The W198X and R173W mutations in the porphobilinogen deaminase gene in acute intermittent porphyria have higher clinical penetrance than R167W. A population-based study.

In northern Sweden, 468 patients with DNA-verified acute intermittent porphyria (AIP) were registered. A higher prevalence of manifest AIP was found in patients with mutations W198X and R173W when separately compared with mutation R167W, indicating higher clinical penetrance. Signs of increased seriousness of the disease were also found in patients with the W198X and R173W mutations in relation to the number and duration of attacks, impaired renal function and chronic disability. One explanation could be lower PBGD enzyme activity resulting from the W198X and R173W mutations than from the R167W mutation, though other factors might also be the cause.