COL4A4 and IgA glomerulonephritis: However, some variants in the COL4A3, COL4A4, or COL4A5 gene seem to increase the susceptibility to IgA nephropathy, which is supported by IgA deposits occasionally observed in the AS patients and the COL4A3, COL4A4, or COL4A5 gene variants reported in a minority of IgA nephropathy patients (Kamiyoshi et al., 2016; Li et al., 2020; Cambier et al., 2021).