WES identified a heterozygous mutation in COL4A1, which is known to cause a cerebral small vessel disease (SVD) with symptoms including transient ischaemic attacks, adult-onset haemorrhagic stroke, periventricular brain abnormalities, white matter hyperintensities and leukoencephalopathy (including cerebellar hypoplasia, cerebral atrophy and vascular changes) [51–53]. Here, COL4A1 is linked to snowflake vitreoretinal degeneration.