Acute intermittent porphyria
Is penetrance for HMBS known?
Penetrance for HMBS (the gene that causes acute intermittent porphyria) is not completely known. Most experienced porphyria specialists say the penetrance of HMBS changes is 10-20%. This means that only 10-20% of people with changes in HMBS will experience symptoms in their life. In other words 80-90% of people with the condition will not have symptoms. However, studies of entire populations suggest the penetrance might be as low as 1%. Therefore, the exact penetrance is controversial.
Acute Intermittent Porphyria. Gene Reviews. (http://www.ncbi.nlm.nih.gov/books/NBK1193/)