Carriers for type II 3beta-hydroxysteroid dehydrogenase (HSD3B2) deficiency can only be identified by HSD3B2 genotype study and not by hormone test.

OBJECTIVE

We investigated adrenal steroidogenic function relevant to 3beta-hydroxysteroid dehydrogenase (HSD3B2) activity in vivo and HSD3B2 genotype in clinically normal family members of patients with HSD3B2 genotype-proven HSD3B2 deficiency congenital adrenal hyperplasia (CAH) to determine whether genotype-proven carriers for HSD3B2 deficiency exhibit decreased enzyme activity analogous to the mildly decreased adrenal 21-hydroxylase activity in the carriers of CYP21 gene mutation.

DESIGN/PATIENTS: Nineteen adult family members (ages median/range: 37/19-56 years) including 13 females and six males of six unrelated patients with HSD3B2 genotype-proven HSD3B2 deficiency were studied.

MEASUREMENTS

All family members had HSD3B2 DNA analysis and an ACTH stimulation test (Cortrosyn 0.25 mg IV bolus) for determination of adrenal HSD3B activity.

RESULTS

Ten of 13 females and five of six males were carriers of a proven or predictably deleterious mutation in one allele of the HSD3B2 gene, which was identified in the probands. ACTH-stimulated levels of 17-hydroxypregnenolone (delta5-17P), 17-hydroxyprogesterone (17-OHP), cortisol (F), dehydroepiandrosterone (DHEA) and androstenedione (delta4-A) and ratios of delta5-17P to 17-OHP, delta5-17P to F and DHEA to delta4-A, as well as increments of delta5-17P and DHEA values (ACTH-stimulated - baseline) in the genotype-proven female carriers (age, mean +/- SD: 36 +/- 6.7 years) and male carriers (age, mean +/- SD: 37 +/- 6.7 years) did not differ significantly from age-matched normal females (35 +/- 5.4 years, n = 20) and normal males (35 +/- 6 years, n = 10), respectively. There were no significant differences in any of the ACTH-stimulated hormonal levels or ratios between the female carriers with a seriously deleterious genotype (n = 5) and the female carriers with mildly deleterious genotypes (n = 5). These hormonal levels and ratios in three genotype-normal females and one genotype-normal male overlapped with those of the carriers.

CONCLUSION

These data suggest that normal adrenal HSD3B2 activity is maintained in the genotype-proven carriers because heterodimers of mutant and wild-type HSD3B2 enzymes may be stable and exhibit similar activity compared to homodimers of wild-type enzymes, possibly by a relatively rate-unlimited effect of haplo-wild-type enzyme activity. However, we cannot preclude entirely the possibility of a limited expression of another HSD3B activity under ACTH stimulation contributing to the normal adrenal HSD3B activity in vivo in the HSD3B2 genotype-proven heterozygotes. Which mechanism plays a role in maintaining normal enzyme activity in the heterozygotes remains to be elucidated. The hormone findings in the genotypic-proven carriers for HSD3B2 deficiency also indicate that carriers for this disorder cannot be detected by a hormone test and can only be detected by HSD3B2 genotype study.