Colorblindness-Achromatopsia 5

Clinical Characteristics

Ocular Features:

Poor visual acuity and congenital nystagmus are characteristic of ACHM5 and may be seen in infancy. Vision loss can be progressive for those who have a milder form of colorblindness or incomplete achromatopsia. Such patients have a somewhat later onset and may not have nystagmus or photophobia. Cone responses are usually absent in the ERG whereas rod responses are often normal. However, in the incomplete form there may be reduced but measureable cone responses. There may be some reduction in rod responses with disease progression. Myopia has been found in some patients. Atrophy of the RPE in the posterior pole characteristic of progressive cone dystrophies may be seen.

Systemic Features:

No systemic abnormalities are found in this disorder.

Genetics

This is an autosomal recessive disorder resulting from mutations in the PDE6C [1] gene located at 10q24. This condition is sometimes called cone dystrophy 4.

Other forms of achromatopsia are ACHM3 [2] caused by mutations in CNGB3 [3] (262300 [4]), ACHM2 [5] caused by mutations in CNGA3 [3] (216900 [6]), and ACHM4 [7] by mutations in GNAT2 [8] (139340 [9]).

Treatment

Treatment Options:

There is no treatment for the cone dystrophy but dark glasses and red colored contact lenses are helpful in reducing the photophobia and can improve acuity to some extent. Low vision aids can also be helpful.

References

Article Title:

A Nonsense Mutation in PDE6H Causes Autosomal-Recessive Incomplete Achromatopsia [10]

Kohl S, Coppieters F, Meire F, Schaich S, Roosing S, Brennenstuhl C, Bolz S, van Genderen MM, Riemslag FC; the European Retinal Disease Consortium, Lukowski R, den Hollander AI, Cremers FP, De Baere E, Hoyng CB, Wissinger B. A Nonsense Mutation in PDE6H Causes Autosomal-Recessive Incomplete Achromatopsia. Am J Hum Genet. 2012 Sep 7; 91(3) :527-32.

PubMed ID:

22901948

Homozygosity mapping reveals PDE6C mutations in patients with early-onset cone photoreceptor disorders [11]

Thiadens AA, den Hollander AI, Roosing S, Nabuurs SB, Zekveld-Vroon RC, Collin RW, De Baere E, Koenekoop RK, van Schooneveld MJ, Strom TM, van Lith-Verhoeven JJ, Lotery AJ, van Moll-Ramirez N, Leroy BP, van den Born LI, Hoyng CB, Cremers FP, Klaver CC. Homozygosity mapping reveals PDE6C mutations in patients with early-onset cone photoreceptor disorders. Am J Hum Genet. 2009 Aug;85(2):240-7.

PubMed ID:

19615668

A homologous genetic basis of the murine cpfl1 mutant and human achromatopsia linked to mutations in the PDE6C gene [12]

Chang B, Grau T, Dangel S, Hurd R, Jurklies B, Sener EC, Andreasson S, Dollfus H, Baumann B, Bolz S, Artemyev N, Kohl S, Heckenlively J, Wissinger B. A homologous genetic basis of the murine cpfl1 mutant and human achromatopsia linked to mutations in the PDE6C gene. Proc Natl Acad Sci U S A. 2009 Nov 17;106(46):19581-6.

PubMed ID:

19887631