A homozygous POC1B variant causes recessive cone-rod dystrophy

ABSTRACT

Purpose: To report a case of initial cone dystrophy that advanced to a cone-rod dystrophy with homozygous variants in the POC1B gene.

Methods: Retinal structure and visual function assessments were performed using fundoscopy, spectral-domain optical coherence tomography, full field electroretinography, semi-kinetic perimetry, and Ishihara plate testing. A DNA sample was collected and sent for diagnostic molecular genetic testing with a cone-rod dystrophy panel.

Results: Clinical examination and electroretinography confirmed a clinical diagnosis of cone dystrophy. Molecular genetic testing revealed homozygous variants in POC1B (c.1355 G > A, p.(Arg452Gln)). Follow-up three years later showed progression to a cone-rod dystrophy.

Conclusion: Our case describes an ophthalmological phenotype associated with a homozygous POC1B missense variant and provides clinical support for variant classification.

KEYWORDS:

• Photoreceptors
• cilia
• basal body
• microtubules
• centrosome

Summary Statement

We report the case of a 39-year old male with poor daytime vision, photophobia, and reduced color vision. Ophthalmological investigations were suggestive of cone dystrophy and subsequent follow-up indicated progression to a cone-rod dystrophy. Genetic testing revealed homozygous VUSs in POC1B, providing clinical support for variant reclassification and expanding our knowledge of ocular phenotypes related to variants in POC1B.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.

Additional information

Funding

Supported by Fighting Blindness Canada (AMP, IMM), Alberta Innovates Graduate Student Scholarship (NCLN) and Frederick Banting and Charles Best Canada Graduate Scholarship (CIHR) (NCLN).