Figure 1 Familial primary pulmonary hypertension (PPH). A hypothetical pedigree illustrating reduced genetic penetrance of the disease (that is, skipping of generations) as seen in individuals II:2 and III:2, "anticipation" (earlier age of onset in successive generations), and the female preponderance. Open square, unaffected male; open circle, unaffected female; closed square, affected male; closed circle, affected female; slash, deceased.