ACRD presents with clinical features of hyperandrogenism in females similar to those of PCOS (acne, hirsutism, oligomenorrhea, infertility), and precocious puberty in males. Obesity also occurs in some cases. Increased cortisol clearance leads to an increased hypothalamic-pituitary-adrenal axis drive resulting in elevated serum androgen levels and a decreased urinary cortisol metabolite: cortisone metabolite ratio below 0.5 (normal adult range 0.71.3). These observations are explained by defects in hexose-6-phosphate dehydrogenase (H6PD), an enzyme providing NADPH to 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) - a NADPH-dependant enzyme which converts the inactive pro-hormone cortisone to biologically active cortisol. We have previously indicated that an R453Q mutation observed in ACRD cases is partially responsible for disease manifestation, however recent population studies have reported no association between R453Q and cortisol metabolism or hyperandrogenism.
Our current study aimed to investigate whether individuals selected based on their steroid metabolism profiles had mutations in their H6PD gene that may predispose them to ACRD. Using a DNA bank and biochemical data generated from a cardiovascular study in Scotland we selected 4 individuals with a low cortisol metabolite: cortisone metabolite ratio (<0.35) and sequenced the H6PD gene.
Results identified 5 previously reported single nucleotide polymorphisms (SNPs) (A212A; A247A; R453Q; P554L; T673T). We also identified a novel SNP (R269R) and a novel 8 bp deletion polymorphism located in the genomic sequence encoding the 5′ untranslated region with an allele frequency of 8% in normal individuals from the same study (n=86 alleles). Interestingly we also discovered a novel non-conservative missense mutation, S459C, with a control allele frequency of 0% (n=122 alleles). This individual was heterozygous for the S459C allele which replaces the hydrophilic-neutral amino acid serine with a hydrophobic cysteine residue. The ser459 residue is highly conserved across species suggesting it plays an important structural or functional role. Based on this current data, In vitro mutagenesis studies are underway to determine the effect of this mutation on the activity of H6PD.
This study indicates that the H6PD gene is highly polymorphic and screening on the basis of steroid biochemistry has yielded a potential variant promoting the manifestation of ACRD.