Medical experts don’t know why some people develop corticobasal degeneration. The condition rarely affects members of the same family.
Nine in 10 people with the condition have a gene change (mutation) on chromosome 17. Called the H1 haplotype, this gene change may increase the production of tau, causing the protein to clump together. Or it may cause a carbon atom and hydrogens (a methyl group) to stick to the tau gene, affecting its function. But this gene mutation isn’t the only factor — the same mutation is present in 3 out of 4 people in the general population.