Cone-Rod Dystrophies, X-Linked

Clinical Characteristics
Ocular Features: 

Three X-linked forms of progressive cone-rod dystrophies each with mutations in different genes have been identified.  Central vision is often lost in the second or third decades of life but photophobia is usually noted before vision loss.  Cones are primarily involved but rod degeneration occurs over time.  The ERG reveals defective photopic responses early followed by a decrease in rod responses.   All three types are rare disorders affecting primarily males with symptoms of decreased acuity, photophobia, loss of color vision, and myopia.  The color vision defect early is incomplete but progressive cone degeneration eventually leads to achromatopsia.    Peripheral visual fields are usually full until late in the disease when constriction and nightblindness are evident.  The retina may have a tapetal-like sheen.  RPE changes in the macula often give it a granular appearance and there may be a bull's-eye configuration.   Fine nystagmus may be present as well.  The optic nerve often has some pallor beginning temporally.  Carrier females can have some diminished acuity, myopia, RPE changes, and even photophobia but normal color vision and ERG responses at least among younger individuals.

There is considerable variation in the clinical signs and symptoms in the X-linked cone-rod dystrophies among both affected males and heterozygous females.  Visual acuity varies widely and is to some extent age dependent.  Vision can be normal into the fourth and fifth decades but may reach the count fingers level after that. 

Systemic Features: 



Mutations in at least 3 genes on the X chromosome cause X-linked cone-rod dystrophy.

CORDX1 (304020) is caused by mutations in an alternative exon 15 (ORG15) of the RPGR gene (Xp11.4) which is also mutant in several forms of X-linked retinitis pigmentosa (300455, 300029).  These disorders are sometimes considered examples of X-linked ocular disease resulting from a primary ciliary dyskinesia (244400).

CORDX2 (300085) is caused by mutations in an unidentified gene at Xq27.  A single family has been reported.

CORDX3 (300476) results from mutations in CACNA1F.  Mutations in the same gene also cause a form of congenital stationary night blindness, CSNB2A (300071).  The latter, however, is a stationary disorder with significant nightblindness and mild dyschromatopsia, often with an adult onset, and is associated with high myopia. Aland Island Eye Disease (300600) is another allelic disorder.   

Treatment Options: 

There is no treatment for these dystrophies but red-tinted lenses provide comfort and may sometimes improve acuity to some extent.  Low vision aids can be helpful. 

Article Title: 


Jalkanen R, M?SSntyj?SSrvi M, Tobias R, Isosomppi J, Sankila EM, Alitalo T, Bech-Hansen NT. X linked cone-rod dystrophy, CORDX3, is caused by a mutation in the CACNA1F gene. J Med Genet. 2006 Aug;43(8):699-704.

PubMedID: 16505158

Yang Z, Peachey NS, Moshfeghi DM, Thirumalaichary S, Chorich L, Shugart YY, Fan K, Zhang K. Mutations in the RPGR gene cause X-linked cone dystrophy. Hum Mol Genet. 2002 Mar 1;11(5):605-11.

PubMedID: 11875055

Bergen AA, Pinckers AJ. Localization of a novel X-linked progressive cone dystrophy gene to Xq27: evidence for genetic heterogeneity. Am J Hum Genet. 1997 Jun;60(6):1468-73. Erratum in: Am J Hum Genet 1997 Aug;61(2):471.

PubMedID: 9199568

Hong HK, Ferrell RE, Gorin MB. Clinical diversity and chromosomal localization of X-linked cone dystrophy (COD1). Am J Hum Genet. 1994 Dec;55(6):1173-81.

PubMedID: 7977377