Three novel CYP11B1 mutations in congenital adrenal hyperplasia due to steroid 11Beta-hydroxylase deficiency in a moroccan population

Identification and functional characterization of compound heterozygous CYP11B1 gene mutations

PURPOSE

11β-Hydroxylase deficiency (11β-OHD) is the second leading cause of congenital adrenal hyperplasia (CAH), a rare autosomal recessive disease caused by mutations in the CYP11B1 gene. We previously reported the case of a male Chinese patient with typical 11β-OHD symptoms. Sanger sequencing revealed that the patient carried a splice-site mutation, c.595+1G>A in the CYP11B1 gene. His mother and sister harbored the heterozygous mutation, c.595+1G>A. Paradoxically, Sanger sequencing did not detect any abnormality in the CYP11B1 gene of his father and brother. Therefore, in this study, we aimed to further explore the exact genetic etiology of 11β-OHD in this pedigree and analyze the functional consequence of the c.595+1G>A mutation.

METHODS

Gemomic DNA was extracted from the peripheral blood leukocytes of the family members and normal control individuals, followed by quantitative real-time polymerase chain reaction (qPCR) to detect the copy number of the target CYP11B1 gene fragment. Mutation analysis was also performed via whole-exome sequencing (WES) followed by Sanger sequencing validation. In vitro minigene assay was also performed to investigate the impact of the c.595+1G>A mutation on pre-mRNA splicing.

RESULTS

qPCR results suggested a heterozygous deletion encompassing position c.595+1 along with flanking exonic and intronic sequences in the CYP11B1 gene of the patient and his father. WES followed by Sanger sequencing verified that the patient carried compound heterozygous mutations in the CYP11B1 gene, including a novel 2840-bp deletion (c.395+661_c.1121+180del) and c.595+1G>A, while his father carried the heterozygous c.395+661_c.1121+180del mutation. No other novel CYP11B1 mutations were found in the rest of the family members. Furthermore, minigene assay revealed that the c.595+1G>A mutation resulted in a 70-bp deletion of exon 3 in the mRNA, and this altered the reading frame at amino acid 176 and created a premature stop codon at amino acid 197.

CONCLUSION

We identified a novel 2840-bp-sized large deletion and confirmed that the c.595+1G>A mutation disrupts normal pre-mRNA splicing. Either mutation could significantly alter the reading frame and abolish CYP11B1 enzyme activity. Therefore, our findings widen the mutation spectrum of CYP11B1 and provide an accurate diagnosis of 11β-OHD at a molecular genetic level.

Chimeric Genes Causing 11β-Hydroxylase Deficiency: Implications in Clinical and Molecular Diagnosis

Deficiency of 11β-hydroxylase (11β-OHD) is the second most common cause of congenital adrenal hyperplasia (CAH), accounting for 0.2-8% of all cases. The disease is transmitted as an autosomal recessive trait and the underlying genetic causes of 11β-OHD are primarily small pathogenic variants affecting the CYP11B1 gene coding the 11β-hydroxylase enzyme. However, special events complicate the molecular diagnosis of 11β-OHD such as an unequal crossing over between the CYP11B2 (coding aldosterone synthase enzyme) and CYP11B1 genes. The resulting allele contains a hybrid gene, with a CYP11B2 5'-end and a CYP11B1 3'-end, where the CYP11B1 gene is under the control of the CYP11B2 promoter and thus not responding to the adrenocorticotropin (ACTH) but to angiotensin II and K+. This leads a reduction of cortisol production in 11β-OHD. In particular, CYP11B2/CYP11B1 chimeric genes can be distinguished into two groups depending on the breakpoint site: chimeras with breakpoint after the exon 5 of CYP11B2 preserve the aldosterone synthase activity, the others with breakpoint before exon 5 lose this function. In the last case, a more severe phenotype is expected. The aim of this review was to explore the setting of CYP11B2/CYP11B1 chimeras in 11β-OHD, performing a careful review of clinical literature cases.

Unequal crossing over between CYP11B2 and CYP11B1 causes 11 β -hydroxylase deficiency in a consanguineous family

Cytochrome P450 (CYP) family CYP11B2/CYP11B1 chimeric genes have been shown to arise from unequal crossing over of the genes encoding aldosterone synthase (CYP11B2) and 11β-hydroxylase (CYP11B1) during meiosis. The activity deficiency or impaired activity of aldosterone synthase and 11β-hydroxylase resulting from these chimeric genes are important reasons for 11β-hydroxylase deficiency (11β-OHD). Here，two patients with pseudoprecocious puberty and hypokalemia hypertension and three carriers in a consanguineous marriage family were studied. A single CYP11B2/CYP11B1 chimera consisting of the promoter and exons 1 through 5 of CYP11B2, exons 8 and 9 of CYP11B1, and a breakpoint consisting of part of exon 6 of CYP11B2 and part of exon 6, intron 6, and exon 7 of CYP11B1 were detected in the patients and carriers. At the breakpoint of the chimera, a c 0.1086 G > C ( p.Leu.362 =) synonymous mutation in exon 6 of CYP11B2, a c 0.1157 C＞G(p. A386V) missense mutation in exon 7 of CYP11B1, and an intronic mutation in intron 6 were detected. The allele model of the CYP11B2/CYP11B1 chimera demonstrated homozygosity and heterozygosity in the patients and the carriers, respectively. Molecular docking and enzymatic activity analyses indicated that the CYP11B2/CYP11B1 chimeric protein interacted with the catalytic substrate of aldosterone synthase and had similar enzymatic activity to aldosterone synthase. Our study indicated that deletion of CYP11B1 and CYP11B2 abolished the enzymatic activity of 11 β-hydroxylase and aldosterone synthase; however, the compensation of the enzymatic activity of aldosterone synthase by the CYP11B2/CYP11B1 chimeric protein maintained normal aldosterone levels in vitro. All of the above findings explained the 11β-OHD phenotypes of the proband and patients in the family.

A Novel Homozygous Pathogenic Variant in CYP11B1 in a Female Iranian Patient with 11B Hydroxylase Deficiency

Objective

Congenital adrenal hyperplasia (CAH) addresses a number of autosomal recessive disorders characterized by the enzyme defects in steroid hormones biosynthesis. The second common form of CAH is caused by mutations in the CYP11B1 gene. Here, we reveal a novel mutation in the CYP11B1 gene related to the 11βOHD phenotype.

Methods and Results

Sequence analysis of the CYP11B1 gene in a 19-year-old Iranian woman with the 11βOHD phenotype was performed. In silico analysis and molecular docking were done. A novel missense homozygous variant c.1351C > T (p.L451F) in the CYP11B1 gene was identified in the patient and, according to American College of Medical Genetics and Genomics criteria, was categorized as likely pathogenic. Protein docking showed destructive effects of the variant on the CYP11B1 protein-ligand interactions.

Conclusion

This study broadens the CYP11B1 mutation spectrum and introduces the novel p.L451F likely pathogenic variant leading to destructive effects on protein-ligand interactions. Our results provide reliable information for genetic counseling and molecular diagnostics of CAH.

[Congenital adrenal hyperplasia due to 11β-hydroxylase deficiency: late diagnosis and gender reassignment in a two-year-old child]

11β-hydroxylase deficiency is a rare autosomal recessive disorder due to impaired steroidogenesis in the adrenal cortex caused by pathogenic mutations in the CYP11B1 gene. The main clinical manifestations are determined by a deficiency of cortisol, ACTH hyperproduction, excessive androgens secretion and the accumulation of 11-deoxycorticosterone, which leads to the development of arterial hypertension. In the diagnostic search, it is important to take into account the ethnicity of the patient, since the frequency of the disease and the prevalence of mutations differ between ethnic groups. The article presents a clinical case of 11β-hydroxylase deficiency as the result of compound heterozygous mutations in the CYP11B1 gene in a patient of Turkic origin. This case shows the clinical manifestations and the development of complications of 11β-hydroxylase deficiency, the stages of differential diagnosis of patients with 21-hydroxylase deficiency.

Congenital Adrenal Hyperplasias Presenting in the Newborn and Young Infant

Congenital adrenal hyperplasia includes autosomal recessive conditions that affect the adrenal cortex steroidogenic enzymes (cholesterol side-chain cleavage enzyme; 3β-hydroxysteroid dehydrogenase; 17α-hydroxylase/17,20 lyase; P450 oxidoreductase; 21-hydroxylase; and 11β-hydroxylase) and proteins (steroidogenic acute regulatory protein). These are located within the three major pathways of the steroidogenic apparatus involved in the production of mineralocorticoids, glucocorticoids, and androgens. Many countries have introduced newborn screening program (NSP) based on 17-OH-progesterone (17-OHP) immunoassays on dried blood spots, which enable faster diagnosis and treatment of the most severe forms of 21-hydroxylase deficiency (21-OHD). However, in several others, the use of this diagnostic tool has not yet been implemented and clinical diagnosis remains challenging, especially for males. Furthermore, less severe classic forms of 21-OHD and other rarer types of CAHs are not identified by NSP. The aim of this mini review is to highlight both the main clinical characteristics and therapeutic options of these conditions, which may be useful for a differential diagnosis in the neonatal period, while contributing to the biochemical evolution taking place in the steroidogenic field. Currently, chromatographic techniques coupled with tandem mass spectrometry are gaining attention due to an increase in the reliability of the test results of NPS for detecting 21-OHD. Furthermore, the possibility of identifying CAH patients that are not affected by 21-OHD but presenting elevated levels of 17-OHP by NSP and the opportunity to include the recently investigated 11-oxygenated androgens in the steroid profiles are promising tools for a more precise diagnosis and monitoring of some of these conditions.

46,XX DSD due to Androgen Excess in Monogenic Disorders of Steroidogenesis: Genetic, Biochemical, and Clinical Features

The term 'differences of sex development' (DSD) refers to a group of congenital conditions that are associated with atypical development of chromosomal, gonadal, or anatomical sex. Disorders of steroidogenesis comprise autosomal recessive conditions that affect adrenal and gonadal enzymes and are responsible for some conditions of 46,XX DSD where hyperandrogenism interferes with chromosomal and gonadal sex development. Congenital adrenal hyperplasias (CAHs) are disorders of steroidogenesis that mainly involve the adrenals (21-hydroxylase and 11-hydroxylase deficiencies) and sometimes the gonads (3-beta-hydroxysteroidodehydrogenase and P450-oxidoreductase); in contrast, aromatase deficiency mainly involves the steroidogenetic activity of the gonads. This review describes the main genetic, biochemical, and clinical features that apply to the abovementioned conditions. The activities of the steroidogenetic enzymes are modulated by post-translational modifications and cofactors, particularly electron-donating redox partners. The incidences of the rare forms of CAH vary with ethnicity and geography. The elucidation of the precise roles of these enzymes and cofactors has been significantly facilitated by the identification of the genetic bases of rare disorders of steroidogenesis. Understanding steroidogenesis is important to our comprehension of differences in sexual development and other processes that are related to human reproduction and fertility, particularly those that involve androgen excess as consequence of their impairment.

Typical characteristics of children with congenital adrenal hyperplasia due to 11β-hydroxylase deficiency: a single-centre experience and review of the literature

Background 11β-hydroxylase deficiency (11βOHD) is a rare disease representing the second most common cause of congenital adrenal hyperplasia (CAH) (5-8%) with an incidence of about 1:100,000. In contrast to 21-hydroxylase deficiency (21OHD), 11βOHD is not included in neonatal screening programmes. The objective of this study was to demonstrate the typical features of male patients with 11βOHD. Methods Clinical, biochemical and radiological data of patients with 11βOHD were analysed in this retrospective single-centre analysis. Results Six male patients of four unrelated families with 11βOHD were identified (0.1-13.5 years of chronological age [CA] at diagnosis). The predominant symptoms were arterial hypertension, tall stature and precocious pseudopuberty. Bone ages (BAs) were remarkably advanced at diagnosis in four index patients (median difference BA-CA: 5.5 years, range 1.5-9.2 years). Homozygous mutations were identified in exon 7 (c.1179_1180dupGA [p.Asn394Argfs*37]) and exon 8 (c.1398+2T>C) of the CYP11B1 gene leading both to a complete loss of function. The latter mutation has not yet been described in databases. 11βOHD was identified by the measurement of 11-deoxycortisol in a newborn screening card of one patient retrospectively. Testicular adrenal rest tumours (TARTs) were detected in three patients at 3.7 years, 11 years and 14.4 years. Conclusion The diagnosis of CAH due to 11βOHD is delayed and should be suspected in children with arterial hypertension, tall stature and precocious pseudopuberty. Patients may develop TARTs as early as infancy. 11βOHD should be included in newborn screening programmes, at least in newborns of index families, to allow early diagnosis and the start of treatment to reduce morbidity.

MECHANISMS IN ENDOCRINOLOGY: Rare defects in adrenal steroidogenesis

Congenital adrenal hyperplasia (CAH) is a group of genetic disorders of adrenal steroidogenesis that impair cortisol synthesis, with compensatory increases in ACTH leading to hyperplastic adrenals. The term 'CAH' is generally used to mean 'steroid 21-hydroxylase deficiency' (21OHD) as 21OHD accounts for about 95% of CAH in most populations; the incidences of the rare forms of CAH vary with ethnicity and geography. These forms of CAH are easily understood on the basis of the biochemistry of steroidogenesis. Defects in the steroidogenic acute regulatory protein, StAR, disrupt all steroidogenesis and are the second-most common form of CAH in Japan and Korea; very rare defects in the cholesterol side-chain cleavage enzyme, P450scc, are clinically indistinguishable from StAR defects. Defects in 3β-hydroxysteroid dehydrogenase, which also causes disordered sexual development, were once thought to be fairly common, but genetic analyses show that steroid measurements are generally unreliable for this disorder. Defects in 17-hydroxylase/17,20-lyase ablate synthesis of sex steroids and also cause mineralocorticoid hypertension; these are common in Brazil and in China. Isolated 17,20-lyase deficiency can be caused by rare mutations in at least three different proteins. P450 oxidoreductase (POR) is a co-factor used by 21-hydroxylase, 17-hydroxylase/17,20-lyase and aromatase; various POR defects, found in different populations, affect these enzymes differently. 11-Hydroxylase deficiency is the second-most common form of CAH in European populations but the retention of aldosterone synthesis distinguishes it from 21OHD. Aldosterone synthase deficiency is a rare salt-losing disorder. Mild, 'non-classic' defects in all of these factors have been described. Both the severe and non-classic disorders can be treated if recognized.

Prevalence, clinical characteristics and long-term outcomes of classical 11 β-hydroxylase deficiency (11BOHD) in Turkish population and novel mutations in CYP11B1 gene

Congenital adrenal hyperplasia (CAH) due to 11β-hydroxylase deficiency (11BOHD) is a rare autosomal recessive disorder and the second most common form of CAH.

AIM

To investigate genotype-phenotype correlation and to evaluate clinical characteristics and long-term outcomes of patients with 11BOHD.

METHODS

A total of 28 patients (n = 14, 46,XX; n = 14, 46,XY) with classical 11BOHD from 25 unrelated families were included in this study. Screening of CYP11B1 is performed by Sanger sequencing. Pathogenic features of novel variants are investigated by the use of multiple in silico prediction tools and with family based co-segregation studies. Protein simulations were investigated for two novel coding region alterations.

RESULTS

The age at diagnosis ranged from 6 days to 12.5 years. Male patients received diagnose at older ages than female patients. The rate of consanguinity was high (71.4%). Five out of nine 46,XX patients were diagnosed late (age 2-8.7 years) and were assigned as male due to severe masculinization. Twenty one patients have reached adult height and sixteen were ultimately short due to delayed diagnosis. Two male patients had testicular microlithiasis and 5 (35.7%) patients had testicular adrenal rest tumor during follow up. Four patients (28.6%) had gynecomastia. Mutation analyses in 25 index patients revealed thirteen different mutations in CYP11B1 gene, 4 of which were novel (c.393 + 3A > G, c.428G > C, c.1398 + 2T > A, c.1449_1451delGGT). The most frequent mutations were c.896T > C with 32%, c.954G > A with 16% and c.1179_1180dupGA with 12% in frequency. There was not a good correlation between genotype and phenotype; phenotypic variability was observed among the patients with same mutation.

CONCLUSION

This study presents the high allelic heterogeneity of CYP11B1 mutations in CAH patients from Turkey. Three dimensional protein simulations may provide additional support for the pathogenicity of the genetic alterations. Our results provide reliable information for genetic counseling, preventive and therapeutic strategies for the families.

Identification of seven novel CYP11B1 gene mutations in Chinese patients with 11β-hydroxylase deficiency

Steroid 11β-hydroxylase deficiency (11β-OHD), one of common cause of congenital adrenal hyperplasia (CAH), is an autosomal recessive disorder characterized by virilization, precocious pseudo-puberty, and hypertension. It is caused by CYP11B1 gene mutation. We performed molecular genetic analysis of the CYP11B1 gene in six patients with preliminary clinical diagnosis of 11β-OHD and four patients identified as potential 11β-OHD from a CAH cohort in which CYP21A2 gene mutations consecutively screened. Seven novel CYP11B1 mutations, including p.R454H, p.Q472P, p.Q155X, p.K173X, IVS2-1G>A, R454A fs 573X, and g.2704_g.3154del, and six previously described mutations (p.P94L, p.G267S, p.G379V, p.R448H, p.R454C and p.R141X) were identified. These mutations mainly clustered in exons 3 and 8. Eight of twenty alleles carried mutations occurring at the Arg454 position, which is a mutational hot spot for Han Chinese. The pathogenic nature of novel p.R454H mutation was predicted by protein sequence alignment and in silico analysis. All the identified mutations were responsible for the clinical features observed in these ten unrelated Chinese patients. This study expands the CYP11B1 mutation spectrum and provides evidence for prenatal diagnosis and genetic counseling. Genetic analysis is an alternative approach to help clinicians confirm uncertain 11β-OHD diagnosis, facilitating reasonable steroid replacement.

Characterisation of three novel CYP11B1 mutations in classic and non-classic 11β-hydroxylase deficiency

BACKGROUND

Congenital adrenal hyperplasia (CAH) is one of the most common autosomal recessive inherited endocrine diseases. Steroid 11β-hydroxylase (P450c11) deficiency (11OHD) is the second most common form of CAH.

AIM

The aim of the study was to study the functional consequences of three novel CYP11B1 gene mutations (p.His125Thrfs*8, p.Leu463_Leu464dup and p.Ser150Leu) detected in patients suffering from 11OHD and to correlate this data with the clinical phenotype.

METHODS

Functional analyses were done by using a HEK293 cell in vitro expression system comparing WT with mutant P450c11 activity. Mutant proteins were examined in silico to study their effect on the three-dimensional structure of the protein.

RESULTS

Two mutations (p.His125Thrfs*8 and p.Leu463_Leu464dup) detected in patients with classic 11OHD showed a complete loss of P450c11 activity. The mutation (p.Ser150Leu) detected in a patient with non-classic 11OHD showed partial functional impairment with 19% of WT activity.

CONCLUSION

Functional mutation analysis enables the correlation of novel CYP11B1 mutations to the classic and non-classic 11OHD phenotype respectively. Mutations causing a non-classic phenotype show typically partial impairment due to reduced maximum reaction velocity comparable with non-classic mutations in 21-hydroxylase deficiency. The increasing number of mutations associated with non-classic 11OHD illustrate that this disease should be considered as diagnosis in patients with otherwise unexplained hyperandrogenism.

Two novel CYP11B1 mutations in congenital adrenal hyperplasia due to steroid 11β hydroxylase deficiency in a Tunisian family

Steroid 11β hydroxylase deficiency (11β-OHD) (OMIM # 202010) is the second most common form of congenital adrenal hyperplasia (CAH), accounting for 5-8% of all cases. It is an autosomal recessive enzyme defect impairing the biosynthesis of cortisol. The CYP11B1 gene encoding this enzyme is located on chromosome 8q22, approximately 40kb from the highly homologous CYP11B2 gene encoding for the aldosterone synthase. Virilization and hypertension are the main clinical characteristics of this disease. In Tunisia, the incidence of 11β-OHD appears higher due to a high rate of consanguinity (17.5% of congenital adrenal hyperplasia). The identical presentation of genital ambiguity (females) and pseudo-precocious puberty (males) can lead to misdiagnosis with 21 hydroxylase deficiency. The clinical hallmark of 11β hydroxylase deficiency is variable, and biochemical identification of elevated precursor metabolites is not usually available. In order to clarify the underlying mechanism causing 11β-OHD, we performed the molecular genetic analysis of the CYP11B1 gene in a female patient diagnosed as classical 11β-OHD. The nucleotide sequence of the patient's CYP11B1 revealed two novel mutations in exon 4: a missense mutation that converts codon AGT (serine) to ATT (isoleucine) (c.650G>T; p.S217I) combined with an insertion of a thymine at the c.652-653 position (c.652_653insT). This insertion leads to a reading frame shift, multiple incorrect codons, and a premature stop in codon 258, that drastically affects normal protein function leading to a severe phenotype with ambiguous genitalia of congenital adrenal hyperplasia due to 11β hydroxylase deficiency.

Mineralocorticoid hypertension

Hypertension affects about 10 - 25% of the population and is an important risk factor for cardiovascular and renal disease. The renin-angiotensin system is frequently implicated in the pathophysiology of hypertension, be it primary or secondary. The prevalence of primary aldosteronism increases with the severity of hypertension, from 2% in patients with grade 1 hypertension to 20% among resistant hypertensives. Mineralcorticoid hypertension includes a spectrum of disorders ranging from renin-producing pathologies (renin-secreting tumors, malignant hypertension, coarctation of aorta), aldosterone-producing pathologies (primary aldosteronism - Conns syndrome, familial hyperaldosteronism 1, 2, and 3), non-aldosterone mineralocorticoid producing pathologies (apparent mineralocorticoid excess syndrome, Liddle syndrome, deoxycorticosterone-secreting tumors, ectopic adrenocorticotropic hormones (ACTH) syndrome, congenitalvadrenal hyperplasia), and drugs with mineraocorticoid activity (locorice, carbenoxole therapy) to glucocorticoid receptor resistance syndromes. Clinical presentation includes hypertension with varying severity, hypokalemia, and alkalosis. Ratio of plasma aldosterone concentraion to plasma renin activity remains the best screening tool. Bilateral adrenal venous sampling is the best diagnostic test coupled with a CT scan. Treatment is either surgical (adrenelectomy) for unilateral adrenal disease versus medical therapy for idiopathic, ambiguous, or bilateral disease. Medical therapy focuses on blood pressure control and correction of hypokalemia using a combination of anti-hypertensives (calcium channel blockers, angiotensin converting enzyme inhibitors, or angiotensin receptor blockers) and potassium-raising therapies (mineralcorticoid receptor antagonist or potassium sparing diuretics). Direct aldosterone synthetase antagonists represent a promising future therapy.

Inherited forms of mineralocorticoid hypertension

PURPOSE OF REVIEW

Inherited forms of mineralocorticoid hypertension are a group of monogenic disorders that, although rare, have enlightened our understanding of normal physiology, and subsequent processes implicated in the pathogenesis of 'essential' hypertension. They often present in early life and can be a cause of major morbidity and mortality that can be effectively treated with simple but targeted pharmacological therapy. Interestingly, all the conditions centre on the regulation of sodium transport through its epithelial channel, either directly or through mediators that act via the mineralocorticoid receptor.

RECENT FINDINGS

In recent years, molecular mechanisms of these conditions and their functional consequences have been elucidated. Diagnosis has been facilitated by plasma and urinary biomarkers.

SUMMARY

We provide an overview and diagnostic approach to apparent mineralocorticoid excess, glucocorticoid remediable aldosteronism, familial hyperaldosteronism type 2, Liddle's syndrome, Gordon's syndrome, activating mutations of the mineralocorticoid receptor, generalized glucocorticoid resistance and hypertensive forms of congenital adrenal hyperplasia.

The molecular biology, biochemistry, and physiology of human steroidogenesis and its disorders

Steroidogenesis entails processes by which cholesterol is converted to biologically active steroid hormones. Whereas most endocrine texts discuss adrenal, ovarian, testicular, placental, and other steroidogenic processes in a gland-specific fashion, steroidogenesis is better understood as a single process that is repeated in each gland with cell-type-specific variations on a single theme. Thus, understanding steroidogenesis is rooted in an understanding of the biochemistry of the various steroidogenic enzymes and cofactors and the genes that encode them. The first and rate-limiting step in steroidogenesis is the conversion of cholesterol to pregnenolone by a single enzyme, P450scc (CYP11A1), but this enzymatically complex step is subject to multiple regulatory mechanisms, yielding finely tuned quantitative regulation. Qualitative regulation determining the type of steroid to be produced is mediated by many enzymes and cofactors. Steroidogenic enzymes fall into two groups: cytochrome P450 enzymes and hydroxysteroid dehydrogenases. A cytochrome P450 may be either type 1 (in mitochondria) or type 2 (in endoplasmic reticulum), and a hydroxysteroid dehydrogenase may belong to either the aldo-keto reductase or short-chain dehydrogenase/reductase families. The activities of these enzymes are modulated by posttranslational modifications and by cofactors, especially electron-donating redox partners. The elucidation of the precise roles of these various enzymes and cofactors has been greatly facilitated by identifying the genetic bases of rare disorders of steroidogenesis. Some enzymes not principally involved in steroidogenesis may also catalyze extraglandular steroidogenesis, modulating the phenotype expected to result from some mutations. Understanding steroidogenesis is of fundamental importance to understanding disorders of sexual differentiation, reproduction, fertility, hypertension, obesity, and physiological homeostasis.