A Novel ABCA4 Mutation Associated with a Late-Onset Stargardt Disease Phenotype: A Hypomorphic Allele?

BACKGROUND

Stargardt disease (STGD) is the most common juvenile hereditary macular dystrophy. In the majority of cases, the diagnosis is made prior to 20 years of age and usually leads to loss of central vision. Late-onset STGD affects a smaller number of patients. Identifying genetic changes which could be associated with clinically important differences in severity or presentation of the disease is important for understanding the mechanisms of visual loss and for planning future therapeutic approaches.

METHODS

We report a patient with the classic phenotype of STGD with late-onset mild disease exhibiting a slow clinical progression over 14 months of follow-up.

RESULTS

A 37-year-old man presented with STGD and good vision of 6/24 in the right eye and of 6/6 in the left eye as well as typical electrophysiology findings. Objective and subjective visual deterioration was not noted over a period of 14 months. Macular genetic testing revealed a novel missense mutation in ABCA4 (Thr829Met) combined with Gly1961Glu, a classic STGD mutation usually associated with a moderately severe phenotype.

CONCLUSIONS

It is suggested that the Thr829Met mutation could give rise to a hypomorphic allele of the ABC transporter with a resultant phenotype of comparatively mild STGD.

20/20--Alcohol and age-related macular degeneration: the Melbourne Collaborative Cohort Study

Little evidence exists regarding associations between age-related macular degeneration (AMD) and moderate alcohol consumption, patterns of consumption, or different types of alcoholic beverage. The authors examined associations between AMD prevalence and alcohol intake using 20,963 participants from the Melbourne Collaborative Cohort Study aged 40-69 years at baseline (1990-1994). Participants' alcohol consumption was determined from a structured interview at baseline. At follow-up from 2003 to 2007, digital macula photographs of both eyes were taken and evaluated for early and late AMD signs. Drinking more than 20 g of alcohol per day was associated with an approximate 20% increase in the odds of early AMD (odds ratio = 1.21, 95% confidence interval: 1.06, 1.38; P = 0.004) when compared with those who reported no alcohol intake at baseline, having adjusted for sex, age, smoking, country of birth, education, physical activity, and energy from food. This positive association was apparent for wine, beer, and spirits. The estimates were similar for both sexes. The odds ratio for those drinking more than 20 g of alcohol per day for late AMD was 1.44 (95% confidence interval: 0.85, 2.45; P = 0.17). These results show a modest association between alcohol consumption and increased AMD risk.

Apolipoprotein E gene associations in age-related macular degeneration: the Melbourne Collaborative Cohort Study

The apolipoprotein E gene (APOE) has been found to be associated with age-related macular degeneration (AMD). Reported associations have been questioned, as they are opposite those for Alzheimer's disease and cardiovascular disease. The authors examined associations between APOE genotype and AMD using a case-control study (2,287 cases and 2,287 controls individually matched on age, sex, and country of origin) nested within Melbourne Collaborative Cohort Study participants aged 48-86 years at AMD detection. The odds ratio for early AMD among participants with ε2-containing genotypes (ε2ε2/ε2ε3/ε2ε4) was 1.32 (95% confidence interval (CI): 1.11, 1.58; P = 0.002) versus persons with genotype ε3ε3. Associations with early AMD varied by smoking status; ε2-containing genotypes were positively associated with early AMD for never and previous smokers (never smokers: odds ratio (OR) = 1.40, 95% CI: 1.12, 1.76 (P = 0.003); previous smokers: OR = 1.39, 95% CI: 1.00, 1.93 (P = 0.05)) but not for current smokers (OR = 0.66, 95% CI: 0.34, 1.30 (P = 0.2; interaction P = 0.05). The ε4-containing genotype group (ε3ε4/ε4ε4) had an inverse association with early AMD among current smokers only (OR = 0.41, 95% CI: 0.22, 0.77 (P = 0.005)). These results highlight the importance of stratifying by smoking status in elderly populations. Smokers who survive to old age may be more likely to possess unknown genotypes which modify exposure-disease associations.

Abdominal obesity and age-related macular degeneration

Evidence for an association between age-related macular degeneration (AMD) and obesity is inconsistent. The authors examined associations between adiposity and AMD prevalence using 21,287 participants from the Melbourne Collaborative Cohort Study aged 40-69 years at baseline (1990-1994). For men, each increase of 0.1 in waist/hip ratio (~1 standard deviation) was associated with a 13% increase in the odds of early AMD (odds ratio = 1.13, 95% confidence interval: 1.01, 1.26; P = 0.03) and a 75% increase in the odds of late AMD (odds ratio = 1.75, 95% confidence interval: 1.11, 2.76; P = 0.02). No other adiposity measure was associated with early AMD for men. Smoking status modified the relation between waist/hip ratio and early AMD (P = 0.05), with no association for former smokers. For women, there were inverse associations with early AMD for all adiposity measures (odds ratios = 0.89-0.93; P = 0.002-0.02), but no associations were observed for late AMD. This study confirms abdominal obesity as an AMD risk factor for men despite a survivorship effect from competing risks in morbidity and mortality. The inverse associations for women may reflect weaker true positive associations with AMD that are insufficient to overcome the survivorship effect. New data are provided on complex interactions between environmental exposures and AMD risk.