Autosomal Recessive Deafness‑100 (DFNB100): Comprehensive Research Report

1. Disease Information

Overview. Autosomal recessive deafness‑100 (DFNB100) is an ultra-rare, monogenic form of prelingual, nonsyndromic sensorineural hearing loss caused by biallelic (homozygous) mutation of PPIP5K2 (diphosphoinositol‑pentakisphosphate kinase 2) on chromosome 5q21.1. It was first — and to date only — described in two large, apparently unrelated consanguineous Pakistani families (PKDF041 and PKDF751) from Punjab province, comprising 12 affected individuals, in a 2018 PLOS Genetics report by Yousaf et al. (PMID:29590114; PLOS Genetics 14(3):e1007297). No independent replication family has been published in the subsequent literature search window (through 2024), consistent with DFNB100 being one of the rarest of the >100 numbered DFNB loci.

Key identifiers: - OMIM (phenotype): #618422 — DEAFNESS, AUTOSOMAL RECESSIVE 100; DFNB100 - OMIM (gene): *611648 — DIPHOSPHOINOSITOL PENTAKISPHOSPHATE KINASE 2; PPIP5K2 - MONDO: MONDO:0032740 - MedGen: C5193087 / UID 1682525 - Gene symbol / HGNC: PPIP5K2 (HGNC:29035); NCBI Gene ID 23262; also historically known as VIP2 / IHPK2 - Locus: 5q21.1 (within the broader linkage interval 5q12.2–q23.3 in family PKDF751) - Orphanet umbrella term: ORPHA:90636 (Autosomal recessive nonsyndromic sensorineural deafness type DFNB — the generic Orphanet grouping under which locus-specific DFNB forms including DFNB100 fall; there is no DFNB100-dedicated ORPHA code identified in this search) - Inheritance: Autosomal recessive (HP mode-of-inheritance term HP:0000007)

Synonyms: "Deafness, autosomal recessive 100"; "DFNB100"; "Hearing loss, autosomal recessive 100." The gene itself is also referenced in older literature as IHPK2/VIP2.

Evidence source note: All clinical data derive from a single published aggregated case series (two extended pedigrees, not individual EHR records); the genetic/functional data derive from human genetics plus a purpose-built mouse model, i.e., a mixed HUMAN_CLINICAL + MODEL_ORGANISM + IN_VITRO/COMPUTATIONAL evidence base from one primary study.

2. Etiology

Disease Causal Factor — genetic, monogenic, single reported variant. DFNB100 is caused by a homozygous missense variant in PPIP5K2:

• Variant: c.2510G>A (exon 21), predicting p.Arg837His (R837H), in the phosphatase domain of PPIP5K2.
• The paper states: "The c.2510G>A transition variant is predicted to substitute a highly invariant arginine residue with histidine (p.Arg837His)" (PMID:29590114).
• The variant segregated with hearing loss in both unrelated Pakistani families under a recessive model, was absent from 180 ethnically matched Pakistani control chromosomes, was absent from the 1000 Genomes Project, and was present at low frequency (0.000146) in ExAC — consistent with a rare, pathogenic recessive allele rather than a common polymorphism (PMID:29590114).
• ClinVar accessions reported for this variant include RCV000770902 and RCV003238202 (per aggregator search; not independently verified against a live ClinVar page in this session — treat as a lead requiring confirmation via just fetch-reference against ClinVar directly before KB citation).
• Arg837 is described as evolutionarily invariant across vertebrate orthologs, and in silico prediction tools supported deleteriousness (per the paper's variant-pathogenicity evidence chain, alongside segregation, absence from controls, biochemical functional data, and mouse recapitulation).

Risk factors: - Genetic: Homozygosity for the PPIP5K2 R837H allele; parental consanguinity, which is the mechanism by which both reported families became homozygous for an otherwise rare allele (both families are described as consanguineous). - Founder/population context: Both index families are Pakistani (Punjab); whether R837H represents a regional founder allele versus recurrent independent mutation is not established by the available literature — this should be flagged as an open question rather than asserted. - No other causal or modifier genes for DFNB100 specifically have been reported. - Environmental risk factors: None identified as relevant to DFNB100 causation; nonsyndromic nature and cosegregation strongly indicate the genetic lesion is fully sufficient in the reported pedigrees (i.e., this is not a gene–environment or multifactorial deafness form like some other DFNB loci or aminoglycoside-potentiated forms, e.g., MT-RNR1).

Protective factors: None reported specific to DFNB100 in the literature identified.

Gene–environment interactions: None described for DFNB100. (This contrasts with mitochondrial DFNB forms driven by aminoglycoside exposure — not applicable here.)

3. Phenotypes

Primary phenotype — profound congenital sensorineural hearing loss.

• Type: Clinical sign / audiometric finding (sensorineural hearing loss), nonsyndromic (isolated).
• Onset: Prelingual — "no hearing was reported since birth in all affected individuals" — i.e., congenital onset (PMID:29590114).
• Severity: Severe-to-profound; audiometric testing showed "profound HL in both ears" across the tested frequency range.
• Laterality: Bilateral, symmetric.
• Progression: In the human pedigrees as reported, the phenotype is described at presentation as profound/prelingual without a documented longitudinal progression curve in probands (contrast with the mouse model, which shows late-onset progressive loss — see Mechanism/Model Organisms below). This is an important cross-species discrepancy the authors themselves flag.
• Frequency among affected individuals: 12/12 affected individuals across the two families presented with this core phenotype (fully penetrant in the reported pedigrees).

Otologic / audiologic functional testing: - Otoacoustic emissions: Three affected individuals failed transient evoked otoacoustic emission (TEOAE) testing, "indicative of defective outer hair cell function" — directly implicating cochlear outer hair cells (OHCs) as the primary lesion site, consistent with the mouse histopathology (below). - Vestibular testing: Romberg and tandem gait testing were normal — "did not reveal any overt vestibular dysfunction" — despite PPIP5K2 also being expressed in vestibular sensory hair cells, indicating a cochlea-selective functional vulnerability in humans. - Ophthalmologic screening: Normal funduscopy and electroretinography, excluding a Usher-syndrome-like retinal component and supporting the "nonsyndromic" classification.

Quality of life impact: Not formally quantified in the primary literature (no EQ-5D/SF-36 or disease-specific QOL instrument reported for this cohort); general inference from profound prelingual deafness (impact on spoken-language acquisition, need for early intervention) is standard for this phenotype class but not DFNB100-specific data.

Suggested HPO terms: | Phenotype | Candidate HPO term | |---|---| | Profound bilateral sensorineural hearing loss | HP:0008625 (Sensorineural hearing loss, severe) / consider HP:0001363-adjacent profound-tier term; verify exact profound-tier CURIE via dismech-terms before binding | | Congenital/prelingual onset | HP:0000998 (Prelingual sensorineural hearing loss impairment) — verify exact label match | | Absent otoacoustic emissions / OHC dysfunction | Consider free-text qualifier if no precise HP term exists; note as a functional-test finding rather than a distinct phenotype node | | Normal vestibular function (negative finding) | Document as an excluded/negative finding rather than a phenotype node | | Normal fundus/retina (negative finding) | Document as an excluded/negative finding — supports nonsyndromic classification |

(Per dismech convention, these are leads for the dismech-terms skill to verify exact canonical labels/CURIEs before binding — not pre-verified bindings.)

4. Genetic/Molecular Information

Causal gene: PPIP5K2 (HGNC:29035; NCBI Gene 23262; OMIM *611648; UniProt O43314).

Pathogenic variant details: - Genomic/cDNA change: c.2510G>A, exon 21 - Protein change: p.Arg837His (p.R837H) - Variant class: Missense - Zygosity in affected individuals: Homozygous (biallelic, consistent with consanguinity) - Population frequency: Absent in 180 Pakistani controls and in 1000 Genomes; 0.000146 in ExAC (i.e., ultra-rare, sub-population-level frequency consistent with a rare recessive pathogenic allele) - Functional impact category: The paper's biochemical assays support a mixed/altered-function mechanism rather than simple loss-of-function — see Mechanism section — recorded findings: ~21% decrease in phosphatase activity and increased kinase activity, together yielding ~60% higher IP8 levels relative to wild-type protein in in vitro assays. This pattern (partial loss of one catalytic activity + gain/elevation of the paired activity, net pathway output shifted) should be curated carefully against the functional_impact_category enum — it does not map cleanly to simple LOF or simple GOF and may be best captured descriptively (e.g., partial loss of phosphatase function with consequent kinase/product imbalance) rather than forcing a single enum value; flag for curator judgment. - gnomAD constraint metrics (pLI/LOEUF) for PPIP5K2: not retrievable in this session (gnomAD browser is JavaScript-rendered and did not return data via automated fetch) — this should be looked up directly in the gnomAD browser (gene ENSG00000145725) during curation rather than asserted here.

Modifier genes: None identified specific to DFNB100. Notably, in the mouse model, a compensatory ~3-fold upregulation of the paralog Ppip5k1 transcript was observed in the inner ear of homozygous mutants at P150 (qPCR finding), suggesting Ppip5k1 may act as a partial genetic modifier/buffer in mice — a candidate hypothesis for why the mouse phenotype is milder and later-onset than the human phenotype, but this has not been tested as a human modifier.

Epigenetic information: None reported for DFNB100/PPIP5K2.

Chromosomal abnormalities: Not applicable — this is a point-mutation (missense) disorder, not a copy-number/structural disorder. Linkage mapping in family PKDF751 defined a large homozygous interval at chromosome 5q12.2–q23.3, narrowed by exome sequencing to the single PPIP5K2 variant.

Protein domain architecture: PPIP5K2 is a bifunctional enzyme with (1) an N-terminal kinase domain, (2) a phosphatase (histidine acid phosphatase-like) domain, and (3) an intrinsically disordered C-terminal region mediating protein–protein interactions. Arg837 lies within the phosphatase domain.

5. Environmental Information

No environmental, infectious, or lifestyle contributing factors have been reported for DFNB100. As a fully penetrant monogenic recessive disorder identified in consanguineous pedigrees with segregation-confirmed causation, there is no literature suggesting an environmental co-factor is required for phenotype expression. (This is an appropriate case for an environmental-evidence waiver in environmental[] curation, if that section is populated at all, per the check-environmental-evidence policy — searched, and nothing quotable was found beyond "no other cause identified.")

6. Mechanism / Pathophysiology

Causal chain (numbered, from initiating lesion to clinical manifestation):

1. Biallelic PPIP5K2 c.2510G>A (p.Arg837His) leads to a phosphatase-domain missense substitution at an evolutionarily invariant residue.
2. This substitution results in altered catalytic balance of the bifunctional PPIP5K2 enzyme: reduced phosphatase activity (~21% decrease) combined with increased kinase activity, demonstrated biochemically in vitro (PMID:29590114).
3. The altered kinase/phosphatase balance leads to a shift in the interconversion of the paired inositol pyrophosphate signaling messengers 5-IP7 ⇌ IP8, with the mutant protein producing ~60% higher IP8 levels than wild-type protein in matched in vitro assays. (Inferred mechanistic link — demonstrated biochemically for isolated enzyme activity; the causal step from altered IP7/IP8 ratio to downstream cellular consequence is inferred by analogy to known IP7/IP8 signaling roles rather than directly measured in patient/model cochlear tissue.)
4. Perturbed inositol pyrophosphate signaling is expected to disrupt PP-IP-dependent cellular processes that the pathway is broadly known to govern — endocytosis, vesicle trafficking, apoptosis, and bioenergetic/insulin-secretion homeostasis — within cells that depend on this signaling for normal function. (This step is inferred from general PP-IP biology rather than cochlea-specific mechanistic dissection; the paper does not isolate which specific downstream process is causal in hair cells.)
5. In the cochlea specifically, where PPIP5K2 is expressed in sensory hair cells, supporting cells, and spiral ganglion neurons (confirmed by immunostaining, including all three layers of the stria vascularis — marginal, intermediate, and basal cells), this disruption selectively compromises outer hair cell (OHC) maintenance/survival rather than inner hair cells, spiral ganglion neurons, or the stria vascularis.
6. OHC compromise manifests functionally as absent/failed transient evoked otoacoustic emissions in affected humans (direct evidence of OHC dysfunction) and, in the mouse model, as histologically confirmed degeneration of OHCs in the cochlear basal turn (statistically significant reduction, p<0.01) with inner hair cells spared and no spiral ganglion or stria vascularis degeneration.
7. OHC loss/dysfunction leads to elevated auditory brainstem response (ABR) thresholds, manifesting first and most severely at high frequencies (24 and 32 kHz in mice, p<0.001), consistent with basal-turn (high-frequency-coding) OHC vulnerability, and culminates in the clinical phenotype of severe-to-profound bilateral sensorineural hearing loss.

Branch point / species discrepancy (explicitly flagged by the study authors): In humans, the phenotype presents as prelingual/congenital profound loss; in the Ppip5k2 gene-trap mouse, the loss is late-onset and progressive (thresholds normal through ~P60, becoming significantly elevated by ~P90–P150) and milder in degree than the human phenotype. The authors explicitly attribute this to likely "greater functional redundancy" in mice, plausibly via the ~3-fold compensatory upregulation of the paralogous gene Ppip5k1 observed in mutant mouse inner ear — an unresolved cross-species fidelity question (a candidate HUMAN_MODEL_MISMATCH consideration for KB curation, since the model does not fully recapitulate onset timing or severity, though it does recapitulate cell-type specificity and general pathway involvement).

Molecular pathway: Inositol pyrophosphate (PP-IP) signaling — synthesis/interconversion of 5-IP7 and IP8 by the PPIP5K (VIP1/VIP2 family) enzymes, acting together with IP6 kinases (IP6Ks) upstream in the pathway. This is a comparatively unusual pathway for a hearing-loss gene relative to the canonical DFNB mechanisms (cytoskeletal/stereocilia structural proteins, gap-junction connexins, ion-channel/transporter genes); PPIP5K2 represents an intracellular small-molecule-signaling mechanism rather than a structural or classical channel/transporter mechanism.

Cellular processes implicated (general PP-IP biology, not cochlea-proven): endocytosis, vesicle trafficking, apoptosis regulation, exocytosis/secretion (e.g., insulin secretion in other tissues), cytoskeletal dynamics, and bioenergetic homeostasis.

Cell types involved: - Cochlear outer hair cells (primary lesion site) — candidate CL term: CL:0002095 (outer hair cell of Corti) — verify exact CURIE via dismech-terms. - Cochlear supporting cells and spiral ganglion neurons (express PPIP5K2, not shown to degenerate in the mouse model). - Vestibular sensory hair cells (express PPIP5K2; functionally spared in humans per Romberg/tandem-gait testing). - Stria vascularis (marginal, intermediate, basal cells; PPIP5K2-immunoreactive but not degenerated).

Suggested GO terms (leads, to be verified): - GO:0043647 (inositol phosphate metabolic process) or a more specific PP-IP interconversion term if one exists - GO:0007605 (sensory perception of sound) — phenotype-level - Hair-cell maintenance/homeostasis GO terms if available

Molecular profiling data: Real-time qPCR (targeted, not genome-wide RNA-seq) showing ~3-fold Ppip5k1 upregulation in mutant mouse inner ear at P150; broader transcriptome analysis (cited but not detailed in the extracted text) supporting Ppip5k2 as the dominant Ppip5k paralog expressed in cochlear/vestibular hair cells. No proteomic, metabolomic, lipidomic, single-cell, or spatial transcriptomic datasets specific to DFNB100/PPIP5K2 cochlear pathology were identified in this search.

7. Anatomical Structures Affected

• Organ level: Inner ear (cochlea primarily; vestibular labyrinth anatomically involved by gene expression but not functionally affected). No other organ systems are involved — consistent with the "nonsyndromic" designation (normal retina/fundus, normal gait/balance).
• Tissue/cell level: Organ of Corti — specifically outer hair cells (primary degeneration target); supporting cells, spiral ganglion neurons, and stria vascularis (all express the gene but show no demonstrated degeneration).
• Subcellular level: PPIP5K2 is a cytosolic/cytoplasmic enzyme, also associated with intracellular membrane-bound organelles consistent with its roles in vesicle trafficking; relevant GO Cellular Component terms would include cytosol/cytoplasm annotations (verify exact CURIEs).
• Localization: Bilateral, symmetric cochlear (and by expression pattern, vestibular) involvement; within the cochlea, the mouse histopathology localizes degeneration specifically to the basal turn (high-frequency-coding region), correlating with the high-frequency-predominant ABR threshold elevation.

Candidate UBERON terms: cochlea, organ of Corti, outer hair cell region/basal turn, spiral ganglion, stria vascularis, vestibular apparatus — to be resolved to exact CURIEs during curation.

8. Temporal Development

• Onset (human): Congenital/prelingual — "no hearing... since birth" in all affected individuals; this places DFNB100 in the congenital-onset, nonprogressive-by-report category in humans, though formal longitudinal audiometric follow-up data documenting stability versus progression over time were not described in the primary report.
• Onset (mouse model): Late-onset relative to the animal's lifespan — thresholds are essentially unremarkable through ~P60, become statistically significantly elevated at 32 kHz by ~P90, and extend to 24 kHz involvement by P120–P150, with progressive worsening across this window.
• Progression: In mice, clearly progressive (worsening thresholds and expanding frequency range of involvement with age). In humans, the published cohort was characterized cross-sectionally as profound/prelingual without a documented progression timeline; whether human hearing loss is present at birth in full severity or represents rapid early progression to profound levels is not resolved by the available data.
• Critical periods: As with all forms of prelingual profound deafness, early identification (e.g., via newborn hearing screening) and early intervention are clinically critical for language-outcome reasons, though this is a generic inference for the phenotype class rather than DFNB100-specific outcome data.

9. Inheritance and Population

• Inheritance pattern: Autosomal recessive, confirmed by segregation analysis in two independent consanguineous pedigrees under a strict recessive model (heterozygous carriers unaffected).
• Penetrance: Complete/full in the 12 reported affected homozygotes (no reported subclinical or unaffected homozygotes).
• Expressivity: Reported as consistent (profound, bilateral) across affected individuals in both families, based on the available description; formal variable-expressivity analysis was not performed.
• Consanguinity: Central to disease ascertainment — both families are explicitly consanguineous, which is the mechanism enabling homozygosity for this rare allele; this is characteristic of many DFNB loci discovered in South Asian and Middle Eastern consanguineous cohorts.
• Founder effect: Not established; both families are Pakistani (Punjab), raising the possibility of a shared regional founder allele, but haplotype-sharing analysis to formally test this was not reported in the material reviewed.
• Carrier frequency: Not directly reported; the ExAC frequency of 0.000146 for the pathogenic allele is the only population-frequency data point available, and translating this into a carrier-frequency estimate for any specific population would require formal population-genetics analysis not present in the source.
• Epidemiology: DFNB100 is exceptionally rare — to date reported in only 2 families (12 affected individuals) worldwide in the published literature identified by this search, with no independent replication cohorts found in a 2020–2024 literature sweep. No formal prevalence or incidence estimate exists; it should be treated as an ultra-rare/"cases in literature" measure type rather than assigned a population-prevalence band.
• Geographic distribution: Punjab province, Pakistan (both reported families); no data on occurrence elsewhere.
• Sex ratio / age distribution: Not specifically reported as differing from 1:1 or from other recessive nonsyndromic deafness loci; no sex-specific susceptibility is suggested by an autosomal recessive mechanism.

Broader context (not DFNB100-specific but relevant framing): Autosomal recessive nonsyndromic hearing loss (ARNSHL) as a class is a major cause of prelingual deafness worldwide, and GJB2 (DFNB1A) is by far the most common cause; DFNB100 represents one of the more obscure entries among >100 recognized DFNB loci and, per available literature, remains a private/founder-restricted cause rather than a globally recurrent one.

10. Diagnostics

• Audiometric/functional testing: Pure-tone audiometry (documenting bilateral severe-to-profound sensorineural loss), transient evoked otoacoustic emissions (TEOAE — abnormal/absent in DFNB100, reflecting OHC dysfunction), and vestibular functional testing (Romberg, tandem gait — normal in reported cases) were the diagnostic modalities used in the original description. No ABR, DPOAE, or imaging (temporal bone CT/MRI) findings for the human cohort were reported in the material reviewed.
• Ophthalmologic screening: Funduscopy and electroretinography were used to exclude a syndromic (Usher-like) retinal component — both normal, supporting nonsyndromic classification. This is a standard part of the differential diagnosis workup for profound congenital SNHL (ruling out Usher syndrome type 1, which also presents with profound congenital deafness plus vestibular areflexia and later retinitis pigmentosa — note DFNB100 is distinguished from Usher type 1 by its normal vestibular function).
• Genetic testing: The causal variant was identified via genome-wide linkage/homozygosity mapping (STR markers) followed by exome capture and massively parallel sequencing (whole-exome sequencing) in the index families — this remains the appropriate diagnostic strategy for a suspected DFNB-locus disorder in a consanguineous pedigree without a known familial mutation. Given how recently and narrowly PPIP5K2 has been implicated, it is unlikely to be included on all commercial hearing-loss gene panels; comprehensive panel or exome-based testing would be more reliable than a targeted single-gene test for a first diagnostic workup, with PPIP5K2 as one of many genes on a broad ARNSHL panel/exome reanalysis pipeline once a specific hypothesis is raised.
• Differential diagnosis: Other nonsyndromic DFNB loci (especially DFNB1A/GJB2, the most common cause), and syndromic profound congenital SNHL — particularly Usher syndrome type 1 (distinguished by vestibular areflexia, present in Usher but absent in DFNB100) and Pendred syndrome (distinguished by goiter/enlarged vestibular aqueduct).
• Newborn/population screening: No DFNB100-specific screening protocol exists; standard universal newborn hearing screening (e.g., via OAE/ABR) would detect the phenotype non-specifically as with any congenital profound SNHL, with genetic confirmation required afterward.

11. Outcome/Prognosis

• Severity/stability: The human phenotype is profound and, as reported, present from birth; no data on natural history, hearing aid/cochlear implant outcomes, or long-term morbidity specific to DFNB100 patients were available in this search.
• Life expectancy/mortality: Not applicable — nonsyndromic hearing loss of this type does not carry an independent mortality risk; no systemic organ involvement was identified.
• Functional/QOL outcomes: Not formally studied for this specific cohort; general expectations for profound prelingual SNHL apply (need for early amplification/cochlear implantation and language intervention to optimize communication outcomes), but this is inferred from the general disease class, not DFNB100-specific data.
• Prognostic biomarkers: None identified.

12. Treatment

No DFNB100-specific treatment trials, gene therapy programs, or pharmacological interventions have been reported. Management would follow standard-of-care for profound congenital sensorineural hearing loss:

• Amplification/hearing aids — for residual hearing, though profound loss often limits benefit.
• Cochlear implantation — the standard intervention for profound bilateral congenital SNHL when amplification is insufficient (NCIT term candidates: cochlear implantation procedure — bind the surgical action term per the CLAUDE.md guidance on device-vs-action terms, e.g., NCIT:C15329 Surgical Procedure with a qualifiers predicate-value pair for the cochlear implant device, NCIT:C157820).
• Genetic counseling — appropriate given confirmed autosomal recessive inheritance and consanguinity in the reported families (candidate term NCIT:C15240, Genetic Counseling).
• Speech-language/auditory-verbal therapy — standard supportive intervention for pediatric profound SNHL (candidate NCIT:C159273, Speech Therapy, or NCIT:C15747, Supportive Care).

No pharmacotherapy, gene therapy, or RNA-based therapeutic specific to PPIP5K2/DFNB100 was found in the ClinicalTrials.gov or literature search conducted. There is no mechanistic rationale currently published for a targeted PP-IP-pathway-modulating drug in this disorder.

13. Prevention

• Primary prevention: Genetic counseling for consanguineous couples/families with a known PPIP5K2 pathogenic allele; carrier testing where familial mutation status is known.
• Secondary prevention/early detection: Universal newborn hearing screening (non-specific to DFNB100, standard practice) enabling early diagnosis and intervention.
• Prenatal/preimplantation options: Standard reproductive genetic counseling options (prenatal diagnosis, preimplantation genetic testing) would be applicable once a familial pathogenic variant is confirmed, as for any characterized autosomal recessive disorder, though no DFNB100-specific literature on uptake or outcomes was found.
• Public health relevance: Given the extreme rarity (2 families reported to date), DFNB100 is not a target of population-level carrier screening programs; it would only become clinically actionable within an identified family or population subgroup where the allele is known to segregate.

No immunization, prophylaxis, or environmental-intervention strategies apply, as this is a purely genetic, non-infectious, non-environmentally-modulated disorder.

14. Other Species / Natural Disease

No naturally occurring PPIP5K2-associated deafness has been reported in companion animals, livestock, or wildlife (no OMIA entry identified in this search). All non-human data derive from a purpose-engineered laboratory mouse model (see Section 15) rather than natural disease in another species. No zoonotic or cross-species transmission considerations apply, as this is a non-infectious monogenic disorder.

Orthology: The mouse ortholog is Ppip5k2 (NCBI Gene, MGI); the paralog Ppip5k1 is present in both human and mouse genomes and was noted as compensatorily upregulated in the mouse model's inner ear, a comparative-biology finding of potential relevance to understanding incomplete model penetrance/severity.

15. Model Organisms

Primary and (currently) only reported model: mouse (Mus musculus), NCBITaxon:10090.

• Model type: Genetically engineered, targeted gene-trap mouse line.
• Strain/allele: B6N(Cg)-Ppip5k2^tm1a(EUCOMM)Wtsi^/J, generated from a EUCOMM/KOMP gene-trap embryonic stem cell resource. The gene-trap cassette is inserted downstream of exon 13, producing a truncated protein that retains an intact kinase domain but a phosphatase domain truncated to only 84 residues — insufficient for phosphatase catalytic activity. This models a phosphatase-domain-selective loss rather than a precise knock-in of the human R837H missense allele (an important fidelity caveat: the mouse models phosphatase-domain disruption broadly, not the exact human variant/mechanism of altered kinase/phosphatase balance).
• Phenotype recapitulation:
• Recapitulates: Cell-type-selective cochlear outer hair cell degeneration (basal turn, statistically significant, p<0.01), elevated ABR thresholds with high-frequency predominance (24–32 kHz, p<0.001), sparing of inner hair cells, spiral ganglion, and stria vascularis — broadly consistent with the human OTOAE-based inference of selective OHC dysfunction.
• Does not fully recapitulate: Onset timing (mouse: late-onset/progressive from ~P90–P150; human: congenital/prelingual) and overall severity (mouse: milder than human). Authors explicitly attribute this divergence to likely greater functional redundancy in mice (candidate ~3-fold compensatory Ppip5k1 upregulation).
• This divergence is a strong candidate for HUMAN_MODEL_MISMATCH discussion-kind curation in a dismech entry: the model provides good cell-type/mechanistic-target validation (fidelity: MODERATE for OHC degeneration and pathway involvement) but poor validity for modeling onset timing/severity (fidelity: LOW for that specific claim), which should be recorded as separate modeled_mechanisms links with distinct fidelity/limitations per node rather than a single blanket fidelity rating.
• Applications: The model was used to (1) confirm PPIP5K2 expression pattern in cochlear/vestibular sensory epithelium and neurons via immunostaining, (2) demonstrate that phosphatase-domain loss is sufficient to cause OHC-selective degeneration and hearing loss in vivo, and (3) generate a hypothesis (Ppip5k1 compensation) for the human–mouse severity/onset discrepancy.
• Resources: Strain originates from the EUCOMM/KOMP international knockout mouse consortium resources (accessible via IMSR/MGI for strain sourcing); specific MGI allele accession was not independently confirmed in this session and should be verified directly against MGI before citing a specific MGI ID.

No other model organism data (zebrafish, Drosophila, C. elegans, yeast, cell lines/organoids, iPSC-derived models) were identified for PPIP5K2-related hearing loss in this search; the mouse gene-trap model represents the sole reported in vivo model system for this gene–phenotype relationship.

Summary of Evidence Source Classification for Curation

Single-source caveat: Nearly the entirety of the DFNB100/PPIP5K2 evidence base traces to one primary publication (Yousaf et al. 2018, PMID:29590114). No independent replication family, no independent functional-validation study, and no gnomAD-verified constraint data were retrievable in this session. Any dismech curation should flag this as a thin, single-study evidence base rather than a broadly replicated gene-disease relationship, and should independently verify the ClinVar accessions and gnomAD constraint metrics before quoting them as established facts, since those specific figures were obtained via search-engine synthesis rather than direct primary-source fetch in this session.

Sources

• OMIM #618422 — DEAFNESS, AUTOSOMAL RECESSIVE 100; DFNB100
• OMIM *611648 — PPIP5K2
• Yousaf R, et al. Mutations in Diphosphoinositol-Pentakisphosphate Kinase PPIP5K2 are associated with hearing loss in human and mouse. PLOS Genetics. 2018;14(3):e1007297. — PMID:29590114 — PMC5891075
• MedGen — Hearing loss, autosomal recessive 100 (C5193087 / UID 1682525)
• PPIP5K2 Gene — GeneCards
• PPIP5K2 — NCBI Gene
• Gene: PPIP5K2 (Monogenic hearing loss) — Genomics England PanelApp
• OMIM Clinical Synopsis — #618422

Reference Validation

Checked with linkml-reference-validator 0.2.1.

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:0000998 (1 mention) - the report calls it "Prelingual sensorineural hearing loss impairment"; HP calls it Hypertrichosis

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:

• CL:0002095 (1 mention) - the report calls it "outer hair cell of Corti"; CL calls it hilus cell of ovary, and lists "hilar cell of ovary" among its other names

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.