Retinitis Pigmentosa 2, X-Linked

Clinical Characteristics
Ocular Features: 

Retinitis pigmentosa consists of a group disorders with great clinical and genetic heterogeneity.  The ocular disease is characterized by night blindness, field constriction, and pigmentary changes in the retina.  The later is sometimes described as having a 'bone corpuscle' appearance with a perivascular distribution.  A ring scotoma is sometimes evident.  Age of onset and rate of progression is highly variable, even within families.

The X-linked form described here is a pigmentary retinopathy but sometimes labeled chorioretinal degeneration because of the extensive involvement of the choroid.  The clinical picture is sometimes referred to by the out-dated term 'choroidal sclerosis'.  It is often apparent in males during early childhood and they usually have early deterioration in central vision.  Some carrier females experience vision loss and have mild fundus abnormalities but these do no usually appear until middle age and are usually slowly progressive.  The ERG shows abnormalities in both sexes but these are highly variable.  Older males may have a waxy pallor of the optic nerve.  Posterior subcapsular cataracts are common.  The vitreous may contain fine, colorless particles even before fundus changes are evident.  Prognosis is highly variable but many patients eventually become legally blind by the age of 30 years.

Systemic Features: 

None.

Genetics

Mutations in more than 100 genes may be responsible for retinitis pigmentosa but sporadic disease occurs as well.  Between 5 and 10% of individuals have X-linked disease.

In this form of X-linked retinitis pigmentosa mutations in RP2 (Xp11.3) have been found.  The frequent occurrence of mild disease in females can cause diagnostic confusion with autosomal dominant RP but the disease in females in the latter disorder is usually as severe as in males.

This type of X-linked retinitis pigmentosa is far less common than RP3 (300029)caused by mutations in RPGR.  The two are clinically similar and genotyping is necessary to distinguish them.

Treatment
Treatment Options: 

High doses of vitamin A palmitate slow the rate of vision loss but plasma levels and liver function need to be checked at least annually.  Oral acetazolamide can be helpful in reducing macular edema.  Low vision aids and mobility training can be facilitating for many patients.  Cataract surgery may restore several lines of vision at least temporarily.

Several pharmaceuticals should be avoided, including isotretinioin, sildenafil, and vitamin E.

References
Article Title: 

Comprehensive survey of mutations in RP2 and RPGR in patients affected with distinct retinal dystrophies: genotype-phenotype correlations and impact on genetic counseling

Pelletier V, Jambou M, Delphin N, Zinovieva E, Stum M, Gigarel N, Dollfus H, Hamel C, Toutain A, Dufier JL, Roche O, Munnich A, Bonnefont JP, Kaplan J, Rozet JM. Comprehensive survey of mutations in RP2 and RPGR in patients affected with distinct retinal dystrophies: genotype-phenotype correlations and impact on genetic counseling. Hum Mutat. 2007 Jan;28(1):81-91.

PubMed ID: 
16969763

References

Pelletier V, Jambou M, Delphin N, Zinovieva E, Stum M, Gigarel N, Dollfus H, Hamel C, Toutain A, Dufier JL, Roche O, Munnich A, Bonnefont JP, Kaplan J, Rozet JM. Comprehensive survey of mutations in RP2 and RPGR in patients affected with distinct retinal dystrophies: genotype-phenotype correlations and impact on genetic counseling. Hum Mutat. 2007 Jan;28(1):81-91.

PubMedID: 16969763

Grover S, Fishman GA, Anderson RJ, Lindeman M. A longitudinal study of visual function in carriers of X-linked recessive retinitis pigmentosa. Ophthalmology. 2000 Feb;107(2):386-96.

PubMedID: 10690843