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Fertility in patients with genetic deficiencies of cytochrome P450c17 (CYP17A1): combined 17-hydroxylase/17,20-lyase deficiency and isolated 17,20-lyase deficiency
Division of Reproductive Endocrinology and Infertility, Department of Obstetrics and Gynecology, University of Kansas, KU Medical Center Office, Kansas City, Kansas
Reprint requests: Richard J. Auchus, M.D., Ph.D., University of Michigan, MEND/Internal Medicine, Rm 5560A MSRBII, 1150 W. Medical Center Drive, Ann Arbor, MI 48105.
CYP17A1 catalyzes the 17-hydroxylase and 17,20-lyase reactions, regulating the steroid hormones produced by the adrenal glands and gonads. Mutations that compromise all CYP17A1 activities are extremely rare and cause combined 17-hydroxylase/17,20-lyase deficiency. Clinically, combined 17-hydroxylase/17,20-lyase deficiency presents with hypertension, hypokalemia, primary amenorrhea, and sexual infantilism. A few mutations selectively impair 17,20-lyase activity, and some mutations in cofactor proteins cytochrome P450-oxidoreductase and cytochrome b5 also selectively disrupt 17,20-lyase activity. The defect in sex steroid synthesis impairs fertility in both male and female patients when the deficiency is severe. This paper reviews the genetics, steroidogenesis, and fertility impairments associated with these disorders.
Cytochrome P450c17 (steroid 17α-hydroxylase/17,20 lyase): cloning of human adrenal and testis cDNAs indicates the same gene is expressed in both tissues.
), which yields a 57-kDa microsomal cytochrome P450c17 enzyme (CYP17A1). The CYP17A1 enzyme catalyzes both steroid 17-hydroxylase and 17,20-lyase activities (
), and both activities require one equivalent of molecular oxygen and two electrons from nicotinamide adenine dinucleotide phosphate (reduced form, NADPH). The electron transfer flavoprotein, cytochrome P450 oxidoreductase (POR), serves as a conduit for the electron transfer from NADPH to CYP17A1, but other flavoproteins can substitute for POR, at least for the 17-hydroxylase activity (
). In addition, optimal 17,20-lyase reaction requires the cofactor protein cytochrome b5 (b5); b5 stimulates the maximal rate of the reaction in the steady state over 10-fold (
Nearly 100 disease-causing mutations 17-hydroxylase/17,20-lyase deficiency (17OHD, OMIM 202110) have been described. All forms of CYP17A1 deficiency are extremely rare, and in most populations without founder mutations, 17OHD accounts for <1% of all cases of congenital adrenal hyperplasia (CAH). Although 17OHD patients are found worldwide, the disease is particularly abundant in Brazil owing to two founder mutations, R362C and W406R. Other mutations are found repeatedly, such as Y329 mutations and a deletion of residues 487–489, particularly in Asia. Mutations are found throughout the gene, with the largest number in the C-terminus, up to the last 14 amino acids. The majority of these changes are missense or nonsense single base pair substitutions, and residues prone to mutation of one or more base change include R96, R239, Y329, R362, H373, R347, R416, R440, D487, and R496. A few small deletions and duplications have been described, and large deletions account for a very few cases. In some cases, no CYP17A1 mutations have been located, despite clinical and hormonal evidence for 17-hydroxylase deficiency (
), meaning that CYP17A1 activities determine which steroid products derive from a given cell. CYP17A1 is absent in the zona glomerulosa of the adrenal and the corpora lutea of the ovary, and its expression in the placenta is low. In the adrenal zona glomerulosa, the enzyme steroid 21-hydroxylase (cytochrome P450c21, CYP21A2) converts P to 11-deoxycorticosterone (DOC). Ordinarily, the coexpression of aldosterone synthase (cytochrome P450c11AS, CYP11B2) completes the synthesis of aldosterone from DOC via three sequential oxygenations, one at C-11 and two at C-18. In the placenta and corpora lutea, the steroid hydroxylases are essentially absent, and steroidogenesis stops at P. In 17OHD and isolated 17,20-lyase deficiency, steroidogenesis mirrors the normal steroid biosynthesis in these tissues, and the physiology derives from androgen deficiency and varying degrees of mineralocorticoid excess (Fig. 1).
Figure 1Hormonal abnormalities and pathways in combined 17OHD. The block at CYP17A1 (Xs on arrows and dotted horizontal line) impairs cortisol, androgen, and estrogen synthesis. The low cortisol relieves negative feedback and increases ACTH production. Precursors pregnenolone (Preg), progesterone (Prog), DOC, and corticosterone accumulate. DOC and corticosterone cause plasma volume expansion, hypertension, and hypokalemia, which suppress renin and aldosterone. 17OHPreg = 17-hydroxypregnenolone; 17OHProg = 17-hydroxyprogesterone.
With complete deficiency of CYP17A1 (complete 17OHD), the hormonal abnormalities are summarized as androgen and estrogen deficiency with mineralocorticoid excess (
). In the adrenals, the block in cortisol biosynthesis is compensated physiologically by augmented ACTH-driven corticosterone excess (Fig. 1), which substitutes for cortisol as a glucocorticoid and prevents clinical adrenal insufficiency. The increased flux of steroids in the 17-deoxysteroid pathway, however, allows the cortisol precursor DOC to accumulate to a concentration one to two orders of magnitude above normal or higher. DOC is slightly less potent than aldosterone as a ligand for the mineralocorticoid receptor (MR), and DOC concentrations of 100 ng/dL (3 nM) activate MR and cause the hypertension and hypokalemia characteristic of 17OHD. Corticosterone is also a good MR ligand, and corticosterone excess also contributes to the hypertension of 17OHD.
The DOC and corticosterone excess in 17OHD expands plasma volume and suppresses plasma renin activity. As a result, CYP11B2 expression and aldosterone production are also low or absent in untreated patients with 17OHD (
Distinctive plasma aldosterone, 18-hydroxycorticosterone, and 18-hydroxydeoxycorticosterone profile in the 21-, 17α-, and 11β-hydroxylase deficiency types of congenital adrenal hyperplasia.
) (Fig. 1). These 18-oxygenated steroids derive from the zona fasciculata of the adrenal cortex, where expression of steroid 11β-hydroxylase (cytochrome P450c11β, CYP11B1) is high. CYP11B1 has 18-hydroxylase but not 18-oxidase activity, yielding 18-hydroxysteroids but not 18-oxo-steroids such as aldosterone. In addition, other atypical metabolites of these cortisol precursors are found in 17OHD patients, including 19-norDOC. P also accumulates above the block at 17-hydroxylase, and high P is found in 17OHD (
Impaired androgen production derives both from deficient generation of the 17-hydroxysteroid substrates for the 17,20-lyase reaction and from poor or absent 17,20-lyase activity itself. Estrogens derive from aromatization of androgens via the aromatase enzyme (cytochrome P450aro, CYP19A1). Consequently, neither androgens nor estrogens are produced from the gonads in complete 17OHD.
Based on the physiology and biochemistry described above, all individuals with complete 17OHD are born with sexual infantilism and fail to develop secondary sexual characteristics. Patients with 17OHD and 46,XX karyotypes have internal Müllerian structures with streak gonads. Patients with 17OHD and 46,XY karyotypes have a blind vaginal pouch owing to the absence of masculinization resulting from defective androgen production.
Partial 17OHD
For partial CYP17A1 deficiency to be identified, the defect must be sufficiently severe to cause clinical manifestations. Consequently, these patients are usually similar to complete 17OHD patients but with small amounts of sex steroid production. Females with partial 17OHD typically develop some secondary sexual characteristics and generally have hypertension and hypokalemia with amenorrhea in most but not all (
Induction of endometrial cycles and ovulation in a woman with combined 17α-hydroxylase/17,20-lyase deficiency due to compound heterozygous mutations on the P45017α gene.
) cases. Males with partial 17OHD are born with a disorder of sex development (DSD) with incomplete virilization, such as hypospadias with bifid scrotum or micropenis. The hormonal profile is similar to but not as severe as in complete 17OHD. The diagnosis can be challenging when the deficiency is mild, and patients with >25% residual enzyme activity might never be diagnosed.
Differential inhibition of 17α-hydroxylase and 17,20-lyase activities by three novel missense CYP17 mutations identified in patients with P450c17 deficiency.
). Boys with isolated 17,20-lyase deficiency have the unique biochemical signature of normal cortisol but low DHEA, both basal and cosyntropin-stimulated. DHEAS and testicular 19-carbon steroids are also low, and androstenedione, T, and dihydrotestosterone remain low after hCG stimulation. An hCG-stimulated 17OHP/AD ratio >50 is conclusive evidence of isolated 17,20-lyase deficiency (
), although lower ratios might be consistent with the diagnosis.
Isolated 17,20-lyase deficiency is a syndrome, which can be caused by mutations in any one of the genes encoding the three components of the 17,20-lyase catalytic system (Table 2). In addition to CYP17A1, the specific mutation G539R in its redox partner POR dramatically and rather selectively impairs the 17,20-lyase activity of CYP17A1 but leaves the 17-hydroxylase activity and the 21-hydroxylase activity of CYP21A2 relatively unchanged (
). In patients with the CYP17A1 mutation E305G, urine steroid profiling demonstrated moderately increased corticosterone and DOC metabolites, similar to but not as high as in complete 17OHD (
). These patients clinically presented with isolated 17,20-lyase deficiency, with 46,XY DSD without hypertension or hypokalemia. Finally, the purest form of isolated 17,20-lyase deficiency derives from mutations in the CYB5A gene (
), encoding the allosteric activator b5, which selectively stimulates the 17,20-lyase reaction 10-fold. These patients retain a trace of 17,20-lyase activity, about 10% of normal, which is insufficient to prevent 46,XY DSD. In contrast, all measures of 17-hydroxylase activity, such as cosyntropin-stimulated cortisol values, are normal in these individuals.
Table 2Mutations and genes causing isolated 17,20-lyase deficiency.
Gene
Mutation
Activities
17OHase
17,20-Lyase
CYP17A1
R347H
65%
<5%
R347C
14%
<1%
R358Q
65%
<5%
E305G
80%
Nil (delta-5)
150%
580% (delta-4)
POR
G539R
46%
8%
CYB5A
W27X
ND
ND
H44L
100%
<8%
Note: 17OHase = 17-hydroxylase; activities are given as percent wild-type; ND = not determined.
The decreased enzymatic activity from CYP17A1 is associated with hypergonadotropic hypogonadism and infertility. Decreased production of gonadal steroids is seen in individuals with 17OHD and can cause impaired spermatogenesis and folliculogenesis (
The microenvironment of the human antral follicle: interrelationships among the steroid levels in antral fluid, the population of granulosa cells, and the status of the oocyte in vivo and in vitro.
Arrest of follicular development in a patient with 17α-hydroxylase deficiency: folliculogenesis in association with a lack of estrogen synthesis in the ovaries.
Although generally thought to be anovulatory, there are case reports of females with 17OHD who underwent spontaneous menarche with cyclic menses. Miura and colleagues reported regular menstruation in four females with homozygous deletions of phenylalanine codon at either amino acid position 53 or 54 (delF53/54) in exon 1 of the CYP17A1 gene (
Mutation of cytochrome P-45017α gene (CYP17) in a Japanese patient previously reported as having glucocorticoid-responsive hyperaldosteronism: with a review of Japanese patients with mutations of CYP17.
). Despite a history of regular menses, one of the four females with this deletion had an episode of prolonged menstrual bleeding and underwent total hysterectomy with ovarian biopsy, which revealed an absence of corpora lutea and follicles. The delF53/54 enzyme retains partial activity, consistent with the intermediate phenotype. Similarly, Yanase et al. reported regular menstruation in a female with delF53/54 and 17,20 lyase activity that was only 5% that of normal (
Deletion of a phenylalanine in the N-terminal region of human cytochrome P-45017α results in the partial combined 17α-hydroxylase/17,20-lyase deficiency.
). Singhellakis et al. reported spontaneous sexual development and menarche in a female with 17-hydroxylase deficiency, but diagnostic testing did not include sequencing of the CYP17A1 gene or any measures of 17-hydroxylase or 17,20-lyase enzymatic activities (
Taniyama et al. reported a female with infertility who had a homozygous T-to-A transversion at nucleotide position g.2472 in exon 3 of the CYP17A1 gene (mutation Y201N) and decreased 17-hydroxylase and 17,20-lyase activities of <33% and <35% of normal, respectively (
). Clinical manifestations of her enzymatic deficiencies included hypertension, absent axillary hair, irregular menses, hypoplastic uterus, and infertility. Upon reviewing literature, Araki et al. found reports of menstruation in 15/19 females with 17OHD, with one patient reporting regular menstrual cycles (
Arrest of follicular development in a patient with 17α-hydroxylase deficiency: folliculogenesis in association with a lack of estrogen synthesis in the ovaries.
). Incomplete enzymatic blockade might explain menstruating phenotype in these females, as found in patients with the delF53/54 and Y201N mutations.
After reviewing the 17OHD literature, we found a single report of pregnancy by Levran et al., which resulted in live birth of triplets after transfer of cryopreserved embryos (
). This pregnancy resulted from treatment of four females with partial 17OHD, diagnosed by hormonal profile but not molecular genetics, who presented with infertility. These females were normotensive with hypomenorrhea and well-developed secondary sexual characteristics. All had undergone extensive fertility treatments with multiple unsuccessful IVF cycles. Upon diagnosis of partial 17OHD, an additional IVF cycle was initiated using dexamethasone to control adrenal P production, plus GnRHa, human menopausal gonadotropins, and hCG for controlled ovarian hyperstimulation (COH) during the follicular portion of cycle. Although serum concentrations of E2 were low and those of P were high throughout the cycle despite aggressive therapy, between two and 34 oocytes were aspirated with high fertilization and cleavage rates (≥50% and ≥65%, respectively).
Other attempts at fertility therapy in individuals with 17OHD have not resulted in live birth. Rabinovici et al. diagnosed and treated a 30-year-old female with 17-hydroxylase deficiency with IVF (
). Medications included prednisone as an antihypertensive and P lowering agent, GnRHa for ongoing pituitary-ovarian suppression, IM FSH for folliculogenesis, and hCG to induce ovulation. Although plasma E2 concentrations remained undetectable despite exogenous gonadotropin administration, ultrasound revealed increased follicular size consistent with follicular maturation. On cycle day 16 (day 1 being the first day of FSH administration), three oocytes were aspirated, and two progressed to the pronuclear stage after insemination. Both embryos, however, arrested at the in-cleavage stage with seven cells, and no ET occurred.
Neuwinger et al. treated a 28-year-old female with 17OHD, diagnosed by clinical symptoms and hormonal profile, with two cycles of COH and IUI followed by a cycle of IVF (
Substitution with testosterone as aromatizable substrate for induction of follicular maturation, estradiol production and ovulation in a patient with 17α-hydroxylase deficiency.
). As absence of folliculogenesis was thought to be due to a lack of aromatizable androgens, laparoscopic intraovarian injection of T propionate was administered before exogenous gonadotropins. COH cycles resulted in one to two follicles >18 mm with serum concentrations of E2 between 204 and 253 pg/mL on day 14 of the cycle. After two failed COH cycles, IVF was attempted. In this cycle, vaginal T suppositories were used with high doses of gonadotropins to stimulate folliculogenesis. Despite a relatively low serum concentration of E2 (207 pg/mL), six oocytes were retrieved but appeared markedly abnormal with intracytoplasmic vacuoles and thickened zona pellucida upon examination. No fertilization resulted after insemination.
Pellicer et al. reported a 31-year-old female with primary amenorrhea and infertility. The diagnosis of 17OHD was made during an IVF cycle by analyzing the hormonal profile of ovarian follicular fluid and granulosa-luteal cells (
). She underwent ovarian stimulation with gonadotropins, and hCG was given on cycle day 14 with fertilization of 11/19 oocytes and transfer of four embryos. The remaining embryos were cryopreserved, and as no pregnancy resulted, the embryos were thawed. The four surviving embryos were transferred without evidence of implantation.
Matsuzaki et al. attempted fertility therapy in a 26-year-old female with secondary amenorrhea and 17OHD who was a compound heterozygote for delF53/54 and the missense mutation H373L, which has <23% 17-hydroxylase activity and <5% 17,20-lyase activity compared with wild type (
Induction of endometrial cycles and ovulation in a woman with combined 17α-hydroxylase/17,20-lyase deficiency due to compound heterozygous mutations on the P45017α gene.
). Endometrial preparation with sequential transdermal E2 and IM P yielded a 6-mm endometrial stripe on ultrasound with biopsy revealing absence of stroma. A COH cycle with recombinant FSH produced a 19-mm ovarian follicle and a 6.1-mm endometrial stripe on cycle day 7, with a low serum E2 concentration of 36.5 pg/mL; no pregnancy resulted.
In addition to searching PubMed for reports on fertility in individuals with 17OHD, electronic communications were sent to over 50 authors who had published any articles regarding 17OHD. These communications yielded no additional unpublished reports of fertility therapy or pregnancy. Table 3 summarizes the published experience of fertility treatments and outcomes in patients with 17OHD.
Table 3Fertility outcomes in patients with genetic deficiencies of CYP17A1.
Substitution with testosterone as aromatizable substrate for induction of follicular maturation, estradiol production and ovulation in a patient with 17α-hydroxylase deficiency.
Induction of endometrial cycles and ovulation in a woman with combined 17α-hydroxylase/17,20-lyase deficiency due to compound heterozygous mutations on the P45017α gene.
Although a literature review by Araki et al. reported normal T production in 3/22 males with 17OHD, we found no reports of fertility in males with 17OHD (
Arrest of follicular development in a patient with 17α-hydroxylase deficiency: folliculogenesis in association with a lack of estrogen synthesis in the ovaries.
). All patients thus far described with isolated 17,20-lyase deficiency were infertile. Nevertheless, the literature might be clouded with an ascertainment bias, which might prevent the diagnosis of patients with partial defects. The diagnosis of 17OHD is typically only considered in 46,XY DSD patients when hypertension and hypokalemia are present. Milder cases of 17OHD might be assumed to be “idiopathic hypospadius” if not evaluated thoroughly. Consequently, the capacity of men with partial 17OHD to reproduce might be higher than assumed from more severe cases.
In summary, 17OHD is a rare form of CAH that is associated with infertility. The mechanism of infertility in females is likely primarily anovulation due to arrested folliculogenesis. A lack of aromatizable substrates might account for anovulation-related infertility in females with 17OHD, and chronically elevated adrenal-derived P might also contribute to infertility. The adrenal-derived P can be normalized with glucocorticoid therapy; however, the blockade in sex steroid synthesis has been difficult to overcome with conventional infertility therapies. Furthermore, gonadal-derived P will rise prematurely during gonadotropin stimulation, owing to the block of CYP17A1 in the ovaries as well. Administration of T with assisted reproductive technology did not result in pregnancy, suggesting further defects distal to the CYP17A1-catalyzed reactions. Uterine dysfunction might also contribute to impaired fertility, as hypoplastic uteri are common in females with 17OHD (
Arrest of follicular development in a patient with 17α-hydroxylase deficiency: folliculogenesis in association with a lack of estrogen synthesis in the ovaries.
Substitution with testosterone as aromatizable substrate for induction of follicular maturation, estradiol production and ovulation in a patient with 17α-hydroxylase deficiency.
). Although assisted reproductive technologies bypass some of these defects, uterine underdevelopment has been associated with impaired cervical mucus production, which impedes sperm transport. Although 17OHD case reports did not routinely report endometrial thickness, hypoplasia might also involve the endometrium, preventing implantation. The aberrant hormonal profile seen in females with 17OHD contributes to both ovarian and uterine abnormalities, with high P and low estrogen levels inhibiting follicular and endometrial growth. Successful live birth after exogenous sex steroid hormone administration with a cryopreserved ET cycle supports this theory. Oocyte dysfunction with decreased granulosa cell activity might also contribute in females with 17OHD, as circulating E2 levels were low in cycles despite administration of exogenous gonadotropins. In males, poor gonadal androgen production contributes to arrested spermatogenesis and infertility.
References
Matteson K.J.
Picado-Leonard J.
Chung B.
Mohandas T.K.
Miller W.L.
Assignment of the gene for adrenal P450c17 (17α-hydroxylase/17,20 lyase) to human chromosome 10.
Cytochrome P450c17 (steroid 17α-hydroxylase/17,20 lyase): cloning of human adrenal and testis cDNAs indicates the same gene is expressed in both tissues.
Distinctive plasma aldosterone, 18-hydroxycorticosterone, and 18-hydroxydeoxycorticosterone profile in the 21-, 17α-, and 11β-hydroxylase deficiency types of congenital adrenal hyperplasia.
Induction of endometrial cycles and ovulation in a woman with combined 17α-hydroxylase/17,20-lyase deficiency due to compound heterozygous mutations on the P45017α gene.
Differential inhibition of 17α-hydroxylase and 17,20-lyase activities by three novel missense CYP17 mutations identified in patients with P450c17 deficiency.
The microenvironment of the human antral follicle: interrelationships among the steroid levels in antral fluid, the population of granulosa cells, and the status of the oocyte in vivo and in vitro.
Arrest of follicular development in a patient with 17α-hydroxylase deficiency: folliculogenesis in association with a lack of estrogen synthesis in the ovaries.
Mutation of cytochrome P-45017α gene (CYP17) in a Japanese patient previously reported as having glucocorticoid-responsive hyperaldosteronism: with a review of Japanese patients with mutations of CYP17.
Deletion of a phenylalanine in the N-terminal region of human cytochrome P-45017α results in the partial combined 17α-hydroxylase/17,20-lyase deficiency.
Substitution with testosterone as aromatizable substrate for induction of follicular maturation, estradiol production and ovulation in a patient with 17α-hydroxylase deficiency.
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