Normal genes for the cholesterol side chain cleavage enzyme, P450scc, in congenital lipoid adrenal hyperplasia

History of Adrenal Research: From Ancient Anatomy to Contemporary Molecular Biology

The adrenal is a small, anatomically unimposing structure that escaped scientific notice until 1564 and whose existence was doubted by many until the 18th century. Adrenal functions were inferred from the adrenal insufficiency syndrome described by Addison and from the obesity and virilization that accompanied many adrenal malignancies, but early physiologists sometimes confused the roles of the cortex and medulla. Medullary epinephrine was the first hormone to be isolated (in 1901), and numerous cortical steroids were isolated between 1930 and 1949. The treatment of arthritis, Addison's disease, and congenital adrenal hyperplasia (CAH) with cortisone in the 1950s revolutionized clinical endocrinology and steroid research. Cases of CAH had been reported in the 19th century, but a defect in 21-hydroxylation in CAH was not identified until 1957. Other forms of CAH, including deficiencies of 3β-hydroxysteroid dehydrogenase, 11β-hydroxylase, and 17α-hydroxylase were defined hormonally in the 1960s. Cytochrome P450 enzymes were described in 1962-1964, and steroid 21-hydroxylation was the first biosynthetic activity associated with a P450. Understanding of the genetic and biochemical bases of these disorders advanced rapidly from 1984 to 2004. The cloning of genes for steroidogenic enzymes and related factors revealed many mutations causing known diseases and facilitated the discovery of new disorders. Genetics and cell biology have replaced steroid chemistry as the key disciplines for understanding and teaching steroidogenesis and its disorders.

[Dizygotic pregnancy as a possible mechanism of fetal gestation with a biallel mutation in the CYP11A1 gene: clinical case description]

One of the variants of congenital dysfunction of the adrenal cortex is a deficiency of the enzyme P450scc, which catalyzes the first stage of steroidogenesis. This is a rare autosomal recessive disease, the classic manifestation of which is primary adrenal insufficiency with a deficiency of gluco-and mineralocorticoids and a violation of the synthesis of sex steroids, which usually leads to a complete lack of masculinization in patients with karyotype 46, XY and hypergonadotropic hypogonadism in both sexes. Previously, it was suggested That p450scc deficiency is incompatible with the normal course of pregnancy, since the enzyme is expressed in the placenta, where it is necessary for the synthesis of progesterone, the main pregnancy hormone, and, consequently, the birth of a child with A p450scc deficiency is impossible. However, the literature describes clinical cases of p450scc deficiency with partially preserved enzyme function, which explains the normal course of pregnancy. Whereas cases of confirmed p450scc deficiency with zero enzyme activity are unique, not being explained until now. We present a description of severe p450scc deficiency in a child born from a dizygotic twin pregnancy in which the second Sib was healthy. It is possible that the preserved hormonal function of the second placenta and (or) treatment with progesterone analogs during gestation contributed to gestation in this rare form of steroidogenesis disorder.

Clinical and genetic characterization of congenital lipoid adrenal hyperplasia

Disorders of steroid synthesis are a group of anomalies caused by defects in any step of conversion of cholesterol into steroid hormones. The disorders are characterized by defects leading to abnormalities of salt-water balance and/or sexual differentiation. Congenital lipoid adrenal hyperplasia (CLAH) is the most severe form of steroid synthesis disorder caused by the accumulation of cholesterol in the outer mitochondrial membrane due to steroidogenic acute regulatory protein (StAR) deficiency. Pathogenic sequence variants in the gene STAR encoding StAR protein leads to CLAH. In the present study, a Pakistani family was clinically diagnosed with the LAH phenotype. Sanger sequencing of STAR in the family revealed a novel homozygous nonsense mutation [c.295G>T, p.(Glu99*)] in the living affected individual. The study was designed to assist in carrier testing and prenatal diagnosis within the affected family. In addition, searching for common variants in the STAR gene would help in designing low-cost targeted variation testing in other patients.

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.

An overview of inborn errors of metabolism manifesting with primary adrenal insufficiency

Primary adrenal insufficiency (PAI) results from an inability to produce adequate amounts of steroid hormones from the adrenal cortex. The most common causes of PAI are autoimmune adrenalitis (Addison's disease), infectious diseases, adrenalectomy, neoplasia, medications, and various rare genetic syndromes and inborn errors of metabolism that typically present in childhood although late-onset presentations are becoming increasingly recognized. The prevalence of PAI in Western countries is approximately 140 cases per million, with an incidence of 4 per 1,000,000 per year. Several pitfalls in the genetic diagnosis of patients with PAI exist. In this review, we provide an in-depth discussion and overview on the inborn errors of metabolism manifesting with PAI, including genetic diagnosis, genotype-phenotype relationships and counseling of patients and their families with a focus on various enzymatic deficiencies of steroidogenesis.

Aberrant Splicing Is the Pathogenicity Mechanism of the p.Glu314Lys Variant in CYP11A1 Gene

Context: The cholesterol side chain cleavage enzyme (CYP11A1) catalyzes the conversion of cholesterol to pregnenolone, the first rate-limiting step of steroidogenesis. CYP11A1 mutations are associated with primary adrenal insufficiency (PAI) as well as disorders of sex development (DSD) in 46,XY patients. Objective: To define the pathogenicity mechanism for the p.Glu314Lys variant, previously reported, and found in four additional patients with CYP11A1 deficiency. Subjects and Methods: DNA of four patients presenting with delayed PAI and/or 46,XY DSD were studied by Sanger or Massively Parallel sequencing. Three CYP11A1 mutations were characterized in vitro and in silico, and one by mRNA analysis on testicular tissue. Results: All patients were compound heterozygous for the previously described p.Glu314Lys variant. In silico studies predicted this mutation as benign with no effect on splicing but mRNA analysis found that it led to incomplete exon 5 skipping. This mechanism was confirmed by minigene experiment. The protein carrying this mutation without exon skipping should conserve almost normal activity, according to in vitro studies. Two other mutations found in trans, the p.Arg120Gln and p.Arg465Trp, had similar activity compared to negative control, consistent with the in silico studies. Conclusions: We provide biological proof that the p. Glu314Lys variant is pathogenic due to its impact on splicing and seems responsible for the moderate phenotype of the four patients reported herein. The present study highlights the importance of considering the potential effect of a missense variant on splicing when it is not predicted to be disease causing.

Alternative Polyadenylation in Human Diseases

Varying length of messenger RNA (mRNA) 3'-untranslated region is generated by alternating the usage of polyadenylation sites during pre-mRNA processing. It is prevalent through all eukaryotes and has emerged as a key mechanism for controlling gene expression. Alternative polyadenylation (APA) plays an important role for cell growth, proliferation, and differentiation. In this review, we discuss the functions of APA related with various physiological conditions including cellular metabolism, mRNA processing, and protein diversity in a variety of disease models. We also discuss the molecular mechanisms underlying APA regulation, such as variations in the concentration of mRNA processing factors and RNA-binding proteins, as well as global transcriptome changes under cellular signaling pathway.

Genetics of Congenital Adrenal Hyperplasia

Congenital adrenal hyperplasia (CAH) refers to a group of autosomal recessive disorders due to single-gene defects in the various enzymes required for cortisol biosynthesis. CAH represents a continuous phenotypic spectrum with more than 95% of all cases caused by 21-hydroxylase deficiency. Genotyping is an important tool in confirming the diagnosis or carrier state, provides prognostic information on disease severity, and is essential for genetic counseling. In this article, the authors provide an in-depth discussion on the genetics of CAH, including genetic diagnosis, molecular analysis, genotype-phenotype relationships, and counseling of patients and their families.

Disorders in the initial steps of steroid hormone synthesis

Steroidogenesis begins with cellular internalization of low-density lipoprotein particles and subsequent intracellular processing of cholesterol. Disorders in these steps include Adrenoleukodystrophy, Wolman Disease and its milder variant Cholesterol Ester Storage Disease, and Niemann-Pick Type C Disease, all of which may present with adrenal insufficiency. The means by which cholesterol is directed to steroidogenic mitochondria remains incompletely understood. Once cholesterol reaches the outer mitochondrial membrane, its delivery to the inner mitochondrial membrane is regulated by the steroidogenic acute regulatory protein (StAR). Severe StAR mutations cause classic congenital lipoid adrenal hyperplasia, characterized by lipid accumulation in the adrenal, adrenal insufficiency, and disordered sexual development in 46,XY individuals. The lipoid CAH phenotype, including spontaneous puberty in 46,XX females, is explained by a two-hit model. StAR mutations that retain partial function cause a milder, non-classic disease characterized by glucocorticoid deficiency, with lesser disorders of mineralocorticoid and sex steroid synthesis. Once inside the mitochondria, cholesterol is converted to pregnenolone by the cholesterol side-chain cleavage enzyme, P450scc, encoded by the CYP11A1 gene. Rare patients with mutations of P450scc are clinically and hormonally indistinguishable from those with lipoid CAH, and may also present as milder non-classic disease. Patients with P450scc defects do not have the massive adrenal hyperplasia that characterizes lipoid CAH, but adrenal imaging may occasionally fail to distinguish these, necessitating DNA sequencing.

Thirty-Eight-Year Follow-Up of Two Sibling Lipoid Congenital Adrenal Hyperplasia Patients Due to Homozygous Steroidogenic Acute Regulatory (STARD1) Protein Mutation. Molecular Structure and Modeling of the STARD1 L275P Mutation

Objective: Review the impact of StAR (STARD1) mutations on steroidogenesis and fertility in LCAH patients. Examine the endocrine mechanisms underlying the pathology of the disorder and the appropriate therapy for promoting fertility and pregnancies.

Design: Published data in the literature and a detailed 38-year follow-up of two sibling LCAH patients. Molecular structure and modeling of the STARD1 L275P mutation.

Setting: University hospital.

Patients: Patient A (46,XY female phenotype) and patient B (46,XX female) with LCAH bearing the L275P mutation in STARD1.

Interventions: Since early-age diagnosis, both patients underwent corticoid replacement therapy. Patient A received estrogen therapy at pubertal age. Clomiphene therapy was given to Patient B to induce ovulation. Pregnancies were protected with progesterone administration.

Main Outcome Measures: Clinical and molecular assessment of adrenal and gonadal functions.

Results: Both patients have classic manifestations of corticosteroid deficiency observed in LCAH. Time of onset and severity were different. Patient A developed into a female phenotype due to early and severe damage of Leydig cells. Patient B started a progressive pubertal development, menarche and regular non-ovulatory cycle. She was able to have successful pregnancies.

Conclusions: Understanding the molecular structure and function of STARD1 in all steroidogenic tissues is the key for comprehending the heterogeneous clinical manifestations of LCAH, and the development of an appropriate strategy for the induction of ovulation and protecting pregnancies in this disease.

Congenital lipoid adrenal hyperplasia

Congenital lipoid adrenal hyperplasia (lipoid CAH) is the most fatal form of CAH, as it disrupts adrenal and gonadal steroidogenesis. Most cases of lipoid CAH are caused by recessive mutations in the gene encoding steroidogenic acute regulatory protein (StAR). Affected patients typically present with signs of severe adrenal failure in early infancy and 46,XY genetic males are phenotypic females due to disrupted testicular androgen secretion. The StAR p.Q258X mutation accounts for about 70% of affected alleles in most patients of Japanese and Korean ancestry. However, it is more prevalent (92.3%) in the Korean population. Recently, some patients have been showed that they had late and mild clinical findings. These cases and studies constitute a new entity of 'nonclassic lipoid CAH'. The cholesterol side-chain cleavage enzyme, P450scc (CYP11A1), plays an essential role converting cholesterol to pregnenolone. Although progesterone production from the fetally derived placenta is necessary to maintain a pregnancy to term, some patients with P450scc mutations have recently been reported. P450scc mutations can also cause lipoid CAH and establish a recently recognized human endocrine disorder.

Implications of polyadenylation in health and disease

Polyadenylation is the RNA processing step that completes the maturation of nearly all eukaryotic mRNAs. It is a two-step nuclear process that involves an endonucleolytic cleavage of the pre-mRNA at the 3'-end and the polymerization of a polyadenosine (polyA) tail, which is fundamental for mRNA stability, nuclear export and efficient translation during development. The core molecular machinery responsible for the definition of a polyA site includes several recognition, cleavage and polyadenylation factors that identify and act on a given polyA signal present in a pre-mRNA, usually an AAUAAA hexamer or similar sequence. This mechanism is tightly regulated by other cis-acting elements and trans-acting factors, and its misregulation can cause inefficient gene expression and may ultimately lead to disease. The majority of genes generate multiple mRNAs as a result of alternative polyadenylation in the 3'-untranslated region. The variable lengths of the 3' untranslated regions created by alternative polyadenylation are a recognizable target for differential regulation and clearly affect the fate of the transcript, ultimately modulating the expression of the gene. Over the past few years, several studies have highlighted the importance of polyadenylation and alternative polyadenylation in gene expression and their impact in a variety of physiological conditions, as well as in several illnesses. Abnormalities in the 3'-end processing mechanisms thus represent a common feature among many oncological, immunological, neurological and hematological disorders, but slight imbalances can lead to the natural establishment of a specific cellular state. This review addresses the key steps of polyadenylation and alternative polyadenylation in different cellular conditions and diseases focusing on the molecular effectors that ensure a faultless pre-mRNA 3' end formation.

Steroid hormone synthesis in mitochondria

Mitochondria are essential sites for steroid hormone biosynthesis. Mitochondria in the steroidogenic cells of the adrenal, gonad, placenta and brain contain the cholesterol side-chain cleavage enzyme, P450scc, and its two electron-transfer partners, ferredoxin reductase and ferredoxin. This enzyme system converts cholesterol to pregnenolone and determines net steroidogenic capacity, so that it serves as the chronic regulator of steroidogenesis. Several other steroidogenic enzymes, including 3β-hydroxysteroid dehydrogenase, 11β-hydroxylase and aldosterone synthase also reside in mitochondria. Similarly, the mitochondria of renal tubular cells contain two key enzymes participating in the activation and degradation of vitamin D. The access of cholesterol to the mitochondria is regulated by the steroidogenic acute regulatory protein, StAR, serving as the acute regulator of steroidogenesis. StAR action requires a complex multi-component molecular machine on the outer mitochondrial membrane (OMM). Components of this machine include the 18 kDa translocator protein (TSPO), the voltage-dependent anion chanel (VDAC-1), TSPO-associated protein 7 (PAP7, ACBD3), and protein kinase A regulatory subunit 1α (PKAR1A). The precise fashion in which these proteins interact and move cholesterol from the OMM to P450scc, and the means by which cholesterol is loaded into the OMM, remain unclear. Human deficiency diseases have been described for StAR and for all the mitochondrial steroidogenic enzymes, but not for the electron transfer proteins or for the components of the cholesterol import machine.

Role of mitochondria in steroidogenesis

Adrenal gonadal, placental and brain mitochondria contain several steroidogenic enzymes, notably the cholesterol side chain cleavage enzyme, P450scc, which is the enzymatic rate-limiting step in steroidogenesis which determines cellular steroidogenic capacity. Even before this step, the access of cholesterol to this enzyme system is both rate-limiting and the site of acute regulation via the steroidogenic acute regulatory protein (StAR) which interacts with a complex multi-component 'transduceosome' on the outer mitochondrial membrane (OMM). The components of the transduceosome include the 18 kDa translocator protein (TSPO), the voltage-dependent anion channel (VDAC-1), TSPO-associated protein 7 (PAP7, ACBD3 for acyl-CoA-binding-domain 3), and protein kinase A regulatory subunit 1α (PKAR1A). The precise fashion in which these proteins interact and move cholesterol from the OMM to P450scc, and the means by which cholesterol is loaded into the OMM, remain unclear. Human deficiency diseases have been described for StAR and for P450scc. Mitochondria also contain several 'downstream' steroidogenic enzymes.

A case of lipoid congenital adrenal hyperplasia presenting with cholestasis

BACKGROUND

Lipoid congenital adrenal hyperplasia, is the rarest and usually the most severe form of adrenal steroidogenic defect,which may presents as infantile cholestasis.

CASE PRESENTATION

Here we present a 45 days old infant who came to our attention with cholestasis and severe intractable vomiting and electrolyte disturbances. Evaluation resulted in diagnosis of congenital adrenal hyperplasia. Hydrocortisone and flodrocortisone improved the symptoms including jaundice and vomiting. Hyponatremia and hyperkalemia also resolved with above mentioned treatment.

CONCLUSION

Congenital adrenal hyperplasia as one of the causes of neonatal cholestasis should be kept in mind, whenever there are also electrolytes abnormalities.

Early steps in steroidogenesis: intracellular cholesterol trafficking

Steroid hormones are made from cholesterol, primarily derived from lipoproteins that enter cells via receptor-mediated endocytosis. In endo-lysosomes, cholesterol is released from cholesterol esters by lysosomal acid lipase (LAL; disordered in Wolman disease) and exported via Niemann-Pick type C (NPC) proteins (disordered in NPC disease). These diseases are characterized by accumulated cholesterol and cholesterol esters in most cell types. Mechanisms for trans-cytoplasmic cholesterol transport, membrane insertion, and retrieval from membranes are less clear. Cholesterol esters and "free" cholesterol are enzymatically interconverted in lipid droplets. Cholesterol transport to the cholesterol-poor outer mitochondrial membrane (OMM) appears to involve cholesterol transport proteins. Cytochrome P450scc (CYP11A1) then initiates steroidogenesis by converting cholesterol to pregnenolone on the inner mitochondrial membrane (IMM). Acute steroidogenic responses are regulated by cholesterol delivery from OMM to IMM, triggered by the steroidogenic acute regulatory protein (StAR). Chronic steroidogenic capacity is determined by CYP11A1 gene transcription. StAR mutations cause congenital lipoid adrenal hyperplasia, with absent steroidogenesis, potentially lethal salt loss, and 46,XY sex reversal. StAR mutations initially destroy most, but not all steroidogenesis; low levels of StAR-independent steroidogenesis are lost later due to cellular damage, explaining the clinical findings. Rare P450scc mutations cause a similar syndrome. This review addresses these early steps in steroid biosynthesis.

Partial defect in the cholesterol side-chain cleavage enzyme P450scc (CYP11A1) resembling nonclassic congenital lipoid adrenal hyperplasia

CONTEXT

The cholesterol side-chain cleavage enzyme (P450scc), encoded by the CYP11A1 gene, converts cholesterol to pregnenolone to initiate steroidogenesis. Genetic defects in P450scc cause a rare autosomal recessive disorder that is clinically indistinguishable from congenital lipoid adrenal hyperplasia (lipoid CAH). Nonclassic lipoid CAH is a recently recognized disorder caused by mutations in the steroidogenic acute regulatory protein (StAR) that retain partial function.

OBJECTIVE

We describe two siblings with hormonal findings suggesting nonclassic lipoid CAH, who had a P450scc mutation that retains partial function.

PATIENTS AND METHODS

A 46,XY male presented with underdeveloped genitalia and partial adrenal insufficiency; his 46,XX sister presented with adrenal insufficiency. Hormonal studies suggested nonclassic lipoid CAH. Sequencing of the StAR gene was normal, but compound heterozygous mutations were found in the CYP11A1 gene. Mutations were recreated in the F2 plasmid expressing a fusion protein of the cholesterol side-chain cleavage system. P450scc activity was measured as Vmax/Km for pregnenolone production in transfected COS-1 cells.

RESULTS

The patients were compound heterozygous for the previously described frameshift mutation 835delA and the novel missense mutation A269V. When expressed in the P450scc moiety of F2, the A269V mutant retained 11% activity of the wild-type F2 protein.

CONCLUSIONS

There is a broad clinical spectrum of P450scc deficiency. Partial loss-of-function CYP11A1 mutation can present with a hormonal phenotype indistinguishable from nonclassic lipoid CAH.

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.

Clinical, genetic, and functional characterization of four patients carrying partial loss-of-function mutations in the steroidogenic acute regulatory protein (StAR)

CONTEXT

Nonclassic congenital lipoid adrenal hyperplasia (lipoid CAH) is a recently recognized disorder caused by mutations in the steroidogenic acute regulatory protein (StAR) that retain partial function. Affected individuals can present with a phenotype of late onset adrenal insufficiency with only mild or minimally disordered sexual development.

OBJECTIVES

The aim was to delineate the clinical spectrum of StAR mutations and correlate phenotype with StAR activity.

PATIENTS

Four patients had nonclassic/atypical lipoid CAH. Adrenal insufficiency was manifested at birth in two patients and at 11 months and 4 yr in the other two. Three were 46,XY with underdeveloped genitalia.

METHODS

The StAR gene was sequenced, mutations were recreated in expression vectors, and StAR activity was measured as pregnenolone production in COS-1 cells cotransfected with the cholesterol side-chain cleavage system. StAR mutants were expressed as N-62 StAR in bacteria, and purified proteins were tested for activity with isolated steroidogenic mitochondria and for cholesterol-binding capacity.

RESULTS

DNA sequencing identified mutations on all alleles. Missense mutations were R188C, G221D, L260P, and F267S; we also tested R192C described by others. The respective activities of R188C, R192C, G221D, L260P, and F267S were 8.0, 39.4, 2.4, 3.1, and 6.1% of wild-type in transfected cells, and 12.8, 54.8, 6.3, 1.8, and 9.5% with isolated mitochondria. Cholesterol binding capacities of R188C, R192C, G221D, L260P, and F267S were 6.7, 55.3, 10.2, 4.6, and 20.9%. These data are correlated to the three-dimensional structure of StAR.

CONCLUSIONS

There is a broad clinical spectrum of StAR mutations; StAR activities in vitro correlate well with clinical phenotypes.

46,XY DSD due to impaired androgen production

Disorders of androgen production can occur in all steps of testosterone biosynthesis and secretion carried out by the foetal Leydig cells as well as in the conversion of testosterone into dihydrotestosterone (DHT). The differentiation of Leydig cells from mesenchymal cells is the first walk for testosterone production. In 46,XY disorders of sex development (DSDs) due to Leydig cell hypoplasia, there is a failure in intrauterine and postnatal virilisation due to the paucity of interstitial Leydig cells to secrete testosterone. Enzymatic defects which impair the normal synthesis of testosterone from cholesterol and the conversion of testosterone to its active metabolite DHT are other causes of DSD due to impaired androgen production. Mutations in the genes that codify the enzymes acting in the steps from cholesterol to DHT have been identified in affected patients. Patients with 46,XY DSD secondary to defects in androgen production show a variable phenotype, strongly depending of the specific mutated gene. Often, these conditions are detected at birth due to the ambiguity of external genitalia but, in several patients, the extremely undervirilised genitalia postpone the diagnosis until late childhood or even adulthood. These patients should receive long-term care provided by multidisciplinary teams with experience in this clinical management.

Genetics of congenital adrenal hyperplasia

Congenital adrenal hyperplasia (CAH) is one of the most common inherited metabolic disorders. It comprises a group of autosomal recessive disorders caused by the deficiency of one of four steroidogenic enzymes involved in cortisol biosynthesis or in the electron donor enzyme P450 oxidoreductase (POR) that serves as electron donor to steroidogenic cytochrome P450 (CYP) type II enzymes. The biochemical and clinical phenotype depends on the specific enzymatic defect and the impairment of specific enzyme activity. Defects of steroid 21-hydroxylase (CYP21A2) and 11beta-hydroxylase (CYP11B1) only affect adrenal steroidogenesis, whereas 17alpha-hydroxylase (CYP17A1) and 3beta-hydroxysteroid dehydrogenase type 2 (HSD3B2) deficiency also impact on gonadal steroid biosynthesis. Inactivating POR gene mutations are the cause of CAH manifesting with apparent combined CYP17A1-CYP21A2 deficiency. P450 oxidoreductase deficiency (ORD) has a complex phenotype including two unique features not observed in any other CAH variant: skeletal malformations and severe genital ambiguity in both sexes.

Severe combined adrenal and gonadal deficiency caused by novel mutations in the cholesterol side chain cleavage enzyme, P450scc

CONTEXT

Mitochondrial cytochrome P450scc converts cholesterol to pregnenolone in all steroidogenic tissues. Although progesterone production from the fetally-derived placenta is necessary to maintain pregnancy to term, four patients with mutations in the gene encoding P450scc (CYP11A1), have been described, one in a 46,XX female and three in underandrogenized 46,XY individuals, all with primary adrenal failure.

OBJECTIVE

Our aim was to determine whether P450scc mutations might be found in other children and to explore genotype/phenotype correlations.

METHODS AND PATIENTS

We performed mutational analysis of CYP11A1 in individuals with 46,XY disorders of sex development and primary adrenal failure, followed by functional studies of P450scc activity and of P450scc RNA splicing.

RESULTS

Among nine 46,XY infants with adrenal failure and disordered sexual differentiation, two infants had compound heterozygous mutations in CYP11A1. One patient harbored the novel P450scc missense mutations L141W and V415E, which retained 38 and 0% activity, respectively. The other carried a CYP11A1 frameshift mutation c835delA (0% activity) and a splice site mutation [IVS3+(2-3)insT] that prevented correct splicing of P450scc mRNA.

CONCLUSIONS

P450scc deficiency is a recently recognized disorder that may be more frequent than originally thought. The phenotypic spectrum ranges from severe loss-of-function mutations associated with prematurity, complete underandrogenization, and severe, early-onset adrenal failure, to partial deficiencies found in children born at term with clitoromegaly and later-onset adrenal failure. In contradistinction to congenital lipoid adrenal hyperplasia caused by steroidogenic acute regulatory protein mutations, adrenal hyperplasia has not been reported in any of the six patients with P450scc deficiency.

Basic concepts and recent developments in human steroid hormone biosynthesis

The biosynthesis of steroid hormones requires the coordinated expression of the enzymes that comprise the pathways via which specific hormones are synthesized. These pathways and their associated enzymes are typically subject to regulation consisting of trophic hormone stimuli and feedback mechanisms. Very few tissues contribute substantially to de novo steroidogenesis, primarily the adrenal glands, the gonads, and the placenta. Both the embryonic origins and the signaling mechanisms for the adrenals and gonads are similar, and steroid synthesis in these two glands are the major focus of this review. We will further describe peripheral steroid metabolism and the regulation of steroid hormone potency in target tissues. In addition, we will briefly discuss the congenital adrenal hyperplasias to illustrate the principles developed in the initial sections. Finally, we will discuss some recent developments in steroidogensis, focusing on cytochrome P450 oxidoreductase deficiency and the alternate or "backdoor" pathway to dihydrotestosterone. We will conclude with a description of aberrant signaling mechanisms observed in adrenal tumors as a further example of how these pathways can be disturbed in pathologic states.

StAR Search—What We Know about How the Steroidogenic Acute Regulatory Protein Mediates Mitochondrial Cholesterol Import

Cholesterol is the starting point for biosynthesis of steroids, oxysterols and bile acids, and is also an essential component of cellular membranes. The mechanisms directing the intracellular trafficking of this insoluble molecule have received attention through the discovery of the steroidogenic acute regulatory protein (StAR) and related proteins containing StAR-related lipid transfer domains. Much of our understanding of the physiology of StAR derives from studies of congenital lipoid adrenal hyperplasia, which is caused by StAR mutations. Multiple lines of evidence show that StAR moves cholesterol from the outer to inner mitochondrial membrane, but acts exclusively on the outer membrane. The precise mechanism by which StAR's action on the outer mitochondrial membrane stimulates the flow of cholesterol to the inner membrane remains unclear. When StAR interacts with protonated phospholipid head groups on the outer mitochondrial membrane, it undergoes a conformational change (molten globule transition) that opens and closes StAR's cholesterol-binding pocket; this conformational change is required for cholesterol binding, which is required for StAR activity. The action of StAR probably requires interaction with the peripheral benzodiazepine receptor.

Cholesterol Side-Chain Cleavage Enzyme (SCC) Deficiency

Cholesterol side-chain cleavage enzyme (SCC) catalyzes the conversion of cholesterol to pregnenolone, the first step in the biosynthesis of all steroid hormones. It was once postulated that SCC deficiency would be lethal, but recent studies have established that SCC deficiency is an autosomal recessive disorder caused by inactivating mutations in the CYP11A1 gene. Clinical manifestations include adrenal insufficiency and 46,XY sex reversal due to disrupted steroidogenesis, which are similar to StAR deficiency. Further accumulation of patients with SCC deficiency should clarify the similarities and differences between SCC deficiency and StAR deficiency.

Site-directed mutations (Asp405Ile and Glu124Ile) in cytochrome P450scc: effect on adrenodoxin binding

Cytochrome P450scc, mitochondrial adrenodoxin (Adx), and adrenodoxin reductase (AdR) are an essential components in a steroid hydroxylation system. In particular, mytochondrial cytochrome P450scc enzyme catalyses the first step in steroid hormones biosynthesis, represented by the conversion of cholesterol to pregnenolone. In order to study the effect of single mutations on the Adx binding a model of bovine cytochrome P450scc, previously optimized by molecular modeling, was utilized. It was hypothesized by molecular docking that two residues (Asp405 and Glu124) are involved in Adx binding. By site-directed mutagenesis, two mutants of cytochrome P450scc (Asp405Ile and Glu124Ile) expressed in Escherichia coli, were realized by replacing with isoleucines. The site-directed mutations effect on Adx binding was evaluated by differential spectral titration. The apparent dissociation constant values for Asp405Ile and Glu124Ile cytochrome P450scc show that the mutated residues seem to be at the interaction domain with Adx or at least close to it, as predicted by molecular modeling study. Finally, the engineered enzymes were characterized by biochemical and biophysical techniques such as circular dichroism (CD), UV/Vis spectroscopy, and electrochemical analysis.

Minireview: regulation of steroidogenesis by electron transfer

Cytochrome P450 enzymes catalyze the degradation of drugs and xenobiotics, but also catalyze a wide variety of biosynthetic processes, including most steps in steroidogenesis. The catalytic rate of a P450 enzyme is determined in large part by the rate of electron transfer from its redox partners. Type I P450 enzymes, found in mitochondria, receive electrons from reduced nicotinamide adenine dinucleotide (NADPH) via the intermediacy of two proteins-ferredoxin reductase (a flavoprotein) and ferredoxin (an iron/sulfur protein). Type I P450 enzymes include the cholesterol side-chain cleavage enzyme (P450scc), the two isozymes of 11-hydroxylase (P450c11beta and P450c11AS), and several vitamin D-metabolizing enzymes. Disorders of these enzymes, but not of the two redox partners, have been described. Type II P450 enzymes, found in the endoplasmic reticulum, receive electrons from NADPH via P450 oxidoreductase (POR), which contains two flavin moieties. Steroidogenic Type II P450 enzymes include 17alpha-hydroxylase/17,20 lyase (P450c17), 21-hydroxylase (P450c21), and aromatase (P450aro). All P450 enzymes catalyze multiple reactions, but P450c17 appears to be unique in that the ratio of its activities is regulated at a posttranslational level. Three factors can increase the degree of 17,20 lyase activity relative to the 17alpha-hydroxylase activity by increasing electron flow from POR: a high molar ratio of POR to P450c17, serine phosphorylation of P450c17, and the presence of cytochrome b(5), acting as an allosteric factor to promote the interaction of POR with P450c17. POR is required for the activity of all 50 human Type II P450 enzymes, and ablation of the Por gene in mice causes embryonic lethality. Nevertheless, mutation of the human POR gene is compatible with life, causing multiple steroidogenic defects and a skeletal dysplasia called Antley-Bixler syndrome.

Disorders of androgen synthesis--from cholesterol to dehydroepiandrosterone

Androgens and estrogens are primarily made from dehydroepiandrosterone (DHEA), which is made from cholesterol via four steps. First, cholesterol enters the mitochondria with the assistance of the steroidogenic acute regulatory protein (StAR). Mutations in the StAR gene cause congenital lipoid adrenal hyperplasia (lipoid CAH), a potentially lethal disease in which virtually no steroids are made. Lipoid CAH is common among Palestinian Arabs and people from eastern Arabia, and among Korean and Japanese people. Second, within the mitochondria, cholesterol is converted to pregnenolone by the cholesterol side chain cleavage enzyme, P450scc; disorder of this enzyme is very rare, probably due to embryonic lethality. Third, pregnenolone undergoes 17alpha-hydroxylation by microsomal P450c17. 17alpha-Hydroxylase deficiency, manifesting as female sexual infantilism and hypertension, is rare except in Brazil. Finally, 17-OH pregnenolone is converted to DHEA by the 17,20 lyase activity of P450c17. The ratio of the 17,20 lyase to 17alpha-hydroxylase activity of P450c17 determines the ratio of C21 to C19 steroids produced. This ratio is regulated posttranslationally by at least three factors: the abundance of the electron-donating protein P450 oxidoreductase (POR), the presence of cytochrome b5 and the serine phosphorylation of P450c17. Mutations of POR are a new, recently described disorder manifesting as the Antley-Bixler skeletal dysplasia syndrome, and a form of polycystic ovary syndrome.

Near-miss apparent SIDS from adrenal crisis

OBJECTIVE

Adrenal crisis from salt-losing congenital adrenal hyperplasia (CAH) typically occurs in the first 2 weeks of life. We evaluated 3 infants with adrenal crisis who presented at 6 to 8 months of age with near-miss sudden infant death syndrome (SIDS).

SUBJECTS

Three 46,XY phenotypic female infants presented near death at 6 to 8 months of age with adrenal crisis and unmeasurable steroid hormones consistent with congenital lipoid adrenal hyperplasia (lipoid CAH).

METHODS

We sequenced genes potentially causing this phenotype: steroidogenic acute regulatory protein (StAR), the cholesterol side-chain cleavage enzyme, adrenodoxin reductase, adrenodoxin, and steroidogenic factor 1 (SF1). Site-directed mutagenesis and functional assays were performed for the missense mutation.

RESULTS

Hormonal values showed complete absence of adrenal and gonadal steroids. Patient 1 was a compound heterozygote for missense mutation R140P and an mRNA splice donor site mutation in the StAR gene. The R140P mutation was wholly inactive in vitro. Patient 2 was homozygous for a 7 base pair StAR deletion causing a frameshift. No mutations were found in Patient 3, suggesting a novel disease.

CONCLUSIONS

Although genetic disorders of steroidogenesis typically present in the first month of life, some defects, especially those in StAR, can present in mid-infancy, when adrenal hyperplasias are rarely considered. Adrenal insufficiency is a subtle disorder that may cause cardiovascular collapse, causing unexplained infant death that resembles SIDS.

Critical role of the plasma membrane for expression of mammalian mitochondrial side chain cleavage activity in yeast

Engineered yeast cells efficiently convert ergosta-5-eneol to pregnenolone and progesterone provided that endogenous pregnenolone acetylase activity is disrupted and that heterologous sterol delta7-reductase, cytochrome P450 side chain cleavage (CYP11A1) and 3beta hydroxysteroid dehydrogenase/isomerase (3beta-HSD) activities are present. CYP11A1 activity requires the expression of the mammalian NADPH-adrenodoxin reductase (Adrp) and adrenodoxin (Adxp) proteins as electron carriers. Several parameters modulate this artificial metabolic pathway: the effects of steroid products; the availability and delivery of the ergosta-5-eneol substrate to cytochrome P450; electron flux and protein localization. CYP11A1, Adxp and Adrp are usually located in contact with inner mitochondrial membranes and are directed to the outside of the mitochondria by the removal of their respective mitochondrial targeting sequences. CYP11A1 then localizes to the plasma membrane but Adrp and Adxp are detected in the endoplasmic reticulum and cytosol as expected. The electron transfer chain that involves several subcellular compartments may control side chain cleavage activity in yeast. Interestingly, Tgl1p, a potential ester hydrolase, was found to enhance steroid productivity, probably through both the availability and/or the trafficking of the CYP11A1 substrate. Thus, the observation that the highest cellular levels of free ergosta-5-eneol are found in the plasma membrane suggests that the substrate is freely available for pregnenolone synthesis.

Clinical disorders associated with abnormal cholesterol transport: mutations in the steroidogenic acute regulatory protein

The transport of cholesterol to the inner mitochondrial membrane of steroidogenic cells constitutes the rate-limiting step in trophic hormone regulated steroid biosynthesis and requires de novo protein synthesis. Several years ago a candidate regulator protein was purified and its cDNA cloned from MA-10 mouse Leydig tumor cells. Expression of this protein resulted in an increase in steroidogenesis in unstimulated cells and it was named the Steroidogenic Acute Regulatory protein or StAR. Mutations in the StAR gene were found to be the cause of the potentially lethal disease in humans known as congenital lipoid adrenal hyperplasia (lipoid CAH), a condition characterized by an almost complete inability of the newborn to synthesize steroids. The defect in steroid synthesis in lipoid CAH is caused by the failure of affected individuals to transport cholesterol to the inner mitochondria membrane, thus proving the essential role of StAR in cholesterol transport. StAR null mice display a phenotype that is essentially identical to the human condition. In summary, both naturally occurring disorders in humans and genetic manipulation in mice have demonstrated that the StAR protein is an absolute requirement in the rate-limiting step in steroidogenesis, the transfer of cholesterol into the mitochondria.

The genetics of male undermasculinization

A review of the genetics of male undermasculinization must encompass a description of the embryology of the genital system. The dimorphism of sex development consequent upon the formation of a testis and the subsequent secretion of hormones to impose a male phenotype is highlighted. Thus, an understanding of the causes of male undermasculinization (manifest as XY sex reversal, complete and partial) includes reviewing the genetic factors which control testis determination and the production and action of testicular hormones. The study of disorders of male sex development has contributed substantially to knowledge of normal male development before birth. This knowledge has been complimented in recent years by the use of targeted murine gene disruption experiments to study the sex phenotype, although murine and human phenotypes are not always concordant. The investigation of disorders associated with male undermasculinization of prenatal onset is described briefly to complete the review.

Heterozygous mutation in the cholesterol side chain cleavage enzyme (p450scc) gene in a patient with 46,XY sex reversal and adrenal insufficiency

Cytochrome P450scc, the mitochondrial cholesterol side chain cleavage enzyme, is the only enzyme that catalyzes the conversion of cholesterol to pregnenolone and, thus, is required for the biosynthesis of all steroid hormones. Congenital lipoid adrenal hyperplasia is a severe disorder of steroidogenesis in which cholesterol accumulates within steroidogenic cells and the synthesis of all adrenal and gonadal steroids is impaired, hormonally suggesting a disorder in P450scc. However, congenital lipoid adrenal hyperplasia is caused by mutations in the steroidogenic acute regulatory protein StAR; it has been thought that P450scc mutations are incompatible with human term gestation, because P450scc is needed for placental biosynthesis of progesterone, which is required to maintain pregnancy. In studying patients with congenital lipoid adrenal hyperplasia, we identified an individual with normal StAR and SF-1 genes and a heterozygous mutation in P450scc. The mutation was found in multiple cell types, but neither parent carried the mutation, suggesting it arose de novo during meiosis, before fertilization. The patient was atypical for congenital lipoid adrenal hyperplasia, having survived for 4 yr without hormonal replacement before experiencing life-threatening adrenal insufficiency. The P450scc mutation, an in-frame insertion of Gly and Asp between Asp271 and Val272, was inserted into a catalytically active fusion protein of the P450scc system (H2N-P450scc-Adrenodoxin Reductase-Adrenodoxin-COOH), completely inactivating enzymatic activity. Cotransfection of wild-type and mutant vectors showed that the mutation did not exert a dominant negative effect. Because P450scc is normally a slow and inefficient enzyme, we propose that P450scc haploinsufficiency results in subnormal responses to ACTH, so that recurrent ACTH stimulation leads to a slow accumulation of adrenal cholesterol, eventually causing cellular damage. Thus, although homozygous absence of P450scc should be incompatible with term gestation, haploinsufficiency of P450scc causes a late-onset form of congenital lipoid adrenal hyperplasia that can be explained by the same two-hit model that has been validated for congenital lipoid adrenal hyperplasia caused by StAR deficiency.

StAR protein and the regulation of steroid hormone biosynthesis

Steroid hormone biosynthesis is acutely regulated by pituitary trophic hormones and other steroidogenic stimuli. This regulation requires the synthesis of a protein whose function is to translocate cholesterol from the outer to the inner mitochondrial membrane in steroidogenic cells, the rate-limiting step in steroid hormone formation. The steroidogenic acute regulatory (StAR) protein is an indispensable component in this process and is the best candidate to fill the role of the putative regulator. StAR is expressed in steroidogenic tissues in response to agents that stimulate steroid production, and mutations in the StAR gene result in the disease congenital lipoid adrenal hyperplasia, in which steroid hormone biosynthesis is severely compromised. The StAR null mouse has a phenotype that is essentially identical to the human disease. The positive and negative expression of StAR is sensitive to agents that increase and inhibit steroid biosynthesis respectively. The mechanism by which StAR mediates cholesterol transfer in the mitochondria has not been fully characterized. However, the tertiary structure of the START domain of a StAR homolog has been solved, and identification of a cholesterol-binding hydrophobic tunnel within this domain raises the possibility that StAR acts as a cholesterol-shuttling protein.

Steroidogenic acute regulatory protein (StAR) and the intramitochondrial translocation of cholesterol

The steroidogenic acute regulatory (StAR) protein regulates the rate limiting step in steroidogenesis, the transport of cholesterol from the outer to the inner mitochondrial membrane. Insight into the structure and function of StAR was attained through molecular genetic studies of congenital lipoid adrenal hyperplasia, a rare disease caused by mutations in the StAR gene. Subsequent functional analysis defined two major domains within the StAR protein, the N-terminal mitochondrial targeting sequence and the C-terminus, which promotes the translocation of cholesterol between the two mitochondrial membranes. Two models of StAR's mechanism of action, (1) stimulation of cholesterol desorption from the outer mitochondrial membrane and (2) an intermembrane shuttle hypothesis, are discussed with respect to the known biochemical and biophysical events associated with the process of steroidogenesis and the structure of StAR. StAR gene expression is regulated primarily at the transcriptional level, and the roles of transcription factors that govern basal and cAMP-dependent StAR expression including SF-1, C/EBP beta, Sp1 and GATA-4 are reviewed.

Intramitochondrial cholesterol transfer

Cholesterol serves as the initial substrate for all steroid hormones synthesized in the body regardless of the steroidogenic tissue or final steroid produced. The first steroid formed in the steroidogenic pathway is pregnenolone which is formed by the excision of a six carbon unit from cholesterol by the cytochrome P450 side chain cleavage enzyme system which is located in the inner mitochondrial membrane. It has long been known that the regulated biosynthesis of steroids is controlled by a cycloheximide sensitive factor whose function is to transfer cholesterol from the outer to the inner mitochondrial membrane, thus, the identity of this factor is of great importance. A candidate for the regulatory factor is the mitochondrial protein, the steroidogenic acute regulatory (StAR) protein. Cloning and sequencing of the StAR cDNA indicated that it was a novel protein, and transient transfections with the cDNA for the StAR protein resulted in increased steroid production in the absence of stimulation. Mutations in the StAR gene cause the potentially lethal disease congenital lipoid adrenal hyperplasia, a condition in which cholesterol transfer to the cytochrome P450 side chain cleavage enzyme, P450scc, is blocked, filling the cell with cholesterol and cholesterol esters. StAR knockout mice have a phenotype which is essentially identical to the human condition. The cholesterol transferring activity of StAR has been shown to reside in the C-terminal part of the molecule and a protein sharing homology with a region in the C-terminus of StAR has been shown to display cholesterol transferring capacity. Recent evidence has indicated that StAR can act as a sterol transfer protein and it is perhaps this characteristic which allows it to mobilize cholesterol to the inner mitochondrial membrane. However, while it appears that StAR is the acute regulator of steroid biosynthesis via its cholesterol transferring activity, its mechanism of action remains unknown.

Molecular pathology and mechanism of action of the steroidogenic acute regulatory protein, StAR

The first and rate-limiting step in the synthesis of all steroid hormones is the conversion of cholesterol to pregnenolone by the mitochondrial enzyme, P450scc. Tropic hormones such ACTH and gonadotropins induce steroidogenesis via cAMP by elaborating intracellular cAMP which stimulates P450scc activity in two distinct ways. Chronic stimulation (h to days) occurs through the induction of P450scc gene transcription leading to increased P450scc protein and consequent increased steroidogenic capacity. Acute regulation, over minutes, occurs through the phosphorylation of preexisting StAR and the rapid synthesis of new StAR protein. StAR, the steroidogenic acute regulatory protein, increases the flow of cholesterol into mitochondria, thus regulating substrate availability to whatever amount of P450scc is available. In the absence of StAR, up to 14% of maximal StAR-induced level of steroidogenesis persists as StAR-independent steroidogenesis. Congenital lipoid adrenal hyperplasia, an autosomal recessive disorder in which conversion of cholesterol to pregnenolone is severely impaired, results in female genitalia in 46,XY genetic males, variable onset of a severe salt-losing crisis in the first months of life, but normal feminization and cyclical vaginal bleeding in 46,XX females. Lipoid CAH was once thought to be due to P450scc mutations, but in fact homozygous P450scc mutations cannot exist in human beings as they would prohibit placental progesterone production, causing spontaneous abortion of the affected fetus. Lipoid CAH is caused by StAR mutations, which result in tropic hormone-induced intracellular accumulation of cholesterol in the adrenals and gonads. Our two-hit model, which considers the persistence of StAR-independent steroidogenesis and the differences in the fetal and postnatal ages at which the testis, adrenal zona glomerulosa, adrenal zona fasciculata and ovary are stimulated, predicts and explains all of the various clinical manifestations of lipoid CAH. Structure function studies of StAR show that the critical domains for biological activity reside in the protein's carboxy-terminus. When the N-terminal mitochondrial targeting sequences are deleted and the resulting N-62 StAR remains in the cytoplasm, it retains the ability to stimulate steroidogenesis both in intact cells or when added to isolated mitochondria in vitro. These observations suggest that StAR acts on the outer mitochondrial membrane to promote sterol translocation to P450scc, and that the importation of StAR into mitochondria terminates its action. Data from circular dichroism and Fourier-transform infrared spectroscopy show that the mutant StAR proteins in lipoid CAH are misfolded, suggesting disrupted interaction with another protein. Preliminary data suggest that StAR facilitates cholesterol desorption from membranes, stimulating transfer from the outer mitochondrial (donor) membrane to the inner mitochondrial (acceptor) membrane.

Molecular and clinical characterization of Korean patients with congenital lipoid adrenal hyperplasia

Congenital lipoid adrenal hyperplasia (CLAH) is a rare autosomal recessive disorder of steroid biosynthesis, caused by a molecular defect in the steroidogenic acute regulatory protein (StAR). Patients with CLAH usually manifest severe salt wasting, hypovolemia, enlargement of the adrenal glands and complete female external genitalia irrespective of the gonadal sex. CLAH seems to be more common in Koreans and Japanese than in other ethnic populations, with a preponderance of the mutation of a glutamine to a stop codon at the 258th amino acid residue (Q258X) in the StAR gene. Clinical findings of five unrelated Korean patients with CLAH and their molecular defects in the StAR gene are described, and the gene frequency of the Q258X mutation in the Korean population is investigated. All patients developed hypovolemic shock due to severe salt wasting in the first three months after birth. All were hyperpigmented, and three of five phenotypic females were genetic males. The basal ACTH level was extremely high in all patients with the minimal concentrations of all adrenal and gonadal steroids. The Q258X mutation was identified in 9 out of 10 alleles, indicating that the genetic defect in the StAR gene of Korean patients with CLAH is highly homogeneous probably due to a founder effect. The carrier frequency of the Q258X mutation in the normal Korean population has been estimated as approximately 1 in 250 with the allele frequency of 1 in 500. However, the confidence limits of the gene frequency for the mutant allele are wide (0.5 to 8.0 among 1,000 alleles). This implies that the carrier frequency could be lower, down to 1/1,000, or higher, up to 16/1,000.

Early steps in androgen biosynthesis: from cholesterol to DHEA

Sex steroids, both androgens and oestrogens, are made from dehydroepiandrosterone (DHEA). The biosynthesis of DHEA from cholesterol entails four steps. First, cholesterol enters the mitochondria with the assistance of a recently described factor called the steroidogenic acute regulatory protein (StAR). Mutations in the StAR gene cause congenital lipoid adrenal hyperplasia. Next, cholesterol is converted to pregnenolone by the cholesterol side chain cleavage enzyme, P450scc. Mutations in the gene for P450scc and for its electron transfer partners, ferredoxin reductase and ferredoxin, have not been described and are probably incompatible with term gestation. Third, pregnenolone undergoes 17 alpha-hydroxylation by microsomal P450c17. Finally, 17-OH pregnenolone is converted to DHEA by the 17,20 lyase activity of P450c17. Isolated 17,20 lyase deficiency is rare, but the identification of its genetic basis and the study of P450c17 enzymology have recently clarified the mechanisms by which DHEA synthesis may be regulated in adrenarche, and have suggested that the lesion underlying polycystic ovary syndrome might involve a serine kinase.

A novel splicing junction mutation in the gene for the steroidogenic acute regulatory protein causes congenital lipoid adrenal hyperplasia

Congenital lipoid adrenal hyperplasia (lipoid CAH) is a relatively common genetic disorder of adrenal and gonadal steroidogenesis and is the most severe form of CAH. As typical affected individuals cannot produce any steroid hormones or can only produce low levels of steroid hormones in the adrenals and gonads, including glucocorticoids, mineralcorticoids, and sex steroids, a genetic defect in the cholesterol side-chain cleavage enzyme, cytochrome P450scc (CYPXIA1), has been postulated to be the cause of their insufficient production to date. Recently, Lin and co-workers proved a link between mutations of the steroidogenic acute regulatory protein (StAR) gene and the lipoid CAH phenotype. Therefore, we investigated both the cytochrome P450scc and StAR genes in a Korean family with a fairly mild form of lipoid CAH to identify the mutation(s) causing this disease. The result was that no mutations could be found in the two genes, except for a thymine (T) insertion into intron 2 of the StAR gene, 3 bp from the splice donor site of exon 2. PCR-amplified StAR genes from a normal subject and the patient were cloned into an expression vector and then introduced into COS-7 cells. Northern blot and reverse transcriptase-PCR analyses indicated that the StAR messenger ribonucleic acid derived from the vector with the normal StAR gene spliced exons 2 and 3 correctly, whereas most, but not all, StAR messenger ribonucleic acid derived from the vector with the T-inserted StAR gene could not remove intron 2. We concluded from these results that the T insertion into the StAR gene accounts for the lipoid CAH phenotype in this patient.

Spontaneous feminization in a 46,XX female patient with congenital lipoid adrenal hyperplasia due to a homozygous frameshift mutation in the steroidogenic acute regulatory protein

The most severe form of congenital adrenal hyperplasia (CAH) is lipoid CAH. It was once thought that this disease was due to mutations in the cholesterol side-chain cleavage enzyme system, thus eliminating the ability to convert cholesterol to pregnenolone, causing a complete absence of steroid hormone production. We recently showed that lipoid CAH is due to mutations in the steroidogenic acute regulatory (StAR) protein, thus preventing acutely stimulated adrenal and gonadal responses to tropic stimulation. However, this lesion may permit low levels of StAR-independent steroidogenesis to persist until the accumulation of intracellular lipid deposits destroys steroidogenic capacity. This model would predict that the steroidogenic cells of the ovaries of affected 46,XX females should remain undamaged until puberty, at which time low levels of StAR-independent estrogen biosynthesis should be detectable. We describe a 15.5-yr-old 46,XX female with a classic history of lipoid CAH who underwent spontaneous feminization and cyclical vaginal bleeding beginning at age 13. Genetic analysis of the patient and her parents showed that she was homozygous for the novel StAR frameshift mutation 261delT. This is the first adolescent female with lipoid CAH who has undergone spontaneous feminization and who has been analyzed genetically. Finding an inactive StAR gene in this patient confirms our two-hit model of the pathogenesis of lipoid CAH, in which loss of StAR activity initially preserves StAR-independent steroidogenesis, which is lost only after cells undergo chronic tropic stimulation and subsequent damage from accumulation of cholesterol esters.

New developments in congenital lipoid adrenal hyperplasia and steroidogenic acute regulatory protein

To date, studies of patients with lipoid CAH have shown the indispensable role of StAR in the production of steroids by adrenal gland and gonads. Lipoid CAH is the first and so far only inborn disorder of steroid hormone synthesis and metabolism that is not caused by a defective steroidogenic enzyme but rather by a defect in cholesterol transport.

Spontaneous puberty in 46,XX subjects with congenital lipoid adrenal hyperplasia. Ovarian steroidogenesis is spared to some extent despite inactivating mutations in the steroidogenic acute regulatory protein (StAR) gene

Congenital lipoid adrenal hyperplasia (lipoid CAH) is the most severe form of CAH in which the synthesis of all gonadal and adrenal cortical steroids is markedly impaired. We report here the clinical, endocrinological, and molecular analyses of two unrelated Japanese kindreds of 46,XX subjects affected with lipoid CAH who manifested spontaneous puberty. Phenotypic female infants with 46,XX karyotypes were diagnosed with lipoid CAH as newborns based on a clinical history of failure to thrive, hyperpigmentation, hyponatremia, hyperkalemia, and low basal values of serum cortisol and urinary 17-hydroxycorticosteroid and 17-ketosteroid. These patients responded to treatment with glucocorticoid and 9alpha-fludrocortisone. Spontaneous thelarche occurred in association with increased serum estradiol levels at the age of 10 and 11 yr, respectively. Pubic hair developed at the age of 12 yr 11 mo in one subject and menarche was at the age of 12 yr in both cases. Both subjects reported periodic menstrual bleeding and subsequently developed polycystic ovaries. To investigate the molecular basis of the steroidogenic lesion in these patients, the StAR gene was characterized by PCR and direct DNA sequence analyses. DNA sequence analysis revealed that one patient is homozygous for the Gln 258 Stop mutation in exon 7 and that the other patient is a compound heterozygote with the Gln 258 Stop mutation and a single A deletion at codon 238 in the other allele causing a frame-shift, which renders the StAR protein nonfunctional. These findings demonstrate that ovarian steroidogenesis can be spared to some extent through puberty when the StAR gene product is inactive. This is in marked contrast to the early onset of severe defects in testicular and adrenocortical steroidogenesis which are characteristics of this disease.