Retinitis Punctata Albescens
Retinitis punctata albescens (RPA) is a rare form of non-syndromic, autosomal recessive inherited retinal dystrophy. It is generally referred to as a subtype of autosomal recessive retinitis pigmentosa with specific characteristics.
RPA is an inherited retinal dystrophy characterised by progressive night blindness and presence of small white dots on the retina (in the fundus).
RPA prevalence is currently estimated at 1/ 800 000 people.
RPA is caused in most cases by mutations in the RLBP1 gene
Except for a few patients with autosomal dominant inheritance, most RPA cases are autosomal recessive and show bi-allelic mutations in the RLBP1 gene.
The causative gene, RLBP1, encodes the cellular retinaldehyde binding protein (CRALBP), which plays an important role in the visual cycle. RLBP1 gene is mainly expressed in the retinal pigment epithelium (RPE) and Müller glial cells of the retina. CRALBP protein is involved in the retinoid metabolism, also called vitamin A metabolism, and functions as a carrier protein for endogenous retinoids.
Clinical presentation of Retinitis punctata albescens
Clinical evolution comprises a night blindness from 3 to 4 years of age, and a progressive loss of peripheral visual field. Then, at 40 years, the visual field decreases leading to blindness. ERG profiles show a reduced scotopic response and a slight reduction in the amplitude of the photopic responses.
Occasionally, optic nerve pallor, constriction of retinal vessels, pigment deposits or macular degeneration can be observed.
Albescent punctuations in the fundus are the hallmark of the disease. Numerous white punctate outer retinal spots occur surrounding, but generally not including, the central macula and extend toward the equator.