PHARC syndrome is an autosomal recessive neurodegenerative disorder caused by biallelic ABHD12 loss of function. The syndrome combines polyneuropathy, hearing loss, ataxia, retinitis pigmentosa, and cataract, with frequent pyramidal signs and cerebellar atrophy, reflecting progressive involvement of peripheral nerves, retina, auditory pathways, corticospinal tracts, and cerebellar systems. Mechanistically, loss of ABHD12 lysophosphatidylserine hydrolase activity causes accumulation of proinflammatory very-long-chain lysophosphatidylserine lipids that activate microglial Toll-like receptor 2 signaling and drive age-dependent neuroinflammation.
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Conditions with similar clinical presentations that must be differentiated from PHARC syndrome:
name: PHARC syndrome
creation_date: '2026-04-13T04:00:00Z'
description: PHARC syndrome is an autosomal recessive neurodegenerative disorder caused by biallelic ABHD12 loss of function. The syndrome combines polyneuropathy, hearing loss, ataxia, retinitis pigmentosa, and cataract, with frequent pyramidal signs and cerebellar atrophy, reflecting progressive involvement of peripheral nerves, retina, auditory pathways, corticospinal tracts, and cerebellar systems. Mechanistically, loss of ABHD12 lysophosphatidylserine hydrolase activity causes accumulation of proinflammatory very-long-chain lysophosphatidylserine lipids that activate microglial Toll-like receptor 2 signaling and drive age-dependent neuroinflammation.
category: Mendelian
parents: [hereditary disease, neurodegenerative disease]
synonyms:
- polyneuropathy, hearing loss, ataxia, retinitis pigmentosa, and cataract
disease_term:
preferred_term: PHARC syndrome
term:
id: MONDO:0012984
label: PHARC syndrome
classifications:
harrisons_chapter:
- classification_value: NEUROLOGIC
evidence:
- reference: PMID:40064796
reference_title: 'Characterizing and expanding the neurological clinical spectrum of PHARC syndrome: a systematic review.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: 'PHARC syndrome is an autosomal recessive neurodegenerative disease caused by mutations in the ABHD12 gene and is characterized by five main clinical features: polyneuropathy, hearing loss, ataxia, retinitis pigmentosa, and cataracts.'
explanation: Establishes PHARC syndrome as an autosomal recessive neurodegenerative and neuro-otologic/ophthalmic disorder caused by ABHD12 mutations.
- classification_value: GENETICS_ENVIRONMENT_DISEASE
inheritance:
- name: Autosomal Recessive
inheritance_term:
preferred_term: Autosomal recessive inheritance
term:
id: HP:0000007
label: Autosomal recessive inheritance
description: PHARC syndrome is inherited in an autosomal recessive manner due to biallelic loss-of-function variants in ABHD12.
evidence:
- reference: PMID:40064796
reference_title: 'Characterizing and expanding the neurological clinical spectrum of PHARC syndrome: a systematic review.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: 'PHARC syndrome is an autosomal recessive neurodegenerative disease caused by mutations in the ABHD12 gene and is characterized by five main clinical features: polyneuropathy, hearing loss, ataxia, retinitis pigmentosa, and cataracts.'
explanation: Directly confirms autosomal recessive inheritance of PHARC syndrome.
prevalence:
- population: Global published cases
measure_type: CASES_IN_LITERATURE
prevalence_class: ULTRA_RARE
notes: Ultra-rare disorder; a 2025 systematic review of PubMed/MEDLINE and NLM databases identified 57 unique published cases worldwide.
evidence:
- reference: PMID:40064796
reference_title: 'Characterizing and expanding the neurological clinical spectrum of PHARC syndrome: a systematic review.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: A systematic search of studies reporting cases of PHARC syndrome was conducted using PubMed/MEDLINE and NLM databases, identifying 57 unique cases.
explanation: Documents 57 unique reported cases globally, establishing ultra-rare prevalence.
progression:
- phase: Initial symptom presentation
age_range: Childhood to early adulthood
notes: Hearing loss is the most common initial symptom, though cataract (including congenital forms) or polyneuropathy may appear first; only 31.6% of patients exhibit the complete pentad at reporting, contributing to a mean diagnostic delay of 20.5 years from first symptom to diagnosis.
evidence:
- reference: PMID:40064796
reference_title: 'Characterizing and expanding the neurological clinical spectrum of PHARC syndrome: a systematic review.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: The results showed that hearing loss was the most common initial symptom, with a complete syndrome observed in only 31.6% of reported cases. The mean diagnostic delay from the appearance of the first PHARC-related symptom to diagnosis was 20.5 years.
explanation: Documents initial symptom presentation and the 20.5-year mean diagnostic delay in PHARC syndrome.
- phase: Progressive visual and neurologic decline
notes: Progressive retinal and macular degeneration is accompanied by a trend of declining best-corrected visual acuity (mean 1.1 logMAR), while neurological involvement frequently includes pyramidal tract signs that correlate with ataxia and cerebellar atrophy on MRI.
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: The mean best-corrected visual acuity was 1.1 logMAR (SD ± 0.9; range from 0.1 to 2.8; equivalent to 20/250 Snellen) and showed a trend of progressive decline.
explanation: Demonstrates a trend of progressive decline in best-corrected visual acuity in PHARC syndrome.
- reference: PMID:40064796
reference_title: 'Characterizing and expanding the neurological clinical spectrum of PHARC syndrome: a systematic review.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Patients with pyramidal signs were more likely to exhibit an ataxic phenotype (p-value 0.018), a complete syndrome (p-value 0.092), and cerebellar atrophy on MRI (p-value 0.001), compared to those without pyramidal signs.
explanation: Documents the correlation between pyramidal tract signs, ataxia, and cerebellar atrophy on MRI in progressive neurological disease.
pathophysiology:
- name: ABHD12 loss of lipid hydrolase activity
description: Biallelic ABHD12 deficiency impairs degradation of bioactive lysophosphatidylserine and related oxidized phospholipids.
genes:
- preferred_term: ABHD12
term:
id: hgnc:15868
label: ABHD12
molecular_functions:
- preferred_term: lysophospholipase A1 activity
modifier: DECREASED
term:
id: GO:0120558
label: lysophospholipase A1 activity
- preferred_term: carboxylic ester hydrolase activity
modifier: DECREASED
term:
id: GO:0052689
label: carboxylic ester hydrolase activity
biological_processes:
- preferred_term: lipid catabolic process
modifier: ABNORMAL
term:
id: GO:0016042
label: lipid catabolic process
- preferred_term: phospholipid metabolic process
modifier: ABNORMAL
term:
id: GO:0006644
label: phospholipid metabolic process
chemical_entities:
- preferred_term: lysophosphatidylserine
term:
id: CHEBI:68510
label: lysophosphatidylserine
modifier: INCREASED
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: This study investigated the phenotypic spectrum of PHARC (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa and early-onset cataract) syndrome caused by biallelic variants in the ABHD12 gene.
explanation: This directly supports ABHD12 loss as the initiating cause of PHARC syndrome.
- reference: PMID:23297193
reference_title: ABHD12 controls brain lysophosphatidylserine pathways that are deregulated in a murine model of the neurodegenerative disease PHARC.
supports: SUPPORT
evidence_source: IN_VITRO
snippet: We confirm that recombinant ABHD12 protein exhibits robust LPS lipase activity
explanation: Recombinant protein evidence supports ABHD12 lysophosphatidylserine lipase activity.
- reference: PMID:23297193
reference_title: ABHD12 controls brain lysophosphatidylserine pathways that are deregulated in a murine model of the neurodegenerative disease PHARC.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: which is also substantially reduced in ABHD12(-/-) brain tissue.
explanation: Mouse brain tissue evidence supports reduced ABHD12 LPS lipase activity when ABHD12 is lost.
downstream:
- target: Abnormal lysophosphatidylserine signaling
description: Lipid substrate accumulation perturbs immune and neural homeostasis.
causal_link_type: DIRECT
evidence:
- reference: PMID:23297193
reference_title: ABHD12 controls brain lysophosphatidylserine pathways that are deregulated in a murine model of the neurodegenerative disease PHARC.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: where disruption of ABHD12 causes deregulated LPS metabolism and the accumulation of proinflammatory lipids
explanation: The ABHD12 knockout model links ABHD12 disruption directly to deregulated LPS metabolism and proinflammatory lipid accumulation.
- name: Abnormal lysophosphatidylserine signaling
description: Disordered lysophospholipid handling is thought to drive inflammatory and degenerative injury in nervous system tissues.
cell_types:
- preferred_term: microglial cell
term:
id: CL:0000129
label: microglial cell
biological_processes:
- preferred_term: phospholipid metabolic process
modifier: ABNORMAL
term:
id: GO:0006644
label: phospholipid metabolic process
- preferred_term: inflammatory response
modifier: INCREASED
term:
id: GO:0006954
label: inflammatory response
- preferred_term: toll-like receptor 2 signaling pathway
modifier: INCREASED
term:
id: GO:0034134
label: toll-like receptor 2 signaling pathway
chemical_entities:
- preferred_term: lysophosphatidylserine
term:
id: CHEBI:68510
label: lysophosphatidylserine
modifier: INCREASED
evidence:
- reference: PMID:23297193
reference_title: ABHD12 controls brain lysophosphatidylserine pathways that are deregulated in a murine model of the neurodegenerative disease PHARC.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: Taken together, our data provide a molecular model for PHARC, where disruption of ABHD12 causes deregulated LPS metabolism and the accumulation of proinflammatory lipids that promote microglial and neurobehavioral abnormalities.
explanation: This directly supports dysregulated lysophosphatidylserine metabolism as a downstream consequence of ABHD12 loss in a PHARC model.
- reference: PMID:23297193
reference_title: ABHD12 controls brain lysophosphatidylserine pathways that are deregulated in a murine model of the neurodegenerative disease PHARC.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: ABHD12(-/-) mice display massive increases in a rare set of very long chain LPS lipids that have been previously reported as Toll-like receptor 2 activators.
explanation: The ABHD12 mouse model supports accumulation of LPS species with reported TLR2-activating properties, providing a plausible innate-immune bridge to microglial activation.
downstream:
- target: Microglial activation and neuroinflammation
description: Accumulated proinflammatory LPS lipids promote microglial activation and neurobehavioral abnormalities in the ABHD12-deficient brain model.
causal_link_type: DIRECT
evidence:
- reference: PMID:23297193
reference_title: ABHD12 controls brain lysophosphatidylserine pathways that are deregulated in a murine model of the neurodegenerative disease PHARC.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: the accumulation of proinflammatory lipids that promote microglial and neurobehavioral abnormalities.
explanation: The model directly connects accumulated proinflammatory LPS lipids to microglial and neurobehavioral abnormalities.
- target: Retinal degeneration
description: Human ABHD12-related PHARC includes macular and retinal degeneration, although the tissue-specific lipid intermediates linking dysregulated lysophosphatidylserine metabolism to retinal degeneration remain unresolved.
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Fundus examination revealed macular involvement in all patients, ranging from alterations of the retinal pigment epithelium to macular atrophy.
explanation: The human cohort documents macular and retinal degeneration in all patients with biallelic ABHD12 variants; the link from dysregulated lysophosphatidylserine signaling is inferred from the shared genetic cause across unknown intermediates.
- target: Lens opacification and cataractogenesis
description: Human ABHD12-related PHARC includes early-onset and congenital lens opacification, although the exact lipid-mediated ocular intermediates are not resolved by cached abstract evidence.
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Different types of cataract were observed in 13 out of 15 patients (87%), which also included congenital forms of cataract.
explanation: The human cohort documents cataract in 87% of patients with biallelic ABHD12 variants; the link from dysregulated lysophosphatidylserine signaling is inferred from the shared genetic cause across unknown intermediates.
- name: Microglial activation and neuroinflammation
description: In ABHD12-deficient brain, elevated lysophosphatidylserine lipids precede age-dependent microglial activation and neurobehavioral abnormalities.
cell_types:
- preferred_term: microglial cell
term:
id: CL:0000129
label: microglial cell
biological_processes:
- preferred_term: inflammatory response
modifier: INCREASED
term:
id: GO:0006954
label: inflammatory response
evidence:
- reference: PMID:23297193
reference_title: ABHD12 controls brain lysophosphatidylserine pathways that are deregulated in a murine model of the neurodegenerative disease PHARC.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: Notably, elevations in brain LPS lipids in ABHD12(-/-) mice occur early in life (2-6 mo) and are followed by age-dependent increases in microglial activation and auditory and motor defects that resemble the behavioral phenotypes of human PHARC patients.
explanation: The ABHD12 knockout model places microglial activation downstream of early LPS lipid elevation.
downstream:
- target: Progressive multisystem neurodegeneration
description: Microglial activation and neuroinflammatory lipid signaling contribute to auditory and motor abnormalities resembling PHARC.
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
evidence:
- reference: PMID:23297193
reference_title: ABHD12 controls brain lysophosphatidylserine pathways that are deregulated in a murine model of the neurodegenerative disease PHARC.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: are followed by age-dependent increases in microglial activation and auditory and motor defects that resemble the behavioral phenotypes of human PHARC patients.
explanation: Model evidence links microglial activation to later auditory and motor defects resembling human PHARC.
- name: Progressive multisystem neurodegeneration
description: Chronic neurodegenerative injury contributes to the characteristic combination of neuropathy, ataxia, pyramidal tract dysfunction, hearing loss, and retinal degeneration.
evidence:
- reference: PMID:23297193
reference_title: ABHD12 controls brain lysophosphatidylserine pathways that are deregulated in a murine model of the neurodegenerative disease PHARC.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: Notably, elevations in brain LPS lipids in ABHD12(-/-) mice occur early in life (2-6 mo) and are followed by age-dependent increases in microglial activation and auditory and motor defects that resemble the behavioral phenotypes of human PHARC patients.
explanation: This supports age-dependent neurodegenerative progression downstream of ABHD12 loss in a PHARC model, while the full human multisystem trajectory is inferred across clinical domains.
downstream:
- target: Peripheral nerve degeneration
description: Peripheral nerve degeneration contributes to sensory and motor deficits.
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: This study investigated the phenotypic spectrum of PHARC (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa and early-onset cataract) syndrome caused by biallelic variants in the ABHD12 gene.
explanation: The human cohort defines polyneuropathy as a core PHARC manifestation downstream of ABHD12 disease.
- target: Cerebellar degeneration
description: Cerebellar dysfunction causes progressive gait and coordination impairment.
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: This study investigated the phenotypic spectrum of PHARC (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa and early-onset cataract) syndrome caused by biallelic variants in the ABHD12 gene.
explanation: The human cohort defines ataxia as a core PHARC manifestation downstream of ABHD12 disease.
- target: Auditory pathway degeneration
description: Auditory-system involvement contributes to the hearing-loss component of PHARC syndrome.
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
evidence:
- reference: PMID:23297193
reference_title: ABHD12 controls brain lysophosphatidylserine pathways that are deregulated in a murine model of the neurodegenerative disease PHARC.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: are followed by age-dependent increases in microglial activation and auditory and motor defects that resemble the behavioral phenotypes of human PHARC patients.
explanation: The ABHD12 knockout model supports auditory defects downstream of lipid elevation and microglial activation.
- target: Abnormal pyramidal sign
description: Central corticospinal involvement produces pyramidal tract signs in a substantial subset of PHARC patients.
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
evidence:
- reference: PMID:40064796
reference_title: 'Characterizing and expanding the neurological clinical spectrum of PHARC syndrome: a systematic review.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Although pyramidal signs are not classically associated with PHARC syndrome, they were a prevalent feature when assessed.
explanation: Systematic review confirms pyramidal tract signs as a prevalent central neurological feature of PHARC syndrome.
- name: Peripheral nerve degeneration
description: Progressive peripheral nerve injury contributes to the polyneuropathy component of PHARC syndrome.
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: This study investigated the phenotypic spectrum of PHARC (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa and early-onset cataract) syndrome caused by biallelic variants in the ABHD12 gene.
explanation: Establishes polyneuropathy as a core peripheral nervous system component of PHARC syndrome.
downstream:
- target: Peripheral neuropathy
description: Peripheral nerve degeneration is expressed clinically as polyneuropathy.
causal_link_type: DIRECT
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: This study investigated the phenotypic spectrum of PHARC (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa and early-onset cataract) syndrome caused by biallelic variants in the ABHD12 gene.
explanation: The human cohort directly identifies polyneuropathy as a core component of PHARC.
- name: Cerebellar degeneration
description: Progressive cerebellar involvement with cerebellar atrophy on MRI contributes to gait instability and ataxia.
evidence:
- reference: PMID:40064796
reference_title: 'Characterizing and expanding the neurological clinical spectrum of PHARC syndrome: a systematic review.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Patients with pyramidal signs were more likely to exhibit an ataxic phenotype (p-value 0.018), a complete syndrome (p-value 0.092), and cerebellar atrophy on MRI (p-value 0.001), compared to those without pyramidal signs.
explanation: Systematic review documents cerebellar atrophy and ataxia in PHARC syndrome.
downstream:
- target: Ataxia
description: Cerebellar degeneration is expressed clinically as ataxia.
causal_link_type: DIRECT
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: This study investigated the phenotypic spectrum of PHARC (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa and early-onset cataract) syndrome caused by biallelic variants in the ABHD12 gene.
explanation: The human cohort directly identifies ataxia as a core component of PHARC.
- target: Cerebellar atrophy
description: Progressive cerebellar neurodegeneration manifests structurally as cerebellar atrophy on neuroimaging.
causal_link_type: DIRECT
evidence:
- reference: PMID:40064796
reference_title: 'Characterizing and expanding the neurological clinical spectrum of PHARC syndrome: a systematic review.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Patients with pyramidal signs were more likely to exhibit an ataxic phenotype (p-value 0.018), a complete syndrome (p-value 0.092), and cerebellar atrophy on MRI (p-value 0.001), compared to those without pyramidal signs.
explanation: Links cerebellar neurodegeneration to cerebellar atrophy on brain MRI.
- name: Auditory pathway degeneration
description: Progressive auditory-system involvement contributes to the sensorineural hearing-loss component of PHARC syndrome.
evidence:
- reference: PMID:23297193
reference_title: ABHD12 controls brain lysophosphatidylserine pathways that are deregulated in a murine model of the neurodegenerative disease PHARC.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: Notably, elevations in brain LPS lipids in ABHD12(-/-) mice occur early in life (2-6 mo) and are followed by age-dependent increases in microglial activation and auditory and motor defects that resemble the behavioral phenotypes of human PHARC patients.
explanation: The ABHD12 knockout model supports age-dependent auditory defects resembling human PHARC.
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: This study investigated the phenotypic spectrum of PHARC (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa and early-onset cataract) syndrome caused by biallelic variants in the ABHD12 gene.
explanation: The human cohort defines hearing loss as a core PHARC manifestation.
downstream:
- target: Sensorineural hearing impairment
description: Auditory pathway degeneration is expressed clinically as sensorineural hearing impairment.
causal_link_type: DIRECT
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: This study investigated the phenotypic spectrum of PHARC (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa and early-onset cataract) syndrome caused by biallelic variants in the ABHD12 gene.
explanation: The human cohort directly identifies hearing loss as a core component of PHARC.
- name: Retinal degeneration
description: Retinal and macular degeneration contribute to the rod-cone dystrophy, macular atrophy, and retinal pigmentary abnormalities of PHARC syndrome.
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Fundus examination revealed macular involvement in all patients, ranging from alterations of the retinal pigment epithelium to macular atrophy.
explanation: This directly supports retinal degenerative involvement in PHARC syndrome.
downstream:
- target: Retinitis pigmentosa
description: Retinal degeneration is expressed clinically as rod-cone dystrophy/retinitis pigmentosa.
causal_link_type: DIRECT
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Fundus examination revealed macular involvement in all patients, ranging from alterations of the retinal pigment epithelium to macular atrophy.
explanation: The cohort documents retinal and macular involvement supporting the retinitis pigmentosa phenotype.
- target: Macular atrophy
description: Progressive outer retinal and retinal pigment epithelium degeneration produces central macular atrophy.
causal_link_type: DIRECT
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Fundus examination revealed macular involvement in all patients, ranging from alterations of the retinal pigment epithelium to macular atrophy.
explanation: Documents macular involvement ranging from RPE alterations to macular atrophy across all cohort patients.
- target: Abnormal retinal pigmentation
description: Retinal degeneration produces intraretinal bone-spicule hyperpigmentation and pigmentary alterations.
causal_link_type: DIRECT
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Intraretinal spicular hyperpigmentation was observed in 7 out of 15 patients (47%).
explanation: Directly links retinal degeneration in PHARC syndrome to intraretinal spicular hyperpigmentation.
- name: Lens opacification and cataractogenesis
description: Progressive lens opacification, including congenital and early-onset forms, develops in the majority of patients with PHARC syndrome.
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Different types of cataract were observed in 13 out of 15 patients (87%), which also included congenital forms of cataract.
explanation: Documents frequent lens opacification and cataract formation in the ophthalmic PHARC cohort.
downstream:
- target: Cataract
description: Lens opacification manifests clinically as congenital or early-onset cataract.
causal_link_type: DIRECT
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Different types of cataract were observed in 13 out of 15 patients (87%), which also included congenital forms of cataract.
explanation: Directly connects lens opacification to clinical cataract in 87% of cohort patients.
phenotypes:
- name: Peripheral neuropathy
category: Neurologic
diagnostic: true
description: Length-dependent peripheral polyneuropathy is a core component of the PHARC pentad.
phenotype_term:
preferred_term: Peripheral neuropathy
term:
id: HP:0009830
label: Peripheral neuropathy
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: This study investigated the phenotypic spectrum of PHARC (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa and early-onset cataract) syndrome caused by biallelic variants in the ABHD12 gene.
explanation: This directly supports peripheral neuropathy as part of the defining PHARC acronym.
- name: Sensorineural hearing impairment
category: Otolaryngologic
diagnostic: true
frequency: VERY_FREQUENT
description: Progressive hearing impairment is the most common initial symptom and contributes substantially to disability.
phenotype_term:
preferred_term: Sensorineural hearing impairment
term:
id: HP:0000407
label: Sensorineural hearing impairment
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: This study investigated the phenotypic spectrum of PHARC (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa and early-onset cataract) syndrome caused by biallelic variants in the ABHD12 gene.
explanation: This directly supports hearing loss as part of the defining PHARC syndrome phenotype.
- reference: PMID:40064796
reference_title: 'Characterizing and expanding the neurological clinical spectrum of PHARC syndrome: a systematic review.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: The results showed that hearing loss was the most common initial symptom, with a complete syndrome observed in only 31.6% of reported cases.
explanation: Establishes hearing loss as the most frequent initial symptom of PHARC syndrome.
- name: Ataxia
category: Neurologic
diagnostic: true
frequency: FREQUENT
description: Cerebellar involvement causes progressive gait instability and dyscoordination.
phenotype_term:
preferred_term: Ataxia
term:
id: HP:0001251
label: Ataxia
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: This study investigated the phenotypic spectrum of PHARC (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa and early-onset cataract) syndrome caused by biallelic variants in the ABHD12 gene.
explanation: This directly supports ataxia as a defining component of PHARC syndrome.
- name: Retinitis pigmentosa
category: Ophthalmologic
diagnostic: true
frequency: VERY_FREQUENT
description: Retinal dystrophy causes night blindness and progressive visual loss.
phenotype_term:
preferred_term: Retinitis pigmentosa
term:
id: HP:0000510
label: Rod-cone dystrophy
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Fundus examination revealed macular involvement in all patients, ranging from alterations of the retinal pigment epithelium to macular atrophy.
explanation: This directly supports retinal degenerative disease within the PHARC phenotype.
- name: Macular atrophy
category: Ophthalmologic
frequency: VERY_FREQUENT
description: Macular involvement ranging from retinal pigment epithelium alterations to central macular atrophy is present across ophthalmic cohort patients.
phenotype_term:
preferred_term: Macular atrophy
term:
id: HP:0007401
label: Macular atrophy
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Fundus examination revealed macular involvement in all patients, ranging from alterations of the retinal pigment epithelium to macular atrophy.
explanation: Documents macular involvement ranging from RPE alterations to macular atrophy in all 15 patients of the ophthalmic cohort.
- name: Abnormal retinal pigmentation
category: Ophthalmologic
frequency: FREQUENT
description: Mild-to-distinct intraretinal bone-spicule hyperpigmentation is observed in nearly half (7/15, 47%) of ophthalmic cohort patients.
phenotype_term:
preferred_term: Abnormal retinal pigmentation
term:
id: HP:0007703
label: Abnormal retinal pigmentation
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Intraretinal spicular hyperpigmentation was observed in 7 out of 15 patients (47%).
explanation: Directly documents intraretinal spicular hyperpigmentation in 7 of 15 patients (47%).
- name: Cataract
category: Ophthalmologic
diagnostic: true
frequency: VERY_FREQUENT
description: Lens opacity is part of the canonical PHARC acronym and phenotype (observed in 87% of ophthalmic cohort patients).
phenotype_term:
preferred_term: Cataract
term:
id: HP:0000518
label: Cataract
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Different types of cataract were observed in 13 out of 15 patients (87%), which also included congenital forms of cataract.
explanation: This directly supports cataract as a common PHARC phenotype.
- name: Abnormal pyramidal sign
category: Neurologic
frequency: FREQUENT
description: Pyramidal tract signs (spasticity, hyperreflexia, extensor plantar responses) are prevalent when systematically assessed and correlate with ataxia and cerebellar atrophy.
phenotype_term:
preferred_term: Abnormal pyramidal sign
term:
id: HP:0007256
label: Abnormal pyramidal sign
evidence:
- reference: PMID:40064796
reference_title: 'Characterizing and expanding the neurological clinical spectrum of PHARC syndrome: a systematic review.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Although pyramidal signs are not classically associated with PHARC syndrome, they were a prevalent feature when assessed.
explanation: Documents pyramidal signs as a prevalent neurological manifestation of PHARC syndrome.
- name: Cerebellar atrophy
category: Neurologic
frequency: FREQUENT
description: Structural cerebellar atrophy on brain MRI accompanies progressive cerebellar ataxia and pyramidal involvement.
phenotype_term:
preferred_term: Cerebellar atrophy
term:
id: HP:0001272
label: Cerebellar atrophy
evidence:
- reference: PMID:40064796
reference_title: 'Characterizing and expanding the neurological clinical spectrum of PHARC syndrome: a systematic review.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Patients with pyramidal signs were more likely to exhibit an ataxic phenotype (p-value 0.018), a complete syndrome (p-value 0.092), and cerebellar atrophy on MRI (p-value 0.001), compared to those without pyramidal signs.
explanation: Documents cerebellar atrophy on brain MRI in PHARC syndrome.
biochemical:
- name: Brain lysophosphatidylserine lipids
biomarker_term:
preferred_term: lysophosphatidylserine
term:
id: CHEBI:68510
label: lysophosphatidylserine
presence: INCREASED
context: Elevated brain lysophosphatidylserine lipids are a model-system biochemical readout of ABHD12 loss and dysregulated LPS metabolism.
readouts:
- target: Abnormal lysophosphatidylserine signaling
relationship: READOUT_OF
direction: POSITIVE
interpretation: Increased LPS lipids report the lipid-metabolism abnormality downstream of ABHD12 loss in the PHARC model.
evidence:
- reference: PMID:23297193
reference_title: ABHD12 controls brain lysophosphatidylserine pathways that are deregulated in a murine model of the neurodegenerative disease PHARC.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: ABHD12(-/-) mice display massive increases in a rare set of very long chain LPS lipids
explanation: The ABHD12 knockout mouse metabolomics result directly supports increased LPS lipids as a biochemical readout.
evidence:
- reference: PMID:23297193
reference_title: ABHD12 controls brain lysophosphatidylserine pathways that are deregulated in a murine model of the neurodegenerative disease PHARC.
supports: SUPPORT
evidence_source: MODEL_ORGANISM
snippet: ABHD12(-/-) mice display massive increases in a rare set of very long chain LPS lipids
explanation: The mouse model directly identifies increased brain LPS lipids after ABHD12 loss.
genetic:
- name: ABHD12
gene_term:
preferred_term: ABHD12
term:
id: hgnc:15868
label: ABHD12
association: Causal biallelic loss-of-function variant
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: This study investigated the phenotypic spectrum of PHARC (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa and early-onset cataract) syndrome caused by biallelic variants in the ABHD12 gene.
explanation: This directly supports ABHD12 as the causal gene in PHARC syndrome.
- reference: CGGV:assertion_ccd68c20-2024-4239-be51-26697e19a6b4-2018-06-26T160000.000Z
reference_title: ABHD12 / PHARC syndrome (Definitive)
supports: SUPPORT
evidence_source: OTHER
snippet: ABHD12 | HGNC:15868 | PHARC syndrome | MONDO:0012984 | AR | Definitive
explanation: ClinGen classifies the ABHD12-PHARC syndrome gene-disease relationship as definitive with autosomal recessive inheritance.
environmental: []
treatments:
- name: Supportive multidisciplinary care
treatment_term:
preferred_term: supportive care
term:
id: NCIT:C15747
label: Supportive Care
description: Early multidisciplinary clinical assessment and coordinated supportive care address the variable neurologic, audiologic, and ophthalmic manifestations.
target_phenotypes:
- preferred_term: Peripheral neuropathy
term:
id: HP:0009830
label: Peripheral neuropathy
- preferred_term: Ataxia
term:
id: HP:0001251
label: Ataxia
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Given the variable nature of PHARC, an early multidisciplinary assessment is recommended to assess disease severity.
explanation: Directly recommends early multidisciplinary clinical assessment and care coordination for patients with PHARC syndrome.
- name: Cataract surgery
therapeutic_modality: SURGERY
treatment_term:
preferred_term: surgical procedure
term:
id: NCIT:C15329
label: Surgical Procedure
description: Cataract extraction may improve visual function when lens opacity becomes clinically significant.
target_phenotypes:
- preferred_term: Cataract
term:
id: HP:0000518
label: Cataract
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Different types of cataract were observed in 13 out of 15 patients (87%), which also included congenital forms of cataract.
explanation: Documents high prevalence of cataract in PHARC syndrome requiring ophthalmic management.
diagnosis:
- name: ABHD12 genetic testing
diagnosis_term:
preferred_term: genetic testing
term:
id: NCIT:C15709
label: Genetic Testing
description: Molecular diagnosis depends on identifying biallelic pathogenic ABHD12 variants.
results: Biallelic pathogenic ABHD12 variants support the diagnosis of PHARC syndrome.
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: This study investigated the phenotypic spectrum of PHARC (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa and early-onset cataract) syndrome caused by biallelic variants in the ABHD12 gene.
explanation: Confirms that molecular identification of biallelic ABHD12 variants establishes the diagnosis.
- name: Ophthalmologic evaluation
diagnosis_term:
preferred_term: clinical assessment
term:
id: NCIT:C124351
label: Clinical Evaluation
description: Fundus examination and retinal imaging document macular atrophy, retinal pigment epithelium alterations, and associated cataract.
results: Macular atrophy, rod-cone dystrophy, and cataract support PHARC syndrome.
evidence:
- reference: PMID:34573385
reference_title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Fundus examination revealed macular involvement in all patients, ranging from alterations of the retinal pigment epithelium to macular atrophy.
explanation: Supports ophthalmic fundus and retinal imaging assessment in PHARC syndrome.
- name: Brain magnetic resonance imaging
diagnosis_term:
preferred_term: magnetic resonance imaging procedure
term:
id: NCIT:C16809
label: Magnetic Resonance Imaging
description: Brain MRI evaluates structural cerebellar atrophy, particularly in patients presenting with ataxia and pyramidal tract signs.
results: Cerebellar atrophy on brain MRI supports central neurodegenerative involvement in PHARC syndrome.
evidence:
- reference: PMID:40064796
reference_title: 'Characterizing and expanding the neurological clinical spectrum of PHARC syndrome: a systematic review.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Patients with pyramidal signs were more likely to exhibit an ataxic phenotype (p-value 0.018), a complete syndrome (p-value 0.092), and cerebellar atrophy on MRI (p-value 0.001), compared to those without pyramidal signs.
explanation: Directly documents brain MRI identification of cerebellar atrophy in patients with PHARC syndrome.
- name: Audiometric testing
diagnosis_term:
preferred_term: audiometric testing
term:
id: NCIT:C38036
label: Audiometric Test
description: Hearing assessment evaluates the sensorineural hearing-loss component of PHARC syndrome, which is commonly the initial presenting symptom.
results: Sensorineural hearing loss supports PHARC syndrome.
evidence:
- reference: PMID:40064796
reference_title: 'Characterizing and expanding the neurological clinical spectrum of PHARC syndrome: a systematic review.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: The results showed that hearing loss was the most common initial symptom, with a complete syndrome observed in only 31.6% of reported cases.
explanation: Inferred diagnostic utility from hearing loss being the most common initial symptom of PHARC syndrome.
- name: Electromyography and nerve conduction studies
diagnosis_term:
preferred_term: electromyography procedure
term:
id: NCIT:C38056
label: Electromyography
description: Peripheral nerve evaluation assesses the polyneuropathy component of the PHARC syndrome pentad.
results: Peripheral polyneuropathy supports PHARC syndrome.
evidence:
- reference: PMID:40064796
reference_title: 'Characterizing and expanding the neurological clinical spectrum of PHARC syndrome: a systematic review.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: 'PHARC syndrome is an autosomal recessive neurodegenerative disease caused by mutations in the ABHD12 gene and is characterized by five main clinical features: polyneuropathy, hearing loss, ataxia, retinitis pigmentosa, and cataracts.'
explanation: The snippet establishes polyneuropathy as a defining feature of the PHARC pentad; the use of electrodiagnostic peripheral nerve testing is inferred from this clinical feature rather than named directly in the abstract.
differential_diagnoses:
- name: Usher syndrome
disease_term:
preferred_term: Usher syndrome
term:
id: MONDO:0019501
label: Usher syndrome
description: Usher syndrome (particularly Usher syndrome type 3) overlaps clinically through progressive sensorineural hearing loss, balance defects, and retinitis pigmentosa, and patients with biallelic ABHD12 variants may be misdiagnosed with Usher syndrome if neurological findings are not evaluated.
distinguishing_features:
- Development of peripheral polyneuropathy, cerebellar ataxia, and early-onset cataracts alongside biallelic ABHD12 variants in PHARC syndrome
evidence:
- reference: PMID:35353227
reference_title: 'The genetic and phenotypic landscapes of Usher syndrome: from disease mechanisms to a new classification.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: PHARC should, therefore, be considered as a differential diagnosis for patients with USH3-like phenotypes presenting with progressive hearing loss and balance defects.
explanation: Directly establishes PHARC syndrome as a differential diagnosis for Usher syndrome type 3-like dual sensory loss with balance defects.
- reference: PMID:35353227
reference_title: 'The genetic and phenotypic landscapes of Usher syndrome: from disease mechanisms to a new classification.'
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: One major problem with these studies is that they do not usually include neurological results for the patients, potentially leading to the misdiagnosis of their condition as USH3.
explanation: Explains how omitting neurological evaluations in patients with biallelic ABHD12 variants leads to misdiagnosis of PHARC syndrome as Usher syndrome type 3.
references:
- reference: PMID:23297193
title: ABHD12 controls brain lysophosphatidylserine pathways that are deregulated in a murine model of the neurodegenerative disease PHARC.
findings: []
- reference: PMID:34573385
title: 'The Phenotypic Spectrum of Patients with PHARC Syndrome Due to Variants in ABHD12: An Ophthalmic Perspective.'
findings: []
- reference: PMID:35353227
title: 'The genetic and phenotypic landscapes of Usher syndrome: from disease mechanisms to a new classification.'
findings: []
- reference: PMID:40064796
title: 'Characterizing and expanding the neurological clinical spectrum of PHARC syndrome: a systematic review.'
findings: []
clinical_trials: []
datasets: []
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