Advancements in AAV-mediated Gene Therapy for Pompe Disease

Pompe disease (glycogen storage disease type II) is caused by mutations in acid α-glucosidase (GAA) resulting in lysosomal pathology and impairment of the muscular and cardio-pulmonary systems. Enzyme replacement therapy (ERT), the only approved therapy for Pompe disease, improves muscle function by reducing glycogen accumulation but this approach entails several limitations including a short drug half-life and an antibody response that results in reduced efficacy. To address these limitations, new treatments such as gene therapy are under development to increase the intrinsic ability of the affected cells to produce GAA. Key components to gene therapy strategies include the choice of vector, promoter, and the route of administration. The efficacy of gene therapy depends on the ability of the vector to drive gene expression in the target tissue and also on the recipient's immune tolerance to the transgene protein. In this review, we discuss the preclinical and clinical studies that are paving the way for the development of a gene therapy strategy for patients with early and late onset Pompe disease as well as some of the challenges for advancing gene therapy.

Biochemical and pharmacological characterization of different recombinant acid alpha-glucosidase preparations evaluated for the treatment of Pompe disease

Pompe disease results in the accumulation of lysosomal glycogen in multiple tissues due to a deficiency of acid alpha-glucosidase (GAA). Enzyme replacement therapy for Pompe disease was recently approved in Europe, the U.S., Canada, and Japan using a recombinant human GAA (Myozyme, alglucosidase alfa) produced in CHO cells (CHO-GAA). During the development of alglucosidase alfa, we examined the in vitro and in vivo properties of CHO cell-derived rhGAA, an rhGAA purified from the milk of transgenic rabbits, as well as an experimental version of rhGAA containing additional mannose-6-phosphate intended to facilitate muscle targeting. Biochemical analyses identified differences in rhGAA N-termini, glycosylation types and binding properties to several carbohydrate receptors. In a mouse model of Pompe disease, glycogen was more efficiently removed from the heart than from skeletal muscle for all enzymes, and overall, the CHO cell-derived rhGAA reduced glycogen to a greater extent than that observed with the other enzymes. The results of these preclinical studies, combined with biochemical characterization data for the three molecules described within, led to the selection of the CHO-GAA for clinical development and registration as the first approved therapy for Pompe disease.

Detection and imaging of non-contractile inclusions and sarcomeric anomalies in skeletal muscle by second harmonic generation combined with two-photon excited fluorescence

The large size of the multinucleated muscle fibers of skeletal muscle makes their examination for structural and pathological defects a challenge. Sections and single fibers are accessible to antibodies and other markers but imaging of such samples does not provide a three-dimensional view of the muscle. Regrettably, bundles of fibers cannot be stained or imaged easily. Two-photon microscopy techniques overcome these obstacles. Second harmonic generation (SHG) by myosin filaments and two-photon excited fluorescence (2PEF) of mitochondrial and lysosomal components provides detailed structural information on unstained tissue. Furthermore, the infrared exciting light can penetrate several layers of muscle fibers and the minimal processing is particularly valuable for fragile biopsies. Here we demonstrate the usefulness of SHG, combined with 2PEF, to reveal enlarged lysosomes and accumulations of non-contractile material in muscles from the mouse model for the lysosomal storage disorder Pompe disease (PD), and in biopsies from adult and infant PD patients. SHG and 2PEF also detect sarcomeric defects that may presage the loss of myofibrils in atrophying muscle and signify loss of elasticity. The combination of SHG and 2PEF should be useful in the analysis and diagnosis of a wide range of skeletal muscle pathologies.

Role of autophagy in the pathogenesis of Pompe disease

In Pompe disease, a deficiency of lysosomal acid alpha-glucosidase, glycogen accumulates in multiple tissues, but clinical manifestations are mainly due to skeletal and cardiac muscle involvement. A major advance has been the development of enzyme replacement therapy (ERT), which recently became available for Pompe patients. Based on clinical and pre-clinical studies, the effective clearance of skeletal muscle glycogen appears to be more difficult than anticipated. Skeletal muscle destruction and resistance to therapy remain unsolved problems. We have found that the cellular pathology in Pompe disease spreads to affect both the endocytic and autophagic pathways, leading to excessive autophagic buildup in therapy resistant muscle fibers of knockout mice. Furthermore, the autophagic buildup had a profound effect on the trafficking and processing of the therapeutic enzyme along the endocytic pathway. These findings may explain why ERT often falls short of reversing the disease process, and point to new avenues for the development of pharmacological intervention.

Enzyme replacement therapy in the mouse model of Pompe disease

Deficiency of acid alpha-glucosidase (GAA) results in widespread cellular deposition of lysosomal glycogen manifesting as myopathy and cardiomyopathy. When GAA-/- mice were treated with rhGAA (20 mg/kg/week for up to 5 months), skeletal muscle cells took up little enzyme compared to liver and heart. Glycogen reduction was less than 50%, and some fibers showed little or no glycogen clearance. A dose of 100 mg/kg/week resulted in approximately 75% glycogen clearance in skeletal muscle. The enzyme reduced cardiac glycogen to undetectable levels at either dose. Skeletal muscle fibers with residual glycogen showed immunoreactivity for LAMP-1/LAMP-2, indicating that undigested glycogen remained in proliferating lysosomes. Glycogen clearance was more pronounced in type 1 fibers, and histochemical analysis suggested an increased mannose-6-phosphate receptor immunoreactivity in these fibers. Differential transport of enzyme into lysosomes may explain the strikingly uneven pattern of glycogen removal. Autophagic vacuoles, a feature of both the mouse model and the human disease, persisted despite glycogen clearance. In some groups a modest glycogen reduction was accompanied by improved muscle strength. These studies suggest that enzyme replacement therapy, although at much higher doses than in other lysosomal diseases, has the potential to reverse cardiac pathology and to reduce the glycogen level in skeletal muscle.

Muscle as a putative producer of acid alpha-glucosidase for glycogenosis type II gene therapy

Glycogenosis type II (GSD II) is a lysosomal disorder affecting skeletal and cardiac muscle. In the infantile form of the disease, patients display cardiac impairment, which is fatal before 2 years of life. Patients with juvenile or adult forms can present diaphragm involvement leading to respiratory failure. The enzymatic defect in GSD II results from mutations in the acid alpha-glucosidase (GAA) gene, which encodes a 76 kDa protein involved in intralysosomal glycogen hydrolysis. We previously reported the use of an adenovirus vector expressing GAA (AdGAA) for the transduction of myoblasts and myotubes cultures from GSD II patients. Transduced cells secreted GAA in the medium, and GAA was internalized by receptor-mediated capture, allowing glycogen hydrolysis in untransduced cells. In this study, using a GSD II mouse model, we evaluated the feasibility of GSD II gene therapy using muscle as a secretary organ. Adenovirus vector encoding AdGAA was injected in the gastrocnemius of neonates. We detected a strong expression of GAA in the injected muscle, secretion into plasma, and uptake by peripheral skeletal muscle and the heart. Moreover, glycogen content was decreased in these tissues. Electron microscopy demonstrated the disappearance of destruction foci, normally present in untreated mice. We thus demonstrate for the first time that muscle can be considered as a safe and easily accessible organ for GSD II gene therapy.

Conditional tissue-specific expression of the acid alpha-glucosidase (GAA) gene in the GAA knockout mice: implications for therapy

Both enzyme replacement and gene therapy of lysosomal storage disorders rely on the receptor-mediated uptake of lysosomal enzymes secreted by cells, and for each lysosomal disorder it is necessary to select the correct cell type for recombinant enzyme production or for targeting gene therapy. For example, for the therapy of Pompe disease, a severe metabolic myopathy and cardiomyopathy caused by deficiency of acid alpha-glucosidase (GAA), skeletal muscle seems an obvious choice as a depot organ for local therapy and for the delivery of the recombinant enzyme into the systemic circulation. Using knockout mice with this disease and transgenes containing cDNA for the human enzyme under muscle or liver specific promoters controlled by tetracycline, we have demonstrated that the liver provided enzyme far more efficiently. The achievement of therapeutic levels with skeletal muscle transduction required the entire muscle mass to produce high levels of enzyme of which little found its way to the plasma, whereas liver, comprising <5% of body weight, secreted 100-fold more enzyme, all of which was in the active 110 kDa precursor form. Furthermore, using tetracycline regulation, we somatically induced human GAA in the knockout mice, and demonstrated that the skeletal and cardiac muscle pathology was completely reversible if the treatment was begun early.

Identification and characterization of a tissue-specific silencer element in the first intron of the human acid maltase gene

Deficiency of acid maltase (acid alpha-glucosidase), a lysosomal enzyme that degrades glycogen, results in glycogenosis type II, an autosomal recessive disease whose manifestations and severity largely depend on the level of residual enzyme activity. Previous studies have established that there are transcriptional control elements in the first intron; in particular a silencer responsive to Hes-1 and YY1 has been identified in the human hepatoma line, HepG2. This region functions as an enhancer in human fibroblasts. Here we have localized a silencer active in fibroblasts to a nearby 25-bp element in intron 1. This element repressed thymidine kinase promoter activity by about 50% in both orientations in human fibroblasts. This silencer, as with the previous one, is tissue specific since constructs containing this region are inactive in HepG2 cells. Electrophoretic mobility shift assay revealed three proteins specifically binding to the element in fibroblasts, and site-directed mutagenesis analysis indicated that all the three proteins binding to the element contribute to the silencer function. The data may be helpful for designing therapy to increase the level of enzyme, particularly when, as in most adults with the disease, there is reduced production of structurally normal enzyme.

Surprises of genetic engineering: a possible model of polyglucosan body disease

BACKGROUND

The authors previously reported the generation of a knockout mouse model of Pompe disease caused by the inherited deficiency of lysosomal acid alpha-glucosidase (GAA). The disorder in the knockout mice (GAA-/-) resembles the human disease closely, except that the clinical symptoms develop late relative to the lifespan of the animals. In an attempt to accelerate the course of the disease in the knockouts, the authors increased the level of cytoplasmic glycogen by overexpressing glycogen synthase (GSase) or GlutI glucose transporter.

METHODS

GAA-/- mice were crossed to transgenic mice overexpressing GSase or GlutI in skeletal muscle.

RESULTS

Both transgenics on a GAA knockout background (GS/GAA-/- and GlutI/GAA-/-) developed a severe muscle wasting disorder with an early age at onset. This finding, however, is not the major focus of the study. Unexpectedly, the mice bearing the GSase transgene, but not those bearing the GlutI transgene, accumulated structurally abnormal polysaccharide (polyglucosan) similar to that observed in patients with Lafora disease, glycogenosis type IV, and glycogenosis type VII. Ultrastructurally, the periodic acid-Schiff (PAS)-positive polysaccharide inclusions were composed of short, amorphous, irregular branching filaments indistinguishable from classic polyglucosan bodies. The authors show here that increased level of GSase in the presence of normal glycogen branching enzyme (GBE) activity leads to polyglucosan accumulation. The authors have further shown that inactivation of lysosomal acid alpha-glucosidase in the knockout mice does not contribute to the process of polyglucosan formation.

CONCLUSIONS

An imbalance between GSase and GBE activities is proposed as the mechanism involved in the production of polyglucosan bodies. The authors may have inadvertently created a "muscle polyglucosan disease" by simulating the mechanism for polyglucosan formation.

Intercellular transfer of the virally derived precursor form of acid alpha-glucosidase corrects the enzyme deficiency in inherited cardioskeletal myopathy Pompe disease

Pompe disease is a lethal cardioskeletal myopathy in infants and results from genetic deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA). Genetic replacement of the cDNA for human GAA (hGAA) is one potential therapeutic approach. Three months after a single intramuscular injection of 10(8) plaque-forming units (PFU) of E1-deleted adenovirus encoding human GAA (Ad-hGAA), the activity in whole muscle lysates of immunodeficient mice is increased to 20 times the native level. Direct transduction of a target muscle, however, may not correct all deficient cells. Therefore, the amount of enzyme that can be transferred to deficient cells from virally transduced cells was studied. Fibroblasts from an affected patient were transduced with AdhGAA, washed, and plated on transwell culture dishes to serve as donors of recombinant enzyme. Deficient fibroblasts were plated as acceptor cells, and were separated from the donor monolayer by a 22-microm pore size filter. Enzymatic and Western analyses demonstrate secretion of the 110-kDa precursor form of hGAA from the donor cells into the culture medium. This recombinant, 110-kDa species reaches the acceptor cells, where it can be taken up by mannose 6-phosphate receptor-mediated endocytosis. It then trafficks to lysosomes, where Western analysis shows proteolytic processing to the 76- and 70-kDa lysosomal forms of the enzyme. Patient fibroblasts receiving recombinant hGAA by this transfer mechanism reach levels of enzyme activity that are comparable to normal human fibroblasts. Skeletal muscle cell cultures from an affected patient were also transduced with Ad-hGAA. Recombinant hGAA is identified in a lysosomal location in these muscle cells by immunocytochemistry, and enzyme activity is transferred to deficient skeletal muscle cells grown in coculture. Transfer of the precursor protein between muscle cells again occurs via mannose 6-phosphate receptors, as evidenced by competitive inhibition with 5 mM mannose 6-phosphate. In vivo studies in GAA-knockout mice demonstrate that hepatic transduction with adenovirus encoding either murine or human GAA can provide a depot of recombinant enzyme that is available to heart and skeletal muscle through this mechanism. Taken together, these data show that the mannose 6-phosphate receptor pathway provides a useful strategy for cell-to-cell distribution of virally derived recombinant GAA.

Transcriptional regulation of the human acid alpha-glucosidase gene. Identification of a repressor element and its transcription factors Hes-1 and YY1

Acid alpha-glucosidase, the product of a housekeeping gene, is a lysosomal enzyme that degrades glycogen. A deficiency of this enzyme is responsible for a recessively inherited myopathy and cardiomyopathy, glycogenesis type II. We have previously demonstrated that the human acid alpha-glucosidase gene expression is regulated by a silencer within intron 1, which is located in the 5'-untranslated region. In this study, we have used deletion analysis, electrophoretic mobility shift assay, and footprint analysis to further localize the silencer to a 25-base pair element. The repressive effect on the TK promoter was about 50% in both orientations in expression plasmid, and two transcriptional factors were identified with antibodies binding specifically to the element. Mutagenesis and functional analyses of the element demonstrated that the mammalian homologue 1 of Drosophila hairy and Enhancer of split (Hes-1) binding to an E box (CACGCG) and global transcription factor-YY1 binding to its core site function as a transcriptional repressor. Furthermore, the overexpression of Hes-1 significantly enhanced the repressive effect of the silencer element. The data should be helpful in understanding the expression and regulation of the human acid alpha-glucosidase gene as well as other lysosomal enzyme genes.

Correction of glycogen storage disease type II by enzyme replacement with a recombinant human acid maltase produced by over-expression in a CHO-DHFR(neg) cell line

Inherited genetic deficiency of lysosomal acid alpha glucosidase or acid maltase (GAA) results in the autosomal recessive glycogen storage disease type II (GSD II). To investigate whether we could generate a functional recombinant human GAA (rhGAA) for enzyme replacement therapy, we subcloned the cDNAs for human GAA and mouse dihydrofolate reductase (DHFR) into DHFR(neg) Chinese hamster ovary cells and established a stable cotransformant that expressed rhGAA. We cultured the recombinant cells in media with progressively increasing concentrations of methotrexate and found that human GAA enzyme activity increased to over 2,000 IU per gram protein. Importantly, the human GAA enzyme activity correlated to equivalent amounts of human GAA protein by rocketimmunoelectrophoresis. We confirmed that the human GAA enzyme activity corresponded to an amplification in human GAA mRNA by Northern analysis and human GAA cDNA copy number by Southern analysis. Exposing the rhGAA to human GSDII fibroblast cells or patient's lymphocytes or monocytes resulted in uptake of the rhGAA and reversal of the enzymatic defect. Mannose-6-phosphate in the media blocked uptake. GAA -/- mice were treated with the rhGAA at 1 mg/kg, which resulted in heterozygous levels of GAA in tissues, most notably skeletal muscle, heart and diaphragm after two infusions. More importantly, after multiple infusions, hind, and fore-limb muscle weakness was reversed. This rhGAA would be ideal for enzyme replacement therapy in GSD II.

Molecular scanning for mutations in the insulin receptor substrate-1 (IRS-1) gene in Mexican Americans with Type 2 diabetes mellitus

BACKGROUND

Insulin receptor substrate-1 (IRS-1) is an endogenous substrate for the insulin receptor tyrosine kinase, which plays an important role in insulin signaling. Mutations in the IRS-1 gene are associated in some populations with obesity and Type 2 diabetes.

METHODS

To determine whether variation in the IRS-1 gene contributes to genetic susceptibility to insulin resistance and Type 2 diabetes in Mexican Americans, the entire coding region of the IRS-1 gene was screened for variation in 31 unrelated subjects with Type 2 diabetes using single-stranded conformational polymorphism analysis (SSCP) and dideoxy sequence analysis. Variants encoding amino acid substitutions were genotyped in 27 unrelated nondiabetic Mexican Americans and in all family members of subjects containing these variants, and association analyses were performed. To trace the ancestral origins of the variants, Iberian Caucasians and Pima Indians were also genotyped.

RESULTS

Eight single base changes were found: four silent polymorphisms and four missense mutations (Ala94Thr, Ala512Pro, Ser892Gly and Gly971Arg). Allele frequencies were 0.009, 0.017, 0.017 and 0.043, respectively. There were no significant associations of any of these variants with diabetes, glucose or insulin levels during an oral glucose tolerance test, or with body mass index (BMI) in Mexican American families except for a modest association between the Ala94Thr variant and decreased BMI (30.4 kg/m(2) vs 24.0 kg/m(2); p=0.035). None of these four missense mutations were detected in Pima Indians. In Iberian Caucasians, neither Ala94Thr nor Ser892Gly were detected, and Ala512Pro was detected in only 0/60 diabetic patients and 1/60 nondiabetic controls. Gly971Arg was relatively more common in Iberian Caucasians with 12/58 diabetic patients and 7/60 nondiabetic controls being heterozygous for this variant (p=0.21 for comparison between diabetic and nondiabetic subjects).

CONCLUSIONS

Ala94Thr, Ala512Pro and Ser892Gly mutation are rare in the populations studied. Gly971Arg, is more common in Mexican Americans and Caucasians, but is not a major contributor to genetic susceptibility to Type 2 diabetes.

Conditional up-regulation of MHC class I in skeletal muscle leads to self-sustaining autoimmune myositis and myositis-specific autoantibodies

In the human inflammatory myopathies (polymyositis and dermatomyositis), the early, widespread appearance of MHC class I on the surface of muscle cells and the occurrence of certain myositis-specific autoantibodies are striking features. We have used a controllable muscle-specific promoter system to up-regulate MHC class I in the skeletal muscles of young mice. These mice develop clinical, biochemical, histological, and immunological features very similar to human myositis. The disease is inflammatory, limited to skeletal muscles, self-sustaining, more severe in females, and often accompanied by autoantibodies, including, in some mice, autoantibodies to histidyl-tRNA synthetase, the most common specificity found in the spontaneous human disease, anti-Jo-1. This model suggests that an autoimmune disease may unfold in a highly specific pattern as the consequence of an apparently nonspecific event-the sustained up-regulation of MHC class I in a tissue-and that the specificity of the autoantibodies derives not from the specificity of the stimulus, but from the context, location, and probably the duration of the stimulus. This model further suggests that the presumed order of events as an autoimmune disease develops needs to be reconsidered.

Glycogenosis type II: a juvenile-specific mutation with an unusual splicing pattern and a shared mutation in African Americans

The recessively inherited deficiency of acid alpha-glucosidase (GAA) called Glycogenosis Type II is expressed as three different phenotypes: infantile, juvenile, and adult. At the molecular level, infantile and adult forms of the disease have been extensively studied, but little is known regarding the genetic defects associated with the juvenile form. We describe a novel mutation that defines the intermediate juvenile phenotype in a compound heterozygous patient. A transversion of t to g in intron 6 at position -22 creates a cryptic acceptor site and results in unusual splicing abnormality: insertion of 21 nucleotides of the intronic sequence into mRNA and removal of exon 6 without disruption of the reading frame. The second mutation, Arg854Stop in exon 18, had been previously identified in another African-American patient (Hermans et al., 1993a). Family study indicates that a silent allele harboring the Arg854Stop mutation in our patient is inherited from the patient's father, who is also African-American, thus suggesting a common mutation in this population.

Novel mutations in African American patients with glycogen storage disease Type II. Mutations in brief no. 209. Online

The infantile form of GSD II (an inherited deficiency of the lysosomal enzyme, acid alpha-glucosidase, Pompe disease) is a severe and invariably fatal disease characterized by a rapidly progressive generalized hypotonia, hepatomegaly, and cardiomegaly. We have recently demonstrated that African American patients share a common nonsense R854X mutation in exon 18 (Becker et al., 1998). Two other mutations, D645E and M519V, have been identified in individual African American patients (Hermans et al., 1993a; Huie et al., 1994a). We describe here three novel mutations in this population group: a missense W481R in exon 10, a deletion of a T1441 in exon 10, and a splicing defect at the 5' donor site of intron 8 (IVS g+la) . The splicing defect is shared by two unrelated patients and it is linked to intragenic polymorphic sites identical to those found in patients bearing the common R854X mutation.

Modulation of disease severity in mice with targeted disruption of the acid alpha-glucosidase gene

Glycogen storage disease type II (GSDII) is a recessively inherited disorder caused by defects in lysosomal acid alpha-glucosidase. In an attempt to reproduce the range of clinical manifestations of the human illness we have created null alleles at the acid alpha-glucosidase locus (GAA) with several gene targeting strategies. In each knockout strain, enzyme activity was completely abolished and glycogen accumulated at indistinguishable rates. The phenotypes, however, differed strikingly. Acid alpha-glucosidase deficiency on a 129xC57BL/6 background resulted in a severe phenotype with progressive cardiomyopathy and profound muscle wasting similar to that in patients with glycogen storage disease type II. On a 129/C57BL/6xFVB background, homozygous mutants developed a milder phenotype with a later age of onset. Females were more affected than males irrespective of genetic background. As in humans with glycogen storage disease type II, therefore, other genetic loci affect the phenotypic expression of a single gene mutation.

Systemic correction of the muscle disorder glycogen storage disease type II after hepatic targeting of a modified adenovirus vector encoding human acid-alpha-glucosidase

This report demonstrates that a single intravenous administration of a gene therapy vector can potentially result in the correction of all affected muscles in a mouse model of a human genetic muscle disease. These results were achieved by capitalizing both on the positive attributes of modified adenovirus-based vectoring systems and receptor-mediated lysosomal targeting of enzymes. The muscle disease treated, glycogen storage disease type II, is a lysosomal storage disorder that manifests as a progressive myopathy, secondary to massive glycogen accumulations in the skeletal and/or cardiac muscles of affected individuals. We demonstrated that a single intravenous administration of a modified Ad vector encoding human acid alpha-glucosidase (GAA) resulted in efficient hepatic transduction and secretion of high levels of the precursor GAA proenzyme into the plasma of treated animals. Subsequently, systemic distribution and uptake of the proenzyme into the skeletal and cardiac muscles of the GAA-knockout mouse was confirmed. As a result, systemic decreases (and correction) of the glycogen accumulations in a variety of muscle tissues was demonstrated. This model can potentially be expanded to include the treatment of other lysosomal enzyme disorders. Lessons learned from systemic genetic therapy of muscle disorders also should have implications for other muscle diseases, such as the muscular dystrophies.

Costimulatory markers in muscle of patients with idiopathic inflammatory myopathies and in cultured muscle cells

In an attempt to understand the mechanisms of cell injury in the inflammatory myopathies, we analyzed the expression of costimulatory molecules, CTLA4, CD28, CD86, CD40, and CD154 as well as HLA class I, HLA class II, and ICAM-I in normal muscle and in muscle biopsies from patients with polymyositis (PM) or dermatomyositis (DM). By immunohistochemical staining, DM and PM biopsies showed the presence of CTLA4, CD28, CD86, and CD40 on inflammatory cells. More strikingly, however, low levels of CTLA4 and CD28 were observed on muscle cells. The expression of CTLA4 and CD28 on nonlymphoid cells has not been previously reported. These unexpected findings were confirmed in cultured normal human myoblasts: various proinflammatory cytokines induced the expression of CTLA4 and CD28 on normal human muscle cells. The sequences of the cDNAs were found to be identical to the sequences for these molecules in T cells. The data suggest a novel complexity in the network of cellular interactions between the infiltrated immune cells and the muscle cells in which the normal relationship between infiltrating inflammatory cells and target tissue is under a previously unrecognized set of controls.

Molecular scanning of the beta-3-adrenergic receptor gene in Pima Indians and Caucasians

BACKGROUND

The beta-3-adrenergic receptor (beta3AR) stimulates lipolysis and thermogenesis in adipocytes. The Trp64Arg beta3AR variant is associated in some, but not all, studies with an earlier onset of Type 2 diabetes mellitus and features of the insulin resistance syndrome. Functional studies as to the role of the Trp64Arg variant have been inconclusive. Earlier studies screened the beta3AR gene in only ten obese, diabetic Pima Indians. Potentially another yet to be identified polymorphism in the beta3AR gene in linkage disequilibrium with the Trp64Arg polymorphism could explain the findings in the association and functional studies.

METHODS

We scanned the beta3AR gene in 20 diabetic Pima subjects and 20 Caucasian subjects using single stranded conformational polymorphism (SSCP) analysis. Variants were sequenced using dideoxy sequence analysis and further characterized using allele specific oligonucleotide hybridization (ASO) and RNA template specific-polymerase chain reaction (RS-PCR) assays.

RESULTS

We found a guanine to thymidine substitution in the first intron, 14 bases from the splice donor site in both groups. In virtually all subjects, only two haplotypes were detected, Trp64/g1856 and Arg64/t1856, indicating that the g1856t polymorphism is in linkage disequilibrium with the Trp64Arg polymorphism. The g1856t substitution introduces a new consensus splice donor site which, if used, would encode a truncated protein. RNA levels of the two beta3AR alleles were approximately equal in omental adipose tissue of heterozygotes. No aberrantly spliced beta3AR mRNA was detected, indicating that the new consensus splice donor site is not used in vivo.

CONCLUSION

The g1856t polymorphism is in linkage disequilibrium with the Trp64Arg variant, but does not appear to have a functional role.

A variety of cytokines and immunologically relevant surface molecules are expressed by normal human skeletal muscle cells under proinflammatory stimuli

Muscle is an attractive target for gene therapy and for immunization with DNA vaccines and is also the target of immunological injury in myositis. It is important therefore to understand the immunologic capabilities of muscle cells themselves. In this study, we show that proinflammatory stimuli induce the expression of other cytokines such as IL-6, transforming growth factor-beta (TGF-beta), and granulocyte-macrophage colony-stimulating factor (GM-CSF) by muscle cells themselves, as well as the up-regulation of human leucocyte antigen (HLA) class I, class II and intercellular adhesion molecule-1 (ICAM-1). Thus, muscle cells have an inherent ability to express and respond to a variety of cytokines and chemokines. The levels of HLA class I, class II and ICAM-1 in inflamed muscle may be affected by the secreted products of the stimulation.

Targeted disruption of the acid alpha-glucosidase gene in mice causes an illness with critical features of both infantile and adult human glycogen storage disease type II

We have used gene targeting to create a mouse model of glycogen storage disease type II, a disease in which distinct clinical phenotypes present at different ages. As in the severe human infantile disease (Pompe Syndrome), mice homozygous for disruption of the acid alpha-glucosidase gene (6(neo)/6(neo)) lack enzyme activity and begin to accumulate glycogen in cardiac and skeletal muscle lysosomes by 3 weeks of age, with a progressive increase thereafter. By 3.5 weeks of age, these mice have markedly reduced mobility and strength. They grow normally, however, reach adulthood, remain fertile, and, as in the human adult disease, older mice accumulate glycogen in the diaphragm. By 8-9 months of age animals develop obvious muscle wasting and a weak, waddling gait. This model, therefore, recapitulates critical features of both the infantile and the adult forms of the disease at a pace suitable for the evaluation of enzyme or gene replacement. In contrast, in a second model, mutant mice with deletion of exon 6 (Delta6/Delta6), like the recently published acid alpha-glucosidase knockout with disruption of exon 13 (Bijvoet, A. G., van de Kamp, E. H., Kroos, M., Ding, J. H., Yang, B. Z., Visser, P., Bakker, C. E., Verbeet, M. P., Oostra, B. A., Reuser, A. J. J., and van der Ploeg, A. T. (1998) Hum. Mol. Genet. 7, 53-62), have unimpaired strength and mobility (up to 6.5 months of age) despite indistinguishable biochemical and pathological changes. The genetic background of the mouse strains appears to contribute to the differences among the three models.

Myositis induced by naked DNA immunization with the gene for histidyl-tRNA synthetase

Polymyositis is regarded as an autoimmune inflammatory muscle disease. A major subgroup of patients have autoantibodies to cellular histidyl-transfer RNA synthetase (HRS). We have analyzed the role of the autoantigen HRS in the induction of murine myositis in a comparative study of inoculation of BALB/c mice with recombinant HRS protein versus naked DNA coding for HRS. Adult BALB/c mice produced antibodies to human HRS following inoculation with HRS protein and adjuvant, but myositis was not observed. Alternatively, expression plasmid DNA constructs encoding full-length and truncated human HRS were inoculated intramuscularly in gene transfer studies. DNA-inoculated mice produced relatively low anti-HRS antibody titers. However, in contrast to recombinant HRS protein-inoculated mice, HRS gene transfer induced pathology with evidence of cellular infiltration of perivascular and endomysial regions of the inoculated muscle. Multiple inoculations of a plasmid construct encoding a hybrid molecule consisting of HRS and the transferrin receptor cytoplasmic tail induced the highest levels of antibodies and persisting cellular infiltration. Unlike HRS, expression of influenza virus hemagglutinin (HA) following inoculation of an HA plasmid did not induce myositis. Transfer of naked DNA constructs expressing HRS is likely to provide valuable information on the autoimmune response to this protein and its role in the development of myositis.

Genomic organization of SLC3A1, a transporter gene mutated in cystinuria

The SLC3A1 gene encodes a transport protein for cystine and the dibasic amino acids. Recently mutations in this gene have been shown to cause cystinuria. We report the genomic structure and organization of SLC3A1, which is composed of 10 exons and spans nearly 45 kb. Until now screening for mutations in SLC3A1 has been based on RT-PCR amplification of illegitimate mRNA transcripts from white blood cells. In this report we provide primers for amplification of exons from genomic DNA, thus simplifying the process of screening for SLC3A1 mutations in cystinuria.

Glycogenosis type VII (Tarui disease) in a Swedish family: two novel mutations in muscle phosphofructokinase gene (PFK-M) resulting in intron retentions

Phosphofructokinase (PFK) plays a major role in glycolysis. Human PFK is composed of three isoenzyme subunits (muscle [Ml, liver [L], and platelet [P]), which are encoded by different genes. Deficiency of muscle isoenzyme (PFK-M), glycogenosis type VII (Tarui disease), is an autosomal recessive disorder characterized by an exertional myopathy and hemolytic syndrome. Several disease-causing mutations have been identified in the PFK-M gene in Japanese, Ashkenazi Jewish, Italian, French Canadian, and Swiss patients. We describe the genetic defect in a Swedish family with affected individuals in two generations. The patients are compound heterozygotes: two different mutations result in retention of intron 13 or intron 16 sequences into mRNA. A G1127A transition destroys the 5' donor site of intron 13, resulting in a 155-nt retention of the intronic sequence. An a-to-g base change in intron 16 creates a new acceptor splice site, resulting in a 63-nt retention of intronic sequence. Both mutations are predicted to result in premature termination of translation. Some of the transcripts generated from the intron 16 mutated allele also contain intron 10 sequence unspliced.

A model of mRNA splicing in adult lysosomal storage disease (glycogenosis type II)

Glycogenosis type II is a recessively inherited disorder caused by mutations in the acid maltase (GAA) gene. Clinically, three different phenotypes are recognized: Infantile, juvenile and adult forms. A majority of compound heterozygous adult-onset patients carry a t-13g mutation in intron 1 associated with splicing out the first coding exon (exon 2). We have studied the mechanism of this mutation in a model system with wild-type and mutant minigenes expressed in a GAA deficient cell line. We have demonstrated that the mutation does not prevent normal splicing; low levels of correctly spliced mRNA are generated with the mutant construct. The data explain why the mutation is restricted to a milder, adult-onset phenotype. We also demonstrate that splicing out of exon 2 occurs with the wild-type construct, and thus represents alternative splicing which takes place in normal cells. Three splice variants (SV1, SV2 and SV3) are made with both the mutant and the wild-type constructs. Furthermore, as shown by RNAse protection assay, these mRNA variants are less abundant with the mutant construct. Thus, a major effect of the mutation appears to be a low splicing efficiency, since the total amount of all the transcripts generated from the mutant construct is reduced compared with the wild type. The removal of approximately 90% of the intron 1 (2.6 kb) sequence resulted in a dramatic increase in the levels of correctly spliced mRNA, indicating that the intron may contain a powerful transcriptional repressor.

Time of onset of non-insulin-dependent diabetes mellitus and genetic variation in the beta 3-adrenergic-receptor gene

BACKGROUND

The beta 3-adrenergic receptor is expressed in visceral adipose tissue and is thought to contribute to the regulation of the resting metabolic rate and lipolysis.

METHODS

To investigate whether mutations in the gene for the beta 3-adrenergic receptor predispose patients to obesity and non-insulin-dependent diabetes mellitus (NIDDM), we studied this gene in 10 Pima Indians by analysis of single-stranded conformational polymorphisms and dideoxy sequence analysis. Association studies were performed in 642 Pima subjects (390 with NIDDM and 252 without NIDDM).

RESULTS

A missense mutation was identified in the gene for the beta 3-adrenergic receptor that results in the replacement of tryptophan by arginine (Trp64Arg) in the first intracellular loop of the receptor. This mutation was detected with allelic frequencies of 0.31 in Pima Indians, 0.13 in 62 Mexican Americans, 0.12 in 49 blacks, and 0.08 in 48 whites in the United States. Among Pimas, the frequency of the Trp64Arg mutation was similar in nondiabetic and diabetic subjects. However, in subjects homozygous for the mutation the mean (+/- SD) age at the onset of NIDDM was significantly lower (36 +/- 10 years) than in Trp64Arg heterozygotes (40 +/- 10 years) or normal homozygotes (41 +/- 11 years; P = 0.02). Furthermore, subjects with the mutation tended to have a lower adjusted resting metabolic rate (P = 0.14 by analysis of covariance).

CONCLUSIONS

Pima subjects homozygous for the Trp64Arg beta 3-adrenergic-receptor mutation have an earlier onset of NIDDM and tend to have a lower resting metabolic rate. This mutation may accelerate the onset of NIDDM by altering the balance of energy metabolism in visceral adipose tissue.

Mutations in the SLC3A1 transporter gene in cystinuria

Cystinuria is an autosomal recessive disease characterized by the development of kidney stones. Guided by the identification of the SLC3A1 amino acid-transport gene on chromosome 2, we recently established genetic linkage of cystinuria to chromosome 2p in 17 families, without evidence for locus heterogeneity. Other authors have independently identified missense mutations in SLC3A1 in cystinuria patients. In this report we describe four additional cystinuria-associated mutations in this gene: a frameshift, a deletion, a transversion inducing a critical amino acid change, and a nonsense mutation. The latter stop codon was found in all of eight Ashkenazi Jewish carrier chromosomes examined. This report brings the number of disease-associated mutations in this gene to 10. We also assess the frequency of these mutations in our 17 cystinuria families.

A novel gene oriented in a head-to-head configuration with the human histidyl-tRNA synthetase (HRS) gene encodes an mRNA that predicts a polypeptide homologous to HRS

The human histidyl-tRNA synthetase (HRS) gene encodes an enzyme that catalyzes the esterification of histidine to its cognate tRNA as an early step in protein biosynthesis. Previous reports have described a bidirectional promoter element which coordinates the transcription of both HRS and an unknown mRNA whose gene is oriented in a head-to-head configuration with HRS. We have isolated and characterized a human genomic DNA clone that encodes portions of these oppositely transcribed mRNAs and a putatively full-length cDNA clone (HO3) corresponding to the gene mapping immediately 5' of HRS. The largest open reading frame within HO3 (1518 bp) shares approximately 75% nucleotide sequence identity with human HRS (1527 bp) and predicts a polypeptide with extensive amino acid sequence homology with the HRS protein (72%). Moreover, amino acid sequence motifs characteristic of class II aminoacyl-tRNA synthetases are conserved within HO3. Despite their similarity, HRS and HO3 have divergent amino-terminal domains which correspond to the first two exons of each gene. RNA blot analysis revealed that HRS (2.0 kb) and HO3 (2.5 kb) exhibit distinct patterns of steady-state mRNA expression among multiple human tissues.

NIH conference. Myositis: immunologic contributions to understanding cause, pathogenesis, and therapy

The myositis syndromes, the most common forms of which are polymyositis and dermatomyositis, are defined by idiopathic chronic inflammation in skeletal muscle. Although initially described more than a century ago, these diseases are so rare and heterogeneous that we have only a limited understanding of their causes and treatment. Recently, autoimmune responses to nuclear and cytoplasmic autoantigens that are unique to patients with myositis, the myositis-specific autoantibodies, have proved clinically useful in helping predict signs and symptoms of myositis, immunogenetics, responses to therapy, and prognosis. We summarize this new information on the variety and nature of these autoantibodies, their target epitopes, and their possible use in identifying causes, pathogenetic mechanisms, and better therapies for these increasingly recognized disorders.

Human isoleucyl-tRNA synthetase: sequence of the cDNA, alternative mRNA splicing, and the characteristics of an unusually long C-terminal extension

The human isoleucyl-tRNA synthetase (IRS)-encoding cDNA, whose primary structure we report here, has an open reading frame (ORF) which encodes a protein of 1262 amino acids (aa) with strong homology to IRS from yeast (53.5%) and Tetrahymena (51.0%) and contains all the major consensus motifs of class-I hydrophobic amino-acyl-tRNA synthetases (aaRS; MRS, LRS, VRS, IRS). However, the human enzyme has an unusually long C-terminal extension composed, in part, of a twice-repeated motif which shows no homology to any reported protein. We also report the presence of a coiled-coil-like motif in the C-terminal half of the protein. The mRNA has an additional exon in the 5'-untranslated region (UTR) which is alternatively spliced, giving rise to two types of mRNA, both of which are expressed in several human tissues. The longer of the two transcripts contains predicted secondary structure in the 5'-UTR which may reduce the translational efficiency of this mRNA. Two possible regulatory elements in the 5'-UTR, an interferon-stimulated response element (ISRE)-like sequence and a short ORF, have been identified. Because human IRS has previously been shown to be the target of antibodies in autoimmune disease, we discuss the role of protein structural features in the development of an autoimmune response to IRS.

Leaky splicing mutation in the acid maltase gene is associated with delayed onset of glycogenosis type II

An autosomal recessive deficiency of acid alpha-glucosidase (GAA), type II glycogenosis, is genetically and clinically heterogeneous. The discovery of an enzyme-inactivating genomic deletion of exon 18 in three unrelated genetic compound patients--two infants and an adult--provided a rare opportunity to analyze the effect of the second mutation in patients who displayed dramatically different phenotypes. A deletion of Lys-903 in one patient and a substitution of Arg for Leu-299 in another resulted in the fatal infantile form. In the adult, a T-to-G base change at position -13 of intron 1 resulted in alternatively spliced transcripts with deletion of exon 2, the location of the start codon. The low level of active enzyme (12% of normal) generated from the leakage of normally spliced mRNA sustained the patient to adult life.

Functional expression of human mutant phosphofructokinase in yeast: genetic defects in French Canadian and Swiss patients with phosphofructokinase deficiency

Human phosphofructokinase (PFK) is a tetrameric enzyme, encoded by muscle, liver, and platelet genes. Deficiency of muscle PFK (PFK-M), glycogenosis type VII (Tarui disease), is an autosomal recessive disorder characterized by an exertional myopathy and hemolytic syndrome. Several disease-causing mutations have been identified in the PFK-M gene in Japanese, Ashkenazi Jewish, and Italian patients. We describe the genetic defects in French Canadian and Swiss patients with the disease, and we use a genetically well-defined yeast system devoid of endogenous PFK for structure-function studies of the mutant PFKs. A G-to-A transition at codon 209-in exon 8 of the PFK-M gene, changing an encoded Gly to Asp, is responsible for the disease in a homozygous French Canadian patient. Gly-209-mutated protein is completely inactive in the yeast system. The Swiss patient is a genetic compound, carrying a G-to-A transition at codon 100 in exon 6 (Arg to Gln) and a G-to-A transition at codon 696 in exon 22 (Arg to His). The mutants expressed in yeast generate functional enzyme with modest changes in thermal stability. The advantages and limitations of the yeast system for expression of human mutant PFKs are discussed.

Genetic defects in patients with glycogenosis type II (acid maltase deficiency)

Inherited deficiency of acid alpha-glucosidase (acid maltase, GAA) leads to glycogen storage disease type II. Clinical manifestations and prognosis of the disease depend on the age of onset and tissue involvement. GAA deficiency is extremely heterogeneous, ranging from a rapidly progressive fatal infantile-onset form to a slowly progressive adult-onset myopathy associated with respiratory insufficiency. Biochemical and immunochemical studies of the biosynthesis of the enzyme in GAA-deficient patients established the molecular diversity of the disease. Cloning and sequencing of the cDNA and the gene provided the basis for genetic analysis of the patients with different phenotypes. In this article, we summarize the data on mutations in the GAA gene and discuss the correlation between the genotype and phenotypic expression of the disease.

Mutations in muscle phosphofructokinase gene

Mutations in the muscle phosphofructokinase gene (PFK-M) result in a metabolic myopathy characterized by exercise intolerance and compensated hemolysis. PFK deficiency, glycogenosis type VII (Tarui disease) is a rare, autosomal, recessively inherited disorder. Multiple mutations, including splicing defects, frameshifts, and missense mutations, have recently been identified in patients from six different ethnic backgrounds establishing genetic heterogeneity of the disease. There is no obvious correlation between the genotype and phenotypic expression of the disease. PFK-M deficiency appears to be prevalent among people of Ashkenazi Jewish descent. Molecular diagnosis is now feasible for Ashkenazi patients who share two common mutations in the gene; the more frequent is an exon 5 splicing defect, which accounts for approximately 68% of mutant alleles in this population.

Various classes of mutations in patients with phosphofructokinase deficiency (Tarui's disease)

Muscle phosphofructokinase (PFK-M) deficiency (glycogenosis type VII, Tarui's disease) is characterized by intolerance to vigorous exercise, often accompanied by myoglobinuria. The disease is inherited as an autosomal recessive trait. The clinical manifestations are similar to those in myophosphorylase deficiency (McArdle's disease), and the diagnosis required demonstration of the enzyme defect in muscle biopsy. In the Western hemisphere PFK deficiency appears to be prevalent among people of Ashkenazi Jewish descent. To define the molecular basis of this myopathy, we have studied 11 Ashkenazi and 2 non-Ashkenazi families with the disease. Ashkenazi patients share two common pathogenic mutations, a splicing defect and a nucleotide deletion, which account for approximately 95% of mutant alleles. The molecular diagnosis is now possible in this population by using simple PCR-based tests to screen for these mutations.

A motif in human histidyl-tRNA synthetase which is shared among several aminoacyl-tRNA synthetases is a coiled-coil that is essential for enzymatic activity and contains the major autoantigenic epitope

In myositis, disease-specific autoantibodies may be directed against an aminoacyl-tRNA synthetase, usually histidyl-tRNA synthetase. To explore the basis for this phenomenon, we have made recombinant histidyl-tRNA synthetase in the baculovirus system. It was enzymatically active and recognized by human autoantibodies. A truncated protein lacking the first 60 amino acids was inactive as an antigen and as an enzyme. This region is within the first two exons, is predicted to have a coiled-coil configuration, and is found in some other synthetases but not in Escherichia coli or yeast histidyl-tRNA synthetase. Circular dichroism showed that the peptides from this region (amino acids 1-60 and 1-47) have the predicted high alpha-helical content, but smaller fragments (1-30, 14-45, and 31-60) do not. The peptides with a high alpha-helical content could inhibit autoantibodies almost completely, whereas the smaller peptides were unable to do so. The amino acid sequence of this coiled-coil domain in human histidyl-tRNA synthetase resembles the sequence of the extended this coiled-coil arm near the NH2 terminus of bacterial seryl-tRNA synthetase as well as similar regions in some eukaryotic aminoacyl-tRNA synthetases, raising the possibility that this domain serves a similar tRNA-stabilizing role and has been preserved from a common ancestor.

Common mutations in the phosphofructokinase-M gene in Ashkenazi Jewish patients with glycogenesis VII--and their population frequency

Phosphofructokinase (PFK) catalyzes the rate-limiting step of glycolysis. Deficiency of the muscle enzyme is manifested by exercise intolerance and a compensated hemolytic anemia. Case reports of this autosomal recessive disease suggest a predominance in Ashkenazi Jews in the United States. We have explored the genetic basis for this illness in nine affected families and surveyed the normal Ashkenazi population for the mutations we have found. Genomic DNA was amplified using PCR, and denaturing gradient-gel electrophoresis was used to localize exons with possible mutations. The polymorphic exons were sequenced or digested with restriction enzymes. A previously described splicing mutation, delta 5, accounted for 11 (61%) of 18 abnormal alleles in the nine families. A single base deletion leading to a frameshift mutation in exon 22 (delta C-22) was found in six of seven alleles. A third mutation, resulting in a nonconservative amino acid substitution in exon 4, accounted for the remaining allele. Thus, three mutations could account for all illness in this group, and two mutations could account for 17 of 18 alleles. In screening 250 normal Ashkenazi individuals for all three mutations, we found only one delta 5 allele. Clinical data revealed no correlation between the particular mutations and symptoms, but male patients were more symptomatic than females, and only males had frank hemolysis and hyperuricemia. Because PFK deficiency in Ashkenazi Jews is caused by a limited number of mutations, screening genomic DNA from peripheral blood for the described mutations in this population should enable rapid diagnosis without muscle biopsy.

Late-onset muscular weakness in phosphofructokinase deficiency due to exon 5/intron 5 junction point mutation: a unique disorder or the natural course of this glycolytic disorder?

Late-onset muscle weakness is rare in glycolytic disorders. There are two reports in the literature of phosphofructokinase (PFK)-deficient Ashkenazi Jews with severe vacuolar myopathy manifesting in late adulthood. The genetic abnormality in these patients is unknown. We report a third patient with a similar syndrome: early-onset exercise intolerance in young childhood and progressive weakness in a limb-girdle distribution appearing at 57 years of age, leading to severe incapacity. Muscle histology showed diffuse vacuolar changes, and muscle fibers contained excess glycogen-like material. Muscle biochemistry was diagnostic for PFK deficiency. DNA analysis from the patient and his family showed that he was homozygous for a recently identified point mutation at the exon 5/intron 5 junction (a G-to-A change); two other family members were heterozygous for this mutation. It is not clear whether late-onset weakness is the natural course for all PFK-deficient patients or whether the exon 5 mutation carries increased risk for this severe myopathy.

The cDNAs encoding two forms of the LYN protein tyrosine kinase are expressed in rat mast cells and human myeloid cells

Two isoforms of lck/yes-related novel (LYN) protein tyrosine kinase (PTK) appear to play a role in B-cell-IgM and FcERI receptor signaling. The cDNAs lynA and lynB encoding these two forms were isolated and sequenced; they were derived from rat mucosal mast cell and human myeloid cell lines. The nucleotide (nt) and deduced amino acid (aa) sequences share 94 and 97% identity between rat and mouse lyn, respectively, and 88 and 96% identity between rat and human lyn. In all three species, a region of 20 aa is uniformly inserted at an identical site and its sequence is highly conserved. This suggests an important regulatory role for this region mediated by this PTK.

A 5' splice junction mutation leading to exon deletion in an Ashkenazic Jewish family with phosphofructokinase deficiency (Tarui disease)

A deficiency of the muscle isoform of the enzyme, phosphofructokinase (PFK, EC 2.7.1.11), leads to an illness (glycogenosis, Type VII) characterized by myopathy and hemolysis. A patient with this disease and an affected sister were found to have a G to A substitution at the 5' donor site of intron 5 of the PFK-M gene. This mutation led to a splicing defect: a complete deletion of the preceding exon in the patient's mRNA. The patient, an affected sister, and related and unrelated family members, who were of Ashkenazic Jewish background, were screened for the mutation by denaturing gradient gel electrophoresis and by allele specific hybridization of genomic DNA. The affected sisters are homozygous for the mutation, and their children, who are unaffected, are heterozygous. The only previously characterized genetic defect in this disease, found in a Japanese patient, was a G to T mutation at the beginning of intron 15 with splicing to a cryptic site within exon 15 (1). Both mutations lead to inframe deletions, but of different parts of the protein. The differences between the two aberrant proteins may account for clinical differences between our patients and the Japanese patient.

Detection of mutations in insulin receptor gene by denaturing gradient gel electrophoresis

Denaturing gradient gel electrophoresis (DGGE) has been used to screen for mutations in the insulin receptor gene. Each of the 22 exons was amplified by the polymerase chain reaction (PCR). For each exon, one of the two PCR primers contained a guanine-cytosine (GC) clamp at its 5' end. The DNA was analyzed by electrophoresis through a polyacrylamide gel containing a gradient of denaturants. Two geometries for the gels were compared; the gradient of denaturants was oriented either parallel or perpendicular to the electric field. The sensitivity of the technique was evaluated by determining whether DGGE succeeded in detecting known mutations and polymorphisms in the insulin receptor gene. With parallel gels, 12 of 16 sequence variants were detected. The use of perpendicular gels increased the sensitivity of detection so that all 16 sequence variants were successfully detected when DNA was analyzed by a combination of perpendicular and parallel gels. Furthermore, DGGE was used to investigate a patient with leprechaunism whose insulin receptor genes had not previously been studied. Two mutant alleles were identified in this patient. The allele inherited from the father had a mutation substituting alanine for Val-28; in the allele inherited from the mother, arginine was substituted for Gly-366.

Human histidyl-tRNA synthetase: recognition of amino acid signature regions in class 2a aminoacyl-tRNA synthetases

We have determined the sequence of cDNA for the human histidyl-tRNA synthetase (HRS) in a hepatoma cell line and confirmed it in fetal myoblast and fibroblast cell lines. The newly determined sequence differs in 48 places, including insertions and deletions, from a previously published sequence. By sequence specific probing and by direct sequencing, we have established that only the newly determined sequence is present in genomic DNA and we have sequenced 500 hundred bases upstream of the translation start site. The predicted amino acid sequence now clearly demonstrates all three motifs recognized in class 2 aminoacyl-tRNA synthetases. Alignment of E. coli, yeast, and when available, mammalian predicted amino acid sequences for three of the four members of the class 2a subgroup (his, pro, ser, and thr) shows strong preservation of amino acid specific signature regions proximal to motif 2 and proximal to motif 3. These probably represent the active site binding regions for the proximal acceptor stem and for the amino acid. The first two exons of human HRS contain a 32 amino acid helical motif, first described in human QRS, a class 1 synthetase, which is found also in a yeast RNA polymerase, a rabbit termination factor, and both bovine and human WRS, suggesting that it may be an RNA binding motif.

Normal coding sequence of insulin gene in Pima Indians and Nauruans, two groups with highest prevalence of type II diabetes

The nucleotide sequence of the insulin gene was determined in American Pima Indians and Micronesian Nauruans, two populations in whom the prevalence of non-insulin-dependent (type II) diabetes mellitus is the highest in the world. The insulin gene was amplified by the polymerase chain reaction to generate single-stranded DNA suitable for direct sequencing. The nucleotide sequences of the coding and adjacent regions of the insulin gene in six Pima Indians and two Nauruans with type II diabetes were identical to previously published insulin gene sequences of nondiabetic subjects.

Two unrelated patients with familial hyperproinsulinemia due to a mutation substituting histidine for arginine at position 65 in the proinsulin molecule: identification of the mutation by direct sequencing of genomic deoxyribonucleic acid amplified by polymerase chain reaction

Mutations in the insulin gene can impair the bioactivity of the insulin molecule. Previously, two classes of mutations have been identified: 1) those that impair posttranslational processing of proinsulin to insulin, and 2) those that alter the structure of the insulin molecule, thereby reducing the affinity of the molecule for the insulin receptor. We have investigated two apparently unrelated patients, both of which have mutations that inhibit the conversion of proinsulin to insulin. By directly sequencing genomic DNA amplified by polymerase chain reaction, we have demonstrated that both patients are heterozygous for the same point mutation converting codon 65 from an arginine (CGT) to a histidine (CAT) codon. Because Arg65 is one of the two dibasic amino acids at the site of proteolytic cleavage between the insulin A-chain and C-peptide, this mutation explains the impairment in the cleavage of proinsulin to insulin. Interestingly, the same His65 mutation has been identified in the insulin gene of a Japanese kindred with familial hyperproinsulinemia. Thus, this mutation has occurred in three apparently unrelated kindreds from two different racial groups. This observation is consistent with the hypothesis that the dinucleotide sequence CpG, the first two nucleotides in the arginine (CGT) codon, is a "hot spot" for mutations.