Adult Refsum Disease

Genetic MONDO:0009958 Pathograph 40 Show in embeddings browser Peroxisomal Disease Hereditary Neuropathy

Adult Refsum disease is an autosomal recessive peroxisomal metabolic disorder caused by biallelic pathogenic variants in PHYH (type 1) or, less commonly, PEX7 (type 2). Impaired peroxisomal phytanic acid alpha-oxidation causes phytanic acid accumulation in plasma and tissues, leading to retinitis pigmentosa, anosmia, peripheral neuropathy, ataxia, hearing impairment, ichthyosis, skeletal findings, and potentially severe cardiomyopathy or arrhythmia.

Ask OpenScientist

Ask a research question about Adult Refsum Disease. OpenScientist will conduct autonomous deep research using the Disorder Mechanisms Knowledge Base and PubMed literature (typically 10-30 minutes).

Submitting...

Do not include personal health information in your question. Questions and results are cached in your browser's local storage.

1
Mappings
1
Inheritance
14
Pathophys.
18
Phenotypes
40
Pathograph
2
Genes
2
Variants
4
Medical Actions
2
Subtypes
1
Differentials
1
Datasets
20
References
1
Deep Research
🔗

Mappings

MONDO
MONDO:0009958 adult Refsum disease
skos:narrowMatch MONDO
Recorded as narrowMatch, not exactMatch: the MONDO term is labelled and defined clinically ("anosmia, early-onset retinitis pigmentosa...") but is axiomatized as `is_a MONDO:0100258` phytanoyl-CoA hydroxylase deficiency, which restricts it to PHYH-caused disease. This entry covers both PHYH (type 1, >90%) and PEX7 (type 2, <10%) disease per PMID:20301527, so it is broader than the MONDO class as currently axiomatized. MONDO's own MONDO:0100307 "adult Refsum disease due to PEX7 defect" is defined as "an adult Refsum disease", which cannot hold alongside that is_a edge; MONDO avoids the contradiction only by not asserting it. Retained as the entry's disease_term because it is the closest available grounding.
👪

Inheritance

1
Autosomal recessive inheritance HP:0000007
Adult Refsum disease is inherited in an autosomal recessive manner and is caused by biallelic pathogenic variants in PHYH or PEX7.
Autosomal recessive inheritance
Show evidence (3 references)
ORPHA:773 SUPPORT Other
"Autosomal recessive"
Orphanet lists autosomal recessive inheritance.
PMID:20301527 SUPPORT Human Clinical
"ARD is inherited in an autosomal recessive manner."
GeneReviews states autosomal recessive inheritance.
PMID:20301527 SUPPORT Human Clinical
"If both parents are known to be heterozygous for a PHYH or PEX7 pathogenic variant, each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier."
GeneReviews provides the recurrence risks for autosomal recessive genetic counseling.
◆

Subtypes

2
Type 1 (PHYH-related) MONDO:0100258
PHYH hgnc:8940 HUGO Gene Nomenclature Committee (hgnc) Relation: this subtype is caused by variation in this gene This subtype is caused by variation in PHYH (hgnc:8940). hgnc:8940 is a gene from the HUGO Gene Nomenclature Committee.
The usual form of Adult Refsum disease, caused by biallelic PHYH variants and deficient phytanoyl-CoA 2-hydroxylase activity.
Show evidence (1 reference)
PMID:17325280 SUPPORT Human Clinical
"This usually results from a PHYH gene defect, although some cases have been found to carry a PEX7 defect."
The clinical report distinguishes the usual PHYH-related form from PEX7-related disease.
Type 2 (PEX7-related) MONDO:0100307
PEX7 hgnc:8860 HUGO Gene Nomenclature Committee (hgnc) Relation: this subtype is caused by variation in this gene This subtype is caused by variation in PEX7 (hgnc:8860). hgnc:8860 is a gene from the HUGO Gene Nomenclature Committee.
A less common molecular form caused by biallelic PEX7 variants; the reported Adult Refsum phenotype can be clinically indistinguishable from type 1.
Show evidence (1 reference)
PMID:17325280 SUPPORT Human Clinical
"We describe the phenotype of such a patient, indistinguishable from that of classic ARD."
The PEX7 case supports type 2 as a molecular subtype with the classic Adult Refsum phenotype.
⚙

Pathophysiology

14
PHYH Phytanoyl-CoA Hydroxylase Deficiency
Biallelic PHYH variants impair phytanoyl-CoA 2-hydroxylase, the peroxisomal enzyme catalyzing the first alpha-oxidation step in phytanic acid degradation.
PHYH hgnc:8940 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves PHYH (hgnc:8940). hgnc:8940 is a gene from the HUGO Gene Nomenclature Committee.
phytanoyl-CoA dioxygenase activity GO:0048244 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves phytanoyl-CoA dioxygenase activity (GO:0048244). GO:0048244 is a molecular function from the Gene Ontology.
peroxisome GO:0005777 Gene Ontology (GO) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in peroxisome (GO:0005777). GO:0005777 is an anatomical location from the Gene Ontology.
Downstream
Phytanic Acid Alpha-Oxidation Defect Loss of PHYH activity directly impairs the first alpha-oxidation step.
Show evidence (1 reference)
PMID:16186124 SUPPORT In Vitro
"mutations in phytanoyl-CoA 2-hydroxylase (PAHX), an Fe(II) and 2-oxoglutarate (2OG)-dependent oxygenase that catalyzes the initial alpha-oxidation step in the degradation of phytenic acid in peroxisomes."
Structural enzymology identifies the affected enzyme and reaction.
PEX7 Peroxisomal Matrix Import Defect
Biallelic PEX7 variants impair import of PTS2-containing proteins into the peroxisomal matrix, including machinery required for phytanic acid alpha-oxidation.
PEX7 hgnc:8860 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves PEX7 (hgnc:8860). hgnc:8860 is a gene from the HUGO Gene Nomenclature Committee.
protein import into peroxisome matrix GO:0016558 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased protein import into peroxisome matrix (GO:0016558). GO:0016558 is a biological process from the Gene Ontology. ↓ DECREASED
peroxisome GO:0005777 Gene Ontology (GO) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in peroxisome (GO:0005777). GO:0005777 is an anatomical location from the Gene Ontology.
Downstream
Phytanic Acid Alpha-Oxidation Defect PEX7 deficiency impairs the peroxisomal machinery needed for alpha-oxidation.
PEX7-Related Plasmalogen Synthesis Defect PEX7 deficiency also impairs plasmalogen synthesis in type 2 disease.
Show evidence (1 reference)
PMID:12522768 SUPPORT Human Clinical
"PEX7 gene, which codes for the peroxin 7 receptor protein required for peroxisomal import of proteins containing a peroxisomal targeting signal type 2."
The patient genetic study states the relevant PEX7 import function.
Phytanic Acid Alpha-Oxidation Defect
Defective peroxisomal alpha-oxidation prevents normal degradation of exogenous phytanic acid.
fatty acid alpha-oxidation GO:0001561 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased fatty acid alpha-oxidation (GO:0001561). GO:0001561 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Plasma and Tissue Phytanic Acid Accumulation Reduced degradation causes phytanic acid retention and accumulation.
Show evidence (1 reference)
PMID:4164676 SUPPORT Human Clinical
"patients with Refsum's disease have a relative block in the degradation of phytanic acid and possibly other similar branched-chain compounds."
Human tracer evidence establishes impaired phytanic acid degradation.
Plasma and Tissue Phytanic Acid Accumulation
Exogenous phytanic acid accumulates in plasma and tissues because alpha-oxidation is impaired.
Downstream
Elevated plasma and tissue phytanic acid Accumulation produces the defining biochemical abnormality.
Exogenous phytanic acid retention Dietary phytanic acid persists because its degradation is blocked.
Retinal Photoreceptor Dysfunction Retinal disease co-occurs with phytanic acid elevation, but the intervening human mechanism is unresolved.
Olfactory Dysfunction Anosmia is associated with the storage disorder, but its tissue mechanism is unresolved.
Peripheral Nerve Dysfunction Polyneuropathy is associated with the storage disorder, but the intervening mechanism is unresolved.
Cerebellar Dysfunction Ataxia is associated with the storage disorder, but the intervening mechanism is unresolved.
Auditory Dysfunction Hearing loss is associated with the storage disorder, but the intervening mechanism is unresolved.
Cardiac Mitochondrial Dysfunction Patient-range phytanic acid concentrations disrupt cardiac mitochondrial bioenergetics in vitro.
Cutaneous Dysfunction Ichthyosis is associated with phytanic acid elevation, but the intervening skin mechanism is unresolved.
Distal Limb Skeletal Abnormality Skeletal findings are part of the syndrome, but their relationship to phytanic acid accumulation is unresolved.
Renal Involvement Renal insufficiency is occasionally reported, but its mechanism and attribution are uncertain.
Show evidence (2 references)
PMID:20301527 SUPPORT Human Clinical
"Adult Refsum disease (ARD) is associated with elevated plasma phytanic acid levels"
GeneReviews identifies elevated phytanic acid as the central biochemical feature.
PMID:4164676 SUPPORT Human Clinical
"This labeled phytanic acid had disappeared almost completely from the plasma of the seven control subjects by 24 to 48 hours, whereas it persisted at high concentrations in the plasma of the two patients for many days."
Human tracer data demonstrate prolonged retention.
Retinal Photoreceptor Dysfunction
Retinal degeneration causes rod-cone dysfunction, night blindness, and progressive visual loss.
Downstream
Rod-cone dystrophy The retinal dysfunction manifests as retinitis pigmentosa/rod-cone dystrophy.
Macular dystrophy A recent case extends the retinal phenotype to macular dystrophy.
Cataract Cataract can accompany the retinal phenotype.
Miosis Miosis is an associated ocular feature.
Nyctalopia Rod dysfunction manifests as night blindness.
Show evidence (2 references)
PMID:20301527 SUPPORT Human Clinical
"late childhood-onset (or later) retinitis pigmentosa"
GeneReviews establishes retinal degeneration as a core manifestation.
PMID:32904930 SUPPORT Human Clinical
"His post-intervention 30 Hz flicker electroretinogram demonstrated significantly improved waveform amplitudes and implicit times, suggesting improved retinal function."
A confirmed case demonstrated objective retinal functional improvement after dietary treatment.
Olfactory Dysfunction
Olfactory-system dysfunction manifests as anosmia.
Downstream
Anosmia Olfactory dysfunction manifests clinically as anosmia.
Show evidence (1 reference)
PMID:20301527 SUPPORT Human Clinical
"variable combinations of anosmia, polyneuropathy, deafness, ataxia, and ichthyosis."
GeneReviews establishes anosmia as a core manifestation.
Peripheral Nerve Dysfunction
Peripheral nerve dysfunction produces chronic polyneuropathy.
Downstream
Peripheral neuropathy Peripheral nerve dysfunction manifests clinically as polyneuropathy.
Show evidence (1 reference)
PMID:20301527 SUPPORT Human Clinical
"variable combinations of anosmia, polyneuropathy, deafness, ataxia, and ichthyosis."
GeneReviews establishes polyneuropathy as a core manifestation.
Cerebellar Dysfunction
Cerebellar dysfunction manifests clinically as ataxia.
Downstream
Ataxia Cerebellar dysfunction manifests clinically as ataxia.
Show evidence (1 reference)
PMID:6170281 SUPPORT Human Clinical
"include pigmentary retinal degeneration, chronic polyneuropathy, ataxia, impaired hearing, and cardiopathy"
The long-term clinical series establishes ataxia as a major manifestation.
Auditory Dysfunction
Auditory-system involvement causes sensorineural hearing impairment and may include auditory neuropathy.
Downstream
Sensorineural hearing impairment Auditory dysfunction manifests clinically as hearing impairment.
Show evidence (1 reference)
PMID:11589979 SUPPORT Human Clinical
"Refsum's disease is a disorder of lipid metabolism with pigmentary retinopathy, demyelinating neuropathy, ataxia, and hearing loss."
Clinical cases establish hearing loss as part of the disorder.
Cardiac Mitochondrial Dysfunction
Patient-range phytanic acid disrupts cardiac mitochondrial bioenergetics and calcium homeostasis in vitro; translation to human cardiac disease remains provisional.
Downstream
Cardiomyopathy Mitochondrial toxicity is a plausible contributor to clinical cardiomyopathy.
Arrhythmia Mitochondrial toxicity is a plausible contributor to arrhythmia.
Heart block Cardiac conduction disease can include heart block; its link to mitochondrial toxicity is uncertain.
Show evidence (1 reference)
PMID:36812958 SUPPORT In Vitro
"The present data indicate that Phyt, at concentrations found in the plasma of patients with Refsum disease, disrupts by multiple mechanisms mitochondrial bioenergetics and Ca2+ homeostasis"
Rat-heart mitochondrial and H9C2-cell experiments support the cellular mechanism.
Cutaneous Dysfunction
Cutaneous involvement produces ichthyosis and improves when phytanic acid intake is restricted.
Downstream
Ichthyosis Cutaneous dysfunction manifests as ichthyosis.
Dry skin Cutaneous involvement can also manifest as dry skin.
Show evidence (1 reference)
PMID:20301527 SUPPORT Human Clinical
"Dietary restriction of phytanic acid intake helps resolve ichthyosis, sensory neuropathy, and ataxia."
Treatment response supports disease-linked cutaneous dysfunction.
Distal Limb Skeletal Abnormality
Distal limb skeletal findings include pes cavus, hammertoes, and short metacarpals; their disease mechanism is unresolved.
Downstream
Pes cavus Pes cavus is an associated skeletal feature.
Hammertoe Hammertoe is an associated skeletal feature.
Short metacarpal Short metacarpal is an associated skeletal feature.
Show evidence (1 reference)
ORPHA:773 SUPPORT Other
"Other features can be deafness, ichthyosis, skeletal abnormalities, and cardiac arrhythmia."
Orphanet supports skeletal abnormalities as syndrome features.
Renal Involvement
Renal insufficiency is occasionally reported, but causality and mechanism remain uncertain.
Downstream
Renal insufficiency Renal involvement is represented clinically by renal insufficiency.
Show evidence (1 reference)
ORPHA:773 SUPPORT Other
"HP:0000083 | Renal insufficiency | Occasional (29-5%)"
Orphanet supports an occasional association only.
⬡

Pathograph

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

Phenotypes

18
Cardiovascular 2
Cardiomyopathy VERY_FREQUENT HP:0001638 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cardiomyopathy (HP:0001638). HP:0001638 is a phenotype from the Human Phenotype Ontology.
The Orphanet frequency band is retained as reported, while GeneReviews characterizes cardiomyopathy and arrhythmia as potentially severe findings that develop later in life.
Show evidence (2 references)
ORPHA:773 SUPPORT Other
"HP:0001638 | Cardiomyopathy | Very frequent (99-80%)"
Orphanet supplies the association and frequency band.
PMID:20301527 SUPPORT Human Clinical
"Cardiac arrhythmia and heart failure caused by cardiomyopathy are potentially severe health problems that develop later in life."
GeneReviews establishes cardiomyopathy as a potentially severe later manifestation.
Arrhythmia HP:0011675 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Arrhythmia (HP:0011675). HP:0011675 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:20301527 SUPPORT Human Clinical
"Cardiac arrhythmia and heart failure caused by cardiomyopathy are potentially severe health problems that develop later in life."
GeneReviews directly supports cardiac arrhythmia.
Ear 1
Sensorineural hearing impairment VERY_FREQUENT HP:0000407 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Sensorineural hearing impairment (HP:0000407). HP:0000407 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
ORPHA:773 SUPPORT Other
"HP:0000407 | Sensorineural hearing impairment | Very frequent (99-80%)"
Orphanet supplies the association and frequency band.
PMID:11589979 SUPPORT Human Clinical
"Refsum's disease is a disorder of lipid metabolism with pigmentary retinopathy, demyelinating neuropathy, ataxia, and hearing loss."
Clinical cases independently support hearing loss.
Eye 4
Rod-cone dystrophy HP:0000510 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Rod-cone dystrophy (HP:0000510). HP:0000510 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:20301527 SUPPORT Human Clinical
"late childhood-onset (or later) retinitis pigmentosa"
GeneReviews supports retinitis pigmentosa, represented by its current HPO term rod-cone dystrophy.
PMID:32904930 SUPPORT Human Clinical
"His post-intervention 30 Hz flicker electroretinogram demonstrated significantly improved waveform amplitudes and implicit times, suggesting improved retinal function."
A confirmed case provides objective electrophysiologic evidence of retinal dysfunction and treatment response.
Macular dystrophy HP:0007754 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Macular dystrophy (HP:0007754). HP:0007754 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41290216 SUPPORT Human Clinical
"We document for the first time an association between macular dystrophy and Refsum disease."
The recent case report explicitly extends the ocular phenotype to macular dystrophy.
Cataract VERY_FREQUENT HP:0000518 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cataract (HP:0000518). HP:0000518 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
ORPHA:773 SUPPORT Other
"HP:0000518 | Cataract | Very frequent (99-80%)"
Orphanet supplies the association and frequency band.
Nyctalopia FREQUENT HP:0000662 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Nyctalopia (HP:0000662). HP:0000662 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
ORPHA:773 SUPPORT Other
"HP:0000662 | Nyctalopia | Frequent (79-30%)"
Orphanet supplies the association and frequency band.
Genitourinary 1
Renal insufficiency OCCASIONAL HP:0000083 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Renal insufficiency (HP:0000083). HP:0000083 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
ORPHA:773 SUPPORT Other
"HP:0000083 | Renal insufficiency | Occasional (29-5%)"
Orphanet supports an occasional association; attribution and mechanism remain uncertain.
Head and Neck 1
Anosmia VERY_FREQUENT HP:0000458 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Anosmia (HP:0000458). HP:0000458 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
ORPHA:773 SUPPORT Other
"HP:0000458 | Anosmia | Very frequent (99-80%)"
Orphanet supplies the association and frequency band.
PMID:20301527 SUPPORT Human Clinical
"variable combinations of anosmia, polyneuropathy, deafness, ataxia, and ichthyosis."
GeneReviews identifies anosmia as a core manifestation.
Integument 2
Dry skin HP:0000958 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Dry skin (HP:0000958). HP:0000958 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41290216 SUPPORT Human Clinical
"Both patients shared systemic features of the disease including bilaterally abnormal metatarsals and dry skin"
Both recent molecularly and biochemically confirmed cases had dry skin.
Ichthyosis VERY_FREQUENT HP:0008064 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Ichthyosis (HP:0008064). HP:0008064 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
ORPHA:773 SUPPORT Other
"HP:0008064 | Ichthyosis | Very frequent (99-80%)"
Orphanet supplies the association and frequency band.
PMID:20301527 SUPPORT Human Clinical
"variable combinations of anosmia, polyneuropathy, deafness, ataxia, and ichthyosis."
GeneReviews identifies ichthyosis as a core manifestation.
Limbs 2
Pes cavus OCCASIONAL HP:0001761 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Pes cavus (HP:0001761). HP:0001761 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
ORPHA:773 SUPPORT Other
"HP:0001761 | Pes cavus | Occasional (29-5%)"
Orphanet supplies the association and frequency band.
Short metacarpal FREQUENT HP:0010049 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short metacarpal (HP:0010049). HP:0010049 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
ORPHA:773 SUPPORT Other
"HP:0010049 | Short metacarpal | Frequent (79-30%)"
Orphanet supplies the association and frequency band.
Nervous System 2
Ataxia VERY_FREQUENT HP:0001251 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Ataxia (HP:0001251). HP:0001251 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
ORPHA:773 SUPPORT Other
"HP:0001251 | Ataxia | Very frequent (99-80%)"
Orphanet supplies the association and frequency band.
PMID:6170281 SUPPORT Human Clinical
"include pigmentary retinal degeneration, chronic polyneuropathy, ataxia, impaired hearing, and cardiopathy"
The long-term clinical series independently supports ataxia.
Peripheral neuropathy VERY_FREQUENT HP:0009830 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Peripheral neuropathy (HP:0009830). HP:0009830 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
ORPHA:773 SUPPORT Other
"HP:0009830 | Peripheral neuropathy | Very frequent (99-80%)"
Orphanet supplies the association and frequency band.
PMID:20301527 SUPPORT Human Clinical
"variable combinations of anosmia, polyneuropathy, deafness, ataxia, and ichthyosis."
GeneReviews identifies polyneuropathy as a core manifestation.
Other 3
Miosis FREQUENT HP:0000616 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Miosis (HP:0000616). HP:0000616 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
ORPHA:773 SUPPORT Other
"HP:0000616 | Miosis | Frequent (79-30%)"
Orphanet supplies the association and frequency band.
Hammertoe FREQUENT HP:0001765 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hammertoe (HP:0001765). HP:0001765 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
ORPHA:773 SUPPORT Other
"HP:0001765 | Hammertoe | Frequent (79-30%)"
Orphanet supplies the association and frequency band.
Heart block OCCASIONAL HP:0012722 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Heart block (HP:0012722). HP:0012722 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
ORPHA:773 SUPPORT Other
"HP:0012722 | Heart block | Occasional (29-5%)"
Orphanet supplies the association and frequency band.
🧬

Genetic Associations

2
PHYH (Biallelic pathogenic variants)
Gene: PHYH hgnc:8940 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is PHYH (hgnc:8940). hgnc:8940 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE variant_origin: GERMLINE
Show evidence (2 references)
ORPHA:773 SUPPORT Other
"PHYH | phytanoyl-CoA 2-hydroxylase | hgnc:8940 | Disease-causing germline mutation(s) in"
Orphanet lists PHYH as a disease-causing gene.
PMID:14974078 SUPPORT Other
"two genes, PHYH (also named PAHX) and PEX7, have been identified to cause Refsum disease"
Review identifies PHYH as one of the two causative genes.
Variants (2)
PHYH c.678+5G>T Pathogenic
splice-region variant
This allele causes substantial in-frame skipping of exons 5 and 6 and is associated with isolated retinitis pigmentosa or mild extraocular disease; plasma phytanic acid may be normal, mildly elevated, or markedly elevated.
Show evidence (2 references)
PMID:38411969 SUPPORT Human Clinical
"In all patients, we observed in-frame skipping of exons 5 and 6 in 31.1% to 88.4% of the amplicons and a smaller proportion (0% to 11.3% of amplicons) skipping exon 6 only."
Patient-derived blood RNA sequencing directly demonstrates the splice effect.
PMID:38411969 SUPPORT Human Clinical
"One patient had isolated retinitis pigmentosa and three had mild extraocular findings. Blood phytanic acid levels were normal in two patients, mildly elevated in one, and markedly high in the fourth."
The four-patient series defines the attenuated phenotype and biochemical variability.
PHYH p.(Val93*) and p.(Asn71Ilefs*23) Pathogenic
nonsense and frameshift variants
One recently reported patient had the novel biallelic nonsense and frameshift alleles p.(Val93*) and p.(Asn71Ilefs*23).
Show evidence (1 reference)
PMID:41290216 SUPPORT Human Clinical
"Molecular genetic testing in P1 revealed two novel pathogenic variants in PHYH (NM_006214.4): p.(Val93*) and p.(Asn71Ilefs*23)."
The case report documents representative nonsense and frameshift PHYH alleles.
PEX7 (Biallelic pathogenic variants)
Gene: PEX7 hgnc:8860 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is PEX7 (hgnc:8860). hgnc:8860 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE variant_origin: GERMLINE
Show evidence (2 references)
ORPHA:773 SUPPORT Other
"PEX7 | peroxisomal biogenesis factor 7 | hgnc:8860 | Disease-causing germline mutation(s) in"
Orphanet lists PEX7 as a disease-causing gene.
PMID:12522768 SUPPORT Human Clinical
"Furthermore, we identified mutations in the PEX7 gene."
Human genetic study identified PEX7 mutations in Refsum disease patients.
💊

Medical Actions

4
Phytanic-acid-restricted diet and fasting avoidance
Action: dietary interventionNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is dietary intervention (NCIT:C15447). NCIT:C15447 is a clinical intervention from the NCI Thesaurus. Ontology label: Dietary Intervention NCIT:C15447
Long-term management restricts phytanic-acid-rich foods, avoids fasting and sudden weight loss, and maintains adequate calories to reduce mobilization of stored phytanic acid.
Mechanism Target:
INHIBITS Plasma and Tissue Phytanic Acid Accumulation — Dietary restriction lowers exogenous phytanic acid input and limits mobilization from adipose stores.
Show evidence (1 reference)
PMID:20301527 SUPPORT Human Clinical
"Dietary restriction of phytanic acid intake helps resolve ichthyosis, sensory neuropathy, and ataxia."
GeneReviews supports diet as a phytanic-acid-lowering disease management strategy.
Show evidence (4 references)
PMID:6170281 SUPPORT Human Clinical
"can be either kept from worsening or reversed by elimination of foods rich in phytanic acid from patients' diets."
Long-term clinical experience supports a specific phytanic-acid-restricted diet.
PMID:20301527 SUPPORT Human Clinical
"A high-calorie diet and avoidance of fasting prevent mobilization of phytanic acid stored in adipose tissue into the plasma."
GeneReviews supports fasting avoidance and adequate calories.
PMID:42145913 SUPPORT Human Clinical
"Implementing dietary interventions to ensure adequate energy, carbohydrates and weight stabilisation resulted in a decrease in circulating PA levels by 47%-84% in the outpatient setting."
The six-patient case series quantifies the benefit of adequate energy, carbohydrate, and weight stabilization.
+ 1 more reference
Plasmapheresis or lipid apheresis for severe acute worsening
Action: PlasmapheresisNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Plasmapheresis (NCIT:C15304). NCIT:C15304 is a clinical intervention from the NCI Thesaurus. NCIT:C15304
Plasma exchange or lipid apheresis is reserved for acute arrhythmias, extreme weakness, severe rapidly worsening disease, or failure of dietary control to lower very high phytanic acid levels.
Mechanism Target:
INHIBITS Plasma and Tissue Phytanic Acid Accumulation — Plasma exchange lowers circulating phytanic acid.
Show evidence (1 reference)
PMID:1716665 SUPPORT Human Clinical
"Lowering the plasma phytanic acid by plasma exchange produced a rapid clinical improvement."
Case series supports rapid clinical improvement after lowering phytanic acid by plasma exchange.
Show evidence (3 references)
PMID:20301527 SUPPORT Human Clinical
"Plasmapheresis or lipid apheresis to decrease phytanic acid levels is used only for acute arrhythmias or extreme weakness."
GeneReviews supports restricted use of plasmapheresis/lipid apheresis for severe manifestations.
PMID:10150979 SUPPORT Human Clinical
"Plasma exchange is indicated in Refsum's disease when there is a worsening clinical condition."
Clinical review supports plasma exchange for worsening disease.
PMID:42161578 SUPPORT Other
"Life-long dietary therapy, along with therapeutic plasma exchange/lipoprotein apheresis during acute decompensations, remains the mainstay of management."
The 2026 expert guidance supports apheresis during acute decompensation.
Nutritional monitoring during long-term dietary therapy
Action: supportive careNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is supportive care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. Ontology label: Supportive Care NCIT:C15747
Periodically assess fat-soluble vitamins, vitamin B12, copper, selenium, and sodium intake during a long-term low-phytanic-acid diet.
Show evidence (1 reference)
PMID:26799636 SUPPORT Human Clinical
"Periodic nutritional screening may be necessary for fat-soluble vitamins, vitamin B12 , copper or selenium."
The nutritional cohort identifies specific monitoring needs during dietary treatment.
Medication and catabolic-trigger avoidance
Action: supportive careNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is supportive care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. Ontology label: Supportive Care NCIT:C15747
Avoid phytanic-acid-rich foods, fasting, sudden weight loss, ibuprofen, and amiodarone; provide high-calorie support during severe illness or surgery.
Show evidence (2 references)
PMID:20301527 SUPPORT Human Clinical
"Food products containing phytanic acid, mostly from ruminants (cow, sheep, goat), some fish and walnuts; fasting and/or sudden weight loss; use of either ibuprofen or amiodarone."
GeneReviews explicitly lists disease-specific agents and circumstances to avoid.
PMID:20301527 SUPPORT Human Clinical
"Hypercaloric parenteral infusions are required during periods of severe illness or postoperatively."
GeneReviews supports catabolic prevention during severe illness and surgery.
🔬

Biochemical Markers

2
Elevated plasma and tissue phytanic acid (Elevated)
Show evidence (2 references)
ORPHA:773 SUPPORT Other
"It is characterized biochemically by accumulation of phytanic acid in plasma and tissues."
Orphanet identifies phytanic acid accumulation as the biochemical hallmark.
PMID:2475586 SUPPORT Human Clinical
"Fourteen patients with heredopathia atactica polyneuritiformis had a plasma phytanic acid level before treatment of 992-6400 mumol/l."
Human clinical study quantifies marked pretreatment plasma phytanic acid elevation.
Exogenous phytanic acid retention (Positive)
Show evidence (2 references)
PMID:4164676 SUPPORT Human Clinical
"establishing phytol in the diet as a potential precursor of phytanic acid."
Tracer study supports dietary phytol as a phytanic acid precursor.
PMID:4164676 SUPPORT Human Clinical
"whereas it persisted at high concentrations in the plasma of the two patients for many days."
Tracer study supports delayed clearance in patients.
🔬

Diagnosis

2
Plasma phytanic acid testing
Plasma phytanic acid measurement is the core biochemical diagnostic test and helps distinguish classic Adult Refsum disease from isolated retinitis pigmentosa and other disorders. Some attenuated PHYH genotypes can have a normal result, so molecular testing remains important when suspicion persists.
Results: Marked elevation strongly supports diagnosis; a normal concentration does not fully exclude attenuated retinal-predominant PHYH disease.
Show evidence (3 references)
PMID:2475586 SUPPORT Human Clinical
"The presence of phytanic acid in tissues and plasma has been considered diagnostic of heredopathia atactica polyneuritiformis (Refsum's disease)"
Human clinical study supports plasma/tissue phytanic acid as diagnostic.
PMID:20301527 SUPPORT Human Clinical
"Adult Refsum disease (ARD) is associated with elevated plasma phytanic acid levels"
GeneReviews supports elevated plasma phytanic acid testing.
PMID:38411969 SUPPORT Human Clinical
"Blood phytanic acid levels were normal in two patients, mildly elevated in one, and markedly high in the fourth."
Four genetically confirmed attenuated cases demonstrate that plasma phytanic acid is not uniformly elevated.
PHYH and PEX7 molecular genetic testing
Molecular testing confirms biallelic pathogenic variants in PHYH or PEX7 and distinguishes PHYH-related disease from PEX7-related disease and other peroxisomal disorders.
genetic testing NCIT:C15709 NCI Thesaurus (NCIT)
Results: Biallelic pathogenic variants in PHYH or PEX7 establish the molecular diagnosis.
Show evidence (2 references)
PMID:20301527 SUPPORT Human Clinical
"The diagnosis of ARD is established in a proband with suggestive clinical and biochemical findings by identification of biallelic pathogenic variants in either PHYH or PEX7 on molecular genetic testing."
GeneReviews states the diagnostic role of PHYH/PEX7 molecular testing.
PMID:38411969 SUPPORT Human Clinical
"One patient had isolated retinitis pigmentosa and three had mild extraocular findings. Blood phytanic acid levels were normal in two patients, mildly elevated in one, and markedly high in the fourth."
The attenuated series supports molecular testing when retinal disease is suggestive despite a normal biochemical result.
📈

Progression

1
Late childhood to adult-onset multisystem disease
Age: Childhood to adulthood
Symptoms can begin in late childhood or later, with progressive sensory, neurologic, dermatologic, skeletal, and cardiac involvement.
Show evidence (2 references)
ORPHA:773 SUPPORT Other
"Age of onset: Childhood"
Orphanet includes childhood among onset categories.
PMID:20301527 SUPPORT Human Clinical
"Onset of symptoms ranges from age seven months to older than age 50 years."
GeneReviews supports broad onset from infancy through adulthood.
📊

Prevalence

1
Europe
Point Prevalence 0.1–0.9 per 100,000 1–9 per 1,000,000
Orphanet reports European point prevalence in the 1-9 per million range.
Show evidence (1 reference)
ORPHA:773 SUPPORT Other
"1-9 / 1 000 000 | Europe | Point prevalence | PMID:20301527,EXPERT"
Orphanet provides the European point-prevalence estimate.
🔀

Differential Diagnoses

1

Conditions with similar clinical presentations that must be differentiated from Adult Refsum Disease:

Alpha-methylacyl-CoA racemase deficiency
Overlapping Features AMACR deficiency can resemble an atypical Refsum phenotype with retinal and neurologic disease but may have low plasma phytanic acid; biochemical profiling and molecular testing distinguish it from PHYH- or PEX7-related disease.
Show evidence (1 reference)
PMID:11948235 SUPPORT Other
"Other atypical cases with low-plasma phytanic acid may be caused by alpha-methylacyl-CoA racemase deficiency."
The review directly identifies AMACR deficiency as a differential in low-phytanic-acid atypical cases.
📊

Related Datasets

1
Fibroblast-specific genome-scale modelling predicts an imbalance in amino acid metabolism in Refsum disease geo:GSE138379
In this study, we reconstructed a fibroblast-specific genome-scale model based on the recently published, FAD-curated model, based on Recon3D reconstruction. To constrain the model we used transcriptomics, and proteomics data, which we obtained from healthy controls and Refsum disease patient fibroblasts incubated with phytol, a precursor of phytanic acid. Using this model, we investigated the metabolic phenotype of Refsum disease at the genome-scale, and we studied the effect of phytanic acid on cell metabolism. We identified 20 metabolites that were predicted to discriminate between Healthy and Refsum disease patients, several of which with a link to amino acid metabolism.
human BULK RNA SEQ n=96
PMID:32160399
Identified by GEO DataSets index search for Adult Refsum Disease (scripts/discover_datasets.py); accession and metadata verified against NCBI E-utilities on 2026-08-01. Title, sample count, and organism are GEO's own values.
{ }

Source YAML

click to show 
name: Adult Refsum Disease
creation_date: "2026-05-07T03:23:42Z"
category: Genetic
parents:
- Peroxisomal Disease
- Hereditary Neuropathy
synonyms:
- Classic Refsum disease
- HMSN 4
- Hereditary motor and sensory neuropathy type 4
- Heredopathia atactica polyneuritiformis
- Phytanic-CoA hydroxylase deficiency
description: >-
  Adult Refsum disease is an autosomal recessive peroxisomal metabolic disorder
  caused by biallelic pathogenic variants in PHYH (type 1) or, less commonly,
  PEX7 (type 2).
  Impaired peroxisomal phytanic acid alpha-oxidation causes phytanic acid
  accumulation in plasma and tissues, leading to retinitis pigmentosa,
  anosmia, peripheral neuropathy, ataxia, hearing impairment, ichthyosis,
  skeletal findings, and potentially severe cardiomyopathy or arrhythmia.
disease_term:
  preferred_term: adult Refsum disease
  term:
    id: MONDO:0009958
    label: adult Refsum disease
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0009958
      label: adult Refsum disease
    mapping_predicate: skos:narrowMatch
    mapping_source: MONDO
    mapping_justification: >-
      Recorded as narrowMatch, not exactMatch: the MONDO term is labelled and
      defined clinically ("anosmia, early-onset retinitis pigmentosa...") but is
      axiomatized as `is_a MONDO:0100258` phytanoyl-CoA hydroxylase deficiency,
      which restricts it to PHYH-caused disease. This entry covers both PHYH
      (type 1, >90%) and PEX7 (type 2, <10%) disease per PMID:20301527, so it is
      broader than the MONDO class as currently axiomatized. MONDO's own
      MONDO:0100307 "adult Refsum disease due to PEX7 defect" is defined as "an
      adult Refsum disease", which cannot hold alongside that is_a edge; MONDO
      avoids the contradiction only by not asserting it. Retained as the entry's
      disease_term because it is the closest available grounding.
    tracked_issues:
    - url: https://github.com/monarch-initiative/mondo/issues/10377
      title: Request for new term [Adult Refsum Disease] PARENT CONCEPT
      tracked_issue_role: ontology_term_request
      tracked_issue_status: OPEN
      notes: >-
        Requests exactly this fix - rename MONDO:0009958 to a PHYH-specific
        label and create a new parent term for adult Refsum disease over the
        PHYH and PEX7 subtypes, citing the same GeneReviews source this entry
        cites. If it lands, reground this entry to the new parent term and
        reground the "Type 1" subtype from MONDO:0100258 to the renamed
        MONDO:0009958.
references:
- reference: ORPHA:773
  title: Adult Refsum disease
  found_in:
  - Adult_Refsum_Disease-deep-research-fallback.md
  findings:
  - statement: >-
      Orphanet defines Adult Refsum disease as a metabolic disease with
      anosmia, cataract, early-onset retinitis pigmentosa, neurologic
      manifestations, and phytanic acid accumulation.
    supporting_text: >-
      A metabolic disease characterized by anosmia, cataract, early-onset
      retinitis pigmentosa and possible neurological manifestations
- reference: PMID:20301527
  title: Adult Refsum Disease.
  tags:
  - GeneReviews
  found_in:
  - Adult_Refsum_Disease-deep-research-fallback.md
  findings:
  - statement: >-
      GeneReviews summarizes the clinical phenotype, diagnostic criteria, diet,
      plasmapheresis/lipid apheresis, and autosomal recessive inheritance of
      Adult Refsum disease.
    supporting_text: >-
      Adult Refsum disease (ARD) is associated with elevated plasma phytanic
      acid levels
- reference: PMID:14974078
  title: "Molecular basis of Refsum disease: sequence variations in phytanoyl-CoA hydroxylase (PHYH) and the PTS2 receptor (PEX7)."
  found_in:
  - Adult_Refsum_Disease-deep-research-fallback.md
  findings:
  - statement: >-
      Review evidence supports Refsum disease as genetically heterogeneous,
      caused by PHYH or PEX7 variants disrupting peroxisomal phytanic acid
      alpha-oxidation.
    supporting_text: >-
      Refsum disease is genetically heterogeneous; two genes, PHYH (also named
      PAHX) and PEX7, have been identified to cause Refsum disease
- reference: PMID:12522768
  title: Identification of PEX7 as the second gene involved in Refsum disease.
  found_in:
  - Adult_Refsum_Disease-deep-research-fallback.md
  findings:
  - statement: >-
      PEX7 variants can cause a milder Refsum phenotype through impaired
      peroxisomal import of PTS2-containing enzymes.
    supporting_text: >-
      Our data show that mutations in the PEX7 gene may result in a broad
      clinical spectrum ranging from severe rhizomelic chondrodysplasia
      punctata to relatively mild RD
- reference: PMID:16186124
  title: Structure of human phytanoyl-CoA 2-hydroxylase identifies molecular mechanisms of Refsum disease.
  found_in:
  - Adult_Refsum_Disease-deep-research-fallback.md
  findings:
  - statement: >-
      Structural enzymology supports PAHX/PHYH mutations as disrupting the
      peroxisomal enzyme that catalyzes the initial alpha-oxidation step.
    supporting_text: >-
      mutations in phytanoyl-CoA 2-hydroxylase (PAHX), an Fe(II) and
      2-oxoglutarate (2OG)-dependent oxygenase that catalyzes the initial
      alpha-oxidation step
- reference: PMID:4164676
  title: Studies on the metabolic error in Refsum's disease.
  found_in:
  - Adult_Refsum_Disease-deep-research-fallback.md
  findings:
  - statement: >-
      Classic metabolic tracer work supports exogenous phytanic acid origin and
      a block in phytanic acid degradation.
    supporting_text: >-
      patients with Refsum's disease have a relative block in the degradation
      of phytanic acid
- reference: PMID:2475586
  title: The significance of plasma phytanic acid levels in adults.
  found_in:
  - Adult_Refsum_Disease-deep-research-fallback.md
  findings:
  - statement: >-
      Plasma phytanic acid measurement distinguishes classic Refsum disease
      from normal controls and many retinitis pigmentosa cases.
    supporting_text: >-
      Fourteen patients with heredopathia atactica polyneuritiformis had a
      plasma phytanic acid level before treatment of 992-6400 mumol/l.
- reference: PMID:6170281
  title: "Heredopathia atactica polyneuritiformis phytanic-acid storage disease, Refsum's disease:\" a biochemically well-defined disease with a specific dietary treatment."
  found_in:
  - Adult_Refsum_Disease-deep-research-fallback.md
  findings:
  - statement: >-
      Dietary elimination of phytanic-acid-rich foods is a disease-specific
      treatment that can improve or stabilize manifestations.
    supporting_text: >-
      can be either kept from worsening or reversed by elimination of foods rich
      in phytanic acid from patients' diets.
- reference: PMID:1716665
  title: "Plasma exchange in the treatment of Refsum's disease (heredopathia atactica polyneuritiformis)."
  found_in:
  - Adult_Refsum_Disease-deep-research-fallback.md
  findings:
  - statement: >-
      Plasma exchange can rapidly lower phytanic acid and improve acute or
      severe worsening disease.
    supporting_text: >-
      Lowering the plasma phytanic acid by plasma exchange produced a rapid
      clinical improvement.
- reference: PMID:10150979
  title: Plasma exchange for Refsum's disease.
  found_in:
  - Adult_Refsum_Disease-deep-research-fallback.md
  findings:
  - statement: >-
      Additional plasma-exchange clinical evidence supports use during worsening
      disease or failure of dietary control.
    supporting_text: >-
      Plasma exchange is indicated in Refsum's disease when there is a worsening
      clinical condition.
- reference: PMID:11589979
  title: The site of the hearing loss in Refsum's disease.
  found_in:
  - Adult_Refsum_Disease-deep-research-fallback.md
  findings:
  - statement: >-
      Case evidence supports hearing loss as part of the Refsum phenotype and
      suggests auditory neuropathy in some cases.
    supporting_text: >-
      Refsum's disease is a disorder of lipid metabolism with pigmentary
      retinopathy, demyelinating neuropathy, ataxia, and hearing loss.
- reference: PMID:11948235
  title: "Refsum's disease: a peroxisomal disorder affecting phytanic acid alpha-oxidation."
  findings:
  - statement: >-
      Low-phytanic-acid atypical cases may instead reflect
      alpha-methylacyl-CoA racemase deficiency, an important biochemical and
      molecular differential diagnosis.
    supporting_text: >-
      Other atypical cases with low-plasma phytanic acid may be caused by
      alpha-methylacyl-CoA racemase deficiency.
- reference: PMID:17325280
  title: Phenotype of adult Refsum disease due to a defect in peroxin 7.
  findings:
  - statement: >-
      Adult Refsum disease can be divided into PHYH-related type 1 and
      PEX7-related type 2, whose reported clinical phenotype can be
      indistinguishable from classic disease.
    supporting_text: >-
      Hence, we propose the subdivision of ARD into type 1 and type 2,
      depending on which gene is defective.
- reference: PMID:38411969
  title: PHYH c.678+5G>T Leads to In-Frame Exon Skipping and Is Associated With Attenuated Refsum Disease.
  findings:
  - statement: >-
      The PHYH c.678+5G>T splice variant can produce an attenuated presentation
      with isolated retinitis pigmentosa or mild extraocular findings and
      normal-to-markedly-elevated plasma phytanic acid.
    supporting_text: >-
      One patient had isolated retinitis pigmentosa and three had mild
      extraocular findings. Blood phytanic acid levels were normal in two
      patients, mildly elevated in one, and markedly high in the fourth.
- reference: PMID:41290216
  title: Identification of novel pathogenic variants in the PHYH gene and extending the phenotypic range in Refsum disease.
  findings:
  - statement: >-
      Two recent retinal-clinic cases identified novel biallelic PHYH variants and
      extended the reported ocular spectrum to macular dystrophy.
    supporting_text: >-
      We document for the first time an association between macular dystrophy
      and Refsum disease.
- reference: PMID:36812958
  title: "Disruption of mitochondrial bioenergetics and calcium homeostasis by phytanic acid in the heart: Potential relevance for the cardiomyopathy in Refsum disease."
  findings:
  - statement: >-
      In vitro cardiac experiments support phytanic-acid-induced disruption of
      mitochondrial respiration, ATP synthesis, membrane potential, calcium
      retention, and cardiomyocyte viability as a provisional cardiac mechanism.
    supporting_text: >-
      The present data indicate that Phyt, at concentrations found in the plasma
      of patients with Refsum disease, disrupts by multiple mechanisms
      mitochondrial bioenergetics and Ca2+ homeostasis
- reference: PMID:32904930
  title: Improved electroretinographic responses following dietary intervention in a patient with Refsum disease.
  findings:
  - statement: >-
      A molecularly and biochemically confirmed case showed improved
      electroretinographic responses after starting a phytanic-acid-restricted diet.
    supporting_text: >-
      His post-intervention 30 Hz flicker electroretinogram demonstrated
      significantly improved waveform amplitudes and implicit times, suggesting
      improved retinal function.
- reference: PMID:26799636
  title: "Safety of long-term restrictive diets for peroxisomal disorders: vitamin and trace element status of patients treated for Adult Refsum Disease."
  findings:
  - statement: >-
      Long-term low-phytanic-acid diets can be managed without routine
      supplementation, but periodic nutritional screening is warranted.
    supporting_text: >-
      Periodic nutritional screening may be necessary for fat-soluble vitamins,
      vitamin B12 , copper or selenium.
- reference: PMID:42145913
  title: "Adult Refsum Disease: Case Series of Reducing Circulating Phytanic Acid Levels With Dietary Interventions."
  findings:
  - statement: >-
      Recent case-series evidence shows that phytanic-acid restriction must be
      paired with adequate energy and carbohydrate intake and weight stability.
    supporting_text: >-
      These cases demonstrate that PA restriction, and weight and carbohydrate
      management have integral roles in ensuring metabolic stability in ARD.
- reference: PMID:42161578
  title: "Diagnosis and Metabolic Management of Adult Refsum Disease: Guidance From the Medical and Scientific Committee of Global DARE (Defeat Adult Refsum Everywhere)."
  findings:
  - statement: >-
      The 2026 GRADE-aligned expert guidance identifies lifelong dietary therapy
      as the mainstay and reserves therapeutic plasma exchange or lipoprotein
      apheresis for acute decompensation.
    supporting_text: >-
      Life-long dietary therapy, along with therapeutic plasma
      exchange/lipoprotein apheresis during acute decompensations, remains the
      mainstay of management.
has_subtypes:
- name: Type 1
  display_name: Type 1 (PHYH-related)
  classification: molecular_etiology
  subtype_term:
    preferred_term: phytanoyl-CoA hydroxylase deficiency
    term:
      id: MONDO:0100258
      label: phytanoyl-CoA hydroxylase deficiency
  genes:
  - preferred_term: PHYH
    term:
      id: hgnc:8940
      label: PHYH
  description: >-
    The usual form of Adult Refsum disease, caused by biallelic PHYH variants
    and deficient phytanoyl-CoA 2-hydroxylase activity.
  evidence:
  - reference: PMID:17325280
    reference_title: Phenotype of adult Refsum disease due to a defect in peroxin 7.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This usually results from a PHYH gene defect, although some cases have
      been found to carry a PEX7 defect.
    explanation: The clinical report distinguishes the usual PHYH-related form from PEX7-related disease.
- name: Type 2
  display_name: Type 2 (PEX7-related)
  classification: molecular_etiology
  subtype_term:
    preferred_term: adult Refsum disease due to PEX7 defect
    term:
      id: MONDO:0100307
      label: adult Refsum disease due to PEX7 defect
  genes:
  - preferred_term: PEX7
    term:
      id: hgnc:8860
      label: PEX7
  description: >-
    A less common molecular form caused by biallelic PEX7 variants; the reported
    Adult Refsum phenotype can be clinically indistinguishable from type 1.
  evidence:
  - reference: PMID:17325280
    reference_title: Phenotype of adult Refsum disease due to a defect in peroxin 7.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We describe the phenotype of such a patient, indistinguishable from that
      of classic ARD.
    explanation: The PEX7 case supports type 2 as a molecular subtype with the classic Adult Refsum phenotype.
prevalence:
- population: Europe
  measure_type: POINT_PREVALENCE
  prevalence_class: BAND_1_9_PER_1000000
  rate_low: 0.1
  rate_high: 0.9
  percentage: 1-9 per 1,000,000
  notes: Orphanet reports European point prevalence in the 1-9 per million range.
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "1-9 / 1 000 000 | Europe | Point prevalence | PMID:20301527,EXPERT"
    explanation: Orphanet provides the European point-prevalence estimate.
progression:
- phase: Late childhood to adult-onset multisystem disease
  age_range: Childhood to adulthood
  notes: >-
    Symptoms can begin in late childhood or later, with progressive sensory,
    neurologic, dermatologic, skeletal, and cardiac involvement.
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Age of onset: Childhood"
    explanation: Orphanet includes childhood among onset categories.
  - reference: PMID:20301527
    reference_title: Adult Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Onset of symptoms ranges from age seven months to older than age 50 years."
    explanation: GeneReviews supports broad onset from infancy through adulthood.
inheritance:
- name: Autosomal recessive inheritance
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    Adult Refsum disease is inherited in an autosomal recessive manner and is
    caused by biallelic pathogenic variants in PHYH or PEX7.
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Autosomal recessive"
    explanation: Orphanet lists autosomal recessive inheritance.
  - reference: PMID:20301527
    reference_title: Adult Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ARD is inherited in an autosomal recessive manner."
    explanation: GeneReviews states autosomal recessive inheritance.
  - reference: PMID:20301527
    reference_title: Adult Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      If both parents are known to be heterozygous for a PHYH or PEX7
      pathogenic variant, each sib of an affected individual has at conception
      a 25% chance of being affected, a 50% chance of being an asymptomatic
      carrier, and a 25% chance of being unaffected and not a carrier.
    explanation: GeneReviews provides the recurrence risks for autosomal recessive genetic counseling.
genetic:
- name: PHYH
  subtype: Type 1
  association: Biallelic pathogenic variants
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  presence: Positive
  gene_term:
    preferred_term: PHYH
    term:
      id: hgnc:8940
      label: PHYH
  notes: >-
    PHYH encodes phytanoyl-CoA 2-hydroxylase, the peroxisomal enzyme that
    initiates alpha-oxidation of phytanic acid. Pathogenic alleles include
    nonsense, frameshift, missense, and splice-altering variants; residual
    in-frame transcript can produce an attenuated retinal-predominant phenotype.
  variants:
  - name: PHYH c.678+5G>T
    type: splice-region variant
    clinical_significance: PATHOGENIC
    description: >-
      This allele causes substantial in-frame skipping of exons 5 and 6 and is
      associated with isolated retinitis pigmentosa or mild extraocular disease;
      plasma phytanic acid may be normal, mildly elevated, or markedly elevated.
    evidence:
    - reference: PMID:38411969
      reference_title: PHYH c.678+5G>T Leads to In-Frame Exon Skipping and Is Associated With Attenuated Refsum Disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        In all patients, we observed in-frame skipping of exons 5 and 6 in 31.1%
        to 88.4% of the amplicons and a smaller proportion (0% to 11.3% of
        amplicons) skipping exon 6 only.
      explanation: Patient-derived blood RNA sequencing directly demonstrates the splice effect.
    - reference: PMID:38411969
      reference_title: PHYH c.678+5G>T Leads to In-Frame Exon Skipping and Is Associated With Attenuated Refsum Disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        One patient had isolated retinitis pigmentosa and three had mild
        extraocular findings. Blood phytanic acid levels were normal in two
        patients, mildly elevated in one, and markedly high in the fourth.
      explanation: The four-patient series defines the attenuated phenotype and biochemical variability.
  - name: PHYH p.(Val93*) and p.(Asn71Ilefs*23)
    type: nonsense and frameshift variants
    clinical_significance: PATHOGENIC
    description: >-
      One recently reported patient had the novel biallelic nonsense and
      frameshift alleles p.(Val93*) and p.(Asn71Ilefs*23).
    evidence:
    - reference: PMID:41290216
      reference_title: Identification of novel pathogenic variants in the PHYH gene and extending the phenotypic range in Refsum disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Molecular genetic testing in P1 revealed two novel pathogenic variants
        in PHYH (NM_006214.4): p.(Val93*) and p.(Asn71Ilefs*23).
      explanation: The case report documents representative nonsense and frameshift PHYH alleles.
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "PHYH | phytanoyl-CoA 2-hydroxylase | hgnc:8940 | Disease-causing germline mutation(s) in"
    explanation: Orphanet lists PHYH as a disease-causing gene.
  - reference: PMID:14974078
    reference_title: 'Molecular basis of Refsum disease: sequence variations in phytanoyl-CoA hydroxylase (PHYH) and the PTS2 receptor (PEX7).'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "two genes, PHYH (also named PAHX) and PEX7, have been identified to cause Refsum disease"
    explanation: Review identifies PHYH as one of the two causative genes.
- name: PEX7
  subtype: Type 2
  association: Biallelic pathogenic variants
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  presence: Positive
  gene_term:
    preferred_term: PEX7
    term:
      id: hgnc:8860
      label: PEX7
  notes: >-
    PEX7 encodes the PTS2 receptor required for peroxisomal matrix import of
    PTS2-containing proteins, including enzymes required for phytanic acid
    alpha-oxidation.
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "PEX7 | peroxisomal biogenesis factor 7 | hgnc:8860 | Disease-causing germline mutation(s) in"
    explanation: Orphanet lists PEX7 as a disease-causing gene.
  - reference: PMID:12522768
    reference_title: Identification of PEX7 as the second gene involved in Refsum disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Furthermore, we identified mutations in the PEX7 gene."
    explanation: Human genetic study identified PEX7 mutations in Refsum disease patients.
pathophysiology:
- name: PHYH Phytanoyl-CoA Hydroxylase Deficiency
  conforms_to: "peroxisomal_metabolic_failure#Peroxisomal Biogenesis or Enzyme Defect"
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Biallelic PHYH variants impair phytanoyl-CoA 2-hydroxylase, the peroxisomal
    enzyme catalyzing the first alpha-oxidation step in phytanic acid degradation.
  genes:
  - preferred_term: PHYH
    term:
      id: hgnc:8940
      label: PHYH
  locations:
  - preferred_term: peroxisome
    term:
      id: GO:0005777
      label: peroxisome
  molecular_functions:
  - preferred_term: phytanoyl-CoA dioxygenase activity
    term:
      id: GO:0048244
      label: phytanoyl-CoA dioxygenase activity
  evidence:
  - reference: PMID:16186124
    reference_title: Structure of human phytanoyl-CoA 2-hydroxylase identifies molecular mechanisms of Refsum disease.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "mutations in phytanoyl-CoA 2-hydroxylase (PAHX), an Fe(II) and 2-oxoglutarate (2OG)-dependent oxygenase that catalyzes the initial alpha-oxidation step in the degradation of phytenic acid in peroxisomes."
    explanation: Structural enzymology identifies the affected enzyme and reaction.
  downstream:
  - target: Phytanic Acid Alpha-Oxidation Defect
    causal_link_type: DIRECT
    description: Loss of PHYH activity directly impairs the first alpha-oxidation step.
    evidence:
    - reference: PMID:16186124
      reference_title: Structure of human phytanoyl-CoA 2-hydroxylase identifies molecular mechanisms of Refsum disease.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "mutations in phytanoyl-CoA 2-hydroxylase (PAHX), an Fe(II) and 2-oxoglutarate (2OG)-dependent oxygenase that catalyzes the initial alpha-oxidation step in the degradation of phytenic acid in peroxisomes."
      explanation: The paper directly assigns PHYH to the affected alpha-oxidation reaction.
- name: PEX7 Peroxisomal Matrix Import Defect
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Biallelic PEX7 variants impair import of PTS2-containing proteins into the
    peroxisomal matrix, including machinery required for phytanic acid alpha-oxidation.
  genes:
  - preferred_term: PEX7
    term:
      id: hgnc:8860
      label: PEX7
  locations:
  - preferred_term: peroxisome
    term:
      id: GO:0005777
      label: peroxisome
  biological_processes:
  - preferred_term: protein import into peroxisome matrix
    term:
      id: GO:0016558
      label: protein import into peroxisome matrix
    modifier: DECREASED
  evidence:
  - reference: PMID:12522768
    reference_title: Identification of PEX7 as the second gene involved in Refsum disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "PEX7 gene, which codes for the peroxin 7 receptor protein required for peroxisomal import of proteins containing a peroxisomal targeting signal type 2."
    explanation: The patient genetic study states the relevant PEX7 import function.
  downstream:
  - target: Phytanic Acid Alpha-Oxidation Defect
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - impaired PTS2-dependent peroxisomal enzyme import
    description: PEX7 deficiency impairs the peroxisomal machinery needed for alpha-oxidation.
    evidence:
    - reference: PMID:12522768
      reference_title: Identification of PEX7 as the second gene involved in Refsum disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Biochemical analyses of the patients with RD revealed defects not only in phytanic acid alpha-oxidation but also in plasmalogen synthesis and peroxisomal thiolase."
      explanation: PEX7-related patient samples directly showed an alpha-oxidation defect.
  - target: PEX7-Related Plasmalogen Synthesis Defect
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - impaired PTS2-dependent peroxisomal enzyme import
    description: PEX7 deficiency also impairs plasmalogen synthesis in type 2 disease.
    evidence:
    - reference: PMID:12522768
      reference_title: Identification of PEX7 as the second gene involved in Refsum disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Biochemical analyses of the patients with RD revealed defects not only in phytanic acid alpha-oxidation but also in plasmalogen synthesis and peroxisomal thiolase."
      explanation: Biochemical analysis of PEX7-related patients directly supports the additional plasmalogen defect.
- name: PEX7-Related Plasmalogen Synthesis Defect
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    PEX7-related type 2 disease includes impaired plasmalogen synthesis in
    addition to the shared phytanic acid alpha-oxidation defect.
  genes:
  - preferred_term: PEX7
    term:
      id: hgnc:8860
      label: PEX7
  evidence:
  - reference: PMID:12522768
    reference_title: Identification of PEX7 as the second gene involved in Refsum disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Biochemical analyses of the patients with RD revealed defects not only in phytanic acid alpha-oxidation but also in plasmalogen synthesis and peroxisomal thiolase."
    explanation: PEX7-related patient biochemical data distinguish this additional type 2 defect from PHYH-related type 1 disease.
- name: Phytanic Acid Alpha-Oxidation Defect
  conforms_to: "peroxisomal_metabolic_failure#Failure of Peroxisomal Fatty-Acid Oxidation and Ether-Lipid Synthesis"
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: Defective peroxisomal alpha-oxidation prevents normal degradation of exogenous phytanic acid.
  biological_processes:
  - preferred_term: fatty acid alpha-oxidation
    term:
      id: GO:0001561
      label: fatty acid alpha-oxidation
    modifier: DECREASED
  evidence:
  - reference: PMID:4164676
    reference_title: Studies on the metabolic error in Refsum's disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "patients with Refsum's disease have a relative block in the degradation of phytanic acid and possibly other similar branched-chain compounds."
    explanation: Human tracer evidence establishes impaired phytanic acid degradation.
  downstream:
  - target: Plasma and Tissue Phytanic Acid Accumulation
    causal_link_type: DIRECT
    description: Reduced degradation causes phytanic acid retention and accumulation.
    evidence:
    - reference: PMID:4164676
      reference_title: Studies on the metabolic error in Refsum's disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We conclude that the phytanic acid accumulating in Refsum's disease is primarily of exogenous origin and that patients with Refsum's disease have a relative block in the degradation of phytanic acid and possibly other similar branched-chain compounds."
      explanation: The tracer study directly links the degradation block to accumulation.
- name: Plasma and Tissue Phytanic Acid Accumulation
  conforms_to: "peroxisomal_metabolic_failure#Toxic Fatty-Acid Accumulation with Ether-Lipid Deficiency"
  biological_scale: ORGANISM
  mechanism_confidence: ESTABLISHED
  description: Exogenous phytanic acid accumulates in plasma and tissues because alpha-oxidation is impaired.
  chemical_entities:
  - preferred_term: phytanic acid
    term:
      id: CHEBI:16285
      label: phytanic acid
    modifier: INCREASED
  evidence:
  - reference: PMID:20301527
    reference_title: Adult Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Adult Refsum disease (ARD) is associated with elevated plasma phytanic acid levels"
    explanation: GeneReviews identifies elevated phytanic acid as the central biochemical feature.
  - reference: PMID:4164676
    reference_title: Studies on the metabolic error in Refsum's disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This labeled phytanic acid had disappeared almost completely from the plasma of the seven control subjects by 24 to 48 hours, whereas it persisted at high concentrations in the plasma of the two patients for many days."
    explanation: Human tracer data demonstrate prolonged retention.
  downstream:
  - target: Elevated plasma and tissue phytanic acid
    causal_link_type: DIRECT
    description: Accumulation produces the defining biochemical abnormality.
    evidence:
    - reference: ORPHA:773
      reference_title: Adult Refsum disease
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "It is characterized biochemically by accumulation of phytanic acid in plasma and tissues."
      explanation: Orphanet directly supports the biochemical manifestation.
  - target: Exogenous phytanic acid retention
    causal_link_type: DIRECT
    description: Dietary phytanic acid persists because its degradation is blocked.
    evidence:
    - reference: PMID:4164676
      reference_title: Studies on the metabolic error in Refsum's disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "This labeled phytanic acid had disappeared almost completely from the plasma of the seven control subjects by 24 to 48 hours, whereas it persisted at high concentrations in the plasma of the two patients for many days."
      explanation: The tracer experiment directly supports retention.
  - target: Retinal Photoreceptor Dysfunction
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Retinal disease co-occurs with phytanic acid elevation, but the intervening human mechanism is unresolved.
    evidence:
    - reference: PMID:20301527
      reference_title: Adult Refsum Disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Adult Refsum disease (ARD) is associated with elevated plasma phytanic acid levels, late childhood-onset (or later) retinitis pigmentosa"
      explanation: GeneReviews supports disease-level association, not a direct tissue-causal intermediate.
  - target: Olfactory Dysfunction
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Anosmia is associated with the storage disorder, but its tissue mechanism is unresolved.
    evidence:
    - reference: PMID:20301527
      reference_title: Adult Refsum Disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "variable combinations of anosmia, polyneuropathy, deafness, ataxia, and ichthyosis."
      explanation: GeneReviews supports association rather than direct causality.
  - target: Peripheral Nerve Dysfunction
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Polyneuropathy is associated with the storage disorder, but the intervening mechanism is unresolved.
    evidence:
    - reference: PMID:20301527
      reference_title: Adult Refsum Disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "variable combinations of anosmia, polyneuropathy, deafness, ataxia, and ichthyosis."
      explanation: GeneReviews supports association rather than direct causality.
  - target: Cerebellar Dysfunction
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Ataxia is associated with the storage disorder, but the intervening mechanism is unresolved.
    evidence:
    - reference: PMID:20301527
      reference_title: Adult Refsum Disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "variable combinations of anosmia, polyneuropathy, deafness, ataxia, and ichthyosis."
      explanation: GeneReviews supports association rather than direct causality.
  - target: Auditory Dysfunction
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Hearing loss is associated with the storage disorder, but the intervening mechanism is unresolved.
    evidence:
    - reference: PMID:11589979
      reference_title: The site of the hearing loss in Refsum's disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Refsum's disease is a disorder of lipid metabolism with pigmentary retinopathy, demyelinating neuropathy, ataxia, and hearing loss."
      explanation: The case evidence supports association but does not prove the upstream causal path.
  - target: Cardiac Mitochondrial Dysfunction
    causal_link_type: DIRECT
    description: Patient-range phytanic acid concentrations disrupt cardiac mitochondrial bioenergetics in vitro.
    evidence:
    - reference: PMID:36812958
      reference_title: 'Disruption of mitochondrial bioenergetics and calcium homeostasis by phytanic acid in the heart: Potential relevance for the cardiomyopathy in Refsum disease.'
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "The present data indicate that Phyt, at concentrations found in the plasma of patients with Refsum disease, disrupts by multiple mechanisms mitochondrial bioenergetics and Ca2+ homeostasis"
      explanation: Rat-heart mitochondrial and H9C2-cell experiments directly support phytanic-acid toxicity.
  - target: Cutaneous Dysfunction
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Ichthyosis is associated with phytanic acid elevation, but the intervening skin mechanism is unresolved.
    evidence:
    - reference: PMID:20301527
      reference_title: Adult Refsum Disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Dietary restriction of phytanic acid intake helps resolve ichthyosis, sensory neuropathy, and ataxia."
      explanation: Treatment response supports a relationship without identifying the skin intermediate.
  - target: Distal Limb Skeletal Abnormality
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Skeletal findings are part of the syndrome, but their relationship to phytanic acid accumulation is unresolved.
    evidence:
    - reference: ORPHA:773
      reference_title: Adult Refsum disease
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Other features can be deafness, ichthyosis, skeletal abnormalities, and cardiac arrhythmia."
      explanation: Orphanet supports disease association, not a direct causal mechanism.
  - target: Renal Involvement
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Renal insufficiency is occasionally reported, but its mechanism and attribution are uncertain.
    evidence:
    - reference: ORPHA:773
      reference_title: Adult Refsum disease
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0000083 | Renal insufficiency | Occasional (29-5%)"
      explanation: Orphanet supports an occasional association only.
- name: Retinal Photoreceptor Dysfunction
  biological_scale: TISSUE
  mechanism_confidence: PROVISIONAL
  description: Retinal degeneration causes rod-cone dysfunction, night blindness, and progressive visual loss.
  evidence:
  - reference: PMID:20301527
    reference_title: Adult Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "late childhood-onset (or later) retinitis pigmentosa"
    explanation: GeneReviews establishes retinal degeneration as a core manifestation.
  - reference: PMID:32904930
    reference_title: Improved electroretinographic responses following dietary intervention in a patient with Refsum disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "His post-intervention 30 Hz flicker electroretinogram demonstrated significantly improved waveform amplitudes and implicit times, suggesting improved retinal function."
    explanation: A confirmed case demonstrated objective retinal functional improvement after dietary treatment.
  downstream:
  - target: Rod-cone dystrophy
    causal_link_type: DIRECT
    description: The retinal dysfunction manifests as retinitis pigmentosa/rod-cone dystrophy.
    evidence:
    - reference: PMID:20301527
      reference_title: Adult Refsum Disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "late childhood-onset (or later) retinitis pigmentosa"
      explanation: GeneReviews directly supports the retinal phenotype.
  - target: Macular dystrophy
    causal_link_type: DIRECT
    description: A recent case extends the retinal phenotype to macular dystrophy.
    evidence:
    - reference: PMID:41290216
      reference_title: Identification of novel pathogenic variants in the PHYH gene and extending the phenotypic range in Refsum disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We document for the first time an association between macular dystrophy and Refsum disease."
      explanation: The case report explicitly expands the ocular phenotype to macular dystrophy.
  - target: Cataract
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Cataract can accompany the retinal phenotype.
    evidence:
    - reference: ORPHA:773
      reference_title: Adult Refsum disease
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "anosmia, cataract, early-onset retinitis pigmentosa"
      explanation: Orphanet supports co-occurrence but not a causal link from photoreceptor dysfunction.
  - target: Miosis
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Miosis is an associated ocular feature.
    evidence:
    - reference: ORPHA:773
      reference_title: Adult Refsum disease
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0000616 | Miosis | Frequent (79-30%)"
      explanation: Orphanet supports disease association, not a direct retinal mechanism.
  - target: Nyctalopia
    causal_link_type: DIRECT
    description: Rod dysfunction manifests as night blindness.
    evidence:
    - reference: ORPHA:773
      reference_title: Adult Refsum disease
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0000662 | Nyctalopia | Frequent (79-30%)"
      explanation: Orphanet directly supports nyctalopia as an ocular manifestation.
- name: Olfactory Dysfunction
  biological_scale: TISSUE
  mechanism_confidence: PROVISIONAL
  description: Olfactory-system dysfunction manifests as anosmia.
  evidence:
  - reference: PMID:20301527
    reference_title: Adult Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "variable combinations of anosmia, polyneuropathy, deafness, ataxia, and ichthyosis."
    explanation: GeneReviews establishes anosmia as a core manifestation.
  downstream:
  - target: Anosmia
    causal_link_type: DIRECT
    description: Olfactory dysfunction manifests clinically as anosmia.
    evidence:
    - reference: ORPHA:773
      reference_title: Adult Refsum disease
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0000458 | Anosmia | Very frequent (99-80%)"
      explanation: Orphanet directly supports anosmia.
- name: Peripheral Nerve Dysfunction
  biological_scale: TISSUE
  mechanism_confidence: PROVISIONAL
  description: Peripheral nerve dysfunction produces chronic polyneuropathy.
  evidence:
  - reference: PMID:20301527
    reference_title: Adult Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "variable combinations of anosmia, polyneuropathy, deafness, ataxia, and ichthyosis."
    explanation: GeneReviews establishes polyneuropathy as a core manifestation.
  downstream:
  - target: Peripheral neuropathy
    causal_link_type: DIRECT
    description: Peripheral nerve dysfunction manifests clinically as polyneuropathy.
    evidence:
    - reference: PMID:20301527
      reference_title: Adult Refsum Disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "variable combinations of anosmia, polyneuropathy, deafness, ataxia, and ichthyosis."
      explanation: GeneReviews directly supports polyneuropathy.
- name: Cerebellar Dysfunction
  biological_scale: TISSUE
  mechanism_confidence: PROVISIONAL
  description: Cerebellar dysfunction manifests clinically as ataxia.
  evidence:
  - reference: PMID:6170281
    reference_title: "Heredopathia atactica polyneuritiformis phytanic-acid storage disease, Refsum's disease:\" a biochemically well-defined disease with a specific dietary treatment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "include pigmentary retinal degeneration, chronic polyneuropathy, ataxia, impaired hearing, and cardiopathy"
    explanation: The long-term clinical series establishes ataxia as a major manifestation.
  downstream:
  - target: Ataxia
    causal_link_type: DIRECT
    description: Cerebellar dysfunction manifests clinically as ataxia.
    evidence:
    - reference: PMID:6170281
      reference_title: "Heredopathia atactica polyneuritiformis phytanic-acid storage disease, Refsum's disease:\" a biochemically well-defined disease with a specific dietary treatment."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "include pigmentary retinal degeneration, chronic polyneuropathy, ataxia, impaired hearing, and cardiopathy"
      explanation: The clinical series directly supports ataxia.
- name: Auditory Dysfunction
  biological_scale: TISSUE
  mechanism_confidence: PROVISIONAL
  description: Auditory-system involvement causes sensorineural hearing impairment and may include auditory neuropathy.
  evidence:
  - reference: PMID:11589979
    reference_title: The site of the hearing loss in Refsum's disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Refsum's disease is a disorder of lipid metabolism with pigmentary retinopathy, demyelinating neuropathy, ataxia, and hearing loss."
    explanation: Clinical cases establish hearing loss as part of the disorder.
  downstream:
  - target: Sensorineural hearing impairment
    causal_link_type: DIRECT
    description: Auditory dysfunction manifests clinically as hearing impairment.
    evidence:
    - reference: ORPHA:773
      reference_title: Adult Refsum disease
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0000407 | Sensorineural hearing impairment | Very frequent (99-80%)"
      explanation: Orphanet directly supports sensorineural hearing impairment.
- name: Cardiac Mitochondrial Dysfunction
  biological_scale: CELLULAR
  mechanism_confidence: PROVISIONAL
  description: >-
    Patient-range phytanic acid disrupts cardiac mitochondrial bioenergetics and
    calcium homeostasis in vitro; translation to human cardiac disease remains provisional.
  evidence:
  - reference: PMID:36812958
    reference_title: 'Disruption of mitochondrial bioenergetics and calcium homeostasis by phytanic acid in the heart: Potential relevance for the cardiomyopathy in Refsum disease.'
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The present data indicate that Phyt, at concentrations found in the plasma of patients with Refsum disease, disrupts by multiple mechanisms mitochondrial bioenergetics and Ca2+ homeostasis"
    explanation: Rat-heart mitochondrial and H9C2-cell experiments support the cellular mechanism.
  downstream:
  - target: Cardiomyopathy
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Mitochondrial toxicity is a plausible contributor to clinical cardiomyopathy.
    evidence:
    - reference: PMID:20301527
      reference_title: Adult Refsum Disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Cardiac arrhythmia and heart failure caused by cardiomyopathy are potentially severe health problems that develop later in life."
      explanation: GeneReviews establishes cardiomyopathy clinically but does not prove the experimental intermediate in humans.
  - target: Arrhythmia
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Mitochondrial toxicity is a plausible contributor to arrhythmia.
    evidence:
    - reference: PMID:20301527
      reference_title: Adult Refsum Disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Cardiac arrhythmia and heart failure caused by cardiomyopathy are potentially severe health problems that develop later in life."
      explanation: GeneReviews establishes arrhythmia clinically but does not prove the experimental intermediate in humans.
  - target: Heart block
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Cardiac conduction disease can include heart block; its link to mitochondrial toxicity is uncertain.
    evidence:
    - reference: ORPHA:773
      reference_title: Adult Refsum disease
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0012722 | Heart block | Occasional (29-5%)"
      explanation: Orphanet supports heart block as an associated feature only.
- name: Cutaneous Dysfunction
  biological_scale: TISSUE
  mechanism_confidence: PROVISIONAL
  description: Cutaneous involvement produces ichthyosis and improves when phytanic acid intake is restricted.
  evidence:
  - reference: PMID:20301527
    reference_title: Adult Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Dietary restriction of phytanic acid intake helps resolve ichthyosis, sensory neuropathy, and ataxia."
    explanation: Treatment response supports disease-linked cutaneous dysfunction.
  downstream:
  - target: Ichthyosis
    causal_link_type: DIRECT
    description: Cutaneous dysfunction manifests as ichthyosis.
    evidence:
    - reference: PMID:20301527
      reference_title: Adult Refsum Disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "variable combinations of anosmia, polyneuropathy, deafness, ataxia, and ichthyosis."
      explanation: GeneReviews directly supports ichthyosis.
  - target: Dry skin
    causal_link_type: DIRECT
    description: Cutaneous involvement can also manifest as dry skin.
    evidence:
    - reference: PMID:41290216
      reference_title: Identification of novel pathogenic variants in the PHYH gene and extending the phenotypic range in Refsum disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Both patients shared systemic features of the disease including bilaterally abnormal metatarsals and dry skin"
      explanation: Both recent molecularly and biochemically confirmed cases had dry skin.
- name: Distal Limb Skeletal Abnormality
  biological_scale: TISSUE
  mechanism_confidence: HYPOTHETICAL
  description: Distal limb skeletal findings include pes cavus, hammertoes, and short metacarpals; their disease mechanism is unresolved.
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Other features can be deafness, ichthyosis, skeletal abnormalities, and cardiac arrhythmia."
    explanation: Orphanet supports skeletal abnormalities as syndrome features.
  downstream:
  - target: Pes cavus
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Pes cavus is an associated skeletal feature.
    evidence:
    - reference: ORPHA:773
      reference_title: Adult Refsum disease
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0001761 | Pes cavus | Occasional (29-5%)"
      explanation: Orphanet supports disease association, while the mechanism remains unknown.
  - target: Hammertoe
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Hammertoe is an associated skeletal feature.
    evidence:
    - reference: ORPHA:773
      reference_title: Adult Refsum disease
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0001765 | Hammertoe | Frequent (79-30%)"
      explanation: Orphanet supports disease association, while the mechanism remains unknown.
  - target: Short metacarpal
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Short metacarpal is an associated skeletal feature.
    evidence:
    - reference: ORPHA:773
      reference_title: Adult Refsum disease
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0010049 | Short metacarpal | Frequent (79-30%)"
      explanation: Orphanet supports disease association, while the mechanism remains unknown.
- name: Renal Involvement
  biological_scale: TISSUE
  mechanism_confidence: HYPOTHETICAL
  description: Renal insufficiency is occasionally reported, but causality and mechanism remain uncertain.
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0000083 | Renal insufficiency | Occasional (29-5%)"
    explanation: Orphanet supports an occasional association only.
  downstream:
  - target: Renal insufficiency
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Renal involvement is represented clinically by renal insufficiency.
    evidence:
    - reference: ORPHA:773
      reference_title: Adult Refsum disease
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0000083 | Renal insufficiency | Occasional (29-5%)"
      explanation: Orphanet supports an occasional association only.
phenotypes:
- category: Renal
  name: Renal insufficiency
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Renal insufficiency
    term:
      id: HP:0000083
      label: Renal insufficiency
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0000083 | Renal insufficiency | Occasional (29-5%)"
    explanation: Orphanet supports an occasional association; attribution and mechanism remain uncertain.
- category: Auditory
  name: Sensorineural hearing impairment
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Sensorineural hearing impairment
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0000407 | Sensorineural hearing impairment | Very frequent (99-80%)"
    explanation: Orphanet supplies the association and frequency band.
  - reference: PMID:11589979
    reference_title: The site of the hearing loss in Refsum's disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Refsum's disease is a disorder of lipid metabolism with pigmentary retinopathy, demyelinating neuropathy, ataxia, and hearing loss."
    explanation: Clinical cases independently support hearing loss.
- category: Neurologic
  name: Anosmia
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Anosmia
    term:
      id: HP:0000458
      label: Anosmia
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0000458 | Anosmia | Very frequent (99-80%)"
    explanation: Orphanet supplies the association and frequency band.
  - reference: PMID:20301527
    reference_title: Adult Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "variable combinations of anosmia, polyneuropathy, deafness, ataxia, and ichthyosis."
    explanation: GeneReviews identifies anosmia as a core manifestation.
- category: Ophthalmologic
  name: Rod-cone dystrophy
  phenotype_term:
    preferred_term: Rod-cone dystrophy
    term:
      id: HP:0000510
      label: Rod-cone dystrophy
  evidence:
  - reference: PMID:20301527
    reference_title: Adult Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "late childhood-onset (or later) retinitis pigmentosa"
    explanation: GeneReviews supports retinitis pigmentosa, represented by its current HPO term rod-cone dystrophy.
  - reference: PMID:32904930
    reference_title: Improved electroretinographic responses following dietary intervention in a patient with Refsum disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "His post-intervention 30 Hz flicker electroretinogram demonstrated significantly improved waveform amplitudes and implicit times, suggesting improved retinal function."
    explanation: A confirmed case provides objective electrophysiologic evidence of retinal dysfunction and treatment response.
- category: Ophthalmologic
  name: Macular dystrophy
  phenotype_term:
    preferred_term: Macular dystrophy
    term:
      id: HP:0007754
      label: Macular dystrophy
  evidence:
  - reference: PMID:41290216
    reference_title: Identification of novel pathogenic variants in the PHYH gene and extending the phenotypic range in Refsum disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We document for the first time an association between macular dystrophy and Refsum disease."
    explanation: The recent case report explicitly extends the ocular phenotype to macular dystrophy.
- category: Ophthalmologic
  name: Cataract
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Cataract
    term:
      id: HP:0000518
      label: Cataract
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0000518 | Cataract | Very frequent (99-80%)"
    explanation: Orphanet supplies the association and frequency band.
- category: Ophthalmologic
  name: Miosis
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Miosis
    term:
      id: HP:0000616
      label: Miosis
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0000616 | Miosis | Frequent (79-30%)"
    explanation: Orphanet supplies the association and frequency band.
- category: Ophthalmologic
  name: Nyctalopia
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Nyctalopia
    term:
      id: HP:0000662
      label: Nyctalopia
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0000662 | Nyctalopia | Frequent (79-30%)"
    explanation: Orphanet supplies the association and frequency band.
- category: Dermatologic
  name: Dry skin
  phenotype_term:
    preferred_term: Dry skin
    term:
      id: HP:0000958
      label: Dry skin
  evidence:
  - reference: PMID:41290216
    reference_title: Identification of novel pathogenic variants in the PHYH gene and extending the phenotypic range in Refsum disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Both patients shared systemic features of the disease including bilaterally abnormal metatarsals and dry skin"
    explanation: Both recent molecularly and biochemically confirmed cases had dry skin.
- category: Neurologic
  name: Ataxia
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Ataxia
    term:
      id: HP:0001251
      label: Ataxia
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0001251 | Ataxia | Very frequent (99-80%)"
    explanation: Orphanet supplies the association and frequency band.
  - reference: PMID:6170281
    reference_title: "Heredopathia atactica polyneuritiformis phytanic-acid storage disease, Refsum's disease:\" a biochemically well-defined disease with a specific dietary treatment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "include pigmentary retinal degeneration, chronic polyneuropathy, ataxia, impaired hearing, and cardiopathy"
    explanation: The long-term clinical series independently supports ataxia.
- category: Cardiovascular
  name: Cardiomyopathy
  frequency: VERY_FREQUENT
  notes: >-
    The Orphanet frequency band is retained as reported, while GeneReviews
    characterizes cardiomyopathy and arrhythmia as potentially severe findings
    that develop later in life.
  phenotype_term:
    preferred_term: Cardiomyopathy
    term:
      id: HP:0001638
      label: Cardiomyopathy
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0001638 | Cardiomyopathy | Very frequent (99-80%)"
    explanation: Orphanet supplies the association and frequency band.
  - reference: PMID:20301527
    reference_title: Adult Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cardiac arrhythmia and heart failure caused by cardiomyopathy are potentially severe health problems that develop later in life."
    explanation: GeneReviews establishes cardiomyopathy as a potentially severe later manifestation.
- category: Cardiovascular
  name: Arrhythmia
  phenotype_term:
    preferred_term: Arrhythmia
    term:
      id: HP:0011675
      label: Arrhythmia
  evidence:
  - reference: PMID:20301527
    reference_title: Adult Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cardiac arrhythmia and heart failure caused by cardiomyopathy are potentially severe health problems that develop later in life."
    explanation: GeneReviews directly supports cardiac arrhythmia.
- category: Skeletal
  name: Pes cavus
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Pes cavus
    term:
      id: HP:0001761
      label: Pes cavus
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0001761 | Pes cavus | Occasional (29-5%)"
    explanation: Orphanet supplies the association and frequency band.
- category: Skeletal
  name: Hammertoe
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Hammertoe
    term:
      id: HP:0001765
      label: Hammertoe
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0001765 | Hammertoe | Frequent (79-30%)"
    explanation: Orphanet supplies the association and frequency band.
- category: Dermatologic
  name: Ichthyosis
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Ichthyosis
    term:
      id: HP:0008064
      label: Ichthyosis
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0008064 | Ichthyosis | Very frequent (99-80%)"
    explanation: Orphanet supplies the association and frequency band.
  - reference: PMID:20301527
    reference_title: Adult Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "variable combinations of anosmia, polyneuropathy, deafness, ataxia, and ichthyosis."
    explanation: GeneReviews identifies ichthyosis as a core manifestation.
- category: Neurologic
  name: Peripheral neuropathy
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Peripheral neuropathy
    term:
      id: HP:0009830
      label: Peripheral neuropathy
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0009830 | Peripheral neuropathy | Very frequent (99-80%)"
    explanation: Orphanet supplies the association and frequency band.
  - reference: PMID:20301527
    reference_title: Adult Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "variable combinations of anosmia, polyneuropathy, deafness, ataxia, and ichthyosis."
    explanation: GeneReviews identifies polyneuropathy as a core manifestation.
- category: Skeletal
  name: Short metacarpal
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Short metacarpal
    term:
      id: HP:0010049
      label: Short metacarpal
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0010049 | Short metacarpal | Frequent (79-30%)"
    explanation: Orphanet supplies the association and frequency band.
- category: Cardiovascular
  name: Heart block
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Heart block
    term:
      id: HP:0012722
      label: Heart block
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0012722 | Heart block | Occasional (29-5%)"
    explanation: Orphanet supplies the association and frequency band.
biochemical:
- name: Elevated plasma and tissue phytanic acid
  presence: Elevated
  notes: >-
    Elevated phytanic acid in plasma and tissues is the defining biochemical
    abnormality and is used diagnostically and for treatment monitoring.
  evidence:
  - reference: ORPHA:773
    reference_title: Adult Refsum disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "It is characterized biochemically by accumulation of phytanic acid in plasma and tissues."
    explanation: Orphanet identifies phytanic acid accumulation as the biochemical hallmark.
  - reference: PMID:2475586
    reference_title: The significance of plasma phytanic acid levels in adults.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Fourteen patients with heredopathia atactica polyneuritiformis had a plasma phytanic acid level before treatment of 992-6400 mumol/l."
    explanation: Human clinical study quantifies marked pretreatment plasma phytanic acid elevation.
- name: Exogenous phytanic acid retention
  presence: Positive
  notes: >-
    Dietary phytol and phytanic acid are normally cleared, but persist in plasma
    in Adult Refsum disease because degradation is blocked.
  evidence:
  - reference: PMID:4164676
    reference_title: Studies on the metabolic error in Refsum's disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "establishing phytol in the diet as a potential precursor of phytanic acid."
    explanation: Tracer study supports dietary phytol as a phytanic acid precursor.
  - reference: PMID:4164676
    reference_title: Studies on the metabolic error in Refsum's disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "whereas it persisted at high concentrations in the plasma of the two patients for many days."
    explanation: Tracer study supports delayed clearance in patients.
diagnosis:
- name: Plasma phytanic acid testing
  description: >-
    Plasma phytanic acid measurement is the core biochemical diagnostic test and
    helps distinguish classic Adult Refsum disease from isolated retinitis
    pigmentosa and other disorders. Some attenuated PHYH genotypes can have a
    normal result, so molecular testing remains important when suspicion persists.
  results: >-
    Marked elevation strongly supports diagnosis; a normal concentration does
    not fully exclude attenuated retinal-predominant PHYH disease.
  evidence:
  - reference: PMID:2475586
    reference_title: The significance of plasma phytanic acid levels in adults.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The presence of phytanic acid in tissues and plasma has been considered diagnostic of heredopathia atactica polyneuritiformis (Refsum's disease)"
    explanation: Human clinical study supports plasma/tissue phytanic acid as diagnostic.
  - reference: PMID:20301527
    reference_title: Adult Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Adult Refsum disease (ARD) is associated with elevated plasma phytanic acid levels"
    explanation: GeneReviews supports elevated plasma phytanic acid testing.
  - reference: PMID:38411969
    reference_title: PHYH c.678+5G>T Leads to In-Frame Exon Skipping and Is Associated With Attenuated Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Blood phytanic acid levels were normal in two patients, mildly elevated
      in one, and markedly high in the fourth.
    explanation: Four genetically confirmed attenuated cases demonstrate that plasma phytanic acid is not uniformly elevated.
- name: PHYH and PEX7 molecular genetic testing
  diagnosis_term:
    preferred_term: genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  description: >-
    Molecular testing confirms biallelic pathogenic variants in PHYH or PEX7
    and distinguishes PHYH-related disease from PEX7-related disease and other
    peroxisomal disorders.
  results: Biallelic pathogenic variants in PHYH or PEX7 establish the molecular diagnosis.
  evidence:
  - reference: PMID:20301527
    reference_title: Adult Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of ARD is established in a proband with suggestive clinical and biochemical findings by identification of biallelic pathogenic variants in either PHYH or PEX7 on molecular genetic testing."
    explanation: GeneReviews states the diagnostic role of PHYH/PEX7 molecular testing.
  - reference: PMID:38411969
    reference_title: PHYH c.678+5G>T Leads to In-Frame Exon Skipping and Is Associated With Attenuated Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      One patient had isolated retinitis pigmentosa and three had mild
      extraocular findings. Blood phytanic acid levels were normal in two
      patients, mildly elevated in one, and markedly high in the fourth.
    explanation: The attenuated series supports molecular testing when retinal disease is suggestive despite a normal biochemical result.
treatments:
- name: Phytanic-acid-restricted diet and fasting avoidance
  description: >-
    Long-term management restricts phytanic-acid-rich foods, avoids fasting and
    sudden weight loss, and maintains adequate calories to reduce mobilization
    of stored phytanic acid.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: dietary intervention
    term:
      id: NCIT:C15447
      label: Dietary Intervention
  target_mechanisms:
  - target: Plasma and Tissue Phytanic Acid Accumulation
    treatment_effect: INHIBITS
    description: Dietary restriction lowers exogenous phytanic acid input and limits mobilization from adipose stores.
    evidence:
    - reference: PMID:20301527
      reference_title: Adult Refsum Disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Dietary restriction of phytanic acid intake helps resolve ichthyosis, sensory neuropathy, and ataxia."
      explanation: GeneReviews supports diet as a phytanic-acid-lowering disease management strategy.
  evidence:
  - reference: PMID:6170281
    reference_title: "Heredopathia atactica polyneuritiformis phytanic-acid storage disease, Refsum's disease:\" a biochemically well-defined disease with a specific dietary treatment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "can be either kept from worsening or reversed by elimination of foods rich in phytanic acid from patients' diets."
    explanation: Long-term clinical experience supports a specific phytanic-acid-restricted diet.
  - reference: PMID:20301527
    reference_title: Adult Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A high-calorie diet and avoidance of fasting prevent mobilization of phytanic acid stored in adipose tissue into the plasma."
    explanation: GeneReviews supports fasting avoidance and adequate calories.
  - reference: PMID:42145913
    reference_title: 'Adult Refsum Disease: Case Series of Reducing Circulating Phytanic Acid Levels With Dietary Interventions.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Implementing dietary interventions to ensure adequate energy,
      carbohydrates and weight stabilisation resulted in a decrease in
      circulating PA levels by 47%-84% in the outpatient setting.
    explanation: The six-patient case series quantifies the benefit of adequate energy, carbohydrate, and weight stabilization.
  - reference: PMID:42161578
    reference_title: 'Diagnosis and Metabolic Management of Adult Refsum Disease: Guidance From the Medical and Scientific Committee of Global DARE (Defeat Adult Refsum Everywhere).'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Life-long dietary therapy, along with therapeutic plasma
      exchange/lipoprotein apheresis during acute decompensations, remains the
      mainstay of management.
    explanation: The 2026 GRADE-aligned expert guidance confirms lifelong dietary therapy as the mainstay.
- name: Plasmapheresis or lipid apheresis for severe acute worsening
  description: >-
    Plasma exchange or lipid apheresis is reserved for acute arrhythmias,
    extreme weakness, severe rapidly worsening disease, or failure of dietary
    control to lower very high phytanic acid levels.
  treatment_term:
    preferred_term: Plasmapheresis
    term:
      id: NCIT:C15304
      label: Plasmapheresis
  therapeutic_modality: OTHER
  target_mechanisms:
  - target: Plasma and Tissue Phytanic Acid Accumulation
    treatment_effect: INHIBITS
    description: Plasma exchange lowers circulating phytanic acid.
    evidence:
    - reference: PMID:1716665
      reference_title: Plasma exchange in the treatment of Refsum's disease (heredopathia atactica polyneuritiformis).
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Lowering the plasma phytanic acid by plasma exchange produced a rapid clinical improvement."
      explanation: Case series supports rapid clinical improvement after lowering phytanic acid by plasma exchange.
  evidence:
  - reference: PMID:20301527
    reference_title: Adult Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Plasmapheresis or lipid apheresis to decrease phytanic acid levels is used only for acute arrhythmias or extreme weakness."
    explanation: GeneReviews supports restricted use of plasmapheresis/lipid apheresis for severe manifestations.
  - reference: PMID:10150979
    reference_title: Plasma exchange for Refsum's disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Plasma exchange is indicated in Refsum's disease when there is a worsening clinical condition."
    explanation: Clinical review supports plasma exchange for worsening disease.
  - reference: PMID:42161578
    reference_title: 'Diagnosis and Metabolic Management of Adult Refsum Disease: Guidance From the Medical and Scientific Committee of Global DARE (Defeat Adult Refsum Everywhere).'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Life-long dietary therapy, along with therapeutic plasma
      exchange/lipoprotein apheresis during acute decompensations, remains the
      mainstay of management.
    explanation: The 2026 expert guidance supports apheresis during acute decompensation.
- name: Nutritional monitoring during long-term dietary therapy
  description: >-
    Periodically assess fat-soluble vitamins, vitamin B12, copper, selenium,
    and sodium intake during a long-term low-phytanic-acid diet.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:26799636
    reference_title: 'Safety of long-term restrictive diets for peroxisomal disorders: vitamin and trace element status of patients treated for Adult Refsum Disease.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Periodic nutritional screening may be necessary for fat-soluble vitamins,
      vitamin B12 , copper or selenium.
    explanation: The nutritional cohort identifies specific monitoring needs during dietary treatment.
- name: Medication and catabolic-trigger avoidance
  description: >-
    Avoid phytanic-acid-rich foods, fasting, sudden weight loss, ibuprofen, and
    amiodarone; provide high-calorie support during severe illness or surgery.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:20301527
    reference_title: Adult Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Food products containing phytanic acid, mostly from ruminants (cow,
      sheep, goat), some fish and walnuts; fasting and/or sudden weight loss;
      use of either ibuprofen or amiodarone.
    explanation: GeneReviews explicitly lists disease-specific agents and circumstances to avoid.
  - reference: PMID:20301527
    reference_title: Adult Refsum Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Hypercaloric parenteral infusions are required during periods of severe
      illness or postoperatively.
    explanation: GeneReviews supports catabolic prevention during severe illness and surgery.
differential_diagnoses:
- name: Alpha-methylacyl-CoA racemase deficiency
  description: >-
    AMACR deficiency can resemble an atypical Refsum phenotype with retinal and
    neurologic disease but may have low plasma phytanic acid; biochemical
    profiling and molecular testing distinguish it from PHYH- or PEX7-related disease.
  evidence:
  - reference: PMID:11948235
    reference_title: "Refsum's disease: a peroxisomal disorder affecting phytanic acid alpha-oxidation."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Other atypical cases with low-plasma phytanic acid may be caused by
      alpha-methylacyl-CoA racemase deficiency.
    explanation: The review directly identifies AMACR deficiency as a differential in low-phytanic-acid atypical cases.
clinical_trials: []
datasets:
- accession: geo:GSE138379
  title: Fibroblast-specific genome-scale modelling predicts an imbalance in amino acid metabolism in Refsum disease
  description: In this study, we reconstructed a fibroblast-specific genome-scale model based on the recently published, FAD-curated model, based on Recon3D reconstruction. To constrain the model we used transcriptomics, and proteomics data, which we obtained from healthy controls and Refsum disease patient fibroblasts incubated with phytol, a precursor of phytanic acid. Using this model, we investigated the metabolic phenotype of Refsum disease at the genome-scale, and we studied the effect of phytanic acid on cell metabolism. We identified 20 metabolites that were predicted to discriminate between Healthy and Refsum disease patients, several of which with a link to amino acid metabolism.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: BULK_RNA_SEQ
  sample_count: 96
  publication: PMID:32160399
  notes: Identified by GEO DataSets index search for Adult Refsum Disease (scripts/discover_datasets.py); accession and metadata verified against NCBI E-utilities on 2026-08-01. Title, sample count, and organism are GEO's own values.
📚

References & Deep Research

References

20
ORPHA:773
Adult Refsum disease
1 finding
Orphanet defines Adult Refsum disease as a metabolic disease with anosmia, cataract, early-onset retinitis pigmentosa, neurologic manifestations, and phytanic acid accumulation.
"A metabolic disease characterized by anosmia, cataract, early-onset retinitis pigmentosa and possible neurological manifestations"
PMID:20301527
Adult Refsum Disease.
1 finding
GeneReviews summarizes the clinical phenotype, diagnostic criteria, diet, plasmapheresis/lipid apheresis, and autosomal recessive inheritance of Adult Refsum disease.
"Adult Refsum disease (ARD) is associated with elevated plasma phytanic acid levels"
PMID:14974078
Molecular basis of Refsum disease: sequence variations in phytanoyl-CoA hydroxylase (PHYH) and the PTS2 receptor (PEX7).
1 finding
Review evidence supports Refsum disease as genetically heterogeneous, caused by PHYH or PEX7 variants disrupting peroxisomal phytanic acid alpha-oxidation.
"Refsum disease is genetically heterogeneous; two genes, PHYH (also named PAHX) and PEX7, have been identified to cause Refsum disease"
PMID:12522768
Identification of PEX7 as the second gene involved in Refsum disease.
1 finding
PEX7 variants can cause a milder Refsum phenotype through impaired peroxisomal import of PTS2-containing enzymes.
"Our data show that mutations in the PEX7 gene may result in a broad clinical spectrum ranging from severe rhizomelic chondrodysplasia punctata to relatively mild RD"
PMID:16186124
Structure of human phytanoyl-CoA 2-hydroxylase identifies molecular mechanisms of Refsum disease.
1 finding
Structural enzymology supports PAHX/PHYH mutations as disrupting the peroxisomal enzyme that catalyzes the initial alpha-oxidation step.
"mutations in phytanoyl-CoA 2-hydroxylase (PAHX), an Fe(II) and 2-oxoglutarate (2OG)-dependent oxygenase that catalyzes the initial alpha-oxidation step"
PMID:4164676
Studies on the metabolic error in Refsum's disease.
1 finding
Classic metabolic tracer work supports exogenous phytanic acid origin and a block in phytanic acid degradation.
"patients with Refsum's disease have a relative block in the degradation of phytanic acid"
PMID:2475586
The significance of plasma phytanic acid levels in adults.
1 finding
Plasma phytanic acid measurement distinguishes classic Refsum disease from normal controls and many retinitis pigmentosa cases.
"Fourteen patients with heredopathia atactica polyneuritiformis had a plasma phytanic acid level before treatment of 992-6400 mumol/l."
PMID:6170281
Heredopathia atactica polyneuritiformis phytanic-acid storage disease, Refsum's disease:" a biochemically well-defined disease with a specific dietary treatment.
1 finding
Dietary elimination of phytanic-acid-rich foods is a disease-specific treatment that can improve or stabilize manifestations.
"can be either kept from worsening or reversed by elimination of foods rich in phytanic acid from patients' diets."
PMID:1716665
Plasma exchange in the treatment of Refsum's disease (heredopathia atactica polyneuritiformis).
1 finding
Plasma exchange can rapidly lower phytanic acid and improve acute or severe worsening disease.
"Lowering the plasma phytanic acid by plasma exchange produced a rapid clinical improvement."
PMID:10150979
Plasma exchange for Refsum's disease.
1 finding
Additional plasma-exchange clinical evidence supports use during worsening disease or failure of dietary control.
"Plasma exchange is indicated in Refsum's disease when there is a worsening clinical condition."
PMID:11589979
The site of the hearing loss in Refsum's disease.
1 finding
Case evidence supports hearing loss as part of the Refsum phenotype and suggests auditory neuropathy in some cases.
"Refsum's disease is a disorder of lipid metabolism with pigmentary retinopathy, demyelinating neuropathy, ataxia, and hearing loss."
PMID:11948235
Refsum's disease: a peroxisomal disorder affecting phytanic acid alpha-oxidation.
1 finding
Low-phytanic-acid atypical cases may instead reflect alpha-methylacyl-CoA racemase deficiency, an important biochemical and molecular differential diagnosis.
"Other atypical cases with low-plasma phytanic acid may be caused by alpha-methylacyl-CoA racemase deficiency."
PMID:17325280
Phenotype of adult Refsum disease due to a defect in peroxin 7.
1 finding
Adult Refsum disease can be divided into PHYH-related type 1 and PEX7-related type 2, whose reported clinical phenotype can be indistinguishable from classic disease.
"Hence, we propose the subdivision of ARD into type 1 and type 2, depending on which gene is defective."
PMID:38411969
PHYH c.678+5G>T Leads to In-Frame Exon Skipping and Is Associated With Attenuated Refsum Disease.
1 finding
The PHYH c.678+5G>T splice variant can produce an attenuated presentation with isolated retinitis pigmentosa or mild extraocular findings and normal-to-markedly-elevated plasma phytanic acid.
"One patient had isolated retinitis pigmentosa and three had mild extraocular findings. Blood phytanic acid levels were normal in two patients, mildly elevated in one, and markedly high in the fourth."
PMID:41290216
Identification of novel pathogenic variants in the PHYH gene and extending the phenotypic range in Refsum disease.
1 finding
Two recent retinal-clinic cases identified novel biallelic PHYH variants and extended the reported ocular spectrum to macular dystrophy.
"We document for the first time an association between macular dystrophy and Refsum disease."
PMID:36812958
Disruption of mitochondrial bioenergetics and calcium homeostasis by phytanic acid in the heart: Potential relevance for the cardiomyopathy in Refsum disease.
1 finding
In vitro cardiac experiments support phytanic-acid-induced disruption of mitochondrial respiration, ATP synthesis, membrane potential, calcium retention, and cardiomyocyte viability as a provisional cardiac mechanism.
"The present data indicate that Phyt, at concentrations found in the plasma of patients with Refsum disease, disrupts by multiple mechanisms mitochondrial bioenergetics and Ca2+ homeostasis"
PMID:32904930
Improved electroretinographic responses following dietary intervention in a patient with Refsum disease.
1 finding
A molecularly and biochemically confirmed case showed improved electroretinographic responses after starting a phytanic-acid-restricted diet.
"His post-intervention 30 Hz flicker electroretinogram demonstrated significantly improved waveform amplitudes and implicit times, suggesting improved retinal function."
PMID:26799636
Safety of long-term restrictive diets for peroxisomal disorders: vitamin and trace element status of patients treated for Adult Refsum Disease.
1 finding
Long-term low-phytanic-acid diets can be managed without routine supplementation, but periodic nutritional screening is warranted.
"Periodic nutritional screening may be necessary for fat-soluble vitamins, vitamin B12 , copper or selenium."
PMID:42145913
Adult Refsum Disease: Case Series of Reducing Circulating Phytanic Acid Levels With Dietary Interventions.
1 finding
Recent case-series evidence shows that phytanic-acid restriction must be paired with adequate energy and carbohydrate intake and weight stability.
"These cases demonstrate that PA restriction, and weight and carbohydrate management have integral roles in ensuring metabolic stability in ARD."
PMID:42161578
Diagnosis and Metabolic Management of Adult Refsum Disease: Guidance From the Medical and Scientific Committee of Global DARE (Defeat Adult Refsum Everywhere).
1 finding
The 2026 GRADE-aligned expert guidance identifies lifelong dietary therapy as the mainstay and reserves therapeutic plasma exchange or lipoprotein apheresis for acute decompensation.
"Life-long dietary therapy, along with therapeutic plasma exchange/lipoprotein apheresis during acute decompensations, remains the mainstay of management."

Deep Research

1
Adult Refsum Disease research fallback ▸

Adult Refsum Disease research fallback

Provider attempts

  • Falcon deep-research: attempted with timeout 75s just research-disorder falcon Adult_Refsum_Disease on 2026-05-07 UTC; no artifact was produced before the command timed out.
  • OpenAI deep-research: attempted with timeout 75s just research-disorder openai Adult_Refsum_Disease on 2026-05-07 UTC; no artifact was produced before the command timed out.
  • Perplexity deep-research: not attempted after two bounded provider timeouts; curation proceeded from generated Orphanet and cached PubMed evidence.

Literature scope used for curation

This fallback curation uses generated Orphanet cache ORPHA:773, GeneReviews PMID:20301527, molecular genetics reviews and primary studies for PHYH/PEX7 (PMID:14974078, PMID:12522768), structural enzymology for PAHX/PHYH (PMID:16186124), classic tracer and biochemical diagnostic studies (PMID:4164676, PMID:2475586), and treatment evidence for phytanic-acid dietary restriction and plasma exchange (PMID:6170281, PMID:1716665, PMID:10150979).

Curation synthesis

Adult Refsum disease is a peroxisomal metabolic disorder in which PHYH defects or PEX7-dependent peroxisomal matrix import defects impair phytanic acid alpha-oxidation. Dietary phytol/phytanic acid cannot be cleared normally, causing plasma and tissue phytanic acid accumulation. The modeled consequences include retinal/olfactory disease, peripheral neuropathy with ataxia, cardiac conduction/myocardial involvement, ichthyosis, and skeletal manifestations. Treatment targets the biochemical driver by restricting phytanic-acid-rich foods, avoiding fasting and sudden weight loss, and using plasmapheresis or lipid apheresis only for severe acute worsening or failure of dietary control.

Key references

  • ORPHA:773
  • PMID:20301527
  • PMID:14974078
  • PMID:12522768
  • PMID:16186124
  • PMID:4164676
  • PMID:2475586
  • PMID:6170281
  • PMID:1716665
  • PMID:10150979
  • PMID:11589979