RLBP1 retinal dystrophy

RLBP1 retinal dystrophy is a rare form of non-syndromic, autosomal recessive inherited retinal dystrophy. It is generally considered a subtype of autosomal recessive retinitis pigmentosa with specific characteristics.

RLBP1 retinal dystrophy is characterised by early onset night blindness and the presence of small white dots on the retina (in the fundus). According to Hartong et al. (Lancet 2006; 368: 1795–809) this dystrophy affects between 900 and 1,200 persons (North America + EU 5 main countries).

RLBP1 retinal dystrophy is caused in most cases by mutations in the RLBP1 gene. With the exception of a few patients with autosomal dominant inheritance, most cases are autosomal recessive and characterised by 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 is mainly expressed in the retinal pigment epithelium (RPE) and Müller glial cells of the retina. CRALBP protein is involved in retinoid metabolism, also known as vitamin A metabolism or the visual cycle, and functions as a carrier protein for endogenous retinoids.

 

Clinical presentation of RLBP1 retinal dystrophy

Clinical symptoms are similar to those of retinitis pigmentosa, but with two features unique to this dystrophy: night blindness, which is usually present from birth or the first years of life; and the presence of numerous white dots in fundus, surrounding but generally not affecting the central macula and extending towards the equator. These white dots enable early clinical diagnosis of RLBP1 retinal dystrophy. In adulthood, the peripheral visual field progressively decreases in daylight, as also occurs in retinitis pigmentosa. The results of fundus examination are similar to those found in retinitis pigmentosa patients, albeit with greater preservation of the macular zone. ERG responses are absent in the adults. Over time, the macula becomes atrophic, leading to blindness.

Appearance of the fundus

Appearance of the fundus

Photo courtesy of Christian Hamel.