Isolated 17,20-lyase deficiency
Isolated 17,20-lyase deficiency (ILD), also called isolated 17,20-desmolase deficiency, is a rare endocrine and autosomal recessive genetic disorder which is characterized by a complete or partial loss of 17,20-lyase activity and, in turn, impaired production of the androgen and estrogen sex steroids. The condition manifests itself as pseudohermaphroditism (partially or fully underdeveloped genitalia) in males, in whom it is considered to be a form of intersex, and, in both sexes, as a reduced or absent puberty/lack of development of secondary sexual characteristics, resulting in a somewhat childlike appearance in adulthood (if left untreated).[1][2][3][4]
Unlike the case of combined 17α-hydroxylase/17,20-lyase deficiency, isolated 17,20-lyase deficiency does not affect glucocorticoid production (or mineralocorticoid levels), and for that reason, does not result in adrenal hyperplasia or hypertension.[1][3]
Cause
Isolated 17,20-lyase deficiency is caused by genetic mutations in the gene CYP17A1, which encodes for 17,20-lyase, while not affecting 17α-hydroxylase, which is encoded by the same gene.[2][4][5]
Observed physiological abnormalities of the condition include markedly elevated serum levels of progestogens such as progesterone and 17-hydroxyprogesterone (due to upregulation of precursor availability for androgen and estrogen synthesis), very low or fully absent peripheral concentrations of androgens such as dehydroepiandrosterone (DHEA), androstenedione, and testosterone and estrogens such as estradiol (due to the lack of 17,20-lyase activity, which is essential for their production), and high serum concentrations of the gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) (due to a lack of negative feedback on account of the lack of sex hormones).[6][7]
Symptoms
The symptoms of isolated 17,20-lyase deficiency, in males, include pseudohermaphroditism (i.e., feminized, ambiguous, or mildly underdeveloped (e.g., micropenis, perineal hypospadias, and/or cryptorchidism (undescended testes)) external genitalia), female gender identity, and, in non-complete cases of deficiency where partial virilization occurs, gynecomastia up to Tanner stage V (due to low androgen levels, which results in a lack of suppression of estrogen); in females, amenorrhoea or, in cases of only partial deficiency, merely irregular menses, and enlarged cystic ovaries (due to excessive stimulation by high levels of gonadotropins); and in both sexes, hypergonadotropic hypogonadism (hypogonadism despite high levels of gonadotropins), delayed, impaired, or fully absent adrenarche and puberty with an associated reduction in or complete lack of development of secondary sexual characteristics (sexual infantilism), impaired fertility or complete sterility, tall stature (due to delayed epiphyseal closure), eunuchoid skeletal proportions, delayed or absent bone maturation, and osteoporosis.[1][3][4][6]
Treatment
Males and females may be treated with hormone replacement therapy (i.e., with androgens and estrogens, respectively), which will result in normal sexual development and resolve most symptoms. In the case of 46,XY (genetically male) individuals who are phenotypically female and/or identify as the female gender, they should be treated with estrogens instead. Removal of the undescended testes should be performed in 46,XY females to prevent their malignant degeneration, whereas in 46,XY males surgical correction of the genitals is generally required, and, if necessary, an orchidopexy (relocation of the undescended testes to the scrotum) may be performed as well.[2] Namely in genetic females presenting with ovarian cysts, GnRH analogues may be used to control high FSH and LH levels if they are unresponsive to estrogens.[7]
See also
- Inborn errors of steroid metabolism
- Disorders of sexual development
- Intersexuality, pseudohermaphroditism, and ambiguous genitalia
- Combined 17α-hydroxylase/17,20-lyase deficiency
- GnRH, FSH, and LH insensitivities
- CYP17A1 (17α-hydroxylase/17,20-lyase)
- Sex hormone (androgen and estrogen)
References
- ↑ 1.0 1.1 1.2 "Chapter 11 – 46,XY Disorders of Sexual Development". Pediatric Endocrinology. Retrieved 2012-05-25.
- ↑ 2.0 2.1 2.2 Marschall Stevens Runge; Cam Patterson (20 June 2006). Principles of Molecular Medicine. Humana Press. p. 483. ISBN 978-1-58829-202-5. Retrieved 25 May 2012.
- ↑ 3.0 3.1 3.2 Stuart Handwerger (26 February 1999). Molecular and Cellular Pediatric Endocrinology. Humana Press. pp. 148–. ISBN 978-0-89603-406-8. Retrieved 25 May 2012.
- ↑ 4.0 4.1 4.2 Miller WL (January 2012). "The syndrome of 17,20 lyase deficiency". The Journal of Clinical Endocrinology and Metabolism 97 (1): 59–67. doi:10.1210/jc.2011-2161. PMID 22072737.
- ↑ J. I. Mason (23 May 2002). Genetics of Steroid Biosynthesis and Function. CRC Press. p. 278. ISBN 978-0-415-27878-2. Retrieved 25 May 2012.
- ↑ 6.0 6.1 Simsek E, Ozdemir I, Lin L, Achermann JC (May 2005). "Isolated 17,20-lyase (desmolase) deficiency in a 46,XX female presenting with delayed puberty". Fertility and Sterility 83 (5): 1548–51. doi:10.1016/j.fertnstert.2004.11.063. PMID 15866602.
- ↑ 7.0 7.1 ten Kate-Booij MJ, Cobbaert C, Koper JW, de Jong FH (February 2004). "Deficiency of 17,20-lyase causing giant ovarian cysts in a girl and a female phenotype in her 46,XY sister: case report". Human Reproduction (Oxford, England) 19 (2): 456–9. PMID 14747197.
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