Human molecular genetics vol:22 issue:2 pages:391-397
Mutations in COL4A1 have been identified in families with hereditary small vessel disease of the brain presumably due to a dominant negative mechanism. Here we report on two novel mutations in COL4A1 in two families with porencephaly, intracerebral hemorrhage and severe white matter disease caused by haploinsufficiency.Two families with various clinical presentations of cerebral microangiopathy and autosomal dominant inheritance were examined. Clinical, neuroradiological and genetic investigations were performed. Electron microscopy of the skin was also performed.In one of the families, sequence analysis revealed a one base deletion, c.2085del, leading to a frameshift and a premature stopcodon, p.(Gly696fs). In the other family, a splice site mutation was identified, c.2194-1G>A, which most likely leads to skipping of an exon with a frameshift and premature termination as a result. In fibroblasts of affected individuals from both families nonsense mediated decay of the mutant COL4A1 mRNAs and a clear reduction of COL4A1 protein expression was demonstrated, indicating haploinsufficiency of COL4A1. Moreover thickening of the capillary basement membrane in the skin was documented, similar to reports in patients with COL4A1 missense mutations.These findings suggest haploinsufficiency, a different mechanism than the commonly assumed dominant-negative effect, for COL4A1 mutations as a cause of (antenatal) intracerebral hemorrhage and white matter disease.