Index
Choroideremia ( CHM) is a progressive, bilateral form of chorioretinal dystrophy, characterized by the progressive degeneration of the retinal pigment epithelium (RPE) and its photoreceptors that make the choroidal blood vessels visible. The initially focal lesions located in the retinal periphery with the advancement of the pathology tend to merge and progress towards the center spreading over the entire retina.
The macular region remains preserved until the last stages of the pathology allowing an easy clinical instrumental diagnosis and completely preserving the central visual quality of the patient even if tubular.
In addition to the loss of the peripheral visual field, the patient presents an enormous difficulty in adapting to the dark and in the more advanced phases presents an alteration of the chromatic sense, that is in the perception of colors, especially blue. The prevalence of this pathology is about 1 / 50.000-1 / 100.000 and usually begins in the first decade of life. The prognosis is very poor even if most patients retain useful vision up to the sixth decade of life, but then usually there is a major and sudden loss of vision. For a correct and precise diagnosis it is essential to carry out a genetic test since this pathology is caused by numerous genes. Choroideremia is caused by a mutation in the CHM gene, which encodes the proteins REP-1 and REP-2 (Rab Escort Protein) linked to Ras-GTPase, located on the X chromosome in fact the mode of transmission is X-linked recessive.
Diagnosis
For the diagnosis of this pathology it is necessary to undergo a thorough eye examination with instrumental examinations. Among these the most important are the Tomography a Optical Coherence (OCT) which will show a preservation of the normal retinal anatomy in the macular area, up to the last stages of the pathology; then going to analyze the peripheral parts you will notice the typical alterations of the photoreceptors and of the pigment epithelium; there computerized perimetry it is a fundamental examination to monitor the progression of the disease especially in the initial stage, the Electroretinogram (ERG) appears subnormal with an initial impairment of the scotopic component and in the advanced stages also of the photopic part; L'Fluorescein angiography (FAG) and theAngiography with Indocyanine Green (ICGA) are minimally invasive tests that use two different contrast media and that highlight the filling of the retinal vessels and the large choroidal vessels, but not of the choriocapillary: instead the foveal region is intact and hypofluorescent; to control the progression of the pathology that develops from the periphery to the most central area, it is advisable to use a Wilde-Field Retinography(CF).
Treatment
To date, there is no therapy in use for this pathology, but different therapeutic approaches are being tested: among these, the one that seems to be the most promising, even if still in the approval phase, is gene therapy. It aims to interrupt the degenerative process of the disease by intervening with the intraocular administration of an adeno-associated viral vector (AVV) specifically rAAV2.REP1 which allows the coding of the missing protein in originally pathological retinal cells.
Pathology and treatment on video
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