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Biomedical subjects

M I New

Publications and source records attributed to M I New.

At least 73 records · Page 4Linked to original sources
PubMed1994

Natural mutagenesis study of the human steroid 5 alpha-reductase 2 isozyme.

The enzyme steroid 5 alpha-reductase utilizes NADPH to reduce the double bonds of a variety of steroid substrates with generalized 3-oxo, delta 4,5 structures. One substrate for this membrane-bound enzyme is testosterone, whose reduction to dihydrotestosterone is required for the embryonic differentiation of the external male genitalia and prostate. There are two 5 alpha-reductase isozymes, designated types 1 and 2, which have different biochemical and pharmacological properties. Inherited deficiencies of 5 alpha-reductase type 2 result in a form of male pseudohermaphroditism in which the external genitalia fail to develop normally. Here, nine additional mutations in the 5 alpha-reductase 2 gene in subjects with 5 alpha-reductase deficiency are described. The biochemical consequences of these mutations, as well as 13 previously identified missense mutations, were characterized by recreating the mutations in an expressible cDNA and transfecting into mammalian cells. Twelve of the 22 mutations inactivated the enzyme. The remaining 10 mutations impaired enzyme function by affecting either substrate or cofactor binding. Almost all mutations decreased the half-life of the protein, and all but one of the impaired enzymes had an altered pH optimum. The mutations provide insight into functional domains in the protein as well as an unusual acidic pH optimum characteristic of the 5 alpha-reductase type 2 isozyme.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed1994

Mutations in steroid 21-hydroxylase (CYP21).

The inherited inability to synthesize cortisol is termed congenital adrenal hyperplasia. More than 90% of cases are caused by 21-hydroxylase deficiency. This syndrome is characterized by signs of androgen excess and often mineralocorticoid deficiency. Steroid 21-hydroxylase (P450c21) is a microsomal enzyme expressed in the adrenal gland that catalyzes conversion of 17-hydroxyprogesterone and progesterone to 11-deoxycortisol and deoxycorticosterone respectively. In man, this enzyme is encoded by the CYP21 (CYP21B) gene which is located in the HLA major histocompatibility complex along with a pseudogene, CYP21P (CYP21A). Mutations in CYP21 causing congenital adrenal hyperplasia are almost all generated by recombinations between CYP21 and CYP21P. These recombinations either delete CYP21 or transfer deleterious mutations from CYP21P to CYP21, a process termed apparent gene conversion. The degree of enzymatic compromise caused by each mutation is correlated with the clinical severity of the deficiency observed in patients carrying that mutation.

Adrenal Hyperplasia, Congenital↗
PubMed1994

Prenatal diagnosis of congenital adrenal hyperplasia due to 21-hydroxylase deficiency by allele-specific hybridization and Southern blot.

The feasibility and accuracy of gene-specific molecular genetic diagnosis for congenital adrenal hyperplasia due to 21-hydroxylase deficiency was studied in a group of 24 pregnancies at 25% risk of carrying an affected fetus. Chorionic villus sampling was performed at 9-10 weeks' gestation. Southern analysis and polymerase chain reaction, followed by allele-specific hybridization for a panel of nine known mutations, were performed for each family. Mutations were identified in 95% of chromosomes examined; the molecular diagnosis was accurate in 96% of infants as confirmed by postnatal examination. The most common mutation identified was an A-to-G transition at base 656 in the second intron, the result of an apparent gene conversion. In one family, there had been a de novo mutation in intron 2, which was detected in the proband, but not in the mother or in the fetus. We conclude that first trimester prenatal diagnosis of congenital adrenal hyperplasia due to 21-hydroxylase deficiency is feasible and accurate employing CYP21-specific probes.

Adrenal Hyperplasia, Congenital↗
PubMed1994

21-hydroxylase deficiency congenital adrenal hyperplasia.

Congenital adrenal hyperplasia (CAH) results from an enzymatic block at any stage in the synthesis of cortisol. All enzyme defects causing CAH are autosomal recessive traits. It is a relatively common disease, occurring in 1 in 5000 to 1 in 15,000 births in most populations. Since the isolation of the gene responsible for steroid 21-hydroxylase deficiency (involved in about 90% of the cases of CAH) in 1984, knowledge of the specific mutations that cause the different forms of CAH has grown rapidly. Defects in the encoding gene have been confirmed as the basis of endocrine disease in the case of all but one of the adrenal steroidogenic enzymes. Analysis of DNA obtained by chorionic villus sampling in early pregnancy permits prenatal diagnosis and treatment of 21-hydroxylase deficiency CAH. The correlation between the clinical expression of endocrine disease and the mutations of the primary structural gene is not absolute. Clinicians cannot accurately predict the course of the disease or make therapeutic decisions based on the genotype alone. We will review the various forms of clinical presentation of 21-hydroxylase CAH, its etiology, diagnosis, molecular genetics, and treatment.

Adrenal Hyperplasia, Congenital↗
PubMed1994

Molecular genetic prenatal diagnosis of congenital adrenal hyperplasia due to 21-hydroxylase deficiency by allele-specific hybridization.

The feasibility and accuracy of gene-specific molecular genetic diagnosis for congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency were studied in a group of 24 pregnancies at 25% risk of carrying an affected fetus. Chorionic villus sampling was performed in the majority of cases. Southern blot analysis was carried out to identify deletions or other gross rearrangements. In parallel, the polymerase chain reaction (PCR) was performed, followed by allele-specific oligonucleotide hybridization (ASO) for a panel of nine known mutations. Mutations were identified in 95% of the chromosomes examined. The molecular diagnosis was accurate in 23 of 24 infants. The most common mutation identified was an A-to-G transition in the second intron (52% of affected chromosomes), the result of an apparent gene conversion. One fetus carried homozygous deletion of CYP21, which accounted for 13% of all affected chromosomes. Other mutations identified included an 8-bp deletion in the third exon (22%); Ile172 to Asn, a nonconservative substitution, in the fourth exon (9%); and Gln318 to term, a nonsense mutation, in the eight exon (4%). No mutation was detected in CYP21 in 5% of obligate-affected chromosomes examined by these methods.

Adrenal Hyperplasia, Congenital↗
PubMed1994

Enzyme-linked immunosorbent assay (ELISA) method for screening of non-classical steroid 21-hydroxylase deficiency.

Morning salivary 17-hydroxyprogesterone (17-OHP) determination is a useful method to diagnose non-classical 21-hydroxylase deficiency (NC 21-OHD). In ethnic groups with high frequency of NC 21-OHD, mass screening is thought to be necessary. A pilot screening test for NC 21-OHD was performed by measuring morning salivary 17-OHP by enzyme-linked immunosorbent assay (ELISA). Two individuals were found NC 21-OHD from 230 subjects. Results of this ELISA were well correlated with those of established radioimmunoassay. ELISA can be performed in any laboratory because of non-radioactivity and the procedure is very easy by the use of a microplate. This ELISA is suitable for large scale population studies. We conclude that morning salivary 17-OHP determination by ELISA is a useful method for NC 21-OHD screening test.

17-alpha-Hydroxyprogesterone↗
PubMed1994

The prismatic case of apparent mineralocorticoid excess.

A personal memoir of the discovery of a new form of hypertension, apparent mineralocorticoid excess, came about through painstaking analysis of the symptoms of a Zuñi Indian girl. The study of this patient opened a new field of receptor biology, i.e. how glucocorticoids and mineralocorticoids interact with receptors. Therefore, the patient was a prismatic case.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1994

No evidence of mutations in the genes for type I and type II 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) in nonclassical 3 beta HSD deficiency.

Nonclassical 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4-isomerase deficiency (NC3 beta HSDD) has been diagnosed in hyperandrogenic women with an increasing frequency during the last 14 yr. Fifteen menarcheal women with androgen excess syndrome, diagnosed with NC3 beta HSDD previously were restudied, in 12 after discontinuation of glucocorticoid treatment, in 2 patients never treated with glucocorticoids, and in 1 both before and after glucocorticoid therapy. Each of the 15 patients underwent ACTH stimulation testing, in some cases on multiple occasions. Although some (very few) patients seem to have improved with time, others remained the same or got worse. Molecular DNA analysis was also performed in 6 of the patients, using the strategy successfully used to detect point mutations in the type II 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) gene, which are responsible for classical 3 beta HSD deficiency. This strategy consists of the direct sequencing of polymerase chain reaction-amplified DNA fragments corresponding to the complete coding sequence and all intron-exon junctions and to the 5'- and 3'-noncoding region of this gene. We were unable to demonstrate any mutation of the type II 3 beta HSD gene in these 6 patients. To gain additional information about potential mutations, direct sequencing of the type I 3 beta HSD gene was also performed using this same strategy, and no mutations were found. The present study strongly suggests that unlike the salt-losing and nonsalt-losing forms of classical 3 beta HSD deficiency, NC3 beta HSDD is not due to a mutant type II 3 beta HSD enzyme. However, the possibility remains of a mutation(s) in the unsequenced regions of the type II 3 beta HSD gene or elsewhere, such as in a gene for modulatory protein, playing a specific role in the expression of the type II 3 beta HSD gene. On the other hand, knowing the multiple hormonal controls to which 3 beta HSD activity is subject, it cannot be excluded that at least in some cases, NC3 beta HSDD may be an acquired defect, the result of endogenous or environmental factors.

3-Hydroxysteroid Dehydrogenases↗
PubMed1994

Prenatal diagnosis and management of congenital adrenal hyperplasia.

Congenital adrenal hyperplasia is one of a few inherited disorders that can be managed by administering medication to the fetus via oral maternal administration. Dexamethasone given in the first trimester ameliorates genital ambiguity in the affected female fetus. Mother and fetus should be monitored during and after pregnancy for treatment-related complications. Therapy can be coordinated with prenatal diagnostic testing.

Adrenal Hyperplasia, Congenital↗
PubMed1993

Nonclassical congenital adrenal hyperplasia and the polycystic ovarian syndrome.

PCOS has a hormonal pattern that includes an apparent dysfunction in ovarian steroidogenesis, although the sequence (or sequences) of endocrine changes, possibly with inherent paracrine abnormalities that can establish PCOS, are only postulated. Development of PCOS in the setting of androgen overproduction (or persistent disturbances of the hypothalamic-pituitary-adrenal axis even after normalization of androgen levels) points to adrenal enzyme defects, but the precise interaction of gonad and adrenal cortex via serum steroids remains open. Several interesting schemas for the development of PCOS have been proposed, but the subject remains controversial. Sonographic abnormalities of the ovaries may be similar in women with PCOS and women with adrenal enzyme defects, and differentiation of PCOS from nonclassical 21-hydroxylase deficiency on the basis of pituitary gonadotropin response to LHRH is also nonspecific. The 17-OHP response to ACTH testing is necessary to make the diagnosis (see nomogram). The preliminary data on the subgroup of women with PCOS and nonclassical 21-hydroxylase deficiency indicate that (1) the size of cystic changes of ovaries on sonography and (2) LH:FSH ratios may improve with dexamethasone treatment. Identification of an adrenal enzymatic disorder by ACTH testing is cost-effective in patients with symptoms of androgen excess, offers a good prognosis for improved fertility in couples, and as well is informative in family genetic studies.

3-Hydroxysteroid Dehydrogenases↗
PubMed1993

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.

Adrenal Hyperplasia, Congenital↗
PubMed1993

Investigation of the mechanism of hypertension in apparent mineralocorticoid excess.

Apparent mineralocorticoid excess (AME) is a rare form of low renin hypertension caused by deficiency of 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD), the enzyme responsible for conversion of cortisol to the bio-inactive metabolite, cortisone. This results in prolonged cortisol half-life, activation of type I (mineralocorticoid) receptors by cortisol, sodium and fluid retention, and consequent childhood-onset hypertension. The cortisol secretion rate is low, perhaps due to cortisol's binding to type II (glucocorticoid) receptors and suppressing corticotropin secretion. Patients with AME thus lack stigmata of Cushing's syndrome. To evaluate any potential contribution of the type II (glucocorticoid) receptor to the development of hypertension in AME patients, we administered RU486, a steroid analogue that acts as a pure type II receptor blocker. Selective glucocorticoid receptor blockade did not decrease blood pressure in our patient; instead, a significant increase in average blood pressure was observed (125.1 +/- 1.7 pre-RU486 v 144.7 +/- 1.2 during RU486 treatment, P = .0001). We conclude that the type II receptor does not contribute to the development of hypertension in patients with AME.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1993

Molecular cloning of multiple cDNAs encoding human enzymes structurally related to 3 alpha-hydroxysteroid dehydrogenase.

Rat liver 3 alpha-hydroxysteroid dehydrogenase cDNA was previously cloned by us. In this study, we used the rat cDNA as the probe to screen a human liver lambda gt11 cDNA library. A total of four different cDNAs were identified and sequenced. The sequence of one of the cDNAs is identical to that of the human chlordecone reductase cDNA except that our clone contains a much longer 5'-coding sequence than previously reported. The other three cDNAs display high degrees of sequence homology to those of both rat 3 alpha-hydroxysteroid dehydrogenase and human chlordecone reductase. Because 3 alpha-hydroxysteroid dehydrogenase and human chlordecone reductase belong to the aldo-keto reductase superfamily, we named these human clones HAKRa to HAKRd. Northern blot analysis showed that the liver expresses the highest levels of all four clones. Expression of all four clones was also detected in the brain, kidney, lung, and testis, whereas the placenta expressed only the messenger RNA for HAKRb. Genomic blot analysis using HAKRb as the probe detected multiple DNA fragments hybridized to the probe and a high degree of restriction fragment length polymorphism, suggesting the complexity of this supergene family.

3-Hydroxysteroid Dehydrogenases↗
PubMed1993

Defects in the HSD11 gene encoding 11 beta-hydroxysteroid dehydrogenase are not found in patients with apparent mineralocorticoid excess or 11-oxoreductase deficiency.

The syndrome of apparent mineralocorticoid excess (AME) is a form of low renin hypertension that is thought to be caused by congenital deficiency of 11 beta-hydroxysteroid dehydrogenase (11HSD) activity. This enzyme converts cortisol to cortisone and apparently prevents cortisol from acting as a ligand for the mineralocorticoid (type I) receptor. It also catalyzes the reverse oxoreductase (cortisone to cortisol) reaction. Four patients with AME and the parents of the first patient described (now decreased) were analyzed for mutations in the cloned HSD11 gene encoding an 11HSD enzyme. A patient with suspected cortisone reductase deficiency was also studied. No gross deletions or rearrangements in the HSD11 gene were apparent on hybridizations of blots of genomic DNA. Direct sequencing of polymerase chain reaction-amplified fragments corresponding to the coding sequences, intronexon junctions, and proximal untranslated regions of this gene revealed no mutations. AME may involve mutations in a gene for another enzyme with 11HSD activity or perhaps another cortisol-metabolizing enzyme.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1993

Congenital adrenal hyperplasia. Molecular insights learned from patients.

Congenital adrenal hyperplasia (CAH) results from enzymatic blocks in the synthesis of cortisol. All enzyme defects causing CAH are autosomal recessive traits. It is a relatively common disease, occurring in 1 in 5000 to 1 in 15,000 births in most populations. Since the isolation of the gene responsible for steroid 21-hydroxylase deficiency (involved in about 90% of the cases of CAH) in 1984, knowledge of the specific mutations that cause the different forms of CAH has grown rapidly. Mutations in the encoding gene have been confirmed as the basis of endocrine disease in the case of all of the adrenal steroidogenic enzymes required for synthesis of cortisol but one (cholesterol desmolase). The clinical expression of endocrine disease is not always correlated with the mutations of the primary structural gene. Clinicians cannot accurately predict the course of the disease or make therapeutic decisions based on the genotype alone. We will review the various forms of clinical presentation of CAH, their etiology, diagnosis, molecular genetics, and treatment.

3-Hydroxysteroid Dehydrogenases↗