Showing papers in "Nature Genetics in 1996"

A novel MHC class I–like gene is mutated in patients with hereditary haemochromatosis

Abstract: Hereditary haemochromatosis (HH), which affects some 1 in 400 and has an estimated carrier frequency of 1 in 10 individuals of Northern European descent, results in multi-organ dysfunction caused by increased iron deposition, and is treatable if detected early. Using linkage-disequilibrium and full haplotype analysis, we have identified a 250-kilobase region more than 3 megabases telomeric of the major histocompatibility complex (MHC) that is identical-by-descent in 85% of patient chromosomes. Within this region, we have identified a gene related to the MHC class I family, termed HLA-H, containing two missense alterations. One of these is predicted to inactivate this class of proteins and was found homozygous in 83% of 178 patients. A role of this gene in haemochromatosis is supported by the frequency and nature of the major mutation and prior studies implicating MHC class I-like proteins in iron metabolism.

Use of a cDNA microarray to analyse gene expression patterns in human cancer.

Abstract: The development and progression of cancer and the experimental reversal of tumorigenicity are accompanied by complex changes in patterns of gene expression. Microarrays of cDNA provide a powerful tool for studying these complex phenomena. The tumorigenic properties of a human melanoma cell line, UACC-903, can be suppressed by introduction of a normal human chromosome 6, resulting in a reduction of growth rate, restoration of contact inhibition, and suppression of both soft agar clonogenicity and tumorigenicity in nude mice. We used a high density microarray of 1,161 DNA elements to search for differences in gene expression associated with tumour suppression in this system. Fluorescent probes for hybridization were derived from two sources of cellular mRNA [UACC-903 and UACC-903(+6)] which were labelled with different fluors to provide a direct and internally controlled comparison of the mRNA levels corresponding to each arrayed gene. The fluorescence signals representing hybridization to each arrayed gene were analysed to determine the relative abundance in the two samples of mRNAs corresponding to each gene. Previously unrecognized alterations in the expression of specific genes provide leads for further investigation of the genetic basis of the tumorigenic phenotype of these cells.

Positional cloning of a novel potassium channel gene: KVLQT1 mutations cause cardiac arrhythmias.

Abstract: Genetic factors contribute to the risk of sudden death from cardiac arrhythmias. Here, positional cloning methods establish KVLQT1 as the chromosome 11-linked LQT1 gene responsible for the most common inherited cardiac arrhythmia. KVLQT1 is strongly expressed in the heart and encodes a protein with structural features of a voltage-gated potassium channel. KVLQT1 mutations are present in affected members of 16 arrhythmia families, including one intragenic deletion and ten different missense mutations. These data define KVLQT1 as a novel cardiac potassium channel gene and show that mutations in this gene cause susceptibility to ventricular tachyarrhythmias and sudden death.

Correction of the sterility defect in homozygous obese female mice by treatment with the human recombinant leptin.

Abstract: The sterility of male and female homozygous ob/ob mice is a recognized feature of the ob mutation (1). Whereas ob/ob males can occasionally reproduce if maintained on a restricted diet, ob/ob females are always sterile (2). Thinning of the ob/ob females to normal weight by diet-restriction failed to correct their sterility. Early sexual development is normal in ob/ob females; however, ovulation never follows and the mice remain prepuberal indefinitely with no occurrence of oestrus cycles. Reproductive hormones are reduced in ob/ob females (3) demonstrating a functional defect from the hypothalamic-pituitary axis (4-6). The ovaries of ob/ob females are capable of producing viable eggs when transplanted into lean female recipients (7). Reconstitution of reproductive functions in the ob/ob female necessitates delivery of hypothalamic extracts to the third ventricle (8) and administration of pituitary extract (9), gonadotropic hormones (10), progesterone (11) and relaxin (12). These previous findings demonstrate that the sterility of ob/ob females is caused by an insufficiency of hormones at the hypothalamic-pituitary level rather than physical hindrance of copulatory activity, pregnancy and parturition caused by excess adipose tissue. We show here that repeated administration of only the recombinant human ob protein, leptin, into homozygous female ob/ob mice can correct their sterility, thus resulting in ovulation, pregnancy and parturition.

Hereditary pancreatitis is caused by a mutation in the cationic trypsinogen gene.

Abstract: Hereditary pancreatitis (HP) is a rare, early-onset genetic disorder characterized by epigastric pain and often more serious complications. We now report that an Arg–His substitution at residue 117 of the cationic trypsinogen gene is associated with the HP phenotype. This mutation was observed in all HP affected individuals and obligate carriers from five kindreds, but not in individuals who married into the families nor in 140 unrelated individuals. X-ray crystal structure analysis, molecular modelling, and protein digest data indicate that the Arg 117 residue is a trypsin-sensitive site. Cleavage at this site is probably part of a fail-safe mechanism by which trypsin, which is activated within the pancreas, may be inactivated; loss of this cleavage site would permit autodigestion resulting in pancreatitis.

Dopamine D4 receptor (D4DR) exon III polymorphism associated with the human personality trait of Novelty Seeking.

Abstract: Human personality traits which can be reliably measured by any of a number of rating scales, show a considerable heritable component1,2 The tridimensional personality questionnaire (TPQ) is one such instrument and was designed by Cloninger to measure four distinct domains of temperament — Novelty Seeking, Harm Avoidance, Reward Dependence and Persistence — that are hypothesized to be based on distinct neurochemical and genetic substrates Cloninger proposed that individual variations in the Novelty Seeking trait are mediated by genetic variability in dopamine transmission2 Individuals who score higher than average on the TPQ Novelty Seeking scale are characterized as impulsive, exploratory, fickle, excitable, quick-tempered and extravagant, whereas those who score lower than average tend to be reflective, rigid, loyal, stoic, slow-tempered and frugal We now show that higher than average Novelty Seeking test scores in a group of 124 unrelated Israeli subjects are significantly associated with a particular exonic polymorphism, the 7 repeat allele in the locus for the D4 dopamine receptor gene (D4DR) The association of high Novelty Seeking and the 7-repeat allele was independent of ethnicity, sex or age of the subjects This work, together with the accompanying confirmations in this issue3, provides the first replicated association between a specific genetic locus involved in neuro-transmission and a normal personality trait

Karyotyping human chromosomes by combinatorial multi-fluor FISH

Abstract: We have developed epifluorescence filter sets and computer software for the detection and discrimination of 27 different DNA probes hybridized simultaneously. For karyotype analysis, a pool of human chromosome painting probes, each labelled with a different fluor combination, was hybridized to metaphase chromosomes prepared from normal cells, clinical specimens, and neoplastic cell lines. Both simple and complex chromosomal rearrangements could be detected rapidly and unequivocally; many of the more complex chromosomal abnormalities could not be delineated by conventional cytogenetic banding techniques. Our data suggest that multiplex-fluorescence in situ hybridization (M-FISH) could have wide clinical utility and complement standard cytogenetics, particularly for the characterization of complex karyotypes.

Motor neurons in Cu/Zn superoxide dismutase-deficient mice develop normally but exhibit enhanced cell death after axonal injury.

Abstract: The discovery that some cases of familial amyotrophic lateral sclerosis (FALS) are associated with mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1) has focused much attention on the function of SOD1 as related to motor neuron survival. Here we describe the creation and characterization of mice completely deficient for this enzyme. These animals develop normally and show no overt motor deficits by 6 months in age. Histological examination of the spinal cord reveals no signs of pathology in animals 4 months in age. However Cu/Zn SOD-deficient mice exhibit marked vulnerability to motor neuron loss after axonal injury. These results indicate that Cu/Zn SOD is not necessary for normal motor neuron development and function but is required under physiologically stressful conditions following injury.

Genetic dissection of complex traits.

Abstract: Medical genetics was revolutionized during the 1980s by the application of genetic mapping to locate the genes responsible for simple Mendelian diseases. Most diseases and traits, however, do not follow simple inheritance patterns. Genetics have thus begun taking up the even greater challenge of the genetic dissection of complex traits. Four major approaches have been developed: linkage analysis, allele-sharing methods, association studies, and polygenic analysis of experimental crosses. This article synthesizes the current state of the genetic dissection of complex traits--describing the methods, limitations, and recent applications to biological problems.

Population and familial association between the D4 dopamine receptor gene and measures of Novelty Seeking

Abstract: Twin and adoption studies suggest that 30 to 60% of the variance in many personality traits is due to inherited factors. However, there is little knowledge of the number or identity of the responsible genes, how they differ between individuals, or how their gene products interact with the developing brain and with environmental and experiential factors to generate the complex blend of attitudes and actions that comprise human temperament1. In the accompanying paper, Ebstein et al.2 have found a population association between a long allele of polymorphic exon III repeat sequence of the D4 dopamine receptor gene (DADR) and the normal personality trait of Novelty Seeking. The possibility of a causal relationship between DADR and Novelty Seeking is further supported by studies showing that the number of exon III repeats can affect the binding of ligands to the receptor3,4; that DADR is expressed in lim-bic areas involved in cognition and emotion5,6; that dopamine mediates exploratory behaviour in experimental animals7–12; that the rewarding effects of amphetamines and cocaine are related to dopamine release13; and that Novelty Seeking is low in dopamine-deficient patients with Parkinson's disease14. We investigated the relationship between DADR exon III sequence variants and personality test scores in a population of 315 mostly male siblings, other family members and individuals from the United States. The association between long alleles of exon III and personality traits related to Novelty Seeking was confirmed. Moreover, family studies showed that this association is the result of genetic transmission rather than of population stratification.

Gitelman's variant of Bartter's syndrome, inherited hypokalaemic alkalosis, is caused by mutations in the thiazide-sensitive Na-Cl cotransporter

Abstract: Maintenance of fluid and electrolyte homeostasis is critical for normal neuromuscular function Bartter's syndrome is an autosomal recessive disease characterized by diverse abnormalities in electrolyte homeostasis including hypokalaemic metabolic alkalosis; Gitelman's syndrome represents the predominant subset of Bartter's patients having hypomagnesemia and hypocalciuria We now demonstrate complete linkage of Gitelman's syndrome to the locus encoding the renal thiazide-sensitive Na–Cl cotransporter, and identify a wide variety of non-conservative mutations, consistent with loss of function alleles, in affected subjects These findings demonstrate the molecular basis of Gitelman's syndrome We speculate that these mutant alleles lead to reduced sodium chloride reabsorption in the more common heterozygotes, potentially protecting against development of hypertension

Mutations in the human Sonic Hedgehog gene cause holoprosencephaly.

Abstract: Holoprosencephaly (HPE) is a common developmental defect of the forebrain and frequently the midface in humans, with both genetic and environmental causes HPE has a prevalence of 1:250 during embryogenesis and 1:16,000 newborn infants, and involves incomplete development and septation of midline structures in the central nervous system (CNS) with a broad spectrum of clinical severity Alobar HPE, the most severe form which is usually incompatible with postnatal life, involves complete failure of division of the forebrain into right and left hemispheres and is characteristically associated with facial anomalies including cyclopia, a primitive nasal structure (proboscis) and/or midfacial clefting At the mild end of the spectrum, findings may include microcephaly, mild hypotelorism, single maxillary central incisor and other defects (Fig 1) This phenotypic variability also occurs between affected members of the same family The molecular basis underlying HPE is not known, although teratogens, non-random chromosomal anomalies and familial forms with autosomal dominant and recessive inheritance have been described HPE3 on chromosome 7q36 is one of at least four different loci implicated in HPE Here, we report the identification of human Sonic Hedgehog (SHH) as HPE3-the first known gene to cause HPE Analyzing 30 autosomal dominant HPE (ADHPE) families, we found five families that segregate different heterozygous SHH mutations Two of these mutations predict premature termination of the SHH protein, whereas the others alter highly conserved residues in the vicinity of the alpha-helix-1 motif or signal cleavage site

Moderate expansion of a normally biallelic trinucleotide repeat in spinocerebellar ataxia type 2

Abstract: The gene for spinocerebellar ataxia type 2 (SCA2) has been mapped to 12q24.1. A 1.1-megabase contig in the candidate region was assembled in P1 artificial chromosome and bacterial artificial chromosome clones. Using this contig, we identified a CAG trinucleotide repeat with CAA interruptions that was expanded in patients with SCA2. In contrast to other unstable trinucleotide repeats, this CAG repeat was not highly polymorphic in normal individuals. In SCA2 patients, the repeat was perfect and expanded to 36-52 repeats. The most common disease allele contained (CAG)37, one of the shortest expansions seen in a CAG expansion syndrome. The repeat occurs in the 5'-coding region of SCA2 which is a member of a novel gene family.

Leptin activation of Stat3 in the hypothalamus of wild–type and ob/ob mice but not db/db mice

Abstract: Leptin, a hormone secreted by adipocytes, regulates the size of the adipose tissue mass through effects on satiety and energy metabolism. Leptin's precise sites of action are not known. The leptin receptor (Ob-R) is found in many tissues in several alternatively spliced forms raising the possibility that leptin exerts effects on many tissues including the hypothalamus. Ob-R is a member of the gp130 family of cytokine receptors which are known to stimulate gene transcription via activation of cytosolic STAT proteins. In order to identify the sites of leptin action in vivo, we assayed for activation of STAT proteins in mice treated with leptin. The STAT proteins bind to phosphotyrosine residues in the cytoplasmic domain of the ligand-activated receptor where they are phosphorylated. The activated STAT proteins dimerize and translocate to the nucleus where they bind DNA and activate transcription. The activation of STAT proteins in response to leptin was assayed in a variety of mouse tissues known to express Ob-R. Leptin injection activated Stat3 but no other STAT protein in the hypothalamus of ob/ob and wild-type mice but not db/db mice, mutants that lack an isoform of the leptin receptor. Leptin did not induce STAT activation in any of the other tissues tested. Activation of Stat3 by leptin was dose dependent and first observed after 15 minutes and maximal at 30 minutes. Our data indicate the hypothalamus is a direct target of leptin action and that this activation is critically dependent on the gp-130-like leptin receptor isoform missing in C57BLKS/J db/db mice. This is the first in vivo demonstration of leptin signal transduction.

Mutations in the activin receptor–like kinase 1 gene in hereditary haemorrhagic telangiectasia type 2

Abstract: Hereditary haemorrhagic telangiectasia, or Osler-Rendu-Weber (ORW) syndrome, is an autosomal dominant vascular dysplasia. So far, two loci have been demonstrated for ORW. Linkage studies established an ORW locus at chromosome 9q3; endoglin was subsequently identified as the ORW1 gene. A second locus, designated ORW2, was mapped to chromosome 12. Here we report a new 4 cM interval for ORW2 that does not overlap with any previously defined. A 1.38-Mb YAC contig spans the entire interval. It includes the activin receptor like kinase 1 gene (ACVRLK1 or ALK1), a member of the serine-threonine kinase receptor family expressed in endothelium. We report three mutations in the coding sequence of the ALK1 gene in those families which show linkage of the ORW phenotype to chromosome 12. Our data suggest a critical role for ALK1 in the control of blood vessel development or repair.

Apolipoprotein E allele-specific antioxidant activity and effects on cytotoxicity by oxidative insults and beta-amyloid peptides.

Abstract: The apolipoprotein E (APOE) E4 allele is associated with Alzheimer's disease, cardiovascular disease, and decreased longevity To probe the mechanism of these associations, cell lines were created which secrete each apoE isoform ApoE conditioned media, purified apoE, and commercially obtained apoE protected B12 cells from hydrogen peroxide cytotoxicity with E2 > E3 > E4 Physiological levels of apoE protected cells from beta-amyloid peptides, while higher doses of apoE led to increased cytotoxicity E2 > E3 > E4 possessed antioxidant activity, and apoE bound certain metal ions The decreased antioxidant activity of E4 could contribute to its association with Alzheimer's disease, cardiovascular disease and decreased longevity

Cloning and characterization of a novel bicoid-related homeobox transcription factor gene, RIEG, involved in Rieger syndrome

Abstract: Rieger syndrome (REG) is an autosomal–dominant human disorder that includes anomalies of the anterior chamber of the eye, dental hypoplasia and a protuberant umbilicus. We report the human cDNA and genomic characterization of a new homeobox gene, RIEG, causing this disorder. Six mutations in RIEG were found in individuals with the disorder. The cDNA sequence of Rieg, the murine homologue of RIEG, has also been isolated and shows strong homology with the human sequence. In mouse embryos Rieg mRNA localized in the periocular mesenchyme, maxillary and mandibular epithelia, and umbilicus, all consistent with RIEG abnormalities. The gene is also expressed in Rathke's pouch, vitelline vessels and the limb mesenchyme. RIEG characterization provides opportunities for understanding ocular, dental and umbilical development and the pleiotropic interactions of pituitary and limb morphogenesis.

Cloning of the gene for spinocerebellar ataxia 2 reveals a locus with high sensitivity to expanded CAG/glutamine repeats

Abstract: Two forms of the neurodegenerative disorder spinocerebellar ataxia are known to be caused by the expansion of a CAG (polyglutamine) trinucleotide repeat. By screening cDNA expression libraries, using an antibody specific for polyglutamine repeats, we identified six novel genes containing CAG stretches. One of them is mutated in patients with spinocerebellar ataxia linked to chromosome 12q (SCA2). This gene shows ubiquitous expression and encodes a protein of unknown function. Normal SCA2 alleles (17 to 29 CAG repeats) contain one to three CAAs in the repeat. Mutated alleles (37 to 50 repeats) appear particularly unstable, upon both paternal and maternal transmissions. The sequence of three of them revealed pure CAG stretches. The steep inverse correlation between age of onset and CAG number suggests a higher sensitivity to polyglutamine length than in the other polyglutamine expansion diseases.

Skeletal overgrowth and deafness in mice lacking fibroblast growth factor receptor 3.

Abstract: Fibroblast growth factor receptor 3 (Fgfr3) is a tyrosine kinase receptor expressed in developing bone, cochlea, brain and spinal cord. Achondroplasia, the most common genetic form of dwarfism, is caused by mutations in FGFR3. Here we show that mice homozygous for a targeted disruption of Fgfr3 exhibit skeletal and inner ear defects. Skeletal defects include kyphosis, scoliosis, crooked tails and curvature and overgrowth of long bones and vertebrae. Contrasts between the skeletal phenotype and achondroplasia suggest that activation of FGFR3 causes achondroplasia. Inner ear defects include failure of pillar cell differentiation and tunnel of Corti formation and result in profound deafness. Our results demonstrate that Fgfr3 is essential for normal endochondral ossification and inner ear development.

The complete BRCA2 gene and mutations in chromosome 13q-linked kindreds.

Abstract: Breast carcinoma is the most common malignancy among women in developed countries. Because family history remains the strongest single predictor of breast cancer risk, attention has focused on the role of highly penetrant, dominantly inherited genes in cancer-prone kindreds. BRCA1 was localized to chromosome 17 through analysis of a set of high-risk kindreds, and then identified four years later by a positional cloning strategy. BRCA2 was mapped to chromosomal 13q at about the same time. Just fifteen months later, Wooster et al. reported a partial BRCA2 sequence and six mutations predicted to cause truncation of the BRCA2 protein. While these findings provide strong evidence that the identified gene corresponds to BRCA2, only two thirds of the coding sequence and 8 out of 27 exons were isolated and screened; consequently, several questions remained unanswered regarding the nature of BRCA2 and the frequency of mutations in 13q-linked families. We have now determined the complete coding sequence and exonic structure of BRCA2 (GenBank accession #U43746), and examined its pattern of expression. Here, we provide sequences for a set of PCR primers sufficient to screen the entire coding sequence of BRCA2 using genomic DMA. We also report a mutational analysis of BRCA2 in families selected on the basis of linkage analysis and/or the presence of one or more cases of male breast cancer. Together with the specific mutations described previously, our data provide preliminary insight into the BRCA2 mutation profile.

Early death due to defective neonatal lung liquid clearance in alpha-ENaC-deficient mice

Abstract: The amiloride-sensitive epithelial sodium channel, ENaC, is a heteromultimeric protein made up of three homologous subunits (alpha, beta and gamma) (1,2). In vitro, assembly and expression of functional active sodium channels in the Xenopus oocyte is strictly dependent on alpha-ENaC--the beta and gamma subunits by themselves are unable to induce an amiloride-sensitive sodium current in this heterologous expression system (2). In vivo, ENaC constitutes the limiting step for sodium absorption in epithelial cells that line the distal renal tubule, distal colon and the duct of several exocrine glands. The adult lung expresses alpha, beta and gamma ENaC (3,4), and an amiloride-sensitive electrogenic sodium reabsorption has been documented in upper and lower airways (3-7), but it is not established whether this sodium transport is mediated by ENaC in vivo. We inactivated the mouse alpha-ENaC gene by gene targeting. Amiloride-sensitive electrogenic Na+ transport was abolished in airway epithelia from alpha-ENaC(-/-) mice. Alpha-ENaC(-/-) neonates developed respiratory distress and died within 40 h of birth from failure to clear their lungs of liquid. This study shows that ENaC plays a critical role in the adaptation of the newborn lung to air breathing.

Bartter's syndrome, hypokalaemic alkalosis with hypercalciuria, is caused by mutations in the Na-K-2Cl cotransporter NKCC2.

Abstract: Inherited hypokalaemic alkalosis with low blood pressure can be divided into two groups-Gitelman's syndrome, featuring hypocalciuria, hypomagnesaemia and milder clinical manifestations, and Bartter's syndrome, featuring hypercalciuria and early presentation with severe volume depletion. Mutations in the renal Na-Cl cotransporter have been shown to cause Gitelman's syndrome. We demonstrate linkage of Bartter's syndrome to the renal Na-K-2Cl cotransporter gene NKCC2, and identify frameshift or non-conservative missense mutations for this gene that co-segregate with the disease. These findings demonstrate the molecular basis of Bartter's syndrome, provide the basis for molecular classification of patients with inherited hypokalaemic alkalosis, and suggest potential phenotypes in heterozygous carriers of NKCC2 mutations.

Sox9 expression during gonadal development implies a conserved role for the gene in testis differentiation in mammals and birds

Abstract: Heterozygous mutations in SOX9 lead to a human dwarfism syndrome, Campomelic dysplasia. Consistent with a role in sex determination, we find that Sox9 expression closely follows differentiation of Sertoli cells in the mouse testis, in experimental sex reversal when fetal ovaries are grafted to adult kidneys and in the chick where there is no evidence for a Sry gene. Our results imply that Sox9 plays an essential role in sex determination, possibly immediately downstream of Sry in mammals, and that it functions as a critical Sertoli cell differentiation factor, perhaps in all vertebrates.

Involvement of mouse Mlh1 in DNA mismatch repair and meiotic crossing over.

Abstract: Mice that are deficient in either the Pms2 or Msh2 DNA mismatch repair genes have microsatellite instability and a predisposition to tumours. Interestingly, Pms2–deficient males display sterility associated with abnormal chromosome pairing in meiosis. Here mice deficient in another mismatch repair gene, Mlh1, possess not only microsatellite instability but are also infertile (both males and females). Mlh 1 –deficient spermatocytes exhibit high levels of prematurely separated chromosomes and arrest in first division meiosis. We also show that Mlh1 appears to localize to sites of crossing over on meiotic chromosomes/Together these findings suggest that Mlh1 is involved in DNA mismatch repair and meiotic crossing over.

Germline mutations in the p16INK4a binding domain of CDK4 in familial melanoma.

Abstract: Protein complexes consisting of a cyclin-dependent kinase (CDK4 or CDK6) and cyclin D control passage through the G1 checkpoint of the cell cycle by phosphorylating the retinoblastoma (RB) protein1. The ability of these complexes to phosphorylate RB is inhibited by a family of low molecular weight proteins including p16INK4a (refs 2,3), p15iNK4B (ref 4)? and p18 (ref 5) Germline mutations in the p16INK4a gene have been identified in approximately half of families with hereditary melanoma6–12. In this report, we describe an Arg24Cys mutation in CDK4 in two unrelated melanoma families which do not carry germline p16INK4a mutations6. This mutation was detected in 11/11 melanoma patients, 2/17 unaffecteds and 0/5 spouses. The CDK4-Arg24Cys substitution has previously been identified as a somatic mutation in a melanoma that gives rise to a tumour-specific antigen recognized by autologous cytolytic T lymphocytes13. This mutation has a specific effect on the p16INK4a binding domain of CDK4, but has no effect on its ability to bind cyclin D and form a functional kinase13. Therefore, the germline Arg24Cys mutation in CDK4 generates a dominant oncogene that is resistant to normal physiological inhibition by p16INK4a. The only previous example of a dominant oncogene transmitted in the human germline is the RET gene that gives rise to MEN2A14,15 and MEN2B16.

Mutations in subunits of the epithelial sodium channel cause salt wasting with hyperkalaemic acidosis, pseudohypoaldosteronism type 1

Abstract: Autosomal recessive pseudohypoaldosteronism type I is a rare life-threatening disease characterized by severe neonatal salt wasting, hyperkalaemia, metabolic acidosis, and unresponsiveness to mineralocorticoid hormones. Investigation of affected offspring of consanguineous union reveals mutations in either the alpha or beta subunits of the amiloride-sensitive epithelial sodium channel in five kindreds. These mutations are homozygous in affected subjects, co-segregate with the disease, and introduce frameshift, premature termination or missense mutations that result in loss of channel activity. These findings demonstrate the molecular basis and explain the pathophysiology of this disease.

Genetic heterogeneity of Bartter's syndrome revealed by mutations in the K+ channel, ROMK

Abstract: Mutations in the Na-K-2Cl cotransporter (NKCC2), a mediator of renal salt reabsorption, cause Bartter's syndrome, featuring salt wasting, hypokalaemic alkalosis, hypercalciuria and low blood pressure. NKCC2 mutations can be excluded in some Bartter's kindreds, prompting examination of regulators of cotransporter activity. One regulator is believed to be ROMK, an ATP-sensitive K+ channel that 'recycles' reabsorbed K+ back to the tubule lumen. Examination of the ROMK gene reveals mutations that co-segregate with the disease and disrupt ROMK function in four Bartter's kindreds. Our findings establish the genetic heterogeneity of Bartter's syndrome, and demonstrate the physiologic role of ROMK in vivo.

Identification of the spinocerebellar ataxia type 2 gene using a direct identification of repeat expansion and cloning technique, DIRECT.

Abstract: Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominant, neurodegenerative disorder that affects the cerebellum and other areas of the central nervous system. We have devised a novel strategy, the direct identification of repeat expansion and cloning technique (DIRECT), which allows selective detection of expanded CAG repeats and cloning of the genes involved. By applying DIRECT, we identified an expanded CAG repeat of the gene for SCA2. CAG repeats of normal alleles range in size from 15 to 24 repeat units, while those of SCA2 chromosomes are expanded to 35 to 59 repeat units. The SCA2 cDNA is predicted to code for 1,313 amino acids-with the CAG repeats coding for a polyglutamine tract. DIRECT is a robust strategy for identification of pathologically expanded trinucleotide repeats and will dramatically accelerate the search for causative genes of neuropsychiatric diseases caused by trinucleotide repeat expansions.

Mutations in GPC3, a glypican gene, cause the Simpson-Golabi-Behmel overgrowth syndrome

Abstract: Simpson-Golabi-Behmel syndrome (SGBS) is an X-linked condition characterized by pre- and postnatal overgrowth with visceral and skeletal anomalies. To identify the causative gene, breakpoints in two female patients with X;autosome translocations were identified. The breakpoints occur near the 5' and 3' ends of a gene, GPC3, that spans more than 500 kilobases in Xq26; in three families, different microdeletions encompassing exons cosegregate with SGBS. GPC3 encodes a putative extracellular proteoglycan, glypican 3, that is inferred to play an important role in growth control in embryonic mesodermal tissues in which it is selectively expressed. Initial western- and ligand-blotting experiments suggest that glypican 3 forms a complex with insulin-like growth factor 2 (IGF2), and might thereby modulate IGF2 action.