To further complicate matters, phenotypic variations have been found, where identical gene alterations have been associated with (i) considerably different disease phenotypes, e.g., in phenylalanine hydroxylase deficiency (PAH)[8], or (ii) in a more extreme manner in the androgen receptor (AR) gene, with both androgen insensitivity syndrome (AIS) and prostate cancer[9]. This evidence concerns the gene AR and pulmonary arterial hypertension.