ABCA4 mutational spectrum in Mexican patients with Stargardt disease: Identification of 12 novel mutations and evidence of a founder effect for the common p.A1773V mutation.

The aim of this study was to assess the mutational spectrum of the ABCA4 gene in a cohort of patients with Stargardt disease from Mexico, a previously uncharacterized population. Clinical diagnosis in each patient was supported by a complete ophthalmological assessment that included visual acuity measurement, a slit lamp examination, a fundus examination and photography, electroretinography, fluorescein angiography, and computerized visual fields testing. Molecular analysis was performed by PCR amplification and direct nucleotide sequence of the 50 exons of the ABCA4 gene in genomic DNA. A total of 31 unrelated subjects with the disease were enrolled in the study. Molecular analysis in the total group of 62 alleles allowed the identification of 46 mutant ABCA4 alleles carrying 29 different pathogenic disease-associated mutations. Two ABCA4 mutant alleles were detected in 20 of the 31 patients (64.5%), a single disease allele was identified in six (19.4%), and no mutant alleles were detected in five of the cases (16.1%). Most patients with two ABCA4 mutations (11/20, 55%) were compound heterozygotes. Twelve variants were novel ABCA4 mutations. Nucleotide substitutions were the most frequent type of variation, occurring in 26 out of 29 (89.7%) different mutations. The two most common mutations in our study were the missense changes p.A1773V and p.G818E, which were identified in eight (17%) and seven (15%) of the total 46 disease-associated alleles, respectively. Haplotype analyses of intragenic SNPs in four subjects carrying the p.A1773V mutation supported a common origin for this mutation. In conclusion, this is the first report of ABCA4 molecular screening in Latin American Stargardt disease patients. Our results expand the mutational spectrum of the disease by adding 12 novel ABCA4 pathogenic variants and support the occurrence of a founder effect for the p.A1773V mutation in the Mexican population. The identification of recurrent mutations in our cohort will direct future ABCA4 molecular screening in patients from this ethnic group.