COL4A4 and Alport syndrome: During the recent International Workshops on Alport Syndrome held in Siena, Italy, from 22 to 26 October 2019, and online, from 30 November to 4 December 2021, members of the International Alport Syndrome Alliance discussed the issue of clinical heterogeneity in patients who carry heterozygous pathogenic variants in the COL4A3 or COL4A4 genes and present with Alport spectrum disease, while others present with later-onset phenotypes due to a thinner than normal GBM.