Complete achromatopsia (type 2) and Incomplete achromatopsia

Achromatopsia, or color blindness, is a rare autosomal recessive retinal disorder characterized by color blindness, nystagmus, photophobia and visual acuity. It is caused by a deficiency in the photoreceptor cells known as cones.

Achromatopsia (ACHM) is a rare vision disease that affects approximately one in 30,000 people. This pathology damages certain photoreceptor cells of the retina (specifically the cones) in a way that has serious consequences on vision.

Most individuals who suffer from it have total achromatopsia, with complete absence of activity in all three types of cones. Rarely, incomplete forms of the disease are found with similar, but generally less severe, symptoms.

It is currently known that there are up to 6 genes related to this pathology and about 90% of cases of achromatopsia are due to alterations in the CNGA3 and CNGB3 genes.

Symptoms

Patients with ACHM have poor visual acuity, photophobia and nystagmus (rapid involuntary eye movements) and are unable to distinguish colors. Nystagmus usually appears after birth or in early childhood.

Since photoreceptor function is impaired almost from birth there is no true progression of symptoms over time.

Disease management

No approved therapy is available. Treatment is symptomatic and includes the use of lenses or glasses with special filters to reduce photophobia, improve visual acuity and prevent light damage to the retina. Patients must be followed up by ophthalmologists for the rest of their lives.

Genes analyzed

ATF6 CNGA3 CNGB3 PDE6C PDE6H

Bibliography

Kohl S, Varsanyi B, Antunes GA, et al. CNGB3 mutations account for 50% of all cases with autosomal recessive achromatopsia. Eur J Hum Genet. 2005 Mar;13(3):302-8.

Kohl S, Coppieters F, Meire F, et al. A nonsense mutation in PDE6H causes autosomal-recessive incomplete achromatopsia. Am J Hum Genet. 2012 Sep 7;91(3):527-32.

Michalakis S, Gerhardt M, Rudolph G, et al. Achromatopsia: Genetics and Gene Therapy. Mol Diagn Ther. 2022 Jan;26(1):51-59.

Solaki M, Baumann B, Reuter P, et al. Comprehensive variant spectrum of the CNGA3 gene in patients affected by achromatopsia. Hum Mutat. 2022 Jul;43(7):832-858.