USH2A and Down syndrome: On the other hand, biallelic mutations in USH2A gene (located at 1q41), which encodes for usherin, a basement membrane protein in the inner ear and retina, underlie ∼20% of cases of non-syndromic retinitis pigmentosa, ∼7% of non-syndromic hearing loss, and up to 80% of cases of Usher syndrome (USH) type II (Koenekoop et al., 1999; McGee et al., 2010; Del Castillo et al., 2022).