Andrea Rivera

Age-related macular degeneration is associated with an unstable ARMS2 (LOC387715) mRNA

Age-related macular degeneration (AMD) is a prevalent multifactorial disorder of the central retina. Genetic variants at two chromosomal loci, 1q31 and 10q26, confer major disease risks, together accounting for more than 50% of AMD pathology. Signals at 10q26 center over two nearby genes, ARMS2 (age-related maculopathy susceptibility 2, also known as LOC387715) and HTRA1 (high-temperature requirement factor A1), suggesting two equally probable candidates. Here we show that a deletion-insertion polymorphism in ARMS2 (NM_001099667.1:c.*372_815del443ins54) is strongly associated with AMD, directly affecting the transcript by removing the polyadenylation signal and inserting a 54-bp element known to mediate rapid mRNA turnover. As a consequence, expression of ARMS2 in homozygous carriers of the indel variant is not detectable. Confirming previous findings, we demonstrate a mitochondrial association of the normal protein and further define its retinal localization to the ellipsoid region of the photoreceptors. Our data suggest that ARMS2 has a key role in AMD, possibly through mitochondria-related pathways.

A Comprehensive Survey of Sequence Variation in the ABCA4 (ABCR) Gene in Stargardt Disease and Age-Related Macular Degeneration

Stargardt disease (STGD) is a common autosomal recessive maculopathy of early and young-adult onset and is caused by alterations in the gene encoding the photoreceptor-specific ATP-binding cassette (ABC) transporter (ABCA4). We have studied 144 patients with STGD and 220 unaffected individuals ascertained from the German population, to complete a comprehensive, population-specific survey of the sequence variation in the ABCA4 gene. In addition, we have assessed the proposed role for ABCA4 in age-related macular degeneration (AMD), a common cause of late-onset blindness, by studying 200 affected individuals with late-stage disease. Using a screening strategy based primarily on denaturing gradient gel electrophoresis, we have identified in the three study groups a total of 127 unique alterations, of which 90 have not been previously reported, and have classified 72 as probable pathogenic mutations. Of the 288 STGD chromosomes studied, mutations were identified in 166, resulting in a detection rate of approximately 58%. Eight different alleles account for 61% of the identified disease alleles, and at least one of these, the L541P-A1038V complex allele, appears to be a founder mutation in the German population. When the group with AMD and the control group were analyzed with the same methodology, 18 patients with AMD and 12 controls were found to harbor possible disease-associated alterations. This represents no significant difference between the two groups; however, for detection of modest effects of rare alleles in complex diseases, the analysis of larger cohorts of patients may be required.

Insertion and Topology of Normal and Mutant Bestrophin-1 in the Endoplasmic Reticulum Membrane

The vitelliform macular dystrophy type 2 (VMD2) gene mutated in Best macular dystrophy encodes a 585-amino acid putative transmembrane protein termed bestrophin-1. The vast majority of known disease-associated alterations are of the missense type, which cluster near predicted transmembrane domains (TMDs). To investigate bestrophin-1 membrane topology and to assess consequences of point mutations on membrane integration, we have analyzed the insertion of putative TMDs into the endoplasmic reticulum (ER) membrane. Out of six potential TMDs, our data suggest a topological model of bestrophin-1 with four transmembrane-spanning segments and one large cytoplasmatic loop between putative TMD2 and TMD5. Consequently, a relatively hydrophobic segment containing putative TMD3 (aa 130-149) and TMD4 (aa 179-201) is located within the cytoplasm. Furthermore, we show that three out of 18 disease-associated alterations investigated (I73N, Y85H, F281del) reveal measurable effects on membrane insertion suggesting that defective membrane integration of bestrophin-1 may represent a potential disease mechanism for a small subset of Best macular dystrophy-related mutations.

Assessment of the contribution of CFH and chromosome 10q26 AMD susceptibility loci in a Russian population isolate

Background/aims: A strong association has been confirmed between age-related macular degeneration (AMD) and variants at two independent loci including Tyr402His in the complement factor H (CFH) on 1q32 and Ser69Ala at LOC387715, a hypothetical gene on chromosome 10q26. The contribution of both loci to AMD was investigated in an isolated north-west Russian population. Methods: Together with a PLEKHA1 variant at 10q26, the CFH Tyr402His and LOC387715 Ser69Ala polymorphisms were genotyped in 155 patients with AMD and 151 age-matched controls. χ2 and Mantel–Haenszel (M–H) score tests were used to test for association. Sex-adjusted ORs were calculated. Results: The frequency of the Tyr402His C allele was significantly higher in patients with AMD compared with controls (pM–H = 0.0035). The increased risk observed in patients homozygous for the C allele (ORHOM = 2.71, 95% CI 1.25 to 5.90) in this indigenous Russian population was considerably lower than that observed in previous western Caucasian populations. A significant increase in the frequency of the LOC387715 variant was observed in patients with late-stage AMD compared with controls (pM–H = 0.007), with a homozygous OR of 3.47 (95% CI 1.01 to 11.9), although this association was not seen with early-stage AMD. Conclusion: The CFH gene contributes to AMD in this Russian population, although the risk conferred is considerably lower in this population than that found in other Western populations. A contribution of LOC387715 to disease in this population is also likely to be of weak effect.