COL4A4 and Alport syndrome: Starting from the observation that patients with AD Alport syndrome due to heterozygous mutations in COL4A3 and COL4A4 could present with a variable clinical phenotype, including isolated severe proteinuria with FSGS at kidney biopsy, Malone et al. [81] speculated that some patients receiving a generic diagnosis of FSGS could instead be mutations carriers in COL4A3 and COL4A4 and so be misclassified.