Apparent pregnene hydroxylation deficiency (APHD): seeking the parentage of an orphan metabolome

This paper collates and reviews a number of clinical cases published over the last 20 years that we believe describe a novel steroid disorder associated with genital ambiguity. The authors of the original papers were unable to diagnose their patients conclusively. Females with the disorder are frequently masculinized and males feminized. The central feature of steroid biosynthesis is overproduction of pregnenolone and progesterone, which results in elevated concentrations of these steroids in plasma and exaggerated response to ACTH. Equivalent urinary data show elevated excretion of 5-pregnene-3beta,20alpha-diol (the major pregnenolone metabolite) and pregnanediol. Another notable feature of the metabolome is the relatively high plasma concentrations of the analytes for 21-hydroxylase deficiency (17-hydroxyprogesterone) and 17-hydroxylase deficiency (corticosterone). Correspondingly, metabolites of these steroids are prominent in urine. Circulating cortisol was generally normal but had blunted response to ACTH. Taken together these features pointed to an apparent relative deficiency of 21- and 17-hydroxylation, but no mutations have been found in the enzymes responsible for these transformations in cases where it has been investigated. The simultaneous presence of mutated genes on two chromosomes is also extremely unlikely. Until more is known of this interesting condition, and the genetic cause (presumed) is known, we propose naming it apparent pregnene hydroxylation deficiency (APHD). The metabolome is similar to that of isolated 17,20-lyase deficiency with which it has been confused. In fact, diminished (but not isolated) lyase activity is probably a significant factor in some patients. We believe that the attenuated steroid hydroxylation could be associated with deficiency of the required co-factors and modulators of hydroxylation such as P450 reductase and cytochrome b5. Post-translational modifications of the hydroxylases such as phosphorylation/dephosphorylation have also been suggested as influential in directionally regulating steroid synthesis. Some patients with the disorder have no dysmorphology apart from genital malformations while others have skeletal abnormalities attributed to Antley-Bixler syndrome. Whether we are looking at different conditions, or a severity continuum is not known. It is possible that the presence of this metabolome may become a required feature for diagnosis of Antley-Bixler syndrome. A combination of intersex phenotype and dysmorphology suggests that an error in a transcription factor may be an alternative to hydroxylation redox partner deficit as causative of the condition.The virilization of female patients with APHD probably results from a transient hyperandrogenism prior to birth.