According to the USH2A model of allelic hierarchy proposed by Lenassi et al., patients with two ‘null’ alleles (variants in trans that lead to protein truncation and/or NMD) present with USH2 due to the loss of functional protein, whereas patients with at least one ‘retinal disease-specific’ allele (missense/splice site-altering/other variants not leading to significant protein truncation) undergo normal cochlear development due to the presence of a partially functional protein [4]. This evidence concerns the gene USH2A and Abnormal retinal morphology.