Characterization of the ABCA4 gene in Stargardt's Disease in Trinidad and Tobago

ABSTRACT

Objectives: Stargardt's disease is an autosomal recessive macular dystrophy caused by mutations in the photoreceptor cell-specific ATP-binding cassette sub-family A member 4, transporter (ABCA4) gene. We studied (i) the predicted effects of mutations on the function of the ABCA4 transporter and (ii) the existence of four common mutations in local Stargardt patients. Design and Methodology: (i) The freeware PROVEAN (Protein VariationEffect Analyzer; J. Craig Venter Institute, CA,USA) was used to predict the deleterious effect257 mutations in the ABCA4 gene. PROVEANscores below -2.5 were considered deleterious.One-way ANOVAs were used to detect anysignificant differences in mean (±SE) PROVEANscores among mutation types or protein domains I,II, III or IV. (ii) Using saliva, DNA was isolated from three Stargardt patients. Chromosomal regions were amplified by PCR, sequenced (Macrogen Inc., Seoul, Korea) and sequence alignment (NCBI, MD, USA) used to detect the presence of four mutations; c.768G>T (p.Val256=), c.4469G>A (p.Cys1490Tyr), c.6079C>T (p.Leu2027Phe) and c.1804C>T (p.Arg602Trp). Results: (i) Sixty-three percent of mutations predicted deleterious effects. There were no significant (p<0.05) differences between mean PROVEAN scores among mutation types (substitutions, - 4.49±0.20; deletions/insertions, -6.35±0.67) or protein domains (domain I, -4.79 ± 0.39; domain II, -4.65 ± 0.36; domain III, -5.48 ± 0.51; domain IV, -4.39 ± 0.34). (ii) These mutations were not detected in Stargardt's patients. Conclusion: (i) Functionality of the ABCA4 protein is affected by multiple mutations. (ii) Novel mutations are present in local patients. Currently, we seek to profile novel mutations in six families using molecular inversion probes.