Cloning of cDNA encoding steroid 11 beta-hydroxylase (P450c11)

The molecular basis of hypertension

More than 50 million Americans display blood pressures outside the safe physiological range. Unfortunately for most individuals, the molecular basis of hypertension is unknown, in part because pathological elevations of blood pressure are the result of abnormal expression of multiple genes. This review identifies a number of important blood pressure regulatory genes including their loci in the human, mouse, and rat genome. Phenotypes of gene deletions and overexpression in mice are summarized. More detailed discussion of selected gene products follows, beginning with proteins involved in ion transport, specifically the epithelial sodium channel and sodium proton exchangers. Next, proteins involved in vasodilation/natriuresis are discussed with emphasis on natriuretic peptides, guanylin/uroguanylin, and nitric oxide. The renin angiotensin aldosterone system has an important role antagonizing the vasodilatory cyclic GMP system.

Structure of an ovine CYP11B1 gene

Glucocorticoids play an important role in the normal development and proliferation of cells, and are also involved in inflammatory responses. The level of active glucocorticoids in the body is controlled in part by the enzyme CYP11B1, which catalyses the final step of its biosynthesis. In this report, we have completely characterised the ovine CYP11B1 gene using two overlapping clones isolated from an lambdaEMBL3 sheep liver genomic library. The gene comprised 9 exons and 8 introns, spanning over a region of 8.0 kb. Two ovine CYP11B1 transcripts, with molecular sizes of 1.9 and 4.0 kb, have also been isolated from the adrenal zona fasciculata region, which showed that they arose from the usage of the two polyadenylation sites situated 2.1 kb apart in exon 9. The transcriptional start sites of the gene has been mapped using primer extension analysis. Three major start sites were identified at positions -5, -6 and -77 from the first ATG codon (Met), with two minor sites located at positions -306 and -413. When examined in context with the ovine CYP11B1 5' regulatory region, the results suggested that the ovine CYP11B1 gene contained two additional core promoters located further upstream of a proximal TATA box which could be utilised to produce mRNAs with alternative transcriptional start sites.

Amino acid residue 147 of human aldosterone synthase and 11beta-hydroxylase plays a key role in 11beta-hydroxylation

A number of amino acids differ between aldosterone synthase and 11beta-hydroxylase. To assess their importance in determining the different functional specificities, we substituted aldosterone synthase-specific (aspartate D147, isoleucine I248, glutamine Q43, and threonine T493) with 11beta-hydroxylase-specific amino acids (glutamate E147, threonine T248, arginine R43, and methionine M493), respectively. I248T, Q43R, and T493M had no effect on steroid production compared to wild-type aldosterone synthase. However, CYP11B2-D147E caused a significant increase in corticosterone production and a smaller increase in aldosterone production from 11-deoxycorticosterone (DOC). This appeared to be predominantly due to an increase in the 11beta-hydroxylation of DOC to corticosterone mediated by a decrease in Km, which was 1.4 micromol/L for the mutant compared with 5 micromol/L for the wild-type enzyme. CYP11B2-D147E had no effect on the conversion of 11-deoxycortisol to cortisol. The reverse construct (CYP11B1-E147D), substituting the 11beta-hydroxylase residue with the aldosterone synthase equivalent, decreased the conversion of DOC to corticosterone, which was mediated by an increase in Km that was 7.5 micromol/L for the mutant compared with 2.5 micromol/L for the wild-type enzyme. Again, the conversion of 11-deoxycortisol to cortisol was unimpaired. Thus, amino acid 147 is involved in the transformation of the 17-deoxysubstrate, but not the 17alpha-hydroxysubstrate. The results demonstrate that a conservative change in amino acid, even at some linear distance from known active centers, can significantly affect enzyme substrate affinity and subsequent steroid hormone production.

Nonclassic 11 beta-hydroxylase deficiency: report of two patients and review

Congenital adrenal hyperplasia (CAH) is well recognized as a disorder which can result in virilization of females, accelerated skeletal maturation and resultant adult short stature in both genders, and, in certain varieties, life-threatening adrenal crisis. Among the enzymatic defects resulting in CAH, nonclassic or partial 11 beta-hydroxylase deficiency is a relatively uncommon etiology. However, the subtlety with which it can present and the difficulties associated with its diagnosis can delay its identification and result in a significant reduction in adult stature. This paper describes the presentation and evaluation of two children with partial 11 beta-hydroxylase deficiency, discusses its pathogenesis, and compares the disorder with the more common varieties of congenital adrenal hyperplasia.

Mutations in CYP11B1 gene converting 11beta-hydroxylase into an aldosterone-producing enzyme are not present in aldosterone-producing adenomas

In the human adrenal cortex, cortisol and aldosterone are synthesized by the isozymes 11beta-hydroxylase and aldosterone synthase, respectively, encoded by the 93% identical CYP11B1 and CYP11B2 genes. In vitro mutagenesis of CYP11B1 complementary DNA, resulting in the replacement of CYP11B1 codons by those encoding the corresponding amino acid residues of CYP11B2 enzyme (exon 5, Ser288Gly; exon 6, Val320Ala), yields a complementary DNA encoding a mutant enzyme with an efficient aldosterone synthase activity. Identical somatic mutations in the CYP11B1 gene in vivo would produce a gene encoding an enzyme with C18 activity and that would preserve ACTH responsiveness due to the retained 5'-promoter in the mutated CYP11B1 gene. An ACTH-responsive aldosterone synthase activity of this type is commonly seen in patients with aldosterone-producing adenomas (APA). We examined the occurrence of mutations in exons 5 and 6 of the CYP11B1 gene in APA from 10 patients with primary aldosteronism. Patients were selected on preoperative evidence of a 50% or greater plasma aldosterone decrease after short term dexamethasone trial and no aldosterone response to upright posture. DNA from adenomas was amplified by PCR using two pairs of primers spanning the regions of CYP11B1 gene, i.e. exons 3-5 and exons 6-9, where mutations could be located. Targeted regions were screened for mutations by automated sequencing of PCR products. No point mutations of the CYP11B1 gene over the two regions examined were found in APA. This argues against involvement of mutations in the pathogenesis of ACTH-responsive APA.

Congenital adrenal hyperplasia in pregnancy

The congenital adrenal hyperplasias (CAH) are a group of inherited enzymatic defects of adrenal steroid biosynthesis. Deficiencies of each enzyme required in the steroid biosynthesis pathway are known, and these deficiencies are all inherited as autosomal recessive disorders. During pregnancy, maternal and fetal problems are confined to women who have 21-hydroxylase deficiency (P450c21 deficiency), 11-hydroxylase deficiency (P450c11 deficiency), and 3 beta-hydroxysteroid dehydrogenase deficiency (3 beta HSD deficiency), because other adrenal enzyme deficiencies are not compatible with fertility. The interposition of the placenta on the hypothalamic-pituitary-adrenal axis and other endocrine changes during pregnancy impact considerably on the clinical evaluation of the congenital adrenal hyperplasias. Successful management of CAH in pregnancy requires a firm knowledge of normal adrenal anatomic and endocrine changes that occur during gestation. Women with severe forms of CAH have decreased fertility rates because of oligo-ovulation, and successful conception requires a combination of good therapeutic compliance, careful endocrine monitoring, and often ovulation induction. From a fetal and neonatal standpoint, accurate prenatal diagnosis of 21-hydroxylase deficiency and 11-hydroxylase deficiency is now possible, which allows for prenatal treatment in an attempt to minimize clinical problems in the neonates. Prevention of masculinization of affected female fetuses by corticosteroid suppression has been attempted in both 21-hydroxylase deficiency and 11beta-hydroxylase deficiency CAH, with variable degrees of success. This review provides an overview of the congenital adrenal hyperplasias and their management during pregnancy.

Structure-function relationships of aldosterone synthase and 11 beta-hydroxylase enzymes: implications for human hypertension

1. The genes encoding aldosterone synthase (CYP11B2) and 11 beta-hydroxylase (CYP11B1) are very similar at the nucleotide level (> 95% homology). Despite this and the corresponding similarity of amino acid sequence, there are considerable differences in functional and substrate specificity of the two enzymes. In the present study we have examined the role of two amino acids that differ between the two enzymes (147 and 248) to determine the difference between aldosterone synthase and 11 beta-hydroxylase capacity to 11-hydroxylate 11-deoxycorticosterone (DOC). 2. Plasmids containing cDNA encoding wild-type aldosterone synthase, wild-type 11 beta-hydroxylase and mutated forms of aldosterone synthase (D147E and I248T), in which the codons for residues 147 (aspartate exon 3) or 248 (isoleucine exon 4) had been altered to encode the corresponding amino acids (glutamate and threonine respectively) from 11 beta-hydroxylase were transiently expressed in non-steroidogenic COS-7 cells. All transfections were cotransfected with bovine adrenodoxin. Cells were then incubated with [3H]-DOC for 48 h and the production of corticosterone (B), 18-hydroxycorticosterone (18-OHB) and aldosterone measured by measuring tritriated products using thin layer chromatography. 3. Compared with wild-type aldosterone synthase, the mutated form (D147E) encoding amino acid 147 from 11 beta-hydroxylase was more efficient in 11 beta-hydroxylation of deoxycorticosterone (B:DOC ratio 0.53 +/- 0.05 (wild type) to 3.05 +/- 0.37 (mutant); P < 0.001). However, 18-hydroxylation of B and conversion of this steroid into aldosterone were unaffected. There was a 20% increase in the production of aldosterone from DOC (P < 0.05). However, in comparison with wild-type 11 beta-hydroxylase, the mutated aldosterone synthase (D147E) was still less efficient (B:DOC ratio 6.2 +/- 0.41). The mutated aldosterone synthase (I248T) encoding amino acid 248 from 11 beta-hydroxylase showed no changes in conversion of DOC to B or in the production of aldosterone. 4. These data demonstrate that position 147 has an important effect on the efficiency of 11 beta-hydroxylation of DOC and indicate that this is a key difference between the two enzymes in determining functional specificity. However, other residues must also contribute to efficiency of 11-hydroxylation of 11 beta-hydroxylase. In contrast, amino acid 248, which is one of the few differences between the two enzymes in exon 4, does not affect enzyme efficiency. As altered activity of aldosterone synthase and 11 beta-hydroxylase has been proposed as an important intermediate phenotype in essential hypertension, such studies will help our understanding of the structure-function relationships that will be necessary in order to understand how genetic changes may contribute to observed differences in phenotype.

Structural analysis and evaluation of the aldosterone synthase gene in hypertension

Anomalies in either of the tightly linked genes encoding the enzymes CYP11B1 (11beta-hydroxylase) or CYP11B2 (aldosterone synthase) can lead to important changes in arterial pressure and are responsible for several monogenically inherited forms of hypertension. Mutations in these genes or their regulatory regions could thus contribute to genetic variation in susceptibility to essential hypertension. To test this hypothesis, we performed 2 complementary studies of the CYP11B1/CYP11B2 locus in essential hypertension. After characterizing a DNA contig containing the CYP11B1 gene and mapping the gene in the Centre d'Etudes du Polymorphisme Humain reference panel of families, we performed a linkage study with 292 hypertensive sibling pairs and a highly informative microsatellite marker near CYP11B1. We also analyzed the association of 2 frequent biallelic polymorphisms of the CYP11B2 gene, 1 in the promoter at position -344 (-344C/T) and the other, a common gene conversion in intron 2, with hypertension in 380 hypertensive patients and 293 normotensive individuals. Statistical analyses did not show significant linkage of the CYP11B1 microsatellite marker to hypertension. No positive association with hypertension was found with the gene conversion in intron 2, but a positive association with hypertension was found with the -344T allele. The hypertensive and normotensive samples differed significantly in both genotype (P=0.023) and allele frequencies (P=0.010). Our data suggest a modest contribution of the CYP11B2 gene to essential hypertension.

Mutation THR-185 ILE is associated with corticosterone methyl oxidase deficiency type II

Two boys presenting with infection-triggered, life-threatening salt-loss and hyperkalaemia were published in 1991 in the European Journal of Pediatrics. In both boys, the diagnosis of corticosterone methyl oxidase (CMO) deficiency type II has been established on the basis of determinations of plasma and urinary steroids. We had the opportunity to perform a molecular genetic study in one of the two boys. This boy had an elevated plasma 18-hydroxycorticosterone/aldosterone ratio which is pathognomonic for CMO deficiency type II. Sequence analysis of the CYP11B2 gene revealed a homozygous single base exchange in codon 185 of CYP11B2 causing an amino acid substitution Thr185Ile.

CONCLUSION

A Thr185Ile mutation in the CYP11B2 gene was found in a patient with CMO deficiency type II. This mutation may change the secondary structure of the enzyme leading to its decreased activity.

Diagnosis and management of congenital adrenal hyperplasia

Congenital adrenal hyperplasia is a family of inborn errors of steroidogenesis, each characterized by a specific enzyme deficiency that impairs cortisol production by the adrenal cortex, and can lead to sexual ambiguity in both genetic males and females. The enzymes most often affected are 21-hydroxylase, 11 beta-hydroxylase, and 3 beta-hydroxysteroid dehydrogenase, and less often, 17 alpha-hydroxylase/17, 20-lyase and cholesterol desmolase. Decreased production of cortisol results in increased pituitary secretion of adrenocorticotropic hormone. The elevated adrenocorticotropic hormone stimulates both the accumulation of precursor steroids in the impeded pathways and excessive steroid synthesis in other adrenal biosynthetic pathways unaffected by the enzyme deficiency. Correct identification of the enzyme affected is achieved by the observation of clinical syndromes reflecting distinct hormonal patterns, and it is measured quantitatively as low levels of cortisol and other adrenal steroids, as well as increased levels of steroids proximal to the blocked step. Many of the corresponding genes for the described enzymes have been isolated and characterized, and specific mutations causing many cases of congenital adrenal hyperplasia have been identified. These advances have important implications for early prenatal diagnosis and prenatal treatment.

Inactivating mutations in the 25-hydroxyvitamin D3 1alpha-hydroxylase gene in patients with pseudovitamin D-deficiency rickets

BACKGROUND

Pseudovitamin D-deficiency rickets is characterized by the early onset of rickets with hypocalcemia and is thought to be caused by a deficit in renal 25-hydroxyvitamin D3 1alpha-hydroxylase, the key enzyme for the synthesis of 1alpha,25-dihydroxyvitamin D3.

METHODS

We cloned human 25-hydroxyvitamin D3 1alpha-hydroxylase complementary DNA (cDNA) using a mouse 1alpha-hydroxylase cDNA fragment as a probe. Its genomic structure was determined, and its chromosomal location was mapped by fluorescence in situ hybridization. We then identified mutations in the 1alpha-hydroxylase gene in four unrelated patients with pseudovitamin D-deficiency rickets by DNA-sequence analysis. Both the normal and the mutant 1alpha-hydroxylase proteins were expressed in COS-1 cells and were assayed for 1alpha-hydroxylase activity.

RESULTS

The gene for 25-hydroxyvitamin D3 1alpha-hydroxylase was mapped to chromosome 12q13.3, which had previously been reported to be the locus for pseudovitamin D-deficiency rickets by linkage analysis. Four different homozygous missense mutations were detected in this gene in the four patients with pseudovitamin D-deficiency rickets. The unaffected parents and one sibling tested were heterozygous for the mutations. Functional analysis of the mutant 1alpha-hydroxylase protein revealed that all four mutations abolished 1alpha-hydroxylase activity.

CONCLUSIONS

Inactivating mutations in the 25-hydroxyvitamin D3 1alpha-hydroxylase gene are a cause of pseudovitamin D-deficiency rickets.

Hereditary defect in biosynthesis of aldosterone: aldosterone synthase deficiency 1964-1997

We studied two of the three patients with a hereditary defect in the biosynthesis of aldosterone originally described by Visser and Cost in 1964. All three presented as newborns with salt-losing syndrome and failure to thrive. The original biochemical studies showed a defect in the 18-hydroxylation of corticosterone. According to the nomenclature proposed by Ulick, this defect would be termed corticosterone methyl oxidase deficiency type I. We measured plasma steroids in the untreated adult patients and performed molecular genetic studies. Aldosterone and 18-OH-corticosterone were decreased, whereas corticosterone and 11-deoxycorticosterone were elevated, thus confirming the diagnosis of corticosterone methyl oxidase deficiency type I. Cortisol and its precursors were in the normal range. Genetic defects in the gene CYP11B2 encoding aldosterone synthase (P450c11Aldo) have been described in a few cases. We identified a homozygous single base exchange (G to T) in codon 255 (GAG) causing a premature stop codon E255X (TAG). This mutation destroys a Aoc II restriction site. Digestion of a PCR fragment containing exon 4 of CYP11B2 (261 bp) with this restriction enzyme revealed in the two patients homozygous for the E255X mutation only a 261-bp fragment, whereas the heterozygous parents had three fragments (261 bp from the mutant allele and 194 and 67 bp from the wild-type allele). The mutant enzyme had lost the five terminal exons containing the heme binding site, and thus there was a loss of function enzyme. We conclude that the biochemical phenotype of these prismatic cases of congenital hypoaldosteronism can be explained by the patients genotype.

Inherited forms of mineralocorticoid hypertension

Aldosterone, the most important mineralocorticoid, regulates electrolyte excretion and intravascular volume mainly through its effects on renal distal convoluted tubules and cortical collecting ducts. Excess secretion of aldosterone or other mineralocorticoids or abnormal sensitivity to mineralocorticoids may result in hypertension, suppressed plasma renin activity, and hypokalemia. Such conditions often have a genetic basis, and studies of these conditions have provided valuable insights into the normal and abnormal physiology of mineralocorticoid action. Deficiencies of steroid 11 beta-hydroxylase or 17 alpha-hydroxylase are types of congenital adrenal hyperplasia, the autosomal recessive inability to synthesize cortisol. These two defects often cause hypertension because of overproduction of cortisol precursors that are, or are metabolized to, mineralocorticoid agonists. These disorders result from mutations in the CYP11B1 and CYP17 genes encoding the corresponding enzymes. Glucocorticoid-suppressible hyperaldosteronism is an autosomal dominant form of hypertension in which aldosterone secretion is abnormally regulated by corticotropin. It is caused by recombinations between linked genes encoding closely related isozymes, 11 beta-hydroxylase (CYP11B1) and aldosterone synthase (CYP11B2), generating a dysregulated chimeric gene with aldosterone synthase activity. Apparent mineralocorticoid excess is a loss of functional ligand specificity of the mineralocorticoid receptor caused by a deficiency of the kidney isozyme of 11 beta-hydroxysteroid dehydrogenase, an enzyme that normally metabolizes cortisol to cortisone to prevent cortisol from occupying the receptor. This autosomal recessive form of severe hypertension results from mutations in the HSD11K (HSD11B2) gene.

MANAGEMENT OF CONGENITAL ADRENAL HYPERPLASIA DURING PREGNANCY

OBJECTIVE

To provide an overview of the congenital adrenal hyperplasias (CAHs) and their management during pregnancy.

METHODS

Pathways of steroid biosynthesis and inherited deficiencies of required enzymes are reviewed, and applications to prenatal diagnosis and treatment of affected fetuses are discussed.

RESULTS

The CAHs are a group of inherited enzymatic defects of adrenal steroid biosynthesis. During pregnancy, maternal problems are confined to women with 21-hydroxylase deficiency, 11b-hydroxylase deficiency, and 3b-hydroxysteroid dehydrogenase deficiency because other adrenal enzyme deficiencies are incompatible with fertility. The interposition of the placenta on the hypothalamic-pituitary-adrenal axis has a major effect on clinical evaluation of CAH during pregnancy. Women with severe forms of CAH have decreased fertility rates because of oligo-ovulation, and successful conception requires a combination of good therapeutic compliance, careful endocrine monitoring, and often induction of ovulation. 21-Hydroxylase deficiency in the fetus can now be diagnosed accurately prenatally by endocrine testing and molecular genetic techniques. Prenatal diagnosis of 11b-hydroxylase deficiency in the fetus by endocrine testing is not as sensitive. Prevention of masculinization of affected female fetuses by corticosteroid suppression has been attempted in both 21-hydroxylase deficiency and 11b-hydroxylase deficiency CAH, with variable degrees of success. To date, no reports have been published of prenatal diagnosis or treatment of affected female fetuses with 3b-hydroxysteroid dehydrogenase deficiency CAH.

CONCLUSION

Endocrine and genetic studies of CAH during pregnancy have improved the diagnosis and management.

11 beta-hydroxylase activity in recombinant yeast mitochondria. In vivo conversion of 11-deoxycortisol to hydrocortisone

In mammals, the final 11 beta-hydroxylation step of the hydrocortisone biosynthesis pathway is performed by a mitochondrial enzyme, namely cytochrome P-450(11 beta), together with the electron carriers adrenodoxin and NADPH adrenodoxin oxidoreductase. Successful production of a functional steroid 11 beta-hydroxylase activity was obtained in recombinant yeast in vivo. This conversion was achieved by coexpression of a mitochondrially targeted adrenodoxin and a modified bovine P-450(11 beta) whose natural presequence was replaced by a yeast presequence, together with an unexpected yeast endogenous NADPH-adrenodoxin-reductase-like activity. Adrenodoxin and P-450(11 beta) behave as a mitochondrial matrix and membrane protein, respectively. Saccharomyces cerevisiae apparently produces a mitochondrial protein which is capable of transferring electrons to bovine adrenodoxin, which in turn transfers the electrons to P-450(11 beta). The endogenous adrenodoxin oxidoreductase gains electrons specifically from NADPH. The notion that a yeast microsomal NADPH P-450 oxidoreductase can transfer electrons to mammalian microsomal P-450s can be extended to mitochondria, where an NADPH adrenodoxin oxidoreductase protein transfers electrons to adrenodoxin and renders a mitochondrial mammalian P-450 functional in vivo. The physiological function of this yeast NADPH adrenodoxin oxidoreductase activity is not known.

Engineering a mineralocorticoid- to a glucocorticoid-synthesizing cytochrome P450

Site-directed mutagenesis of a domain (amino acids 299-338) aligning to the I-helix region of P450cam, P450BM3 and P450terp was used to investigate the different regioselectivities displayed in the hydroxylation reactions performed by human aldosterone synthase (P450aldo) and 11beta-hydroxylase (P45011beta). The two enzymes are 93% identical and are essential for the synthesis of mineralocorticoids and glucocorticoids in the human adrenal gland. Single replacement of P450aldo residues for P45011 beta-specific residues at positions 296, 301, 302, 320, and 335 only gave rise to slightly increased 11beta-hydroxylase activities. However, a L301P/A320V double substitution increased 11beta-hydroxylase activity to 60% as compared with that of P45011 beta. Additionally substituting Ala-320 for Val-320 of P45011 beta further enhanced this activity to 85%. The aldosterone synthase activities of the mutant P450aldo proteins were suppressed to a varying degree, with triple replacement mutant L301P/E302D/A320V retaining only 10% and double replacement mutant L301P/A320V retaining only 13% of the P450aldo wild type activity. These results demonstrate a switch in regio- and stereoselectivities of the engineered P450aldo enzyme due to manipulation of residues at three critical positions, and we attribute the determination of these features in P450aldo to the structure of a region analogous to the I-helix in P450cam.

Congenital hypoaldosteronism: the Visser-Cost syndrome revisited

In 1964, H. K. A. Visser and W. S. Cost were the first to suggest a defect of the terminal aldosterone (Aldo) biosynthesis in patients with hypoaldosteronism. In the last years, the molecular basis of the terminal Aldo biosynthesis has been elucidated. Aldo biosynthesis requires 11beta-hydroxylation of 11-deoxycorticosterone to form corticosterone, hydroxylation at position C-18 to form 18-hydroxycorticosterone (18-OHB), and finally oxidation at position C-18. One single cytochrome P450 enzyme (P450aldo) catalyzes all three reactions in the zona glomerulosa. The coding gene is termed CYP11B2. Two inborn errors of terminal Aldo biosynthesis characterized by overproduction of corticosterone and deficient synthesis of Aldo have been described. Corticosterone methyl oxidase deficiency type I (CMO I) is distinguished by decreased production of 18-OHB while CMO II is characterized by overproduction of 18-OHB and an elevated ratio of 18-OHB to Aldo. Both disorders are inherited by an autosomal recessive trait and cause salt-wasting and failure to thrive in early infancy. Our present series includes 14 CMO deficient infants diagnosed by multisteroid analysis (RIA after extraction and automated high performance gel chromatography) which provides precise biochemical criteria for the differentiation of the two CMO variants. So far, three different mutations within the CYP11B2 gene in patients with P450aldo deficiency have been described. Introduction of these mutations into a CYP11B2 cDNA expression vector construct and subsequent expression in COS cells revealed loss of 11beta-hydroxylase, 18-hydroxylase, and 18-dehydrogenase activity of P450aldo. Further molecular studies on more P450aldo-deficient patients might clarify in the future the still existing discrepancies in CYP11B2 (P450aldo) structure-function relationship.

Mutation T318M in the CYP11B2 gene encoding P450c11AS (aldosterone synthase) causes corticosterone methyl oxidase II deficiency

Corticosterone methyl oxidase (CMO) deficiency refers to disorders of aldosterone synthesis due to mutations in the CYP11B2 gene encoding cytochrome P450c11AS, which is the adrenal aldosterone synthase. Type I CMO deficiency is associated with low concentrations of 18OH-corticosterone and aldosterone, due to severe mutations in P450c11AS; while type II CMO deficiency is associated with high concentrations of 18OH-corticosterone and low concentrations of aldosterone, due to less severe mutations of P450c11AS. A single type of mutation, compound homozygosity for R181W and V386A, has been reported as the cause of CMOII deficiency in an inbred population. We now report a patient with a typical clinical and hormonal picture of CMOII deficiency. Direct sequencing of patient and parent DNAs showed that the mother's allele contributed R181W and the deletion/frameshift mutation delta C372, while the father's allele contributed T318M and V386A. These mutants were recreated in cDNA expression vectors singly and in the parental pairs, showing that neither allele contributed any measurable activity. This would suggest the patient should have CMOI deficiency. These studies suggest that other factors besides P450c11AS are involved in the genesis of the distinctive CMOI and CMOII phenotypes.

Glucocorticoid-remediable aldosteronism

GRA is an inherited disorder of aldosterone biosynthesis. To date, all cases have been the result of chimeric gene duplications in which the regulatory region of the 11-beta hydroxylase gene is fused to more distal coding sequences of the aldosterone synthase gene. This results in ectopic expression of aldosterone synthase in fasciculata cells. Genetic testing has been remarkably precise in identifying these individuals with 100% concordance of the presence of the chimeric gene with increases in 18-oxygenated cortisol products. Several implications follow from these findings. First, GRA may be more common in the hypertensive population than had been previously estimated, and second, genetic testing of subsets of the essential hypertensive population (e.g., those who have low plasma renin activity) may allow the identification of GRA patients who could then be treated specifically. We recommend that hypertensive patients with signs of aldosteronism and no radiologic evidence of an aldosteronoma, especially young hypertensive subjects with low renin activity, be genetically screened for GRA. To track the success of this approach and to identify responses to various therapeutic programs, a central international registry for GRA has been established. This registry not only provides access to screening for GRA, but also informational resources for patients and physicians.

Frog cytochrome P-450 (11 beta,aldo), a single enzyme involved in the final steps of glucocorticoid and mineralocorticoid biosynthesis

A cDNA for cytochrome P-450(11 beta,aldo) was cloned from a library of bullfrog interrenal tissue (tissue corresponding to the mammalian adrenal gland). The 1919-bp cDNA encoded a protein of 517 amino acids. Its amino acid sequence was highly similar to the sequences of bovine P-450(11 beta) and rat P-450(11 beta,aldo) when P-450(11 beta) family enzymes reported to date were examined. The enzyme expressed in COS7 cells had the 11 beta-hydroxylation, 18-hydroxylation activities and aldosterone synthetic activity. Northern-blot and immunoblot analyses suggested that a single P-450(11 beta) enzyme was expressed in bullfrog interrenal tissue. These results suggest that a single enzyme catalyzes the final steps of glucocorticoid and mineralocorticoid biosynthesis in bullfrog interrenal tissue as in bovine adrenal gland. A phylogenetic tree of CYP11B genes suggests that the frog enzyme diverged at an earlier evolutionary time from other vertebrate enzymes. Immunohistochemical and in situ hybridization studies indicated that steroidogenic cells existed in the outer region of interrenal tissue more densely than in the inner region, whereas some medullary cells made clusters like islets. Most of the cells were diffusely distributed in the tissue.

Human adrenal CYP11B1: localization by in situ-hybridization and functional expression in cell cultures

CYP11B1 was detected in the human adrenal cortex and in human adenomas by in situ-hybridization methods. Specific riboprobes were generated and hybridized to sections of an Aldosterone Producing Adenoma (APA), the non-tumour portion of the corresponding adrenal gland and two adenomas not related to hyperaldosteronism. P45011B1 mRNA was clearly localized in the zona fasciculata/reticularis. Semi-quantitative analysis has been performed and seems to be applicable for a further classification of adrenal tumours. Stable expression of CYP11B1 cDNA was performed in V79 cells. The interference of different substances (metyrapone, spironolactone and different imidazole derivatives) with CYP11B1 activity was studied using this cell line. The cell line revealed to be suitable for analysis of the active site of CYP11B1 as well as for analysis of side effects of drugs on steroidogenesis.

Characterization of zona glomerulosa function in patients with classic and non-classic forms of congenital adrenal hyperplasia due to 11 beta-hydroxylase deficiency

The function of the adrenal zona glomerulosa was studied in 18 patients with 11-hydroxylase deficiency confirmed by elevated plasma levels of 11-deoxycortisol. Patients were divided into two groups. Group I (4 males, 7 females; aged 1.2-2.8 yrs) had symptoms at birth or shortly after (classic form), and Group II (4 males, 3 females; aged 7.3-20.1 yrs) had their first clinical manifestation during childhood (non-classic form). To study zona glomerulosa function, patients were given dexamethasone p.o. 2 mg/m2/day x6 days, thus suppressing the zona fasciculata. Six hours after the last dose of dexamethasone, the zona glomerulosa was stimulated by i.v. administration of furosemide 1.0 mg/kg as a single dose. Blood was drawn 2 h later. In the untreated state, all patients had striking elevation of ACTH (Group I: 1,070 +/- 380 pg/ml; Group II: 764 +/- 180 pg/ml), 11-deoxycortisol (Group I: 63,000 +/- 22,000 ng/dl; Group II: 17,200 +/- 5,200 ng/dl) and deoxycorticosterone (Group I: 1,100 +/- 67 ng/dl; Group II: 499 +/- 27 ng%) while plasma renin activity (< 0.5 ng/ml/h in both groups) and aldosterone (Group I: 3.0 +/- 1.8 ng/dl; Group II: 2.3 +/- 1.8 ng/dl) were markedly suppressed. After the administration of furosemide 4 patients in Group I were unable to increase aldosterone (2.8 +/- 0.9 ng/dl) secretion in spite of marked elevation of plasma renin activity (28 +/- 7 ng/ml/h), suggesting an impairment of 11-hydroxylase in the zona glomerulosa.(ABSTRACT TRUNCATED AT 250 WORDS)

Alignment of physical and genetic maps of human 8q23-qter using somatic cell hybrid mapping panel

We describe a mapping panel for the 8q23-qter region composed of human-hamster hybrid cell lines carrying deletion and translocation derivatives of human chromosome 8. The panel divides this region of the chromosome into nine intervals and has been used to map 40 loci by Southern blot hybridization and PCR. Use of this mapping panel has allowed us to align the terminal portions of two different genetic maps of chromosome 8 with each other and with the physical map of the chromosome.

Genetic diseases of steroid metabolism

All major classes of biologically active steroid hormones (progestins, mineralocorticoids, glucocorticoids, and sex steroids) are synthesized from cholesterol through 11 different bioconversions. With the exception of 5 alpha-reductase, all the enzymes mediating these reactions fall into two classes, cytochromes P450 and short-chain dehydrogenases. Cytochromes P450 are heme-containing membrane-bound proteins with molecular weights of approximately 50,000 that utilize molecular oxygen and electrons from NADPH-dependent accessory proteins to hydroxylate substrates. Short-chain dehydrogenases have molecular weights of 30,000-40,000, have tyrosine and lysine residues at the active site, and remove a hydride from the substrate, transferring the electrons of the hydride to NAD+ or NADP+. In most cases, this reaction is reversible so that the dehydrogenase can also function as a reductase under appropriate conditions. Inherited disorders in enzymes required for steroid biosynthesis have varying effects. Defects that prevent cortisol from being synthesized are referred to collectively as congenital adrenal hyperplasia. Because the enzymes required for cortisol biosynthesis in the adrenal cortex are in many cases required for the synthesis of mineralocorticoids and/or sex steroids, these classes of steroids may also not be synthesized normally. Thus, cholesterol desmolase and 3 beta-hydroxysteroid dehydrogenase deficiencies affect synthesis of all classes of steroids in both the adrenals and gonads. Steroid 21-hydroxylase deficiency, the most common cause (> 90% of cases) of congenital adrenal hyperplasia, can affect both mineralocorticoid and glucocorticoid synthesis, but androgen secretion is usually abnormally high due to shunting of accumulated precursors into this pathway. Excessive secretion of androgens and mineralocorticoids occurs in 11 beta-hydroxylase deficiency (the second most frequent form of congenital adrenal hyperplasia). Mineralocorticoid excess is also seen in 17 alpha-hydroxylase deficiency, but in this disorder sex steroid synthesis is defective. All defects that affect estrogen synthesis (deficiencies of cholesterol desmolase, 3 beta-hydroxysteroid dehydrogenase, 17 alpha-hydroxylase, aromatase, and 17 beta-hydroxysteroid dehydrogenase) are very rare, suggesting that the inability to synthesize placental estrogens may adversely affect fetal survival. A number of enzymes are expressed at sites of steroid action and regulate the amount of active steroid available to steroid receptors. Steroid 5 alpha-reductase converts testosterone to the more active dihydrotestosterone. Deficiency of this activity leads to incomplete development of male genitalia; 17 beta-hydroxysteroid dehydrogenase deficiency has similar phenotypic effects.(ABSTRACT TRUNCATED AT 400 WORDS)

Restriction fragment length polymorphisms of the CYP11B1 gene in the Japanese population

Restriction fragment length polymorphisms (RFLPs) of the CYP11B1 gene were studied in Japanese using cDNA clone P450c11 as a probe. Genomic DNAs from 60 unrelated Japanese individuals were digested with 8 different restriction enzymes and analyzed by Southern blot hybridization. Two RFLPs were detected in MspI digests of the DNA. One (A) was characterized by polymorphic bands at 3.4 and 2.5 kilobase-pairs (kb) and the other (B) by polymorphic bands at 1.7 and 1.2 kb. The third RFLP was observed in PvuII-digested samples and was polymorphic at 5.8 and 4.0 kb bands. Two of the three RFLPs found, RFLP (A) and (C), have not been described in the only previous report which was based on Caucasian samples. We also examined the RFLPs of a 3 generation family of 11 beta-hydroxylase deficiency caused by an abnormality of the CYP11B1 gene. All the family members were homozygous in all three RFLPs and was thus not informative.

Mutations in the CYP11B1 gene causing congenital adrenal hyperplasia and hypertension cluster in exons 6, 7, and 8

Steroid 11 beta-hydroxylase deficiency (failure to convert 11-deoxycortisol to cortisol) is the second most common cause of congenital adrenal hyperplasia and results in a hypertensive form of the disease. The 11 beta-hydroxylase enzyme is encoded by the CYP11B1 gene on chromosome 8q22. Two mutations in CYP11B1 have previously been reported in patients with 11 beta-hydroxylase deficiency--Arg-448-->His and a 2-bp insertion in codon 394. We now report eight previously uncharacterized mutations causing this disorder. Seven are point mutations (three nonsense and four missense) and one is a single base pair deletion causing a frameshift. We have used an in vitro transfection assay to show that all five known missense mutations causing 11 beta-hydroxylase deficiency abolish enzymatic activity. In principle, deletions of CYP11B1 could be generated by unequal crossing-over between CYP11B1 and the adjacent CYP11B2 gene, but no such deletions were found among the deficiency alleles in this study. Seven of the 10 known mutations are clustered in exons 6-8, a nonrandom distribution within the gene. This may reflect the location of functionally important amino acid residues within the enzyme or an increased tendency to develop mutations within this region of the gene.

Steroid 21-hydroxylase (P450c21): a new allele and spread of mutations through the pseudogene

Lesions in the gene encoding the adrenal enzyme steroid 21-hydroxylase (P450c21) result in defective adrenal cortisol synthesis, often accompanied by aldosterone deficiency. The symptoms range from severe neonatal disease to inconspicuous symptoms in adulthood depending on the nature of the mutations. The 21-hydroxylase gene is present in close proximity to a highly homologous pseudogene, and both genes show variation in copy number between individuals. For complete DNA sequence characterization, we have applied selective polymerase chain reaction amplification and direct sequencing of all full-length steroid 21-hydroxylase genes present in individuals. Using healthy individuals with only one remaining steroid 21-hydroxylase allele as normal references, a new allele was found in two siblings, in whom clinical and laboratory findings demonstrated moderate enzyme deficiency. Full-length sequencing of this allele displayed an Arg 484 to Pro codon change in exon 10, in the same position as a previously identified GG to C mutation found in a patient with severe 21-hydroxylase deficiency. Arg 484 is located within a stretch of amino acids that are highly conserved between mammalian 21-hydroxylases. The finding of the presently reported 21-hydroxylase allele indicates that the GG to C mutation from the severely affected patient has arisen by a two-step mechanism, consisting of a G to C transversion accompanied by an adjacent G deletion. When sequencing 26 pseudogenes, both these mutations, which are not present in the pseudogenes hitherto reported, were found at low frequency together with a number of other polymorphisms. Thus, also rare mutations can spread via the pseudogene and can therefore be expected to arise independently in unrelated individuals.

Prothymosin alpha gene in humans: organization of its promoter region and localization to chromosome 2

A genomic clone encoding prothymosin alpha (gene symbol: PTMA), a nuclear-targeted protein associated with cell proliferation, was isolated and the 5'-regulatory region subcloned and sequenced. Because of previously reported discrepancies between several cDNA clones and a genomic clone for prothymosin alpha, we determined the sequence of the first exon and of a 1.7-kb region 5' to the first exon. The sequence of the genomic clone reported here corresponds to the published cDNA sequences, suggesting that the previously noted discrepancies may be due to genetic polymorphism in this region. In addition, our sequence data extend the known 5'-upstream sequence by an additional 1.5 kb allowing the identification of numerous, potential cis-acting regulatory sites. This 5'-flanking cloned probe permitted us to localize the prothymosin gene to chromosome 2 in humans.

The P450 superfamily: update on new sequences, gene mapping, accession numbers, early trivial names of enzymes, and nomenclature

We provide here a list of 221 P450 genes and 12 putative pseudogenes that have been characterized as of December 14, 1992. These genes have been described in 31 eukaryotes (including 11 mammalian and 3 plant species) and 11 prokaryotes. Of 36 gene families so far described, 12 families exist in all mammals examined to date. These 12 families comprise 22 mammalian subfamilies, of which 17 and 15 have been mapped in the human and mouse genome, respectively. To date, each subfamily appears to represent a cluster of tightly linked genes. This revision supersedes the previous updates [Nebert et al., DNA 6, 1-11, 1987; Nebert et al., DNA 8, 1-13, 1989; Nebert et al., DNA Cell Biol. 10, 1-14 (1991)] in which a nomenclature system, based on divergent evolution of the superfamily, has been described. For the gene and cDNA, we recommend that the italicized root symbol "CYP" for human ("Cyp" for mouse), representing "cytochrome P450," be followed by an Arabic number denoting the family, a letter designating the subfamily (when two or more exist), and an Arabic numeral representing the individual gene within the subfamily. A hyphen should precede the final number in mouse genes. "P" ("p" in mouse) after the gene number denotes a pseudogene. If a gene is the sole member of a family, the subfamily letter and gene number need not be included. We suggest that the human nomenclature system be used for all species other than mouse. The mRNA and enzyme in all species (including mouse) should include all capital letters, without italics or hyphens. This nomenclature system is identical to that proposed in our 1991 update. Also included in this update is a listing of available data base accession numbers for P450 DNA and protein sequences. We also discuss the likelihood that this ancient gene superfamily has existed for more than 3.5 billion years, and that the rate of P450 gene evolution appears to be quite nonlinear. Finally, we describe P450 genes that have been detected by expressed sequence tags (ESTs), as well as the relationship between the P450 and the nitric oxide synthase gene superfamilies, as a likely example of convergent evolution.

Glucocorticoid-suppressible hyperaldosteronism results from hybrid genes created by unequal crossovers between CYP11B1 and CYP11B2

Glucocorticoid-suppressible hyperaldosteronism (GSH) is an autosomal dominant form of familial hypertension. The biochemical abnormalities seen in this disorder may be remedied by administration of dexamethasone, implying that aldosterone synthesis is being abnormally regulated by corticotropin. The final three steps of aldosterone synthesis, 11 beta- and 18-hydroxylation and 18-oxidation, are mediated by a cytochrome P450 in the zona glomerulosa of the adrenal cortex termed CYP11B2. A related isozyme in the zona fasciculata, CYP11B1, is required for cortisol synthesis; this isozyme, which is normally expressed at much higher levels than CYP11B2, only has 11 beta-hydroxylase activity. These isozymes are encoded by genes on human chromosome 8q22. We have now studied four unrelated patients with GSH. We found that each patient has one chromosome that carries three CYP11B genes instead of two. This has presumably been generated by unequal meiotic crossing-over. The extra gene is a hybrid with 5' regulatory and coding regions corresponding to CYP11B1 and 3' coding regions from CYP11B2. The breakpoint is in intron 2 in two cases, intron 3 in one, and exon 4 in one. Cells transfected with hybrid cDNAs containing up to the first three exons of CYP11B1 synthesized aldosterone at levels near that of cells carrying normal CYP11B2, but cells transfected with hybrids containing the first five or more exons of CYP11B1 could not synthesize detectable amounts of aldosterone. These data demonstrate that GSH is caused by expression of a gene that is regulated like CYP11B1 but that encodes a protein able to synthesize aldosterone.

Hereditary hypertension caused by chimaeric gene duplications and ectopic expression of aldosterone synthase

Patients with glucocorticoid-remediable aldosteronism (GRA) from 12 kindreds possess chimaeric gene duplications arising from unequal crossing-over, fusing regulatory sequences of steroid 11 beta-hydroxylase to coding sequences of aldosterone synthase. These chimaeric genes are specific for GRA and explain the biochemistry, physiology and genetics of this form of hypertension. Sites of crossing over range from intron 2 to intron 4. Most mutations have arisen independently from either sister or non-sister chromatid exchange between these genes, which are only 45 kilobases apart. The possibility of a susceptibility allele for GRA of Irish origin is suggested. These findings indicate the utility of a direct genetic test for this disorder.

Assignment of the gene for human spasmolytic protein (hSP/SML1) to chromosome 21

A human cDNA corresponding to the porcine pancreatic spasmolytic protein (PSP) was isolated, and the recombinant clone was originally termed hSP for human spasmolytic protein. Later, the term SML1 for spasmolysin was suggested for the human gene. This protein shows a remarkable sequence homology to pS2, a protein coded by an estrogen-induced gene isolated from the breast carcinoma cell line MCF-7. Although, at the DNA level, the gene sequences pS2 and hSP/SML1 display insufficient homology for cross-hybridization, their expression in tumor cells occurs with remarkable coordination. The human pS2 gene sequence has been assigned to chromosome 21, and we have therefore attempted to map the hSP/SML1 gene by using cDNA and Southern blotting of genomic DNAs from a panel of human-rodent somatic cell hybrids carrying different complements of human chromosomes. Interestingly, the hSP/SML1 gene is also localized on chromosome 21.

Mutations in the human CYP11B2 (aldosterone synthase) gene causing corticosterone methyloxidase II deficiency

Corticosterone methyloxidase II (CMO-II) deficiency is an autosomal recessive disorder of aldosterone biosynthesis, characterized by an elevated ratio of 18-hydroxycorticosterone to aldosterone in serum. It is genetically linked to the CYP11B1 and CYP11B2 genes that, respectively, encode two cytochrome P450 isozymes, P450XIB1 and P450XIB2. Whereas P450XIB1 only catalyzes hydroxylation at position 11 beta of 11-deoxycorticosterone and 11-deoxycortisol, P450XIB2 catalyzes the synthesis of aldosterone from deoxycorticosterone, a process that successively requires hydroxylation at positions 11 beta and 18 and oxidation at position 18. To determine the molecular genetic basis of CMO-II deficiency, seven kindreds of Iranian-Jewish origin were studied in which members suffered from CMO-II deficiency. No mutations were found in the CYP11B1 genes, but two candidate mutations, R181W and V386A, were found in the CYP11B2 genes. When these mutations were individually introduced into CYP11B2 cDNA and expressed in cultured cells, R181W reduced 18-hydroxylase and abolished 18-oxidase activities but left 11 beta-hydroxylase activity intact, whereas V386A caused a small but consistent reduction in the production of 18-hydroxycorticosterone. All individuals affected with CMO-II deficiency were homozygous for both mutations, whereas eight asymptomatic subjects were homozygous for R181W alone and three were homozygous for V386A alone. These findings confirm that P450XIB2 is the major enzyme mediating oxidation at position 18 in the adrenal and suggest that a small amount of residual activity undetectable in in vitro assays is sufficient to synthesize normal amounts of aldosterone.

High frequency of congenital adrenal hyperplasia (classic 11 beta-hydroxylase deficiency) among Jews from Morocco

Steroid 11 beta-hydroxylase deficiency is relatively frequent in Israel among North African Jews. Over a 39-year period, 38 affected individuals from 25 families were diagnosed. Nineteen families came from Morocco, and in another 2, one parent came from Morocco (80% of all parents). Demographic studies showed that most of their grandparents were born in the region of the Atlas Mountains. In Israel, the overall incidence of the disorder is estimated between 1 in 30,000 to 1 in 40,000 births, but in offspring of Moroccan Jews the ratio is 1 in 5,000 to 1 in 7,000, with an allele frequency of 1 in 70 to 1 in 84 and a carrier frequency of 1 in 35 to 1 in 42. The clinical expression is characterized by a wide range of variability in the signs of androgen and mineralocorticoid excess. Virilization in the female ranged from enlarged clitoris in the mildest forms, to markedly hypertrophied clitoris with penile urethra and fused labial-scrotal folds in the most severe forms. Hypertension causing vascular accidents and death was observed in both severe and mildly virilized patients, whereas masculinized females were sometimes normotensive. Based on historical evidence, the origin of the ancestors, and the onomastic analysis of the families surnames, we propose that the mutation of 11 beta-hydroxylase deficiency in Jews from Morocco may have originated in either the ancient Jewish settlers or the native Berber tribes who lived in the region of the Atlas Mountains in the southern region of Morocco before the destruction of the Second Temple by the Romans, in the year 70 C.E.

Corticosterone methyloxydase deficiency type II in a Croatian girl

This is a brief case report on a four-month-old girl who was admitted for failure to thrive and moderate dehydration. On admission she was mildly dehydrated and undernourished but with otherwise normal physical findings. Laboratory investigation disclosed mild but constant hyponatremia and hyperkalemia, very high plasma renin activity (greater than 900 ng/mL per hour) and low plasma aldosterone concentration (2.5 ng/dL). The plasma 18-hydroxycorticosterone (18-OH-B) was very high (1,682 ng/dL), producing thus an abnormally elevated 18-OH-B to aldosterone ratio of 542 (normally 6.3 +/- 3.6). The diagnosis of corticosterone methyloxydase deficiency type II was made, and the administration of fluorohydrocortisone resulted in rapid weight gain with normalization of blood electrolytes and gradual decrease in plasma renin activity. A very efficient catch-up growth resulted in normal body weight and length at the age of 2 years. This is the first well documented case of the disease in the population of Yugoslavia.

Corticosterone methyl oxidase type II deficiency: a cause of failure to thrive and recurrent dehydration in early infancy

Corticosterone methyl oxidase type II (CMO II) deficiency is an uncommon cause of salt-wasting in infancy. We describe a boy who presented with recurrent dehydration and severe failure to thrive in the first 3 months of life, associated with mild hyponatraemia (serum Na+ 127-132 mEq/l) and hyperkalaemia (serum K+ 5.3-5.9 mEq/l). The diagnosis was suggested by an elevated plasma renin activity (PRA): serum aldosterone ratio, and subsequently confirmed by an elevated serum 18-hydroxycorticosterone: aldosterone ratio. Treatment with 9 alpha-fluorohydroxycortisone normalized growth parameters and PRA levels. CMO II deficiency should be considered in infants with recurrent dehydration and failure to thrive, even when serum sodium and potassium levels are not strikingly abnormal.

A chimaeric 11 beta-hydroxylase/aldosterone synthase gene causes glucocorticoid-remediable aldosteronism and human hypertension

Glucocorticoid-remediable aldosteronism (GRA), an autosomal dominant disorder, is characterized by hypertension with variable hyperaldosteronism and by high levels of the abnormal adrenal steroids 18-oxocortisol and 18-hydroxycortisol, which are all under control of adrenocorticotropic hormone and suppressible by glucocorticoids. These abnormalities could result from ectopic expression of aldosterone synthase, which is normally expressed only in adrenal glomerulosa, in the adrenal fasciculata. Genes encoding aldosterone synthase and steroid 11 beta-hydroxylase (expressed in both adrenal fasciculata and glomerulosa), which are 95% identical and lie on chromosome 8q (refs 7, 10), are therefore candidate genes for GRA. Here we demonstrate complete linkage of GRA in a large kindred to a gene duplication arising from unequal crossing over, fusing the 5' regulatory region of 11 beta-hydroxylase to the coding sequences of aldosterone synthase (maximum lod score 5.23 for complete linkage, odds ratio of 170,000:1). This mutation can account for all the physiological abnormalities of GRA. Our result represents the demonstration of a mutation causing hypertension in otherwise phenotypically normal animals or humans.

Analysis of the polyadenylation consensus sequence context in the genes of nuclear encoded mitochondrial proteins

A compilation of the pre-mRNA ends of the genes of nuclear encoded mitochondrial proteins resulted in a consensus sequence of the type (T/A)NTTNNNNNTTTNAATAAA. Nucleotide positions +8, +13, +14, +16 and +17 downstream of the AATAAA sequence show also a predominance of nucleotide T. This consensus sequence suggests the importance of the immediate surroundings of the cannonical polyadenylation signal sequence AATAAA on the efficiency of the cleavage and polyadenylation of this specific group of pre-mRNAs.

Regional mapping of genes encoding human steroidogenic enzymes: P450scc to 15q23-q24, adrenodoxin to 11q22; adrenodoxin reductase to 17q24-q25; and P450c17 to 10q24-q25

Steroid hormones are synthesized by a complex array of 10 enzymes. The genes for each of these have now been cloned, and previous work has determined the regional chromosomal assignments of six of these. We used in situ hybridization to determine the regional chromosomal assignments of the four remaining enzymes. The CYP11A1 gene encodes mitochondrial P450scc, which converts cholesterol to pregnenolone, and is located on 15q23-q24. The gene for adrenodoxin, which receives electrons from adrenodoxin reductase and transfers them to P450scc, is on 11q22 while its pseudogenes are on 20q11-q12. The gene for adrenodoxin reductase is on 17q24-q25. The CYP17 gene encodes P450c17, which has both 17 alpha-hydroxylase and 17,20-lyase activities, and is located on 10q24-q25. None of the 10 genes involved in human steroidogenesis is closely linked to another gene for a steroidogenic enzyme.

Aldosterone deficiency II (CMO II deficiency) is not the result of a mutation of an MspI restriction site within the CYP11B gene

We report our investigations of a German family with aldosterone deficiency (CMO II deficiency). Restriction fragment length polymorphism analysis using a P450c11 probe demonstrates that a MspI restriction site mutation within the CYP11B gene cannot be the underlying cause for this defect, as has been suggested previously.

A mutation in CYP11B1 (Arg-448----His) associated with steroid 11 beta-hydroxylase deficiency in Jews of Moroccan origin

Steroid 11 beta-hydroxylase (P450c11) deficiency (failure to convert 11-deoxycortisol to cortisol) causes less than 10% of cases of congenital adrenal hyperplasia in most populations, but it is relatively frequent in Jews of Moroccan origin. P450c11 is encoded by the CYP11B1 gene which is located on chromosome 8q22 along with a homologous gene of unknown function, CYP11B2. To identify mutations in CYP11B1 associated with 11 beta-hydroxylase deficiency in Moroccan Jews, oligonucleotides were used that selectively amplified portions of CYP11B1 in polymerase chain reactions without amplifying CYP11B2. Sequence analysis of amplified fragments from one patient revealed a single base substitution in exon 8, codon 448 from CGC (arginine) to CAC (histidine). This residue is within the "heme binding" peptide that contains a cysteine that is a ligand to the heme group. The equivalent of Arg-448 is found in every known eukaryotic P450, and therefore it seems likely that a mutation of this residue would adversely affect enzymatic activity. 11 of 12 affected alleles from six Moroccan Jewish families carried the mutation in codon 448. This mutation is not normally present in CYP11B2 and thus appears to have arisen in CYP11B1 as a true point mutation rather than a gene conversion.

A novel human multi-locus DNA family detected by pJU78 (DF31)

pJU78 is a 2.9-kb cloned human DNA segment derived from Xq24-q26. When used as a hybridization probe, it detects some 25 related sequences dispersed over the genome, including several autosomes and the X and Y chromosomes. Several pJU78-related sequences were chromosomally allocated and five different restriction fragment length polymorphisms detected and partially characterized in population and family studies. This sequence family was not found in non-primate species. The sequence appears to lack CpG-island character and is not detectably expressed in a variety of human tissues.