PURPOSE: Galloway-Mowat syndrome (GAMOS) is a clinically heterogenous and rare condition classically described as the combination of nephrotic syndrome associated with brain anomaly and delays in development. It was first reported in the literature in 1968 by Galloway W.H and Mowat A.P. Reports of visual anomaly in these patients are generally limited to decreased visual acuity, nystagmus and optic nerve atrophy. To this day, little is known about retinal function in this disease. Therefore, the purpose of this case report is to reveal abnormal retinal function (including light-adapted and dark-adapted retinal function) in a female patient diagnosed with GAMOS due to mutation of the WDR73 gene. METHODS: Complete dilated pediatric ophthalmic examination and ISCEV full field standard light (10 min of light adaptation; background light: 30 cd.m; flash intensity: 3.0 cd.sec.m) and dark-adapted (20 min of dark adaptation; flash intensities: 0.01, 3.0 and 10.0 cd.sec.m) electroretinograms were performed on a 2-year-old female patient diagnosed with GAMOS due to a biallelic mutation in the WDR73 gene. RESULTS: Ophthalmologic evaluation under anesthesia revealed normal appearing anterior segments. Significant bilateral optic nerve pallor was noted. Fundus examination appeared to be abnormal and demonstrated mid-peripheral whitish glistening appearance with possible gliosis. Retinoscopy revealed bilateral high myopia with a refractive error of -8.00 sphere in both eyes. ISCEV standard ERG revealed residual responses under light-adapted condition. Undetectable responses were obtained after 20 min of dark adaptation when using a dim flash (DA 0.01). However, when brighter flashes were used in a dark-adapted condition (DA 3.0 and DA 10.0), the ERGs were detectable, albeit abnormal in amplitudes and of electronegative morphology. CONCLUSIONS: The results obtained showed significant retinal functional deficit affecting both the cone and the rod photoreceptor pathways, along with the inner retina, in a patient diagnosed with GAMOS due to biallelic mutations in the WDR73 gene. Our report is limited to one patient, and additional studies are needed to verify whether retinal functional anomalies, as measured by the full field electroretinogram, present a novel biomarker in all patients affected with GAMOS or only in patients with a mutation in the WDR73 gene. Given the evidence of retinal functional changes presented in this study, it is strongly suggested to include complete ophthalmic examination, retinal imaging, including OCT, and full field ERG testing in patients affected with GAMOS.