Successful Pregnancy in Isolated 17,20-lyase Deficiency Without Glucocorticoid Use or Assisted Reproduction Techniques.

Isolated 17,20-lyase deficiency (ILD) is a partial form of 17α-hydroxylase/17,20-lyase deficiency that typically presents with infertility and lack of pubertal development. Successful live births have been achieved using assisted reproductive techniques. We present a case of spontaneous pregnancy in an 18-year-old female with ILD without reproduction treatments or glucocorticoid use. She presented to our clinic with absence of pubarche and oligomenorrhea and had typical external genitalia and complete breast development. Follicular phase progesterone and estradiol were within reference values, and androgen levels were undetectable. Corticosterone was increased, and cortisol responded partially to the ACTH-stimulation test. This profile raised a suspicion for ILD, which was confirmed by the finding of the homozygous p.R347H variant in the CYP17A1 gene. Sex steroid replacement and glucocorticoid use during stress were prescribed. She returned 2 years later 20 weeks pregnant. Her gestation was uneventful, and a full-term healthy male was born. This phenomenon could be partially explained by sufficient estrogen synthesis via residual 17,20-lyase enzymatic activity. Intermittent estradiol use may have favored uterine development and fine-tuned the pituitary-gonadal axis rhythm. Normal progesterone levels may have permitted an adequate endometrial "implantation window" without glucocorticoid use. Finally, elevated corticosterone may have compensated for the partial cortisol deficiency.