Hereditary retinal dystrophies

Achromatopsia is characterized by cone dysfunction, being the most common cone disorder occurring at a prevalence ranging from 1/30,000 to 1/50,000.

The diagnosis results from the aggregation of clinical data, examination of the eye fundus and electrophysiological tests. They are characterized by a significant visual defect from birth, a pendular nystagmus, hyperopia, and photophobia. The eye fundus is usually normal, although sometimes we can see a lack of foveolar reflex or pigmentary alterations at the macular level. In the electrophysiological tests, a normal response of the rods and an absence of signal from the cones are observed. Alterations of the IS-OS band in the retinal pigment epithelium can be seen in optical coherence tomography; it has recently also been used to distinguish ACHM from blue cone monochromatism, where symptoms are similar, but of lesser magnitude.

The follow-up of these patients is performed annually with refraction under cycloplegia and study of the anterior segment and eye fundus.

The inheritance pattern is autosomal recessive and 5 genes responsible for the disease have been identified, which encode proteins that participate in the phototransduction cascade of the cones, namely: CNGB3 (representing between 50-87%), CNGA3 (5-23%), GNAT2 (2%), and PDE6C and PDE6H being less frequent. There are already animal models for the 3 most frequent types of genes and gene therapy has been tested, obtaining good results with restoration of the electroretinogram, which has prompted the start of new clinical trials in humans.