A Commentary on Commercial Genetic Testing and the Future of the Genetic Counseling Profession.

Commercial genetic testing laboratories are increasingly employing genetic counselors. As a result, the role of these or many genetic counselors is shifting from primarily direct patient counseling in clinics and hospitals to more laboratory-centered activities that involve case coordination, customer liaison, variant classification, marketing, and sales. Given the importance of these commercial entities to the genetic counseling profession, this commentary examines the current financial situation of four publicly traded, genetic testing companies. It also explores how the various roles of genetic counselors are likely to be affected by the financial pressures these companies face.

Efficient delivery of siRNA for inhibition of gene expression in postnatal mice.

It has recently been shown that RNA interference can be induced in cultured mammalian cells by delivery of short interfering RNAs (siRNAs). Here we describe a method for efficient in vivo delivery of siRNAs to organs of postnatal mice and demonstrate effective and specific inhibition of transgene expression in a variety of organs.

Current status of pharmaceutical and genetic therapeutic approaches to treat DMD.

Duchenne muscular dystrophy (DMD) is a genetic disease affecting about one in every 3,500 boys. This X-linked pathology is due to the absence of dystrophin in muscle fibers. This lack of dystrophin leads to the progressive muscle degeneration that is often responsible for the death of the DMD patients during the third decade of their life. There are currently no curative treatments for this disease but different therapeutic approaches are being studied. Gene therapy consists of introducing a transgene coding for full-length or a truncated version of dystrophin complementary DNA (cDNA) in muscles, whereas pharmaceutical therapy includes the use of chemical/biochemical substances to restore dystrophin expression or alleviate the DMD phenotype. Over the past years, many potential drugs were explored. This led to several clinical trials for gentamicin and ataluren (PTC124) allowing stop codon read-through. An alternative approach is to induce the expression of an internally deleted, partially functional dystrophin protein through exon skipping. The vectors and the methods used in gene therapy have been continually improving in order to obtain greater encapsidation capacity and better transduction efficiency. The most promising experimental approaches using pharmaceutical and gene therapies are reviewed in this article.

Hybrid PET/CT for noninvasive pharmacokinetic evaluation of dynamic PolyConjugates, a synthetic siRNA delivery system.

Positron emission tomography/computed tomography (PET/CT) hybrid imaging can be used to gain insights into a synthetic siRNA delivery system targeted to the liver. Either siRNA or the delivery vehicle was labeled with (64)Cu via 1, 4, 7, 10- tetraazacyclododecane- 1, 4, 7, 10- tetraacetic acid (DOTA) chelation. This study confirmed that the siRNA delivery system was successfully targeted to the liver. Incorporation of the siRNA into the delivery system protected the siRNA from renal filtration long enough so that the siRNA could be delivered to the liver. PET/CT imaging was important for confirming biodistribution and for determining differences in the distribution of labeled siRNA, siRNA incorporated into the delivery system, and the delivery system without siRNA.

Use of Evans blue dye to compare limb muscles in exercised young and old mdx mice.

Evans blue dye (EBD) is used to mark damaged and permeable muscle fibers in mouse models of muscular dystrophy and as an endpoint in therapeutic trials. We counted EBD-positive muscle fibers and extracted EBD from muscles sampled throughout the hindlimbs in young adult and old mdx mice to determine if the natural variability in morphology would allow measurement of a functional improvement in one limb compared to the contralateral limb. Following one bout of rotarod or treadmill exercise that greatly increased serum creatine kinase levels, the number of EBD(+) muscle fibers in 12-19-month-old mdx mice increased 3-fold, EBD in the muscles increased, and, importantly, contralateral pairs of muscles contained similar amounts of EBD. In contrast, the intra- and interlimb amounts of EBD in 2-7-month-old mdx mice were much too variable. A therapeutic effect can more readily be measured in old mdx mice. These results will be useful in the design of therapy protocols using the mdx mouse.

Efficacy of sapropterin dihydrochloride in increasing phenylalanine tolerance in children with phenylketonuria: a phase III, randomized, double-blind, placebo-controlled study.

OBJECTIVE: To evaluate the ability of sapropterin dihydrochloride (pharmaceutical preparation of tetrahydrobiopterin) to increase phenylalanine (Phe) tolerance while maintaining adequate blood Phe control in 4- to 12-year-old children with phenylketonuria (PKU). STUDY DESIGN: This international, double-blind, randomized, placebo-controlled study screened for sapropterin response among 90 enrolled subjects in Part 1. In Part 2, 46 responsive subjects with PKU were randomized (3:1) to sapropterin, 20 mg/kg/d, or placebo for 10 weeks while continuing on a Phe-restricted diet. After 3 weeks, a dietary Phe supplement was added every 2 weeks if Phe control was adequate. RESULTS: The mean (+/-SD) Phe supplement tolerated by the sapropterin group had increased significantly from the pretreatment amount (0 mg/kg/d) to 20.9 (+/-15.4) mg/kg/d (P < .001) at the last visit at which subjects had adequate blood Phe control (<360 micromol/L), up to week 10. Over the 10-week period, the placebo group tolerated only an additional 2.9 (+/-4.0) mg/kg/d Phe supplement; the mean difference from the sapropterin group (+/-SE) was 17.7 +/- 4.5 mg/kg/d (P < .001). No severe or serious related adverse events were observed. CONCLUSIONS: Sapropterin is effective in increasing Phe tolerance while maintaining blood Phe control and has an acceptable safety profile in this population of children with PKU.

Breaking the bonds: non-viral vectors become chemically dynamic.

The delivery of a variety of nucleic acids such as plasmid DNA (pDNA) and small interfering RNA (siRNA) to mammalian cells is both an important research tool and potential therapeutic approach. Synthetic vehicles (SVs) that include lipoplexes and polyplexes, are widely used for non-viral delivery. A promising method of improving the efficacy of this approach is to create SVs that are chemically dynamic, so that delivery is enabled by the cleavage of chemical bonds upon exposure to various physiological environments or external stimuli. An example of this approach is the use of masked endosomolytic agents (MEAs) that improve the release of nucleic acids from endosomes, a key step during transport. When the MEA enters the acidic environment of the endosome, a pH-labile bond is broken, releasing the agent';s endosomolytic capability. Another challenge has been to develop SVs that enable in vivo delivery. Recently, an MEA that was used within dynamic polyconjugates (DPCs) enabled the efficient delivery of siRNA into hepatocytes in vivo. The use of labile bonds to mask endosomolytic agents, provides a critical design feature, because it enables efficient in vivo delivery without sacrificing endosomolytic function for release into the cytoplasm.

Correction of murine PKU following AAV-mediated intramuscular expression of a complete phenylalanine hydroxylating system.

Phenylketonuria (PKU) caused by phenylalanine hydroxylase (PAH) deficiency leads to toxic accumulation of phenylalanine (Phe). PAH is predominantly expressed in liver and its activity requires a supply of tetrahydrobiopterin (BH(4)) cofactor, but we propose that expression of a complete Phe hydroxylating system (PAH plus BH(4) synthetic enzymes) in skeletal muscle will lead to therapeutic reduction of blood Phe levels in Pah(enu2) mice, a model of human PKU. In order to test this hypothesis, we first developed transgenic Pah(enu2) mice that lack liver PAH activity but coexpress, in their skeletal muscle, PAH and guanosine triphosphate cyclohydrolase I (GTPCH). The latter is responsible for the committing enzymatic step in BH(4) biosynthesis. Despite sufficient muscle enzyme expression, these mice remained hyperphenylalaninemic, thereby suggesting that expression of additional BH(4) synthetic enzymes would be necessary. A recombinant triple-cistronic adeno-associated virus-2 (AAV2) pseudotype 1 vector expressing PAH along with GTPCH and 6-pyruvoyltetrahydrobiopterin synthase (PTPS), the next step in BH(4) synthesis, was generated. Injection of this vector into the gastrocnemius muscles of Pah(enu2) mice led to stable and long-term reduction of blood Phe and reversal of PKU-associated coat hypopigmentation. We propose that muscle-directed gene therapy will be a viable alternative treatment approach to PKU and other inborn errors of metabolism.

Sustained liver-specific transgene expression from the albumin promoter in mice following hydrodynamic plasmid DNA delivery.

BACKGROUND: To properly study gene expression in vivo, often long-term expression is desired. Previous studies using plasmid DNA (pDNA) vectors have typically resulted in short-term expression. Here, we evaluated combinations of the albumin promoter with different enhancers and untranslated regions for liver-specific expression in mice. METHODS: A series of pDNA secreted alkaline phosphatase (SEAP) reporter gene expression vectors was constructed using the albumin promoter and various other expression cassette elements. Each was evaluated for level and duration of SEAP expression in mice following hydrodynamic tail vein delivery. RESULTS: Sustained liver expression was obtained from vectors combining the albumin promoter with an albumin 3' untranslated region (3'UTR). The level of expression was increased by inclusion of enhancers and a 5' intron. The optimal expression vector consisted of the albumin promoter combined with an alpha-fetoprotein MERII enhancer, 5' intron from the factor IX gene, and the 3'UTR from the albumin gene including intron 14. With this vector, SEAP reporter gene expression levels remained high for 1 year, at levels comparable to those obtained from the cytomegalovirus (CMV) promoter on day 1. Expression of human apolipoprotein E3 (hApoE) in ApoE knockout mice provided a dose-dependent correction of their hypercholesterolemia. CONCLUSIONS: Liver-specific sustained transgene expression can be obtained at very high levels from optimized pDNA vectors, without the use of integration systems. Such vectors will further facilitate biological studies of genes in vivo and may find application in gene therapy.

A single acyl-CoA dehydrogenase is required for catabolism of isoleucine, valine and short-chain fatty acids in Aspergillus nidulans.

An acyl-CoA dehydrogenase has been identified as part of the mitochondrial beta-oxidation pathway in the ascomycete fungus Aspergillus nidulans. Disruption of the scdA gene prevented use of butyric acid (C(4)) and hexanoic acid (C(6)) as carbon sources and reduced cellular butyryl-CoA dehydrogenase activity by 7.5-fold. While the mutant strain exhibited wild-type levels of growth on erucic acid (C(22:1)) and oleic acid (C(18:1)), some reduction in growth was observed with myristic acid (C(14)). The DeltascdA mutation was found to be epistatic to a mutation downstream in the beta-oxidation pathway (disruption of enoyl-CoA hydratase). The DeltascdA mutant was also unable to use isoleucine or valine as a carbon source. Transcription of scdA was observed in the presence of either fatty acids or amino acids. When the mutant was grown in medium containing either isoleucine or valine, organic acid analysis of culture supernatants showed accumulation of 2-oxo acid intermediates of branched chain amino acid catabolism, suggesting feedback inhibition of the upstream branched-chain alpha-keto acid dehydrogenase.

The role of molecular testing and enzyme analysis in the management of hypomorphic citrullinemia.

Expanded newborn screening detects patients with modest elevations in citrulline; however it is currently unclear how to treat these patients and how to counsel their parents. In order to begin to address these issues, we compared the clinical, biochemical, and molecular features of 10 patients with mildly elevated citrulline levels. Three patients presented with clinical illness whereas seven came to attention as a result of expanded newborn screening. One patient presented during pregnancy and responded promptly to IV sodium phenylacetate/sodium benzoate and arginine therapy with no long-term adverse effects on mother or fetus. Two children presented with neurocognitive dysfunction, one of these responded dramatically to dietary protein reduction. ASS enzyme activity was not deficient in all patients with biallelic mutations suggesting this test cannot exclude the ASS1 locus in patients with mildly elevated plasma citrulline. Conversely, all symptomatic patients who were tested had deficient activity. We describe four unreported mutations (p.Y291S, p.R272H, p.F72L, and p.L88I), as well as the common p.W179R mutation. In silico algorithms were inconsistent in predicting the pathogenicity of mutations. The cognitive benefit in one patient of protein restriction and the lack of adverse outcome in seven others restricted from birth, suggest a role for protein restriction and continued monitoring to prevent neurocognitive dysfunction.

Rapidly reversible hydrophobization: an approach to high first-pass drug extraction.

We have investigated a rapidly reversible hydrophobization of therapeutic agents for improving first-pass uptake in locoregional drug therapy. This approach involves the attachment of a hydrophobic moiety to the drug by highly labile chemical linkages that rapidly hydrolyze upon injection. Hydrophobization drastically enhances cell-membrane association of the prodrug and, consequently, drug uptake, while the rapid lability protects nontargeted tissues from exposure to the highly active agent. Using the membrane-impermeable DNA intercalator propidium iodide, and melphalan, we report results from in vitro cellular internalization and toxicity studies. Additionally, we report in vivo results after a single liver arterial bolus injection, demonstrating both tumor targeting and increased survival in a mouse tumor model.

Transcriptional and phenotypic comparisons of Ppara knockout and siRNA knockdown mice.

RNA interference (RNAi) has great potential as a tool for studying gene function in mammals. However, the specificity and magnitude of the in vivo response to RNAi remains to be fully characterized. A molecular and phenotypic comparison of a genetic knockout mouse and the corresponding knockdown version would help clarify the utility of the RNAi approach. Here, we used hydrodynamic delivery of small interfering RNA (siRNA) to knockdown peroxisome proliferator activated receptor alpha (Ppara), a gene that is central to the regulation of fatty acid metabolism. We found that Ppara knockdown in the liver results in a transcript profile and metabolic phenotype that is comparable to those of Ppara-/- mice. Combining the profiles from mice treated with the PPARalpha agonist fenofibrate, we confirmed the specificity of the RNAi response and identified candidate genes proximal to PPARalpha regulation. Ppara knockdown animals developed hypoglycemia and hypertriglyceridemia, phenotypes observed in Ppara-/- mice. In contrast to Ppara-/- mice, fasting was not required to uncover these phenotypes. Together, these data validate the utility of the RNAi approach and suggest that siRNA can be used as a complement to classical knockout technology in gene function studies.

Magnetic resonance imaging-monitored plasmid DNA delivery in primate limb muscle.

The purpose of this work is to investigate the use of magnetic resonance imaging (MRI) to monitor the effects of high-pressure naked plasmid DNA (pDNA) intravascular injections in primate limbs, studying both the distribution of the injected solution in the muscle space, as well as the effects on the vascular system. The distal portion of the four limbs of each of six rhesus monkeys were hydrodynamically injected with naked pDNA, which expressed the luciferase reporter gene. Three-dimensional (3D) T1-weighted gradient echo and 2D multislice T2-weighted fast spin echo (FSE) series were acquired before and immediately after the injection to confirm the volume of solution injected into the limb, and to study the distribution of the injected solution in the individual muscle groups. Time-resolved contrast-enhanced 3D magnetic resonance angiography (MRA) was performed several days before, immediately after, and in a follow-up examination after the pDNA injection to study the effects of the procedure on the primate peripheral vascular system. T1-weighted gradient echo imaging confirmed the delivery of the majority of the solution after successful pDNA injections. T2-weighted FSE imaging demonstrated the distribution of the saline solution in individual muscles in the target limbs, with enhancement showing a weak but significant correlation with the level of gene expression. Time-resolved contrast-enhanced MRA demonstrated effects of the injection procedure on the arterial and venous vascular systems, and the intramuscular compartments; and these effects largely returned to normal on short-term follow-up.

Progress toward a nonviral gene therapy protocol for the treatment of anemia.

Anemia frequently accompanies chronic diseases such as progressive renal failure, acquired immunodeficiency syndrome, and cancer. Patients are currently treated with erythropoietin (EPO) replacement therapy, using various recombinant human EPO protein formulations. Although this treatment is effective, gene therapy could be more economical and more convenient for the long-term management of the disease. The objective of this study was to develop a naked DNA-based gene therapy protocol that could fill this need. Hydrodynamic limb vein technology has been shown to be an effective and safe procedure for delivering naked plasmid DNA (pDNA) into the skeletal muscles of limbs. Using this method, we addressed the major challenge of an EPO-based gene therapy of anemia: maintaining stable, long-term expression at a level that sufficiently promotes erythropoiesis without leading to polycythemia. The results of our study, using a rat anemia model, provide proof of principle that repeated delivery of small pDNA doses has an additive effect and can gradually lead to the correction of anemia without triggering excessive hematopoiesis. This simple method provides an alternative approach for regulating EPO expression. EPO expression was also proportional to the injected pDNA dose in nonhuman primates. In addition, long-term (more than 450 days) expression was obtained after delivering rhesus EPO cDNA under the transcriptional control of the muscle-specific creatine kinase (MCK) promoter. In conclusion, these data suggest that the repeated delivery of small doses of EPO expressing pDNA into skeletal muscle is a promising, clinically viable approach to alleviate the symptoms of anemia.

Systemic siRNA delivery via hydrodynamic intravascular injection.

The main barrier to the use of RNAi in mammalian systems is the difficulty in delivering siRNA or shRNA to the appropriate tissues. Although progress has been made in this area, many of the technologies developed require specialized expertise and reagents that are beyond the reach of most investigators. In contrast, the hydrodynamic injection technique is simple to perform and enables highly efficient delivery of naked, unmodified siRNA to a number of tissues, especially the liver. This review describes the development of the technique and explores the possible mechanisms that enable uptake of siRNA to biological effect. Examples of the use of hydrodynamic injection in animal models of disease and for the study of gene function are presented and discussed.

In vivo selection and validation of liver-specific ligands using a new T7 phage peptide display system.

In vivo phage display is a powerful source of new peptide ligands for specific organ targeting by drugs and gene therapy vectors. Since the introduction of this methodology a decade ago, a number of peptides that preferentially react with organ-specific endothelium and parenchymal markers have been selected. One organ that has been conspicuously missing from these selection studies is the liver, which possesses a multitude of acquired and hereditary disorders and represents a highly important therapeutic target. Herein, we set out to fill this gap by introducing a novel peptide display system containing cloned sequences in the tail fiber protein (p17) of phage T7. The p17 display effectively avoids the innate immune system and is well suited both for selection of new liver-specific ligands and for validation of protein sequences that have been implicated in liver targeting by the use of conventional biochemical methods.

2-methylbutyryl-CoA dehydrogenase deficiency in Hmong infants identified by expanded newborn screen.

In April 2000, the Wisconsin Newborn Screening Program implemented tandem mass spectrometry (MS/MS) technology to expand the newborn screening panel from 13 to 48 disorders, the majority of which are inborn errors of metabolism. Among other tests, this technology measures the acylcarnitine profile from blood spots collected from infants at 24 to 48 hours of age. During the first 5.75 years of expanded screening, 27 infants were identified with elevated C5-acylcarnitine concentrations, an unexpectedly high number for any inborn error of metabolism. For these infants, elevated C5-acylcarnitines suggested a diagnosis of isovaleric acidemia (IVA), a metabolic defect of leucine metabolism. Subsequent testing showed that the infants did not have isovaleric acidemia, but did have 2-methylbutyryl-CoA dehydrogenase deficiency or 2-MBAD deficiency, a newly described defect of isoleucine metabolism. (An official abbreviation has not been established for this disorder. Other abbreviations include SBCADD, 2-MBG, and 2-MBCD deficiency.) All but 1 of the 27 infants identified with 2-MBAD deficiency are offspring of Hmong parents. To date, those diagnosed with the disorder in the Hmong community have been largely asymptomatic, though further research is needed to determine whether newborns with 2-MBAD deficiency are at risk for neurodevelopmental disorders.

Genetic immunization for antibody generation in research animals by intravenous delivery of plasmid DNA.

Genetic immunization is an attractive approach to generate antibodies because native proteins are expressed in vivo with normal posttranscriptional modifications, avoiding time-consuming and costly antigen isolation or synthesis. Hydrodynamic tail or limb vein delivery of naked plasmid DNA expression vectors was used to induce antigen-specific antibodies in mice, rats, and rabbits. Both methods allowed the efficient generation of high-titer, antigen-specific antibodies with an overall success rate of Western detectable antibodies of 78% and 92%, respectively. High-titer antibodies were typically present after 3 hydrodynamic tail vein plasmid DNA deliveries, 5 weeks after the initial injection (i.e., prime). For hydrodynamic limb vein plasmid DNA delivery, two deliveries were sufficient to induce high-titer antibody levels. Tail vein delivery was less successful at generating antibodies directed against secreted proteins as compared with limb vein delivery. Material for screening was generated by,transfection of the immunization vector into mammalian cell lines. The cell line (COS-7) that produced the highest level of antigen expression performed best in Western blot analysis screens. In summary, intravenous delivery of antigen-expressing plasmid DNA vectors is an effective genetic immunization method for the induction of antigen-specific antibodies in small and large research animals.