Visual function in patients with cone-rod dystrophy (CRD) associated with mutations in the ABCA4(ABCR) gene

Area of Science:

• Ophthalmology
• Genetics
• Molecular Biology

Background:

• Autosomal recessive Stargardt disease (STGD) is caused by mutations in the ABCA4 gene.
• The ABCA4 gene, also known as ABCR, plays a crucial role in retinal function.
• Understanding ABCA4 mutations is key to diagnosing and managing inherited retinal diseases.

Purpose of the Study:

• To investigate the prevalence and clinical significance of ABCA4 (ABCR) mutations in patients with cone-rod dystrophy (CRD) and retinitis pigmentosa (RP).
• To correlate specific ABCA4 genotypes with electroretinographic and visual field findings in affected individuals.
• To explore the potential role of ABCA4 mutations in the pathophysiology of visual impairment beyond STGD.

Main Methods:

• Direct sequencing of all 50 exons of the ABCA4 gene was performed.
• Genetic analysis was conducted on 40 patients diagnosed with either RP or CRD.
• Clinical data, including fundus appearance, electroretinograms (ERGs), and visual fields, were collected and analyzed.

Main Results:

• ABCR mutations were identified in one patient with RP, suggesting a compound heterozygote with characteristic fundus and ERG abnormalities.
• Mutations in ABCR were found in 37% of CRD patients, who generally exhibited reduced rod and cone ERG responses and delayed dark adaptation.
• Patients with ABCR mutations in CRD showed reduced visual acuity and pupillary responses, possibly due to a persistent 'noisy' photoproduct.

Conclusions:

• ABCA4 (ABCR) gene mutations are implicated not only in STGD but also in a significant subset of CRD cases and potentially RP.
• The presence of ABCR mutations correlates with specific clinical phenotypes, including visual acuity, ERG abnormalities, and impaired dark adaptation.
• Further research into the identified photoproduct may elucidate mechanisms of visual dysfunction in ABCR-associated retinal diseases.