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Biomedical subjects

A M DiGeorge

Publications and source records attributed to A M DiGeorge.

At least 19 recordsLinked to original sources
PubMed2000

46,XY monozygotic twins with discordant sex phenotype.

OBJECTIVE: To analyze male and female sex differentiation in monozygotic twins. DESIGN: Retrospective study. SETTING: Multiple academic centers. PATIENT(S): A pair of monozygotic twins. INTERVENTION(S): Skin and blood samples were obtained for DNA analysis and karyotyping. MAIN OUTCOME MEASURE(S): Mutation within the SRY gene was analyzed by the polymerase chain reaction-single-stranded conformation polymorphism test. Monozygosity was ascertained by short tandem repeat analysis. Karyotypes were studied in blood and skin fibroblasts. RESULT(S): SRY was present in both twins, but no mutations were detected in the SRY conserved motif. Monozygosity was confirmed by the use of short tandem repeat analysis in four loci: c-fms, thyroid peroxidase, von Willebrand factor, and tyrosine hydroxylase. The karyotype was 46,XY uniformly in both twins. CONCLUSION(S): Monozygotic twins can develop discordant male and female phenotypes despite the presence of a common karyotype and despite the presence of intact testis-determining genes. In the present case, this could be due to mutation or to mosaicism involving occult 45,X cell lines in the dysgenetic gonads.

DNA-Binding Proteins↗
PubMed1995

Human T-lymphotropic virus type 1 peptides in chimeric and multivalent constructs with promiscuous T-cell epitopes enhance immunogenicity and overcome genetic restriction.

Conventional strategies of viral peptide immunizations often elicit low-affinity antibody responses and have limited ability to elicit immune responses in outbred animals of diverse major histocompatibility (MHC) haplotypes. This genetically restricted T-cell-stimulatory activity of peptides is a serious obstacle to vaccine design. However, the use of promiscuous T-cell epitopes may circumvent this problem. Promiscuous T-cell epitopes from tetanus toxin (amino acids [aa] 580 to 599) and the measles virus F protein (aa 288 to 302) that bind to several isotypic and allotypic forms of human MHC class II molecules have been identified and have been used in highly immunogenic constructs to overcome haplotype-restricted immune responses. Chimeric and beta-template peptide constructs incorporating known human T-lymphotropic virus type 1 (HTLV-1) B- and T-cell epitopes from the surface envelope protein gp46 (SP2 [aa 86 to 107] and SP4a [aa 190 to 209]) and promiscuous T-cell peptides were synthesized, and their immunogenicities were evaluated in both rabbits and mouse strains of divergent haplotypes (C3H/HeJ [H-2k], C57BL/6 [H-2b], and BALB/c [H-2d]). In addition, peptide preparations were structurally characterized by analytical high-performance liquid chromatography, mass spectrometry, and circular dichroism. In contrast to their linear forms, the chimeric constructs of both the SP2 and SP4a epitopes displayed alpha-helical secondary structures. Immunogenicity of the peptide constructs was evaluated by direct and competitive enzyme-linked immunosorbant assay (ELISA), as well as by radioimmunoprecipitation, syncytium inhibition, and antigen-induced lymphocyte proliferation assays. Immunization with the SP4a peptide without conjugation to a carrier protein produced antibodies specific for SP4a in two mouse strains (C3H/HeJ and C57BL/6). However, BALB/c mice failed to respond to the peptide, indicating that the T-cell epitope of the SP4a sequence is MHC restricted. In contrast, the chimeric constructs MVF-SP2 and SP4a-measles virus F protein were highly immunogenic, producing elevated ELISA titers after only two immunizations. Elicited antibodies recognized native forms of gp46 in ELISAs and radioimmunoprecipitation assays, as well as inhibited HTLV-1-mediated syncytium formation. In addition, chimeric constructs were effective at induction of lymphocyte proliferation to the T-cell epitope, SP4a, in each strain of immunized mice. Our data demonstrate that the antibody response to retroviral peptides is enhanced by promiscuous peptide constructs, in part because of the ability of such constructs to promote appropriate secondary structural forms of viral epitopes. In addition, these constructs promote virus-specific helper T-cell responses, thereby overcoming genetically restricted immune responses to the synthetic peptides.

Amino Acid Sequence↗
PubMed1995

A novel mutation of the adrenocorticotropin receptor (ACTH-R) gene in a family with the syndrome of isolated glucocorticoid deficiency, but no ACTH-R abnormalities in two families with the triple A syndrome.

Isolated glucocorticoid deficiency (IGD) is an autosomal recessive disorder characterized by primary adrenocortical insufficiency, usually without mineralocorticoid deficiency. Occasionally, the disorder is associated with alacrima and achalasia of the esophagus (triple A syndrome), suggesting potential heterogeneity in its etiology. Mutations in the ACTH receptor gene have been reported in several families with IGD. We have amplified and directly sequenced the entire intronless ACTH receptor gene in 1 other family with IGD and 2 families with triple A syndrome. The proband with IGD was a homozygote for an A-->G substitution, changing tyrosine 254 to cysteine in the third extracellular loop of the receptor protein, probably interfering with ligand binding. Both of her parents were heterozygotes for this mutation, which was not detected in 100 normal alleles. No mutations were identified in the entire coding area of the ACTH receptor in the 2 families with triple A syndrome, supporting the idea of a developmental or postreceptor defect in this syndrome.

Adenine↗
PubMed1995

Glycosylation-dependent peptide antigenic determinants of env gp46 HTLV-1.

Human T-lymphotropic virus type 1 (HTLV-I) is a retrovirus associated with adult T-cell leukemia/lymphoma, and the virus infection constitutes a growing public health problem. In a continuing effort to engineer conformationally dependent HTLV-I epitopes that elicit a protective immune response, we have examined the role and functional importance of carbohydrate moieties in specific immune recognition and antibody responses. There have been several reports of the importance of N-linked virus glycosylation in the formation of neutralizing antibodies. Residues 230-257 is predicted to encode two beta-turn/loop regions at 240-244 (LYGPN), 248-257 (VPSSSSTPL) and a glycosylation site at N-244 (NVS). We have successfully engineered and synthesized the 233-253 sequence of gp46 of HTLV-1 with and without GlcNAC at Asn244. Circular dichroism spectroscopy and proton NMR showed the presence of beta-turn conformation in both peptide constructs. Chimeras of the glycosylated and non-glycosylated epitope with promiscuous T-cell epitope were synthesized and shown to elicit high titered antibodies in rabbits specific for the immunogen (SC1MVF and SC2MVF) and the B cell epitope 233-253. Additionally, antibodies to the glycosylated form of the peptide recognized the HTLV-I envelope precursor in radioimmunoassay precipitation assay and react with HTLV-I whole virus preparations in ELISA.

Adult↗
PubMed1995

Immunogenicity and conformational properties of an N-linked glycosylated peptide epitope of human T-lymphotropic virus type 1 (HTLV-I).

The identification and characterization of epitopes of human T-lymphotropic virus type 1 (HTLV-I), which elicit an effective humoral or cell-mediated immune response, remains a central obstacle to the development of a peptide-based vaccine against the virus infection. The objective of the studies presented here was to examine the influence of N-linked glycosylation on peptide structure and immunogenicity. We engineered the 233-253 sequence of gp46 of HTLV-I to contain an N-acetylglucosamine (GlcNAc) residue at Asn244. Secondary structure prediction using computer algorithms indicated that this peptide may contain a beta-turn at residues 242-246. Recent work with model glycopeptides suggests that beta-turn conformation in peptides may be induced, and probably is stabilized, by the presence of even a single sugar residue. In the present study, the structures of the 233-253 peptide, SC1, and the 233-253(Asn244-GlcNAc) glycopeptide, SC2, were determined. Similar conformation was exhibited by both the glycosylated and nonglycosylated peptide displaying a beta-turn at residues 243-246 and extended-chain structure at the peptide/glycopeptide termini. Both peptides were engineered into chimeric constructs with a promiscuous T-cell epitope from measles virus and were used as immunogens in rabbits. Both chimeric peptides were highly immunogenic in rabbits, producing high-titered antibodies as early as primary + three weeks. The antibodies generated against either construct were able to bind to whole virus (ELISA) and to gp46 (radioimmunoprecipitation assay). Additionally, human sera of individuals known to be positive for HTLV-I recognized both the glycosylated and nonglycosylated constructs. It appears that the 233-253 peptide is able to adopt a conformation that mimics the structure in native gp46, and addition of a GlcNAc residue at Asn244 does not affect the conformational preference or stability of this construct; nor does glycosylation alter immunogenicity but instead appears to enhance immune recognition.

Amino Acid Sequence↗
PubMed1994

The encephalomyocarditis virus 3C protease is a substrate for the ubiquitin-mediated proteolytic system.

The encephalomyocarditis virus 3C protease has been shown to be rapidly degraded in infected cells and in vitro in rabbit reticulocyte lysate. The in vitro degradation, at least, is accomplished by a virus-independent, ATP-dependent proteolytic system. Here we identify this proteolytic system as the ubiquitin-mediated system. Incubation of the 3C protease in rabbit reticulocyte or cultured mouse cell lysate preparations, alone or in the presence of added ubiquitin or methylated ubiquitin, resulted in the generation of new higher molecular weight species. These new products were shown to be 3C protease-ubiquitin conjugates by their ability to bind antibodies against both the 3C protease and ubiquitin. Supplemental ubiquitin also stimulated the degradation of the 3C protease in these preparations. Large 3C protease-polyubiquitin conjugates were observed to accumulate in reticulocyte lysate in the presence of adenosine 5'-O-(3-thiotriphosphate), an inhibitor of the 26 S multicatalytic protease. This, combined with the fact that the proteolytic activity could be removed from the lysate by sedimentation, implicates the multicatalytic protease in the degradation of the 3C protease-ubiquitin conjugates. It was also found that the slow rate of degradation of a model polyprotein, which resembles the stable viral 3CD diprotein produced in vivo, is likely due to the fact that the polyprotein is a poor substrate for the ubiquitin-conjugating system.

3C Viral Proteases↗
PubMed1994

Substitution of arginine-839 by cysteine or histidine in the androgen receptor causes different receptor phenotypes in cultured cells and coordinate degrees of clinical androgen resistance.

We aim to correlate point mutations in the androgen receptor gene with receptor phenotypes and with clinical phenotypes of androgen resistance. In two families, the external genitalia were predominantly female at birth, and sex-of-rearing has been female. Their androgen receptor mutation changed arginine-839 to histidine. In a third family, the external genitalia were predominantly male at birth, and sex-of-rearing has been male: their codon 839 has mutated to cysteine. In genital skin fibroblasts, both mutant receptors have a normal androgen-binding capacity, but they differ in selected indices of decreased affinity for 5 alpha-dihydrotestosterone or two synthetic androgens. In transiently cotransfected androgen-treated COS-1 cells, both mutant receptors transactivate a reporter gene subnormally. The His-839 mutant is less active than its partner, primarily because its androgen-binding activity is more unstable during prolonged exposure to androgen. Adoption of a nonbinding state explains a part of this instability. In four other steroid receptors, another dibasic amino acid, lysine, occupies the position of arginine-839 in the androgen receptor. Androgen receptors with histidine or cysteine at position 839 are distinctively dysfunctional and appear to cause different clinical degrees of androgen resistance.

Adult↗
PubMed1994

Use of tissue-specific promoters in the regulation of aromatase cytochrome P450 gene expression in human testicular and ovarian sex cord tumors, as well as in normal fetal and adult gonads.

We have previously demonstrated that the tissue-specific regulation of human aromatase cytochrome P450 (P450arom) gene expression is, in part, the consequence of the use of tissue-specific promoters. Promoter I.1 (PI.1) and PI.2-specific transcripts are expressed in the placenta, whereas promoter II (PII) appears to be the only active promoter in the corpus luteum. Testicular and ovarian sex cord tumors with annular tubules (SCTATs) associated with gynecomastia in prepubertal boys and isosexual precocity in girls with Peutz-Jeghers syndrome (P-JS) have been previously reported. In the present study, we investigated the regulatory elements directing P450arom gene transcription in samples of SCTAT from three prepubertal boys and a girl with P-JS and an ovarian granulosa cell tumor from an adult woman, as well as in healthy fetal and adult testicular and ovarian tissues. Placental tissue was used as a control. Using polymerase chain reaction linked to reverse transcription and northern blotting, we determined the tissue-specific use of various P450arom promoters by analyzing specific 5'-termini from messenger RNA templates. Results indicate a universal gonadal promoter (PII) directs P450arom gene expression in healthy fetal and adult ovaries and testes, as well as in SCTAT of the P-JS and an adult ovarian granulosa cell tumor. These results are interpreted to mean that use of PII in human ovary and testis is preserved from the fetal period into adult life as well as in transformed neoplastic Sertoli and granulosa cells. On the other hand, transcripts from placenta are specific for PI.1 (and to a much lesser extent, PI.2). In SCTAT, immunoreactive P450arom is detected only in the cytoplasm of neoplastic cells, whereas the normal-appearing sex cords do not contain any immunoreactive P450arom. These results further suggest that the markedly increased aromatase expression of these transformed neoplastic cells is not a consequence of using different tissue-specific promoters. Rather it appears to involve activation (or failure of inhibition) of the upstream regulatory elements of the same promoter, which is normally functional in all gonadal tissues, namely the proximal PII.

Adolescent↗
PubMed1993

Engineered topographic determinants with alpha beta, beta alpha beta, and beta alpha beta alpha topologies show high affinity binding to native protein antigen (lactate dehydrogenase-C4).

The use of peptides has attracted much interest in the development of synthetic vaccines. Although our current understanding of peptide antigens as immunogens has been greatly advanced recently, there still remain many obstacles. The B cell response elicited by a peptide antigen is governed by a number of poorly understood events such as epitope structure, T cell dependency and major histocompatibility complex restriction, adjuvancy, route of immunization, and immunogen stability. In this paper, we extend our previous studies on the problem of the topographical nature of antigenic sites on native protein antigens, in terms of how much molecular mimicry must be maintained in an antigenic determinant for the induction of high affinity antibodies specific for native protein. We show here that an antigenic epitope from the model contraceptive vaccine candidate lactate dehydrogenase (LDH-C4) can be rationally engineered into a highly structured conformation that mimics the corresponding site in the native three-dimensional protein. Our strategy is based on the selection of an antigenic segment which exhibits certain secondary structural properties and by design principles is fixed in three dimensions by appropriate grafting onto a supersecondary structural motif such as alpha beta, beta alpha beta, or beta alpha beta alpha. The biophysical data are consistent with the proposed secondary structures, and antibodies raised to the various construct show high affinity for the native protein. These studies lend further credence to the conformational nature of peptide epitopes and provide a basis for the rational design of peptide vaccines.

Amino Acid Sequence↗
PubMed1993

Use of tissue-specific promoters in the regulation of aromatase cytochrome P450 gene expression in human testicular and ovarian sex cord tumors, as well as in normal fetal and adult gonads.

We have previously demonstrated that the tissue-specific regulation of human aromatase cytochrome P450 (P450arom) gene expression is, in part, the consequence of the use of tissue-specific promoters. Promoter I.1 (PI.1) and PI.2-specific transcripts are expressed in the placenta, whereas promoter II (PII) appears to be the only active promoter in the corpus luteum. Testicular and ovarian sex cord tumors with annular tubules (SCTATs) associated with gynecomastia in prepubertal boys and isosexual precocity in girls with Peutz-Jeghers syndrome (P-JS) have been previously reported. In the present study, we investigated the regulatory elements directing P450arom gene transcription in samples of SCTAT from three prepubertal boys and a girl with P-JS and an ovarian granulosa cell tumor from an adult woman, as well as in healthy fetal and adult testicular and ovarian tissues. Placental tissue was used as a control. Using polymerase chain reaction linked to reverse transcription and northern blotting, we determined the tissue-specific use of various P450arom promoters by analyzing specific 5'-termini from messenger RNA templates. Results indicate a universal gonadal promoter (PII) directs P450arom gene expression in healthy fetal and adult ovaries and testes, as well as in SCTAT of the P-JS and an adult ovarian granulosa cell tumor. These results are interpreted to mean that use of PII in human ovary and testis is preserved from the fetal period into adult life as well as in transformed neoplastic Sertoli and granulosa cells. On the other hand, transcripts from placenta are specific for PI.1 (and to a much lesser extent, PI.2). In SCTAT, immunoreactive P450arom is detected only in the cytoplasm of neoplastic cells, whereas the normal-appearing sex cords do not contain any immunoreactive P450arom. These results further suggest that the markedly increased aromatase expression of these transformed neoplastic cells is not a consequence of using different tissue-specific promoters. Rather it appears to involve activation (or failure of inhibition) of the upstream regulatory elements of the same promoter, which is normally functional in all gonadal tissues, namely the proximal PII.

Adolescent↗
PubMed1993

The molecular weights of twelve apolipoprotein(a) variants, determined using haptoglobin 2-2 polymer molecular weight standards.

Apolipoprotein(a) [apo(a)] variants were characterized in 398 sera by immunoblotting: (a) by molecular weight, using a haptoglobin 2-2 polymeric series as standards, and (b) by nomenclature, using serum pools containing previously characterized apo(a) variants as standards. The haptoglobin 2-2 standard curve (172-859 kDa) alleviates the necessity of obtaining molecular weights by extrapolation. Among the 398 sera, 40.2% had double apo(a) bands (54 phenotypes), 58.0% had a single apo(a) band and 1.8% were null (no bands observed). An inverse, though non-monotonic, relationship was observed between apolipoprotein(a) molecular weight and serum lipoprotein(a) [Lp(a)] concentration. Due to the large size of apo(a) and the relatively small increment between variants (15-16 kDa), molecular weight could not be used alone to characterize variants. Even with a CV of 3-4%, there was an overlap between variant molecular weight estimates. However, in combination with the identification of variants by comparison with standards, the haptoglobin 2-2 standard curve could be used to obtain mean molecular weight estimates for each variant. 12 distinct variants were identified among the sera, with apparent mean molecular weights of 314, 388, 410, 433, 454, 466, 503, 519, 528, 543, 553 and 572 kDa, respectively. These molecular weight estimates are consistent with the theoretical molecular weight range for apo(a) variants, calculated from sequence and carbohydrate analysis, of 238-643 kDa.

Apolipoproteins A↗
PubMed1991

Cerebral edema causing death in children with maple syrup urine disease.

Four children with the classic form of maple syrup urine disease (MSUD) died of cerebral edema during an intercurrent infection that caused severe dehydration and acidosis. The diagnosis of MSUD had been established during the neonatal period in all four patients, on day 1 of life in three of them. All were in satisfactory control before the intercurrent illness. Two patients underwent peritoneal dialysis. Signs of brain-stem compression occurred after treatment, when biochemical abnormalities were improving. Computed tomography of the head, which was done in two patients, revealed cerebral edema; one of these patients also had subarachnoid hemorrhage. Autopsy in one case revealed cerebral edema with herniation. Our experience documents that cerebral edema may occur in the older child with MSUD as well as in the neonate. The pathogenesis of cerebral edema in MSUD remains unclear. Early treatment of dehydration and acidosis may prevent the catastrophic consequences that we have observed.

Acute Disease↗
PubMed1981

Action of human growth hormone (hGH) on extrathyroidal conversion of thyroxine (T4) to triiodothyronine (T3) in children with hypopituitarism.

To study the action of human growth hormone (hGH) on peripheral metabolism of serum thyroxine (T4), an oral loading dose of levothyroxine (1.2 mg/m2) was administered to seven children with hypopituitarism before initiation of hGH therapy. Serum concentrations of triiodothyronine (T3), T4, reverse triiodothyronine (rT3), and thyroxine-binding globulin (TBG) capacity were measured sequentially for 6 days. The study was repeated after 4 wk of treatment with hGH. Serum concentrations of T4 were not affected by hGH therapy. In contrast, mean basal serum concentration of T3 increased significantly after treatment with hGH. Also, changes in serum concentrations of T3 and in the ratio of T3/T4 after an oral dose of levothyroxine were significantly augmented during hGH therapy. Serum concentrations of rT3 changed in the opposite direction of T3 during therapy. After treatment with hGH, the mean basal level of serum rT3 decreased, and increases in serum concentrations of rT3 after oral levothyroxine were significantly attenuated. No changes in mean serum concentrations of thyroid stimulating hormone (TSH) and TBG capacity were observed. These data suggest that administration of hGH to children with hypopituitarism enhances the extrathyroidal conversion of T4 to T3 and concomitantly decreases the serum concentration of rT3.

Adolescent↗
PubMed1977

Reassessment of the daily dose of oral thyroxine for replacement therapy in hypothyroid children.

The optimal daily requirement of sodium L-thyroxine for replacement therapy of hypothyroidism was evaluated in 11 hypothyroid children ranging from one to 14 years of age. The "optimal" dose of L-T4, defined as the minimal daily dose necessary to suppress the serum concentration of TSH to normal, was determined in each patient and individual growth rates were assessed for periods up to 12 months during the time this dose was being administered. The mean "optimal" dose of L-T4 was 3.78 +/- 0.6 mug/kg or 104.6 +/- 5.2 mug/m2. This dose was considerably lower than the doses of L-T4 generally recommended. All patients appeared clinically euthyroid, and their serum concentrations of T3 and T4 as well as their height velocities remained within the normal range while the "optimal" dose of L-T4 was being adminstered.

Administration, Oral↗