Adolesc Pediatr Gynecol (1994) 7: 167-170
Adolescent and Pediatric Gynecology © 1994 Springer-Verlag New York Inc.
World Literature Reviewed by: S.F. Siegel, M.D., University of Pittsburgh, Children's Hospital of Pittsburgh, Pittsburgh, PA. Distinction Between Transient Hyperglycemia and Early Insulin-dependent Diabetes Mellitus in Childhood: A Prospective Study of Incidence and Prognostic Factors. Hershowitz-Dumont R, Wolfsdorf JI, Jackson RA, Eisenbarth GS. J Pediatr 1993; 123: 347. In children, the relationship of transient hyperglycemia to insulin-dependent diabetes mellitus (IDDM) is unclear. In ill children, transient hyperglycemia is often attributed to stress. To determine if there are predictive factors to distinguish which children, if any, will develop IDDM, these authors prospectively followed 63 children with transient hyperglycemia (plasma glucose > 150 mg/dl). The children, recruited from the emergency department of the Children's Hospital In Boston and pediatricians in private practice, were divided into two groups. One group (n = 31) had been referred for the evaluation of transient hyperglycemia in the absence of a serious intercurrent illness. The other group (n = 32) was noted to have transient hyperglycemia while undergoing evaluation for a serious intercurrent illness. Total glycosylated hemoglobin (HgbA 1C), cytoplasmic islet cell antibodies (ICA; protein-A monoclonal antibody assay system with fresh frozen sections of human pancreas), and insulin autoantibodies (CIAA; competitive binding assay) were measured. The results of intravenous glucose tolerance tests were used to determine first-phase insulin release and stimulated insulin release. At the time of clinical presentation of IDDM, 80% of children have detectable CIAA, ICA, or both. Transient hyperglycemia was identified in 293 (0.46%) of 63,760 children seen at Children's Hospital of Boston and in 4 (0.13%) of 3,000 children followed in a private practice setting. Many of these children were excluded from this study because of the severity of their illnesses . Of the seven children who developed IDDM, six had transient hyperglycemia in the absence of an intercurrent illness. Of these seven, all five children positive for ICA and all six children positive for CIAA developed IDDM. Two children who developed IDDM were negative
for ICA; one was negative for CIAA. The overall accuracy of prediction for subnormal stimulated insulin release was 98%. Clinical Correlation. This prospective study suggests that the risk of developing IDDM is higher when transient hyperglycemia occurs in the absence of an intercurrent illness. Immunologic and endocrinologic markers were helpful predictors of the risk for IDDM in this subgroup. However, because immunologic markers are not well standardized between laboratories , comparable findings may not be achievable in every medical center. Oral glucose tolerance tests are not helpful in determining the propensity for IDDM. In contrast, the risk of developing IDDM appears to be low in the context of transient stress hyperglycemia. It should be noted that six of the seven children who developed IDDM were less than 6 years of age. In view of the recognized association of particular human leukocyte antigen (HLA) haplotypes (nonASp57 in the 13 chain of DQ and Arg52 in the a chain of DQ) with IDDM, characterization of HLA haplotypes would have enhanced this report (Trucco M: To be or not to be ASp57, that is the question. Diabetes Care 1992; 15:705). Detection of a Novel Arginine Vasopressin Defect by Dideoxy Fingerprinting. Krishnamani MRS, Phillips JA, III, Copeland KC. J Clin Endocrinol Metab 1993; 77:596. Familial Neurohypophyseal Diabetes Insipidus Associated with a Signal Peptide Mutation. McLeod JF, Kovacs L, GaskUl MB, Rittig S, Bradley GS, Robertson GL. J Clin Endocrinol Metab 1993; 599A. Glu-47, Which Forms a Salt Bridge Between Neurophysin-II and Arginine Vasopressin, is Deleted in Patients with Familial Central Diabetes Insipidus. Yuasa H, Ito M, Nagasaki H, Oiso Y, Miyamoto S, Sasaki N, Saito H. J Clin Endocrinol Metab 1993; 77:600. Krishnamani et al. Autosomal dominant diabetes insipidus is characterized by polyuria and polydipsia with variable age of onset. Treatment with exogenous arginine vaso-
pressin (A VP) or its analogs decreases the polyuria. A VP and its neurophysin (NPII) are encoded by a single gene located on chromosome 20. Following synthesis as a single protein, A VP and NPII are cleaved and reassembled prior to secretion from the posterior pituitary. DNA was extracted from peripheral blood leukocytes from numerous members of a large kindred affected with autosomal dominant diabetes insipidus by Krishnamani et al. Affected individuals were heterozygous for a single nucleotide substitution which changed codon 19, the last codon of the AVP signal peptide, from alanine to threonine. The highly conserved terminal codon of the signal peptide appears to be important for correct posttranslational cleavage. The authors suggested that this mutation interferes with posttranslational processing such that AVP-NPII precursors accumulate and damage the cells producing them. Dideoxy cycle sequencing using a single dideoxynucleotide enabled rapid screening of other family members for this mutation. One of two infants evaluated carries the Ala19~Thr mutation.
McLeod et al. The same family studied by Krishnamani et al. was independently evaluated by McLeod et al. Fluid intake, urine output, plasma and urine osmolality, electrolytes, AVP levels, and molecular genetic analysis were performed in 35 members of three generations. By history, 12 individuals had polyuria, polydipsia, and enuresis/nocturia. These 12 excreted large volumes of dilute urine and had subnormal A VP responses to osmotic stimulation. DNA sequencing of one affected individual revealed a point mutation changing codon 19 from alanine to threonine. This point mutation eliminates a site for a restriction enzyme, BstUI, and creates a site for another restriction enzyme, Pml!. Restriction fragment length polymorphism analysis of family members showed that all affected individuals were heterozygous for this point mutation whereas none of the unaffected individuals carried this mutation. Linkage analysis for the association of the phenotype with this specific mutation showed that the maximum lod score was 5.7 at e = o. Additional findings from the clinical assessment include variable age of onset. Some patients had progressive A VP deficiency. Mutation of threonine to alanine alters the sequence of the signal peptide portion of the A VP protein. The authors speculate that the incompletely processed vasopressinneurophysin peptide accumulates within the neuro-
secretory cells that synthesize it, leading to cell damage and diabetes insipidus. Yuasa et al. The AVP gene from seven family members with symptoms of diabetes insipidus was investigated with molecular techniques by Yuasa et al. Polyacrylamide gel electrophoresis revealed the presence of heteroduplexes in the affected individuals. Direct nucleotide sequencing showed the deletion of glutamic acid at codon 47. All affected individuals were heterozygous for this mutation. Restriction fragment length polymorphism analysis confirmed that only the affected individuals carried this mutation. From a recent study of the crystal structure of bovine neurophysin, Glu47 appears to form a salt bridge between neurophysin and A VP. The authors speculate that the affinity of neurophysin for A VP is altered in these individuals. Clinical Correlation. These studies of the molecular pathophysiology of autosomal dominant central diabetes insipidus enhance our understanding of the physiology of vasopressin secretion. The A VP gene located on chromosome 20 encodes preproA VP. A signal peptide at the amino terminus of the protein directs the nascent peptide to the endoplasmic reticulum where the signal peptide is cleaved generating pro-A VP. Pro-AVP is packaged into vesicles and cleaved into A VP, neurophysin, and glycoprotein. Subsequently, the vesicles are transported along axons from the supraoptic and paraventricular nuclei in the hypothalamus to the posterior pituitary. The Ala19~Thr mutation is speculated to alter cleavage of the signal peptide within the endoplasmic reticulum. The accompanying editorial (Miller WL. Editorial: Molecular genetics of familial central diabetes insipidus. J Clin Endocrinol Metab 1993; 77:592) summarized the results of an in vitro transcription analysis which showed that the mutant mRNA encoded a partially cleaved preproAVP. The deletion of Glu47 affected the association of vasopressin and neurophysin. These papers illustrate different productive strategies for investigating the molecular basis of an inherited disorder. Autosomal recessive disorders such as congenital adrenal hyperplasia are due to loss of function mutations. Familial diabetes insipidus with AVP deficiency is an autosomal dominant disorder; this implies a change in function mutation rather than a deficiency. Autopsy findings in older, affected individuals have revealed degeneration rather than hypoplasia of the magnocellular neurons. The finding
of heterozygous mutations which are postulated to affect intracellular processing of A VP is consistent with the autopsy data. Additional studies will be necessary to determine if there is accumulation of AVP precursors which injure the magnocellular cells or increased degradation of A VP. True Hermaphroditism in a 46,XY Individual, Caused by a Postzygotic Somatic Point Mutation in the Male Gonadal Sex-Determining Locus (SRY): Molecular Genetics and Histological Findings in a Sporadic Case. Braun A, Kammerer S, Cleve H, Lohrs U, Schwarz H-P, Kuhnle U. Am J Hum Genet 1993; 52:578. The SRY gene located near the pseudoautosomal region of the Y chromosome directs testicular differentiation. The protein product encoded by this gene has a conserved amino acid sequence and appears to function as a transcription factor. Molecular genetic analysis has revealed SRY-negative 46,XY females. Point mutations or microdeletions of the SRY gene have also been detected in 46,XY females. An XX mouse transgenic for only the SRY gene had a male phenotype, suggesting that the presence of the SRY gene is sufficient for male sexual differentiation. True hermaphroditism describes abnormal sexual differentiation in which both identifiable ovarian and testicular tissues are present in the gonads. The most frequent karyotype associated with true hermaphroditism is 46,XX. The role of the SRY gene in the molecular pathogenesis of true hermaphroditism was investigated in a 46,XY patient with ambiguous genitalia (enlarged clitoris, urethral meatus at the base of the clitoris, palpable gonads in the labioscrotal folds, and hypoplastic vaginal pouch without a uterus). Histological examination of one gonad revealed large cells resembling oocytes adjacent to Sertoli cells and spermatogonia. Immature seminiferous tubules were present. Leydig cells and complete primordial follicles with follicle epithelium were not identified. DNA analysis focused on three chromosomal loci: the para-autosomal boundary region, the SRY locus, and the ZFY locus. The SRY and ZFY loci are specific to the Y chromosome. The polymerase chain reaction amplification product for the paraautosomal boundary region had dissimilar sizes for the X (221-bp) and Y (531-bp) chromosomes. DNA extracted from peripheral blood leukocytes of the proband and her father showed peR products of the expected size for all three Y chromosomal loci. DNA obtained from the mother's peripheral blood leukocytes revealed the presence of the 221-bp X
chromosome-specific peR product from the paraautosomal boundary and the absence of Y chromosomal sequences. The conserved region of the SRY gene was amplified from DNA extracted from the paraffin-fixed gonadal specimen. Direct sequencing of the gonadal SRY peR product revealed two mutations. One was a silent mutation in codon 22 and the other resulted in Leu44~ His substitution. Clinical Correlation. This patient with 46,XY true hermaphroditism had an unusual ovotestis with a diffuse distribution of ovarian and testicular elements rather than the more typical polarization. Molecular analysis revealed normal Y chromosomal sequences in the DNA extracted from peripheral tissues in the proband and her father. However, DNA extracted from the ovotestis had two mutations: one was a silent change, the other changed a hydrophobic amino acid into a polar amino acid which presumably altered the function of the protein product of the SRY gene. Additional studies can confirm that the Leu44~ His mutation is truly deleterious. Hence, this patient exhibits somatic cell (gonadal) mosaicism presumably due to a postzygotic mutational event. A Regulatory Cascade Hypothesis for Mammalian Sex Determination: SRY Represses a Negative Regulator of Male Development. McElreavey K, Vilain E, Abbas N, Hershowitz I, FeUous M. Proc Natl Acad Sci 1993; 90:3368. Alterations in the SRY gene are associated with sex reversal. Mutations in the SRY gene have been described in 46,XY females, and translocations of the SRY gene have been identified in 46,XX males. However, 46,XX individuals expressing a male phenotype and lacking the SRY gene have been reported. The authors reassess and classify 107 46,XX individuals with male phenotypes: 35 with normal male phenotypes; 38 with ambiguous genitalia; and 34 true hermaphrodites. For DNA analysis, Southern blot with probes for both the short and long arms of the Y chromosome and polymerase chain reaction amplification of the SRY gene were performed. Approximately 90% of those with a normal male phenotype carried the SRY gene. Approximately 95% of those with genital ambiguities and 88% of the true hermaphrodites lacked the SRY gene. To explain this apparent discrepancy, the presence of virilization and the absence of the SRY gene, these authors postulate the existence of another autosomal gene, Z, which functions to negatively impact on male sexual differentiation. The authors speculate that, because the gene
product of the SRY gene appears to be a transcription factor, one of its functions may be to inhibit the activity of Z. In normal 46,XX individuals, in the absence of SRY, Z prevents the expression of malespecific genes. In normal 46,XY individuals, the protein product of the SRY gene prevents the expression of Z so that male sexual differentiation occurs. The authors speculate that 46,XX males lacking the SRY gene are homozygous for mutations in Z. To explain 46,XY sex-reversed individuals with normal SRY gene sequences, they predict an "SRY insensitivity" mutation in which Z activity is unaffected by the protein product of the SRY gene. Clinical Correlation. The SRY gene was present in 91% of sex-reversed 46,XX individuals with normal male phenotype. In contrast, combining the other two groups, only 9% were positive for the SRY gene. This interesting paper proposes a sexual differentiation cascade which satisfies the current experience regarding abnormal sexual differentiation. The authors suggest that a second gene is involved as a repressor of male sexual differentiation. However, this second gene has not been cloned or mapped to a particular chromosome. In most instances, only DNA extracted from peripheral blood leukocytes was apparently studied. Hence, gonadal mosaicism cannot be completely excluded as an explanation for the incomplete sex reversal. Life with Turner's Syndrome-a Psychosocial Report from 22 Middle-Aged Women. Sylven L, Magnusson C, Hagenfeldt K, von Schoultz B. Acta Endocrinol1993; 129:188. To expand on their previous study which focused on the medical aspects of Turner syndrome (Sylven L, Hagenfeldt K, Brondum-Nielsen L, von Schoultz B: Middle-aged women with Turner's syndrome. Medical status, hormonal treatment and social life. Acta Endocrinol 1991; 125:359), the authors conducted semistructured interviews with 22 women with Turner syndrome. The women ranged in age from 39 to 63 years with a mean of 44.5 years. Their mean age at the time of diagnostic studies, performed at the Karolinska Hospital in Stockholm,
Sweden, was 17.5 years. Ten women had 45,X karyotypes and 22 were mosaics. Topics addressed in the interviews were family background, education, occupation, self-esteem, relationships, feminine identity, sexuality, and their feelings regarding Turner syndrome. Work was described as important for selfesteem. One woman had been denied admission to nursing school because of her height. All were employed outside of their homes. Occupations ranged from day care worker to accountant. Poor selfesteem was common; 86% felt their self-esteem needed to be improved. Although these women tended to be isolated during adolescence because of their delayed puberty, all had acquired friends in subsequent years. Although all the women felt feminine, many felt that something was missing. Fifteen women were married. Although most of the women had experienced orgasm, many had painful intercourse probably related to estrogen deficiency. Five women had experienced spontaneous menarche. One woman with a 45,Xl46,XX karyotype had four spontaneous abortions and two healthy children. All except one desired to have children. Only 11 women were on hormone replacement therapy. Infertility was a significant source of despondency. Additional concerns included negative body image and insufficient edification regarding Turner syndrome. Clinical Correlation. Although these women were satisfied with their lives, their adolescence had been arduous due to the late diagnosis, delayed puberty, and inadequate information regarding Turner syndrome. Infertility rather than short stature was the major burden for them. In vitro fertilization techniques expand the reproductive options for these women. The authors reinforce the need for appropriate long-term hormone replacement therapy. Induction of puberty at the same time their peers are undergoing spontaneous puberty is helpful for positive self-esteem. Further, hormone replacement therapy has beneficial effects on bone mineralization. The results of these two studies from Sweden provide useful guidance for treatment of Turner syndrome from the perspective of the affected individual.