Retinal degeneration associated with RDH12 mutations results from decreased 11- cis retinal synthesis due to disruption of the visual cycle

Abstract

Retinoid dehydrogenases/reductases catalyze key oxidation-reduction reactions in the visual cycle that converts vitamin A to 11-cis retinal, the chromophore of the rod and cone photoreceptors. It has recently been shown that mutations in RDH12, encoding a retinol dehydrogenase, result in severe and early-onset autosomal recessive retinal dystrophy (arRD). In a cohort of 1011 individuals diagnosed with arRD, we have now identified 20 different disease-associated RDH12 mutations, of which 16 are novel, in a total of 22 individuals (2.2%). Haplotype analysis suggested a founder mutation for each of the three common mutations: p.L99I, p.T155I and c.806_810delCCCTG. Patients typically presented with early disease that affected the function of both rods and cones and progressed to legal blindness in early adulthood. Eleven of the missense variants identified in our study exhibited profound loss of catalytic activity when expressed in transiently transfected COS-7 cells and assayed for ability to convert all-trans retinal to all-trans retinol. Loss-of-function appeared to result from decreased protein stability, as expression levels were significantly reduced. For the p.T49M variant, differing activity profiles were associated with each of the alleles of the common p.R161Q RDH12 polymorphism, suggesting that genetic background may act as a modifier of mutation effect. A locus (LCA3) for Leber congenital amaurosis, a severe, early-onset form of arRD, maps close to RDH12 on chromosome 14q24. Haplotype analysis in the family in which LCA3 was mapped excluded RDH12 as the LCA3 gene and thus suggests the presence of a novel arRD gene in this region.

Identity-by-descent–guided mutation analysis and exome sequencing in consanguineous families reveals unusual clinical and molecular findings in retinal dystrophy

“…The causal mutation in F3 and F4 is a known missense mutation (c.464C>T, p.Thr155Ile; see Supplementary Table S1 online), shown to reduce the conversion of all-trans retinal to all-trans retinol. 17 No family members were available for segregation testing in F4. In F5, a novel missense mutation was identified, c.803G>T (p.Cys268Phe), which is predicted to affect protein function by a selection of prediction programs (Supplementary Table S1 online).…”

Mechanisms of RDH12-Induced Leber Congenital Amaurosis and Therapeutic Approaches

“…As mentioned, mutations of RDH12 associated with LCA resulted in a decreased enzymatic activity of RDH12, inhibiting the reduction of all-trans retinal and 4-HNE to the corresponding alcohols in vitro [7,10,11,15].…”

“…Since then, more than 30 RDH12 mutations have been found in the homozygous or compound heterozygous state in LCA13 patients [7][8][9][10][11]. LCA13 is inherited in an autosomal recessive manner and represents about 4% of all LCA cases [2].…”

“…A number of RDH12 mutations leading to LCA have been biochemically evaluated by expressing the mutants in cultured cells and by measuring the enzymatic activities of the recombinant enzymes [7][8][9][10][11]. These studies have shown that mutations in RDH12 result in decreased or abolished enzymatic activity due to a lower affinity for the substrate or a lower affinity for the coenzyme and/or to a decreased specific activity.…”

“…These studies have shown that mutations in RDH12 result in decreased or abolished enzymatic activity due to a lower affinity for the substrate or a lower affinity for the coenzyme and/or to a decreased specific activity. In addition, most of RDH12 mutations resulted in low steady-state levels of the mutant proteins in cells [11,13]. It was hypothesized that these mutants could be recognized as misfolded and targeted for accelerated degradation by the ubiquitin-proteasome system [13].…”