Study Finds a Low Prevalence of Inherited Retinal Diseases in Egyptian Cohort

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Patients in Egypt have a low inherited retinal disease prevalence of 0.2%, with isolated retinitis pigmentosa being the most common subtype, followed by Stargardt disease, cone-rod dystrophy, autosomal recessive bestrophiniopathy, and unspecified subtypes, according to new research.¹

Prior to the study, few population-based studies existed on the prevalence of inherited retinal diseases, and there were limited reports on inherited retinal diseases in an Egyptian population. Still, as investigators point out, inherited retinal disease remains a leading cause of vision loss and blindness in children and young adults. The condition affects more than 1 and a half million individuals worldwide, with many being between the ages of 15 – 45 years old.²

Because of the limited data, the new study, led by Caroline Atef Tawfik, MD, FRCS, of the faculty of medicine at Ain Shams University in Cairo, Egypt, wanted to learn about the prevalence of inherited retinal diseases in general and within the subtypes of isolated retinitis, Stargardt disease, cone-rod dystrophy, and autosomal recessive bestrophininiopathy.¹

“Population-based analysis and estimated prevalence of IRDs in Egypt has, to our knowledge, not been reported before,” wrote the investigators. “Egypt is still lagging behind in terms of diagnostics and the application of new techniques as the public healthcare system is largely underfunded.”

The investigators conducted the retrospective, hospital-based, cross-sectional study by completing an electronic medical record search of all the patients who had gone to the outpatient clinic and investigation unit of Ain Shams University Hospital and Watany Eye Hospital between the dates of January 2015 – October 2022. From there, the team extracted cases from free text by using the “text mining technique.” They sorted through the cases by keyword searches, such as dystrophy, inherited, consanguinity, among other related words. The cases were further extracted by C.A.T to test for the consistency of data.

Tawfik and colleagues studied the variables: residence, sex, age, family history, refractive error, investigations a participant went through, and lens status. The team also recorded the best-corrected visual acuity using a Snellen chart. The cases contained 478,222 patients, with a mean age of 35 years old. Males made up 59.5% of the sample.

The Egyptian participants came from several governorates. The Cairo governorate had a greater number of patients (44%). Meanwhile the Sohag governorate had 8.2% participants, the Minya governorate had 8% of participants, and Asyut governorate had 7.1% of participants.

Fifty-seven participants (5.9%) came from consanguineous families, and no data was available on this topic for 58.3% of the cases. Also, 3.3% of cases missed data for positive family history. As for lens status, cataract was found in 39.2% of patients and 48.4% had surgery for cataract.

Ultimately, the isolated retinitis pigmentosa was the most common inherited retinal disease with a prevalence of 78.9%. Stargardt followed with a prevalence of 6.3%, Usher syndrome had a prevalence of 2.4%, cone-rod dystrophy had a prevalence of 2%, and autosomal recessive bestrophinopathy had a prevalence of 1.9%.

With an overall inherited retinal disease prevalence of 0.2% (1:500), this was greater than reports from Norway (1:3856), Denmark (1:3454), and Northern France (1:1490).

The investigators noted it can be difficult to determine the inherited retinal disease diagnoses due to clinical heterogeneity and the overlap of phenotypes among the various subtypes. Also, factors that could prevent a clear diagnosis is a lack of information about disease symptoms, a lack of accurate family history and proper pedigree labeling, time of patient evaluation, confounding characteristics, and the challenge of disease progression monitoring.

“Moreover, the lack of awareness among general ophthalmologists of IRDs as well as the scarcity of IRD experts with special training who can recognize the different subtypes of IRDs, contribute to the missing or delay in identifying the phenotype which is crucial to focus genetic testing,” the team wrote.

Tawfik and colleagues could not accurately diagnose 1.5% of the cases in the analysis.

“This highlights the importance of raising awareness among ophthalmologists about [inherited retinal diseases] and the multi-modal imaging as well as functional studies that may be needed to reach a probable diagnosis,” the investigators wrote.

References

1. ^{Bunce C, Xing W, Wormald R. Causes of blind and partial sight certifications in England and Wales: April 2007-March 2008. Eye. 2010;24(11):1692–9. https://doi.org/10.1038/eye.2010.122.}
2. ^{Tawfik, C.A., Roshdy, M.M. & Morris, N.M. Prevalence of inherited retinal diseases in a large Egyptian cohort. BMC Ophthalmol 23, 422 (2023). https://doi.org/10.1186/s12886-023-03163-1}