C1QTNF5 (C1q and TNF related 5) is a membrane-associated protein that functions in retinal and systemic biology. As a plasma membrane protein capable of protein binding 1, C1QTNF5 serves multiple physiological roles. In the eye, C1QTNF5 is specifically expressed in retinal pigment epithelium (RPE) and is critical for maintaining normal retinal homeostasis 2. The protein functions as a novel attachment factor for influenza A virus, facilitating viral entry through interaction with hemagglutinin via its N-terminal region 3. Pathogenic mutations in C1QTNF5 cause late-onset retinal degeneration (L-ORD), a rare autosomal dominant macular dystrophy characterized by yellow-white punctate lesions and sub-RPE deposits that accumulate with age 4. Specific mutations like S163R result in aberrant basolateral distribution and progressive deposit formation, while other mutants (P188T, G216C) affect the RPE/photoreceptor interface through distinct mechanisms 2. C1QTNF5 mutations also associate with autosomal dominant gyrate atrophy-like choroidal dystrophy 5. Beyond ocular disease, C1QTNF5 emerges as a potential biomarker in proliferative diabetic retinopathy and Alzheimer's disease, suggesting broader roles in metabolic and inflammatory pathways 67.