Mutational scanning of the ABCR gene with double-gradient denaturing-gradient gel electrophoresis (DG-DGGE) in Italian Stargardt disease patients

Mutations in the retina-specific ABC transporter (ABCR) gene are responsibl e for autosomal recessive Stargardt disease (arSTGD). Mutation detection ef ficiency in ABCR in arSTGD patients ranges between 30% and 66% in previousl y published studies, because of high allelic heterogeneity and technical li mitations of the employed methods. Conditions were developed to screen the ABCR gene by double-gradient denaturing-gradient gel electrophoresis. The e fficacy of this method was evaluated by analysis of DNA samples with previo usly characterized ABCR mutations. This approach was applied to mutation de tection in 44 Italian arSTGD patients corresponding to 36 independent genom es, in order to assess the nature and frequency of the ABCR mutations in th is ethnic group. In 34 of 36 (94.4%) STGD patients, 37 sequence changes wer e identified, including 26 missense, six frameshift, three splicing, and tw o nonsense variations. Among these, 20 had not been previously described. S everal polymorphisms were detected in affected individuals and in matched c ontrols. Our findings extend the spectrum of mutations identified in STGD p atients and suggest the existence of a subset of molecular defects specific to the Italian population. The identification of at least two disease-asso ciated mutations in four healthy control individuals indicates a higher tha n expected carrier frequency of variant ABCR alleles in the general populat ion. Genotype-phenotype analysis in our series showed a possible correlatio n between the nature and location of some mutations and specific ophthalmos copic features of STGD disease.