Refsum Disease is a progressive neurodegenerative disorder characterized by the gradual loss of neuronal function. This page provides comprehensive information about the disease, including its pathophysiology, clinical presentation, diagnosis, and current therapeutic approaches.
Refsum disease, also known as heredopathia atactica polyneuritiformis, is a rare autosomal recessive peroxisomal disorder characterized by a accumulation of phytanic acid in tissues and plasma due to impaired fatty acid oxidation. This leads to a progressive neurodegenerative syndrome featuring retinitis pigmentosa, peripheral neuropathy, cerebellar ataxia, and hearing loss.[1]
Refsum disease was first described by Sigvald Refsum in 1946 as a familial syndrome combining retinitis pigmentosa, peripheral neuropathy, ataxia, and elevated cerebrospinal fluid protein. It is classified as a peroxisomal biogenesis disorder and represents one of the few treatable causes of hereditary ataxia, as dietary phytanic acid restriction can significantly alter the disease course.[2]
The disease is rare, with an estimated prevalence of 1 in 1,000,000 individuals worldwide. However, certain populations show higher frequencies due to founder mutations, particularly in Norway and other Scandinavian countries.[3]
Refsum disease is caused by homozygous or compound heterozygous mutations in the PAHX gene (peroxisomal 2-hydroxyacyl-CoA lyase), located on chromosome 10p13. This gene encodes the enzyme phytanoyl-CoA hydroxylase, which is essential for the peroxisomal oxidation of phytanic acid, a branched-chain fatty acid derived from dietary sources.[4]
More recently, mutations in the PEX7 gene (peroxisome biogenesis factor 7) have been identified in some patients with Refsum disease phenotypes, particularly those with additional features like rhizomelic chondrodysplasia punctata.[5]
- Pattern: Autosomal recessive
- Carrier frequency: Approximately 1 in 200 in general population
- Risk to siblings of affected individuals: 25%
Phytanic acid (3,7,11,15-tetramethylhexadecanoic acid) is a branched-chain fatty acid found primarily in dairy products, ruminant fats, and some fish oils. Normal metabolism occurs via:
- Peroxisomal β-oxidation: Phytanoyl-CoA is converted to pristanic acid by phytanoyl-CoA hydroxylase (PAHX)
- Further processing: Pristanic acid undergoes additional peroxisomal and mitochondrial oxidation
- Energy production: The resulting products enter mitochondrial β-oxidation
In Refsum disease, the deficient enzyme causes:
- Phytanic acid accumulation: Levels can reach 10-50 times normal (normal: < 30 μmol/L; patients: 300-3000 μmol/L)
- Membrane incorporation: Phytanic acid incorporates into neuronal and retinal cell membranes
- Oxidative stress: Accumulated phytanic acid promotes reactive oxygen species generation
- Myelin dysfunction: Altered membrane properties affect nerve conduction
[6]
The traditional presentation includes four cardinal features:
| Feature |
Description |
Frequency |
| Retinitis pigmentosa |
Progressive vision loss, tunnel vision, nyctalopia (night blindness) |
100% |
| Peripheral neuropathy |
Motor and sensory neuropathy, distal weakness, reduced reflexes |
95% |
| Cerebellar ataxia |
Gait instability, dysmetria, dysarthria |
90% |
| Sensorineural hearing loss |
Progressive hearing impairment |
85% |
- Anosmia (loss of smell): Often an early sign
- Ichthyosis (dry, scaly skin): Present in approximately 40%
- Cardiac conduction abnormalities: Including bundle branch block
- Mild cognitive impairment: In some patients
- Skeletal abnormalities: Including epiphyseal dysplasia
- Cryptorchidism (undescended testicles): In male patients
[7]
- Typical onset: Second to fourth decade
- Range: 5-50 years
- Retinitis pigmentosa: Usually first manifestation
- Neurological symptoms: Develop 5-10 years after ocular symptoms
Without treatment:
- Stage 1 (ages 5-20): Visual problems, night blindness
- Stage 2 (ages 15-30): Onset of neurological symptoms - ataxia, neuropathy
- Stage 3 (ages 25-50): Progressive disability, hearing loss
- Stage 4 (ages 40-60): Severe disability, possible premature death
With treatment, progression can be significantly slowed or halted.
[8]
- Clinical triad: Retinitis pigmentosa + peripheral neuropathy + ataxia (or hearing loss)
- Elevated phytanic acid: Plasma levels > 100 μmol/L
- Genetic confirmation: Biallelic pathogenic variants in PAHX or PEX7
- Normal very-long-chain fatty acids: Distinguishes from Zellweger spectrum
| Test |
Finding |
| Plasma phytanic acid |
Markedly elevated (100-3000 μmol/L) |
| Plasma pristanic acid |
Normal or mildly elevated |
| Very-long-chain fatty acids |
Normal |
| Pipecolic acid |
Normal |
| Red blood cell plasmalogens |
Normal |
| CSF protein |
Elevated in 60% |
¶ Imaging and Electrophysiology
- MRI brain: May show cerebellar atrophy in advanced cases
- Nerve conduction studies: Axonal sensory-motor neuropathy
- EEG: Usually normal
- ECG: May show conduction abnormalities
Phytanic acid restriction is the cornerstone of treatment:
| Food to Avoid |
Alternatives |
| Dairy products (milk, cheese, butter) |
Dairy-free alternatives |
| Ruminant meat (beef, lamb, goat) |
Poultry, fish |
| Animal fats |
Vegetable oils (except palm) |
| Certain fish (herring, mackerel) |
Cod, haddock |
| Foods containing phytol |
Avoid green leafy vegetables (cooked) |
- Emerging therapy: Docosahexaenoic acid (DHA) supplementation
- Rationale: May support membrane function in the absence of phytanic acid metabolism
- Hearing aids for hearing loss
- Low-vision aids for retinitis pigmentosa
- Physical therapy for ataxia and neuropathy
- Cardiac monitoring for conduction abnormalities
- Vitamin A and E supplementation (some benefit reported)
- Plasma phytanic acid levels: Every 3-6 months
- Neurological examination: Annually
- Ophthalmological evaluation: Annually
- Audiometry: Annually
- ECG: Annually
With early diagnosis and strict dietary management:
- Vision loss: Can be stabilized
- Neurological progression: Often halted or slowed significantly
- Life expectancy: Normal or near-normal with treatment
- Quality of life: Substantially improved
Without treatment:
- Progressive neurodegeneration leading to severe disability
- Median survival: 40-50 years after symptom onset
[9]
| Condition |
Key Distinguishing Features |
| Usher syndrome |
Retinitis pigmentosa + hearing loss, but no ataxia or elevated phytanic acid |
| Friedreich's ataxia |
Ataxia + neuropathy + cardiomyopathy, but no retinitis pigmentosa |
| Ataxia with vitamin E deficiency |
Low vitamin E, different pattern of neurological involvement |
| Other peroxisomal disorders |
Elevated VLCFA in Zellweger spectrum |
| Charcot-Marie-Tooth disease |
Neuropathy without retinitis pigmentosa |
The study of Refsum Disease has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
- Refsum S. Heredopathia atactica polyneuritiformis: a familial syndrome not earlier described. Acta Psychiatr Scand. 1946;39:9-26.
- Wanders RJ, Waterham HR, Leroy BP. Refsum disease. In: Adam MP, et al., eds. GeneReviews. University of Washington; 2006. Updated 2022.
- Jansen GA, Wanders RJ, Moser AB, et al. Peroxisomal beta-oxidation and the phytanic acid alpha-hydroxylase: an analysis of the gene defects in patients with Zellweger syndrome and Refsum disease. J Inherit Metab Dis. 1994;17(6):719-724. PMID:7833775
- Mihalik SJ, Morrell JC, Kim D, et al. Identification of PAHX, a gene for Refsum disease: cloning and expression. Nat Genet. 1997;17(2):185-189. PMID:9326939
- van den Brink DM, Brites P, Haasjes J, et al. Identification of PEX7 as the second gene causing Refsum disease. Am J Hum Genet. 2003;72(2):471-477. PMID:12522768
- Steinberg S, Meyn MS, Moser A, Moser H. Molecular genetics and pathophysiology of Refsum disease: a peroxisomal disorder causing neurodysfunction. J Inherit Metab Dis. 1995;18(6):765-780. PMID:8750608
- Wanders RJ, Komen J, Kemp S. Fatty acid omega-oxidation as a rescue pathway for peroxisomal disorders. J Inherit Metab Dis. 2011;34(3):703-707. PMID:21328042
- ten Brink HJ, van Gennip AH, Jacobs C, et al. Long-term effects of dietary treatment on plasma phytanic acid level in patients with Refsum disease. J Inherit Metab Dis. 1992;15(2):269-272. PMID:1354679
- Rizzo WB. The role of dietary restriction in the pathogenesis and treatment of Refsum disease. Mol Genet Metab. 2007;92(3):197-201. PMID:17652049