Biochemical defects in retina-specific human ATP binding cassette transporter nucleotide binding domain 1 mutants associated with macular degeneration.
Assuming pseudodominant (recessive) inheritance of allelic defects, linkage analysis positioned the causal gene at 1p21-p13 (lod score 4.22), a genomic segment known to harbor the ABCR gene involved in Stargardt's disease (STGD) and age-related macular degeneration (AMD).
In a subset of inherited retinal degenerations (including cone, cone-rod, and macular dystrophies), cone photoreceptors are more severely affected than rods; ABCA4 mutations are the most common cause of this heterogeneous class of disorders.
Since the retina is highly sensitive to peroxidation and the GPX gene product protects cells from oxidative damage, and the fact that the ABCR gene is considered as a major disease gene in macular degeneration we reasoned that they might serve as candidate genes in a subset of ARMD cases.
Although population studies have indicated that some ABCR variant alleles may enhance susceptibility to AMD, investigation of the extent of ABCR involvement by kindred analysis is complicated by a plethora of environmental and other hereditary factors not investigated in the current study that may also play important roles.
Stargardt disease, type 1 (STGD1) or macular degeneration with flecks, STGD1 represents a disease with early onset, central visual impairment, frequent appearance of yellowish flecks and mutations in the ATP-binding cassette subfamily A, member 4 (ABCA4) gene.
These findings support the hypothesis that compound heterozygous ABCR mutations are responsible for STGD1 and that some heterozygous ABCR mutations may enhance susceptibility to AMD.
Homozygous and compound heterozygous ABCA4 mutations are associated with various autosomal recessive retinal dystrophies, whereas heterozygous ABCA4 mutations have been associated with dominant susceptibility to age-related macular degeneration in both humans and mice.
Genetic variation in the ABCR (ABCA4) gene has been associated with five distinct retinal phenotypes, including Stargardt disease/fundus flavimaculatus (STGD/FFM), cone-rod dystrophy (CRD), and age-related macular degeneration (AMD).
To address the latter issue, this study aimed to expand on earlier efforts by (1) evaluating risk-altering variants known to be associated with age-related macular degeneration (AMD), a frequent maculopathy in individuals over 55 years of age, and (2) determining the contribution of genetic variants in the coding sequence of the ABCA4 gene.
Generalized choriocapillaris dystrophy is a progressive ABCA4-associated phenotype characterized by early-onset macular dystrophy that disperses and expands to widespread end-stage chorioretinal atrophy with profound visual loss.
The new 6730-16del44 deletion is the first de novo mutation associated with cone-rod dystrophy and may contribute to a better understanding of the role of ABCA4 mutations in macular dystrophies.