data (oldest patient documented to age ~15) — do not extrapolate adult prognosis/mortality from other, mechanistically-related but genetically-distinct progeroid syndromes (Werner, Bloom).
4. Keep the biallelic RECON-syndrome entry structurally separate from the monoallelic RECQL breast-cancer-susceptibility literature — different zygosity, variant class, and phenotype (see Section 2).
5. Mouse knockout model is a phenotype mismatch at the organismal level — flag explicitly rather than treating as a validating animal model of the human disease (Section 15).
6. Microcephaly appears in MedGen's phenotype list but was not emphasized as present in the WebFetch-extracted clinical description of the primary paper — verify directly against PMID:35025765 full text before including/excluding in a curated phenotype list.
7. Formal onset staging (congenital vs. ~18-month postnatal onset) should be re-verified against exact wording in the primary source before populating an onset field.

Sources

• RECON syndrome is a genome instability disorder caused by mutations in the DNA helicase RECQL1 — PMC8884905 (primary report; PMID:35025765; J Clin Invest 2022)
• RECON syndrome is a genome instability disorder caused by mutations in the DNA helicase RECQL1 — PubMed
• JCI full article
• Entry - #620370 - RECON PROGEROID SYNDROME — OMIM
• Entry - *600537 - RECQ PROTEIN-LIKE; RECQL — OMIM
• RECON progeroid syndrome (Concept ID: C5830504) — MedGen/NCBI
• Recon Progeroid Syndrome — MalaCards
• RECON progeroid syndrome — UniProt Diseases (DI-06683)
• Discovery of a new hereditary RECQ helicase disorder RECON syndrome positions the replication stress response and genome homeostasis as centrally important processes in aging and age-related disease — PMC10018417
• RECQL gene with submissions organized by classifications — GenCC
• RECQL Gene — GeneCards
• Germline RECQL mutations are associated with breast cancer susceptibility — PubMed (PMID:25915596)
• RECQ1 Promotes Stress Resistance and DNA Replication Progression Through PARP1 Signaling Pathway in Glioblastoma — PMC8350743
• Human RecQ Helicases in DNA Double-Strand Break Repair — PMC7947261
• RECQL4 — Wikipedia (comparator disorder background)
• Frontiers Pediatrics case report (10.3389/fped.2026.1695356) — checked and confirmed not relevant to RECON syndrome (it concerns RECQL4/Rothmund-Thomson type 2, a distinct gene and disease; included here only to document that this search lead was checked and excluded).

Reference Validation

Checked with linkml-reference-validator 0.2.1.

References that may not be about this subject

These identifiers resolve, so they are not fabrications, but the records they resolve to share almost none of this report's vocabulary. That is a clue and not a verdict - a paper can be relevant in ways its title and abstract do not spell out - so read them before deciding:

• PMID:36907310 (1 mention) - Mitochondrial targeted fluorescent nitrite peroxide probe for dynamic monitoring of cellular lung injury.
• shared terms: cellular

Weighed against this report's own most characteristic terms: phenotype, patient, disease, syndrome, primary, progeroid, disorder, mechanism, recon, explicitly, recql, gene, recql1, family, helicase, curation, identified, cellular, dna, directly.

All extracted references resolved successfully. Resolving is not the same as being relevant, though - see the references listed above as possibly off topic.

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:

• MONDO:0957266 (2 mentions) - the report calls it "MONDO"; MONDO calls it RECON progeroid syndrome

Obsolete terms

These terms are real but deprecated. Citing one is not a fabrication; it does mean the report is naming something the ontology has retired:

• HP:0009062 (obsolete Infantile axial hypotonia) (1 mention) - replaced by HP:0008936
• GO:0000784 (GO_0000784) (1 mention) - replaced by GO:0000781