PHARC

Retinitis Pigmentosa, Hearing Loss, Ataxia, Cataract, and Polyneuropathy

Clinical Characteristics
Ocular Features: 

Cataracts and a pigmentary retinopathy occur in this condition but only in some, primarily older, patients.  The lens opacities progress and may become visually significant by the third decade.  Bone-spicule-shaped pigment clumping may be present in the midperiphery while the optic disk is often pale and the retinal vessels are attenuated. The ERG responses are consistent with a rod-cone dystrophy.

Systemic Features: 

This is a progressive neurological disorder with onset of signs and symptoms in childhood although full expression may not occur until adulthood.  Young children can have hyporeflexia, pes cavus, spasticity, and gait ataxia.  A sensorineural hearing loss may also be present in childhood but sometimes not until later.  Hyperreflexia with extensor plantar responses and Achilles tendon contractures are often present later.  The peripheral polyneuropathy is predominantly demyelinating with both sensory and motor components and is present in all adults.  Cerebellar atrophy, primarily in the vermis, can be demonstrated on MRI examination.  Mental function is usually not impaired. Some patients have dysarthria. 

This disorder has some clinical similarities to Refsum disease (266500).

Genetics

This is an autosomal recessive disorder resulting from homozygous mutations in the ABHD12 gene (20p11.21).

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

Treatment is directed at symptoms.  Visually significant cataracts may require removal.  Low vision aids and physical therapy can be helpful.

References
Article Title: 

Mutations in ABHD12 cause the neurodegenerative disease PHARC: An inborn error of endocannabinoid metabolism

Fiskerstrand T, H'mida-Ben Brahim D, Johansson S, M'zahem A, Haukanes BI, Drouot N, Zimmermann J, Cole AJ, Vedeler C, Bredrup C, Assoum M, Tazir M, Klockgether T, Hamri A, Steen VM, Boman H, Bindoff LA, Koenig M, Knappskog PM. Mutations in ABHD12 cause the neurodegenerative disease PHARC: An inborn error of endocannabinoid metabolism. Am J Hum Genet. 2010 Sep 10;87(3):410-7.

PubMed ID: 
20797687
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