Gestational Diabetes Associated with a Novel Mutation (378-379insTT) in the Glycerol Kinase Gene

Glycerol kinase deficiency (GKD) is an X-linked inborn error of metabolism at the interface of fat and carbohydrate metabolism. We report a male patient with GKD and a novel insertion of TT in exon 5 at position 378 of the GK cDNA (378–379insTT). This resulted in a premature stop codon and 0.8% normal GK activity. The mother is a carrier for this mutation and had gestational diabetes requiring insulin during this pregnancy but not in her previous pregnancy. Given the association between GKD and type 2 diabetes mellitus, it is interesting that the mother had gestational diabetes while carrying an affected fetus. Therefore, GKD is another disease where there may be a maternal–fetal interaction based on genotype. Further investigations may help elucidate the role of GKD in the carrier mother's gestational diabetes. In addition, these studies will provide better-informed counseling to families with GKD regarding the risk to carrier females.

Development of catecholamine and cortisol stress responses in zebrafish

Both adrenal catecholamines and steroids are known to be involved in the stress response, immune function, blood pressure and energy homeostasis. The response to stress is characterized by the activation of the hypothalamus–pituitary–adrenal (HPA) axis and the sympathetic-adrenomedullary system, though the correlation with activation and development is not well understood. We evaluated the stress response of both cortisol and catecholamines during development in zebrafish. Zebrafish at two different stages of development were stressed in one of two different ways and cortisol and catecholamine were measured. Cortisol was measured by enzyme immune assay and catecholamine was measured by ELISA. Our results show that stress responses are delayed until after the synthesis of both cortisol and catecholamines. These observations suggest that the development of HPA axis may be required for the acquisition of the stress response for cortisol and catecholamines.

Down syndrome: national conference on patient registries, research databases, and biobanks

A December 2010 meeting, "Down Syndrome: National Conference on Patient Registries, Research Databases, and Biobanks," was jointly sponsored by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) at the National Institutes of Health (NIH) in Bethesda, MD, and the Global Down Syndrome Foundation (GDSF)/Linda Crnic Institute for Down Syndrome based in Denver, CO. Approximately 70 attendees and organizers from various advocacy groups, federal agencies (Centers for Disease Control and Prevention, and various NIH Institutes, Centers, and Offices), members of industry, clinicians, and researchers from various academic institutions were greeted by Drs. Yvonne Maddox, Deputy Director of NICHD, and Edward McCabe, Executive Director of the Linda Crnic Institute for Down Syndrome. They charged the participants to focus on the separate issues of contact registries, research databases, and biobanks through both podium presentations and breakout session discussions. Among the breakout groups for each of the major sessions, participants were asked to generate responses to questions posed by the organizers concerning these three research resources as they related to Down syndrome and then to report back to the group at large with a summary of their discussions. This report represents a synthesis of the discussions and suggested approaches formulated by the group as a whole.

Pathway analysis software: annotation errors and solutions

Genetic databases contain a variety of annotation errors that often go unnoticed due to the large size of modern genetic data sets. Interpretation of these data sets requires bioinformatics tools that may contribute to this problem. While providing gene symbol annotations for identifiers (IDs) such as microarray probe set, RefSeq, GenBank, and Entrez Gene is seemingly trivial, the accuracy is fundamental to any subsequent conclusions. We examine gene symbol annotations and results from three commercial pathway analysis software (PAS) packages: Ingenuity Pathways Analysis, GeneGO, and Pathway Studio. We compare gene symbol annotations and canonical pathway results over time and among different input ID types. We find that PAS results can be affected by variation in gene symbol annotations across software releases and the input ID type analyzed. As a result, we offer suggestions for using commercial PAS and reporting microarray results to improve research quality. We propose a wiki type website to facilitate communication of bioinformatics software problems within the scientific community.

LXXLL motifs and AF-2 domain mediate SHP (NR0B2) homodimerization and DAX1 (NR0B1)-DAX1A heterodimerization

Small heterodimer partner (SHP; NR0B2) is an unusual orphan member of the nuclear receptor superfamily that functions as a corepressor of other nuclear receptors through heterodimeric interactions. Mutations in SHP are associated with mild obesity and insulin resistance. The protein domain structure of SHP is similar to Dosage-sensitive sex reversal adrenal hypoplasia congenita (AHC) critical region on the X chromosome, gene 1 (DAX1; NR0B1). Mutations in DAX1 cause AHC with associated hypogonadotropic hypogonadism. DAX1A is an alternatively spliced isoform of DAX1 that lacks the last 80 amino acids of the DAX1 C-terminal repressor domain and is replaced by a novel 10-amino acid motif. We have previously shown homodimerization of SHP and DAX1 individually, heterodimerization of DAX1 with SHP, and heterodimerization of DAX1 with DAX1A. In these studies, we investigated the domains and residues of SHP involved in SHP homodimerization and DAX1-SHP heterodimerization and also further characterized DAX1-DAX1 homodimerization and DAX1-DAX1A heterodimerization. We showed involvement of the SHP LXXLL motifs and AF-2 domain in SHP homodimerization and DAX1-SHP heterodimerization. We demonstrated redundancy of the LXXLL motifs in DAX1 homodimerization. While DAX1A subcellular localization is mostly cytoplasmic, DAX1-DAX1A heterodimers existed in the nucleus, suggesting differential functions for DAX1A in each compartment. We showed that the AF-2 domain of DAX1 is involved in DAX1-DAX1A heterodimerization. These results indicate that NR0B family members use similar mechanisms for homodimerization as well as heterodimerization. These resemble coactivator-receptor interactions that may have potential functional consequences for molecular mechanisms of the NR0B family.

Conserved family of glycerol kinase loci in Drosophila melanogaster

Glycerol kinase (GK) is an enzyme that catalyzes the formation of glycerol 3-phosphate from ATP and glycerol, the rate-limiting step in glycerol utilization. We analyzed the genome of the model organism Drosophila melanogaster and identified five GK orthologs, including two loci with sequence homology to the mammalian Xp21 GK protein. Using a combination of sequence analysis and evolutionary comparisons of orthologs between species, we characterized functional domains in the protein required for GK activity. Our findings include additional conserved domains that suggest novel nuclear and mitochondrial functions for glycerol kinase in apoptosis and transcriptional regulation. Investigation of GK function in Drosophila will inform us about the role of this enzyme in development and will provide us with a tool to examine genetic modifiers of human metabolic disorders.

Nr0b1 and its network partners are expressed early in murine embryos prior to steroidogenic axis organogenesis

Ahch is an orphan nuclear receptor encoded by Nr0b1 on the murine X chromosome and is the ortholog of human DAX1. Nr0b1/NR0B1 expression at appropriate dosages is required for normal steroidogenic axis development: mutation of the human ortholog, NR0B1, results in adrenal hypoplasia congenita and hypogonadotropic hypogonadism; and duplication or transgenic overexpression in humans or mice, respectively, results in XY phenotypic females, a phenotype known as dosage sensitive sex-reversal. Complete loss of Nr0b1 by targeted deletion has been hypothesized to be lethal in embryonic stem (ES) cells and preliminary evidence suggested that ES cells might express Nr0b1. These investigations examined Nr0b1 expression and its network partners in both cultured ES cells and preimplantation embryos. We cultured ES cells in the absence or presence of differentiation agents and analyzed expression of Nr0b1 and associated network partners by northern blot hybridization and reverse transcriptase-polymerase chain reaction. Nrob1 was highly expressed by totipotent ES cells with reduced expression following induction toward individual germ layer fates. Nr5a1/Sf1, Wt1 and other genes that encode proteins known to interact with Nr0b1 were also expressed. Immunohistochemical analysis of preimplantation embryos for Ahch and key partners confirmed in vivo expression of network components. These findings are consistent with the existence of a potentially functional network of transcription factors, including Ahch, very early in embryonic development. These results validate ES cells as a developmentally dynamic model for mechanistic investigations into this regulatory network early in embryogenesis preceding organogenesis.

Mutations in NR0B1 (DAX1) and NR5A1 (SF1) responsible for adrenal hypoplasia congenita

Adrenal hypoplasia congenita (AHC) causes primary adrenal insufficiency due to the failure of development of the adrenal cortex. Clinical and pedigree data indicate that the condition is genetically heterogeneous. The predominant adrenal hypoplasia congenita locus, however, is the NR0B1 gene, at Xp21, encoding the protein DAX1. In this article, we present a compendium of published NR0B1 mutations and polymorphisms, and discuss them in the contexts of known biology and clinical applicability. The recent descriptions of patients with primary adrenal insufficiency due to mutations of NR5A1, which encodes SF1, are also discussed.

Nine novel mutations in NR0B1 (DAX1) causing adrenal hypoplasia congenita

X-linked adrenal hypoplasia congenita (AHC) is caused by mutations in the NR0B1 gene. This gene encodes an orphan member of the nuclear receptor superfamily, DAX1. Ongoing efforts in our laboratory have identified nine novel NR0B1 mutations in X-linked AHC patients (Y81X, 343delG, 457delT, 629delG, L295P, 926-927delTG, 1130delA, 1141-1155del15, and E428X). Two additional families segregate previously identified NR0B1 mutations (501delA and R425T). Sequence analysis of the mitochondrial D-loop indicates that the 501delA family is unrelated through matrilineal descent to our previously analyzed 501delA family.

Single-tube gene-specific expression analysis by high primer density multiplex reverse transcription

Molecular genetics is rapidly moving from simple identification of a gene of interest to characterization of gene products as components in complex networks. Critical tools for gene product analysis require a rapid method for evaluation of contextual expression. Here, we describe a robust, high primer density, single-tube, multiplex reverse transcription (HD-MRT) technique. This approach is capable of analyzing for the presence of numerous transcripts when polymerase chain reaction (PCR) is subsequently employed for individual gene-specific sequence amplification (HD-MRT-PCR). This assay substantially increases the total number of different cDNAs for amplification beyond previously published techniques. Our approach simultaneously eliminates RNA quality control issues for samples run in parallel while improving efficiency in the use of time and materials. This assay is designed for broad applicability and accessibility, employs modifications of commercially available components, and allows more than 25 independently selected gene-specific primers to be used simultaneously. Our protocol allows multiplexed primers to behave similarly to uniplex RT reactions, while avoiding potential interference between gene-specific and/or nonspecific primers during annealing and reverse transcription. Expression of putatively networked homologous transcripts was analyzed in multiple cell lines and tissues from mouse and human to validate the technique.

Glycerol kinase deficiency: evidence for complexity in a single gene disorder

Glycerol kinase deficiency (GKD) occurs as part of an Xp21 contiguous gene syndrome or as isolated GKD. The isolated form can be either symptomatic with episodic metabolic and central nervous system (CNS) decompensation or asymptomatic with hyperglycerolemia and glyceroluria only. To better understand the pathogenesis of isolated GKD, we sought individuals with point mutations in the GK coding region and measured their GK enzyme activities. We identified six individuals with missense mutations: four (N288D, A305V, M428T, and Q438R) among males who were asymptomatic and two (D198G, R405Q) in individuals who were symptomatic. GK activity measured in lymphoblastoid cell lines or fibroblasts was similar for the symptomatic and the asymptomatic individuals. Mapping of the individuals' missense mutations to the three-dimensional structure of Escherichia coli GK revealed that the symptomatic individuals' mutations are in the same region as a subset of the mutations among the asymptomatic individuals, adjacent to the active-site cleft. We conclude that, like many other disorders, GK genotype does not predict GKD phenotype. We hypothesize that the phenotype of an individual with GKD is a complex trait influenced by additional, independently inherited genes.

Postgenomic medicine. Presymptomatic testing for prediction and prevention

Significant changes are occurring in genetic screening paradigms. Genetic screening is moving from traditional analytes, such as small molecules and proteins, to molecular genetic testing involving DNA and RNA. There are significant consequences to these changes, involving issues for the family unit, such as misattribution of parentage, and concerns regarding discrimination, confidentiality, and privacy. Although these latter issues have broader concerns for medicine and medical information, in the context of genetic testing, information derived from one individual can have a significant impact on others within their family. Screening is also changing from mendelian disease ascertainment to predictive testing. Issues that arise involve appropriate age at testing for adult-onset disorders, the clinical validity and clinical use of genetic testing for complex diseases, and the efficacy of interventions following genetic testing. We are also learning that the phenotypes of even simple mendelian disorders are influenced by complex genetic and environmental factors. The observations that genotypes rarely predict phenotypes absolutely have significant ramifications for counseling based on mutation analysis, for example in neonates who have not yet manifested symptoms and in older children and in adults undergoing predictive testing. Molecular genetic testing often proceeds rapidly from the research laboratory to the clinical setting. We must recognize that for single-gene disorders with high penetrance, the information derived from such testing may be relatively easy to interpret and apply. For complex diseases, however, the populations studied and their demographic characteristics are extremely important for extrapolation to counseling of individual patients. The value of population-based predictive testing is exemplified by newborn screening. It is clear that the Human Genome Project, and the information and technologies from it, will have a much broader impact on public health by presymptomatic prediction and prevention of disease.

Primate DAX1, SRY, and SOX9: evolutionary stratification of sex-determination pathway

The molecular evolution of DAX1, SRY, and SOX9, genes involved in mammalian sex determination, was examined in six primate species. DAX1 and SRY have been added to the X and Y chromosomes, respectively, during mammalian evolution, whereas SOX9 remains autosomal. We determined the genomic sequences of DAX1, SRY, and SOX9 in all six species, and calculated K(a), the number of nonsynonymous substitutions per nonsynonymous site, and compared this with the K(s), the number of synonymous substitutions per synonymous site. Phylogenetic trees were constructed by means of the DAX1, SRY, and SOX9 coding sequences, and phylogenetic analysis was performed using maximum likelihood. Overall measures of gene and protein similarity were closer for DAX1 and SOX9, but DAX1 exhibited nonsynonymous amino acid substitutions at an accelerated frequency relative to synonymous changes, similar to SRY and significantly higher than SOX9. We conclude that, at the protein level, DAX1 and SRY are under less selective pressure to remain conserved than SOX9, and, therefore, diverge more across species than does SOX9. These results are consistent with evolutionary stratification of the mammalian sex determination pathway, analogous to that for sex chromosomes.

Midkine is expressed early in rat fetal adrenal development

Adrenal gland development is complex and poorly understood at the molecular level. Only a subset of patients with adrenal hypoplasia congenita (AHC) carry mutations in DAX1, a member of the nuclear hormone receptor superfamily. Therefore we set out to identify other candidate genes responsible for AHC by characterizing genes involved in fetal adrenal development. To identify these genes, we studied the differential expression of genes in fetal rat adrenals comparing tissues at 14 and 15 days postcoitum (dpc) since this period encompasses major morphological change in rat adrenal development. Fetal rat adrenals were dissected, cDNAs were prepared, and suppressive subtractive hybridization was performed. We isolated 126 clones of putatively differentially expressed clones and approximately 250 bp of each of the clones was sequenced. The most interesting putative developmental genes were examined. One member of the extracellular PTN/MDK (pleiotrophin/midkine) heparin-binding protein family involved in regulation of growth and differentiation was selected for initial study. We obtained full-length transcript by 3' rapid amplification of cDNA ends and performed Northern analysis on rat adrenal RNA from fetuses at 13, 14, 15, 17, and 19 dpc and newborns. Results from those analyses demonstrated the highest Mdk expression at days 13 and 14 followed by a moderate decrease of expression during the fetal stages thereafter. In the newborn, Mdk expression is nearly undetectable. Our results indicate that Mdk has a very specific pattern of fetal expression in the adrenals. We conclude that Mdk is involved early in fetal development of the rat adrenal. Therefore, MDK is a candidate gene for AHC not due to DAX1 mutations.

Cloning and characterization of a putative human glycerol 3-phosphate permease gene (SLC37A1 or G3PP) on 21q22.3: mutation analysis in two candidate phenotypes, DFNB10 and a glycerol kinase deficiency

Using multiple exons trapped from human chromosome 21 (HC21)-specific cosmids with homology to a putative Arabidopsis thaliana glycerol 3-phosphate permease, we have determined the full-length cDNA sequence of a novel HC21 gene encoding a putative sugar-phosphate transporter (HGMW-approved symbol SLC37A1, aka G3PP). The predicted protein has 12 putative transmembrane domains and is also highly homologous to bacterial glpT proteins. The transcript was precisely mapped to 21q22.3 between D21S49 and D21S113. Comparison of the SLC37A1 cDNA to genomic sequence revealed that the gene encompasses 82 kb, and it is split into 19 coding exons and 7 untranslated exons, which are alternatively spliced in a complex and tissue-specific manner. Glycerol 3-phosphate (G3P) is produced by glycerol kinase (GK) and is found in several biochemical pathways in different cellular compartments, such as the glycerol phosphate shuttle and glycerophospholipid synthesis. Thus SLC37A1 mutations may cause a phenotype similar to GK deficiency. Mutational analyses of SLC37A1 in seven patients with no mutations in the GK gene and low GK activity revealed only nonpathogenetic sequence variants, excluding SLC37A1 as the gene for the phenotype in these patients. SLC37A1 maps in the refined critical region of the autosomal recessive deafness locus, DFNB10, on 21q22.3. Mutation analyses also excluded SLC37A1 as the gene for DFNB10.

Final report of the FOPE II Pediatric Subspecialists of the Future Workgroup

The report of the Pediatric Subspecialists of the Future Workgroup of the Second Task Force on Pediatric Education reviews the critical changes of the past 2 decades that have affected the provision of pediatric subspecialty services, education of pediatric health care providers, and the acquisition and application of new knowledge. The report considers the future needs that will determine the ability of pediatric subspecialists to meet identified goals. Recommendations for change in the education, role, and financing of the pediatric subspecialist are reported together with those of other workgroups. Pediatrics 2000;106(suppl):1224-1244; pediatric subspecialist, pediatric subspecialist workforce, education pediatric subspecialist, research pediatric subspecialist.

AluY insertion (IVS4-52ins316alu) in the glycerol kinase gene from an individual with benign glycerol kinase deficiency

Glycerol kinase deficiency has three distinct forms: an isolated form which may be benign or symptomatic, and a complex form which is symptomatic and part of an Xp21 contiguous gene syndrome. Here we report the case of a male with benign isolated glycerol kinase deficiency who was incidentally identified after observation of pseudohypertriglyceridemia. DNA sequencing of this subject's glycerol kinase gene showed the insertion of an AluY sequence in intron 4 of the glycerol kinase gene. Although Alu insertions have been implicated in other diseases, and a closely related AluY element is found as an insert in the C1 inhibitor gene in patients with hereditary angioedema, this is the first case of glycerol kinase deficiency caused by an Alu insertion.

Fructose-1,6-diphosphatase deficiency and glyceroluria: one possible etiology for GIS

Fructose-1,6-diphosphatase (FDPase) deficiency is characterized by episodes of lactic acidemia, hypoglycemia, and ketonuria. Liver biopsy and subsequent enzyme analysis most reliably make the diagnosis. Review of the literature reveals 85 cases. Glycerol intolerance syndrome (GIS) is less well defined. There are only a handful of cases reported. We describe a patient with FDPase deficiency and significant glyceroluria and propose that GIS may be caused by partial deficiency of FDPase.

State-of-the-art for DNA technology in newborn screening

Just as metabolites, hormones and proteins are measured in newborn screening tests, DNA has become an analyte that is important in the screens for certain disorders. DNA confirmatory testing on the original dried blood specimen reduces the age at diagnostic confirmation and antibiotic prophylaxis initiation for neonates with sickle cell disease. Molecular genetic analysis of the initial specimens from newborns with elevated immunoreactive trypsinogen (IRT) for cystic fibrosis (CF) screening permits reduction of the IRT threshold value, improving specificity without compromising sensitivity. Because of this cost reduction, CF neonatal screening programs routinely incorporate DNA confirmatory testing into their initial CF screening algorithm. DNA analysis is also a valuable adjunct in screening programs for congenital adrenal hyperplasia (CAH), improving sensitivity and specificity. Incorporation of DNA into newborn screening programs will continue to be stimulated by development of robust, high throughput technologies for evaluation of this analyte. New paradigms for neonatal screening are evolving, including hearing screening in the newborn nursery. DNA testing, such as for mutations in the connexin 26 gene, may have a role in the evaluation of those screened positive. Newborn screening dried blood specimens are DNA databases. Therefore, there are significant ethical, legal and social issues that must be considered in the storage and utilization of neonatal screening specimens.

IMAGe, a new clinical association of intrauterine growth retardation, metaphyseal dysplasia, adrenal hypoplasia congenita, and genital anomalies

We report three boys with adrenal hypoplasia congenita (AHC) and additional findings that represent a new syndrome, IMAGe: Intrauterine growth retardation, Metaphyseal dysplasia, AHC, and Genital anomalies. Each presented shortly after birth with growth retardation and severe adrenal insufficiency. Each of the three patients had mild dysmorphic features, bilateral cryptorchidism, a small penis, and hypogonadotropic hypogonadism. Skeletal surveys revealed metaphyseal dysplasia in all three and epiphyseal dysplasia in two. The patients had documented or suspected hypercalciuria and/or hypercalcemia, resulting in nephrocalcinosis in one and in prenatal liver and spleen calcifications in another. AHC presents most often either as an isolated abnormality, caused by mutations in the DAX1 gene, or as part of an Xp21 contiguous gene syndrome, caused by a deletion of the Duchenne muscular dystrophy, glycerol kinase, and DAX1 genes. All three patients with the IMAGe association had normal creatine kinase levels and no evidence of glycerol kinase deficiency. Sequence analysis of DNA from these patients revealed no mutation in the DAX1- or steroidogenic factor-1-coding sequences, nor was a deletion of DAX1 detected. Identification of the molecular basis of the IMAGe association will give new insight into the pathogenesis of this syndromic relationship involving bone, adrenal cortical, and pituitary development.

Expression of hexokinase 1 and hexokinase 2 in mammary tissue of nonlactating and lactating rats: evaluation by RT-PCR

Because the initial step in the metabolism of glucose involves phosphorylation by hexokinase (HK), we tested the hypothesis that the expression of the isozymes, hexokinase type 1 (HK1) and hexokinase type 2 (HK2), would be different in rat mammary tissue during pregnancy and lactation. RNA was extracted from mammary tissue dissected from timed pregnant rats (from gestional days 10 to 21) and nursing rat mothers (up to postnatal day 5) for mRNA examination by reverse transcriptase and polymerase chain reaction (RT-PCR) using isozyme specific oligonucleotide primers to the HK1 and HK2 cDNAs. The HK1 mRNA was expressed in both the nonlactating and lactating mammary gland tissue, but HK2 mRNA was found only during lactation. We speculate that the pattern of HK expression might affect human milk production and quality.

Bacterial species identification after DNA amplification with a universal primer pair

The diagnosis of bacterial infections can be difficult and time consuming. Rapid and reliable molecular triage of potentially infected patients, particularly the young and the elderly, would prevent unnecessary hospitalizations, reduce associated medical costs, and improve the quality of care. Polymerase chain reaction (PCR) amplification utilizing a universal bacterial primer pair, followed by hybridization with species-specific probes, would allow rapid identification of the presence or absence of bacterial DNA, along with an identification of the bacterial species present. Molecular microbiological analyses will require access to bacterial strain standards that can be catalogued and distributed to clinical laboratories. We amplified template DNA in filter paper spots containing boiled bacteria from 14 clinical isolates using a universal primer pair for the 16S ribosomal RNA (rDNA) coding sequence. Species-specific probes were hybridized to the amplification products for bacterial species identification. We conclude that template DNA can be identified with species-specific probes after universal bacterial amplification with a single primer pair. We also demonstrate a rapid and efficient method for the long-term storage and cataloguing of bacterial DNA for use in quality control at clinical laboratories adopting molecular diagnostic methodologies. We speculate that PCR amplification combined with species-specific probe hybridization not only will represent an improvement over culture-based methods in terms of speed, sensitivity, and cost, but will also allow for the identification of unculturable bacteria and emerging or reemerging pathogenic organisms.

Mammalian sex determination: from gonads to brain

In mammals, sex is determined by the Y chromosome, which encodes a testis-determining factor (TDF). This factor causes the undifferentiated embryonic gonads to develop as testes rather than ovaries. The testes subsequently produce the male sex hormones that are responsible for all male sexual characteristics. In 1990, the sex-determining gene, TDF, was identified and termed SRY in humans (Sry in mice). It encodes a protein containing a high mobility group (HMG) motif, which confers the ability to bind and to bend DNA. Genetic evidence supporting SRY as TDF came from the observation of a male phenotype in XX mice transgenic for a small genomic fragment containing Sry, and from the study of XY sex-reversed individuals who harbor de novo mutations in the SRY coding sequence. Other non-Y-linked genes involved in sex determination were subsequently found by genetic analysis of XY sex-reversed patients not explained by mutations in SRY. These genes are WT1, SF1, DAX1, and SOX9. A regulatory cascade hypothesis for mammalian sex determination, proposing that SRY represses a negative regulator of male development, was recently supported by observation of mice that expressed a DAX1 transgene and developed as XY sex-reversed females. The role of some sex-determining genes, such as DAX1 and SF1, in the development of the entire reproductive axis, a functionally integrated endocrine axis, leads to a new concept. Normal sexual development may result from the functional and developmental integration of a number of different genes that play roles in sex determination, sexual differentiation, and sexual behavior.

Minipuberty of infancy and adolescent pubertal function in adrenal hypoplasia congenita

An infant and his uncle, both with adrenal hypoplasia congenita, shared the same DAX1 mutation. The adolescent uncle had hypogonadotropic hypogonadism, but the infant had a normal minipuberty of infancy. These observations suggest differences in the physiologic mechanisms regulating the hypothalamic-pituitary-gonadal axis in infancy and adolescence.

DAX1 mutations map to putative structural domains in a deduced three-dimensional model

The DAX1 protein is an orphan nuclear hormone receptor based on sequence similarity in the putative ligand-binding domain (LBD). DAX1 mutations result in X-linked adrenal hypoplasia congenita (AHC). Our objective was to identify DAX1 mutations in a series of families, to determine the types of mutations resulting in AHC and to locate single-amino-acid changes in a DAX1 structural model. The 14 new mutations identified among our 17 families with AHC brought the total number of families with AHC to 48 and the number of reported mutations to 42; 1 family showed gonadal mosaicism. These mutations included 23 frameshift, 12 nonsense, and six missense mutations and one single-codon deletion. We mapped the seven single-amino-acid changes to a homology model constructed by use of the three-dimensional crystal structures of the thyroid-hormone receptor and retinoid X receptor alpha. All single-amino-acid changes mapped to the C-terminal half of the DAX1 protein, in the conserved hydrophobic core of the putative LBD, and none affected residues expected to interact directly with a ligand. We conclude that most genetic alterations in DAX1 are frameshift or nonsense mutations and speculate that the codon deletion and missense mutations give insight into the structure and function of DAX1.

Developmental expression of hexokinase 1 and 3 in rats

Mammalian hexokinase types one and three (HK1 and HK3) are 100 kDa isozymes that phosphorylate glucose to glucose-6-phosphate. HK1 is present in most tissues but is especially prominent in brain and kidney. HK3 is less well studied, but may be most prominent in the spleen and lymphocytes. In this study, we determined the ontogeny of the expression of these isoforms in the rat. Using immunohistochemistry, we identified HK1 and HK3 immunoreactivity in the brain, heart, kidney, liver, skeletal muscle and spleen from gestational day 14 (E14) to 45 days after birth (P45). With the exception of the liver and spleen, we observed a similar age- and cell-dependent staining pattern for both isoforms in all organs studied. The brain and spleen were analyzed in more detail to identify specific regions of immunoreactivity during maturation. A transient expression of HK1 and HK3 was noted in the cell bodies of mature neurons, including layers V and VI of the cerebral cortex and the cerebellar Purkinje cells followed by localization to the white matter of the cerebrum and cerebellum. In the spleen, HK3 immunoreactivity was detected postnatally and appeared to track with the infiltration of B cells. Our demonstration of changing patterns of immunoreactivity for HK1 and HK3 in fetal and postnatal organs suggests that these HK isoforms are involved the process of development. We speculate that HK1 and HK3 share a complex interaction during development of these organs and regulate glucose metabolism at multiple levels during development.

DAX1 gene expression upregulated by steroidogenic factor 1 in an adrenocortical carcinoma cell line

Two nuclear hormone receptor superfamily members, DAX1 and SF1, are required for normal adrenal cortical development. Mutations in DAX1 are responsible for X-linked adrenal hypoplasia congenita (AHC) and hypogonadotropic hypogonadism. Steroidogenic Factor 1 (SF1) regulates the expression of a number of steroidogenic genes and a putative SF1 response element (SF1-RE) in the DAX1 promoter which binds SF1 specifically. Therefore, we examined deletions in the DAX1 promoter driving expression of beta-galactosidase, with and without coexpression of SF1, in the human adrenocortical carcinoma cell line NCI-H295. We defined the DAX initiation start site and localized the putative SF1-RE at -135 to -143 bp. Loss of the putative SF1-RE region or specific removal of the 9-bp SF1 site resulted in decreased transcriptional activity by 2.3-to 2.5-fold. When cotransfected with 1550 bp of the DAX1 promoter, an SF1-containing expression vector increased the transcriptional activity of the DAX1 promoter by 4-fold. No significant change above baseline occurred when the cells were cotransfected with the 1541-bp fragment containing the entire 1550-bp promoter region minus the 9-bp SF1-RE. We conclude that the SF1-RE is an enhancer element within the DAX1 promoter and speculate that SF1 may be a transcription factor that acts, at least in part, through DAX1 for normal adrenal cortical development.

Identification of a ferritin light chain pseudogene near the glycerol kinase locus in Xp21 by cDNA amplification for identification of genomic expressed sequences

We used cDNA amplification for identification of genomic expressed sequences (CAIGES) to identify genes in the glycerol kinase region of the human X chromosome. During these investigations we identified the sequence for a ferritin light chain (FTL) pseudogene in this portion of Xp21. A human liver cDNA library was amplified by vector primers, labeled, and hybridized to Southern blots of EcoRI-digested human genomic DNA from cosmids isolated from yeast artificial chromosomes in the glycerol kinase region of Xp21. A 3.1-kb restriction fragment hybridized with the cDNA library, was subcloned and sequenced, and a 440-bp intronless sequence was found with strong similarity to the FTL coding sequence. Therefore, the FTL pseudogene that had been mapped previously to Xp22.3-21.2 was localized specifically to the glycerol kinase region. The CAIGES method permits rapid screening of genomic material and will identify genomic sequences with similarities to genes expressed in the cDNA library used to probe the cloned genomic DNA, including pseudogenes.

Ahch, the mouse homologue of DAX1: cloning, characterization and synteny with GyK, the glycerol kinase locus

We cloned the murine full-length cDNA encoding Ahch, the mouse homologue of DAX1 (DSS-AHC Region on Human X Chromosome, Gene1) which is the gene responsible for human X-linked adrenal hypoplasia congenita (AHC) and hypogonadotropic hypogonadism (HH). Sequence analysis revealed that the murine and human cDNAs have 65% aa identity and 75% aa similarity overall. The cysteine residues in the putative DNA binding domain, which may interact with Zn2+ ions to form zinc fingers, are 100% conserved between the two species, indicating that the novel zinc-finger structures in DAX1 may be functional. In addition, mouse interspecific backcrosses show that the Ahch gene is closely linked to the glycerol kinase locus, GyK, on the mouse X chromosome, indicating that the order of the loci is conserved in this syntenic region between mouse and human.

Genomic sequence of the DAX1 gene: an orphan nuclear receptor responsible for X-linked adrenal hypoplasia congenita and hypogonadotropic hypogonadism

The gene responsible for X-linked adrenal hypoplasia congenita, DAX1, encodes a member of the nuclear hormone receptor superfamily. We sequenced 8851 bp that contained the DAX1 genomic region. The DAX gene was composed of two exons and one 3.4-kilobase intron. Putative TATA and GC boxes and a putative steroidogenic factor 1 response element were present in the 5'-flanking region. Two potentially polymorphic short tandem repeats were identified. The first exon encoded two putative novel zinc finger motifs within a putative DNA binding domain and part of the ligand binding domain, and the second exon encoded the remainder of the ligand binding domain. Although the putative DNA binding domain of DAX1 does not contain substantial sequence similarity to other nuclear hormone receptor superfamily members, the putative ligand binding domain had remarkable similarity to other family members. Single-strand conformational polymorphism analysis permitted identification of three new mutations in DAX1. In conclusion, single-strand conformational polymorphism analysis facilitates identification of mutations in the DAX1 gene, and the short tandem repeats may permit linkage analysis in families in which mutations are not yet identified. We speculate that DAX1 may be the most primitive member of the nuclear hormone receptor superfamily identified in mammals.

Guidelines for the retention, storage, and use of residual dried blood spot samples after newborn screening analysis: statement of the Council of Regional Networks for Genetic Services

These guidelines provide scientific information for policy development by state health departments considering appropriate use of newborn screening specimens after screening tests are finished. Information was collected, debated, and formulated into a policy statement by the Newborn Screening Committee of the Council of Regional Networks for Genetic Services (CORN), a federally funded national consortium of representatives from 10 regional genetics networks. Newborn screening programs vary widely in approaches and policies concerning residual dried blood spot samples (DBS) collected for newborn screening. Recognition of the epidemiological utility of DBS samples for HIV seroprevalence surveys and a growing interest in DBSs for DNA analysis has intensified consideration of issues regarding retention, storage, and use of residual DBS samples. Potentially these samples provide a genetic material "bank" for all newborns nationwide. Their values as a resource for other uses has already been recognized by scientists, administrators, and judicial officials. Programs should promulgate rules for retention and use of residual newborn screening DBS samples based on scientifically valid information. Banking of newborn samples as sources of genetic material should be considered in light of potential benefit or harm to society.

Comparison of human VDAC1 with streptococcal streptokinase and bovine bactericidal permeability increasing protein: role of structural information in identifying functionally significant domains

Comparison of the primary amino acid sequence of the human X-linked voltage-dependent anion channel, with other sequences in data base searches, identified regions of similarity in streptococcal streptokinase and bovine bactericidal permeability increasing protein. These regions of similarity were in different areas of the protein and were relatively short. However, examination of an empirically derived structural model of the channel showed that each region of similarity in streptokinase and bovine bactericidal permeability increasing protein corresponded to contiguous transmembrane domains within the channel protein. We speculate that these transmembrane domains may be functionally significant for streptokinase and bovine bactericidal permeability increasing protein. These investigations demonstrate the need for incorporation of information regarding secondary, tertiary, and quaternary structures, as well as function, in algorithms used for database searches.

Expression of DAX-1, the gene responsible for X-linked adrenal hypoplasia congenita and hypogonadotropic hypogonadism, in the hypothalamic-pituitary-adrenal/gonadal axis

DAX-1, an orphan member of the nuclear hormone receptor superfamily, is responsible for X-linked adrenal hypoplasia congenita (AHC) and the frequently associated hypogonadotropic hypogonadism (HH). The entire DAX-1 genomic region has been sequenced and a putative steroidogenic factor-1 response element has been identified in the promoter region of the gene. The purpose of these investigations was to determine if DAX-1 was expressed in the central nervous system, particularly the hypothalamus and pituitary, in order to better understand the relationship of mutations in this gene to HH associated with AHC. We used Northern blot analysis and reverse transcription PCR to demonstrate that DAX-1 was expressed in the hypothalamus and the pituitary, and to confirm its expression in adrenal cortex and gonads. The expression of DAX-1 in these tissues indicates the involvement of DAX-1 in the development of the reproductive system at multiple levels within the hypothalamic-pituitary-adrenal/gonadal axis. We also observed the expression of DAX-1 in a human adrenocortical carcinoma cell line, NCI-H295, that has features characteristic of the fetal adrenal cortex. Therefore, NCI-H295 cells will be a useful cellular model for investigating the involvement of DAX-1 in the regulation of steroidogenesis.

Identification of a putative steroidogenic factor-1 response element in the DAX-1 promoter

The nuclear hormone receptor, DAX-1, is responsible for X-linked adrenal hypoplasia congenita and hypogonadotrophic hypogonadism. We recently cloned the 5' flanking region of the human DAX-1 gene and in this report we describe the identification of a putative steroidogenic factor 1 (SF-1) response element approximately 110 bases upstream of the TATA box. Both DAX-1 and SF-1 are expressed in similar tissues including the adrenal cortex, gonads, hypothalamus, and the pituitary gland. Like DAX-1, SF-1 expression has been shown to be essential for the development of the adrenal cortex. We demonstrate that SF-1 is able to efficiently bind to the putative SF-1 response element found in the DAX-1 promoter in vitro. This suggests that SF-1 may directly regulate the expression of DAX-1 and that these two transcription factors may be components of a cascade required for development of steroidogenic tissues.