The essential role of the aromatase/p450arom.

Aromatase (P450arom) catalyzes the conversion of testosterone to estradiol, androstenedione to estrone, and 16a-hydroxylated dehydroepiandrosterone to estriol. P450arom is encoded by the human CYP19 gene (15q21.1) spanning about 123 kb with a coding region of 9 exons (about 30 kb, exon II to exon X). Although there are a number of alternative first exons and nine different transcriptional start sides with individual promoters that permit tissue-specific regulation of expression, the protein expressed in these various tissue sites (placenta, adipose tissue, brain, bone, ovary, etc.) always remains the same. As not only androgens but also estrogens are of importance particularly in male pubertal development including bone changes, which were classically considered androgen dependent, the features of the aromatase deficiency syndrome in affected boys and girls as well as adult males and females are discussed. There is growing awareness that androgens and estrogens have general metabolic roles that reach far beyond reproductive processes. For instance, estrogen has a significant impact on carbohydrate and lipid metabolism, vascular function, and arteriosclerosis. In addition, extragonadal estrogen biosynthesis plays an important but often underestimated physiological and pathophysiological role, for example, in breast cancer and endometriosis. Based on that knowledge, progress has been made as far as treatment and follow-up of this disorder are concerned.