Stargardt Phenotype Associated With Two ELOVL4 Promoter Variants and ELOVL4 Downregulation: New Possible Perspective to Etiopathogenesis?

PURPOSE. Stargardt disease (STGD) is the most common form of inherited juvenile macular degeneration. It is inherited as autosomal recessive trait (STGD1), although STGD3 and STGD4 are inherited as autosomal dominant inheritance pattern. STGD3 is caused by mutations in the elongation of very long-chain fatty acids-like 4 (ELOVL4) gene encoding for a very long-chain fatty acid elongase. Mutations lead to a truncated Elovl4, lacking of a dilysine motif necessary for retention of transmembrane proteins in the endoplasmic reticulum. STGD occurs due to altered synthesis of very long-chain polyunsaturated fatty acids (VLC-PUFA). Our work investigates the role of two variants in the ELOVL4 gene promoter region, c.-236 C>T (rs240307) and c.-90 G>C (rs62407622), identified in a patient with STGD in transconfiguration. METHODS. Their effects on ELOVL4 expression were examined by Dual-Luciferase Reporter assay. RESULTS. rs62407622 and rs240307 variants caused 14% and 18% of expression reduction, respectively, compared with wild-type promoter. A very strong decreased gene expression was caused by coexistence of both variants. CONCLUSIONS. A highly reduced activity of the ELOVL4 promoter was registered due to combination of two variants. Decrease of ELOVL4 enzymatic activity could lead to a deficiency of VLC-PUFA, essential components for rods function and longevity, which are among the parameters involved in the etiopathogenesis of STGD.