Intrathecal Vector Delivery in Juvenile Rats via Lumbar Cistern Injection

Gene therapy is a powerful technology to deliver new genes to a patient for the treatment of disease, be it to introduce a functional gene, inactivate a toxic gene, or provide a gene whose product can modulate the biology of the disease. The delivery method for the therapeutic vector can take many forms, ranging from intravenous infusion for systemic delivery to direct injection into the target tissue. For neurodegenerative disorders, it is often desirable to skew transduction towards the brain and/or spinal cord. The least invasive approach to target the entire central nervous system involves injection into the cerebrospinal fluid (CSF), allowing the therapeutic to reach a large fraction of the central nervous system. The safest approach to deliver a vector into the CSF is the lumbar intrathecal injection, where a needle is introduced into the lumbar cistern of the spinal cord. This technique, also known as a lumbar puncture, has been widely used in neonatal and adult rodents and in large animal models. While the technique is similar across species and developmental stages, subtle differences in size, structure, and elasticity of tissues surrounding the intrathecal space require accommodations in the approach. This article describes a method for performing lumbar puncture in juvenile rats to deliver an adeno-associated serotype 9 vector. Here, 25-35 µL of vector were injected into the lumbar cistern, and a green fluorescent protein (GFP) reporter was used to evaluate the transduction profile resulting from each injection. The benefits and challenges of this approach are discussed.

Current and emerging targeted therapies for spinal muscular atrophy

INTRODUCTION

Spinal muscular atrophy (SMA) is a progressive neurodegenerative disorder caused by insufficiency or total absence of the survival motor neuron protein due to a mutation in the SMN1 gene. The copy number of its paralog, SMN2, influences disease onset and phenotype severity. Current therapeutic approaches include viral and non-viral modalities affecting gene expression. Regulatory-approved drugs Spinraza (Nusinersen), Zolgensma (Onasemnogene abeparvovec), and Evrysdi (Risdiplam) are still being investigated during clinical trials and show benefits in the long-term for symptomatic and pre-symptomatic patients. However, some ongoing interventions require repeated drug administration.

AREAS COVERED

In this review, the authors describe the existing therapy based on point of application, focusing on recent clinical trials of antisense oligonucleotides, viral gene therapy, and splice modulators and thepotential routes for correcting the mutation to provide therapeutic levels of SMN protein.

EXPERT OPINION

In the opinion of the authors, multiple treatment options for patients with SMA shifted the treatment paradigm from palliative supportive care to improvedmotor function, increased survival, and greater quality of life for such patients. They further believe that the future in SMA treatment development lies incombining existing treatment options, targeting aspects of the disease refractory to these treatments, and using gene editing technologies.

Lentiviral-Induced Spinal Cord Gliomas in Rat Model

Intramedullary spinal cord tumors are a rare and understudied cancer with poor treatment options and prognosis. Our prior study used a combination of PDGF-B, HRAS, and p53 knockdown to induce the development of high-grade glioma in the spinal cords of minipigs. In this study, we evaluate the ability of each vector alone and combinations of vectors to produce high-grade spinal cord gliomas. Eight groups of rats (n = 8/group) underwent thoracolumbar laminectomy and injection of lentiviral vector in the lateral white matter of the spinal cord. Each group received a different combination of lentiviral vectors expressing PDGF-B, a constitutively active HRAS mutant, or shRNA targeting p53, or a control vector. All animals were monitored once per week for clinical deficits for 98 days. Tissues were harvested and analyzed using hematoxylin and eosin (H&E) and immunohistochemical (IHC) staining. Rats injected with PDGF-B+HRAS+sh-p53 (triple cocktail) exhibited statistically significant declines in all behavioral measures (Basso Beattie Bresnahan scoring, Tarlov scoring, weight, and survival rate) over time when compared to the control. Histologically, all groups except the control and those injected with sh-p53 displayed the development of tumors at the injection site, although there were differences in the rate of tumor growth and the histopathological features of the lesions between groups. Examination of immunohistochemistry revealed rats receiving triple cocktail displayed the largest and most significant increase in the Ki67 proliferation index and GFAP positivity than any other group. PDGF-B+HRAS also displayed a significant increase in the Ki67 proliferation index. Rats receiving PDGF-B alone and PDGF-B+ sh-p53 displayed more a significant increase in SOX2-positive staining than in any other group. We found that different vector combinations produced differing high-grade glioma models in rodents. The combination of all three vectors produced a model of high-grade glioma more efficiently and aggressively with respect to behavioral, physiological, and histological characteristics than the rest of the vector combinations. Thus, the present rat model of spinal cord glioma may potentially be used to evaluate therapeutic strategies in the future.

Minimally Invasive Injection to the Phrenic Nerve in a Porcine Hemidiaphragmatic Paralysis Model: A Pilot Study

BACKGROUND

Neurodegenerative diseases and spinal cord injury can affect respiratory function often through motor neuron loss innervating the diaphragm. To reinnervate this muscle, new motor neurons could be transplanted into the phrenic nerve (PN), allowing them to extend axons to the diaphragm. These neurons could then be driven by an optogenetics approach to regulate breathing. This type of approach has already been demonstrated in the peripheral nerves of mice. However, there is no established thoracoscopic approach to PN injection. Also, there is currently a lack of preclinical large animal models of diaphragmatic dysfunction in order to evaluate the efficacy of potential treatments.

OBJECTIVE

To evaluate the feasibility of thoracoscopic drug delivery into the PN and to assess the viability of hemidiaphragmatic paralysis in a porcine model.

METHODS

Two Landrace farm pigs underwent a novel procedure for thoracoscopic PN injections, including 1 nonsurvival and 1 survival surgery. Nonsurvival surgery involved bilateral PN injections and ligation. Survival surgery included a right PN injection and transection proximal to the injection site to induce hemidiaphragmatic paralysis.

RESULTS

PN injections were successfully performed in both procedures. The animal that underwent survival surgery recovered postoperatively with an established right hemidiaphragmatic paralysis. Over the 5-d postoperative period, the animal displayed stable vital signs and oxygenation saturation on room air with voluntary breathing.

CONCLUSION

Thoracoscopic targeting of the porcine PN is a feasible approach to administer therapeutic agents. A swine model of hemidiaphragmatic paralysis induced by unilateral PN ligation or transection may be potentially used to study diaphragmatic reinnervation following delivery of therapeutics.

Controlling the Release of Neurotrophin-3 and Chondroitinase ABC Enhances the Efficacy of Nerve Guidance Conduits

Nerve guidance conduits (NGCs) have the potential to replace autografts in repairing peripheral nerve injuries, but their efficacy still needs to be improved. The efficacy of NGCs is augmented by neurotrophic factors that promote axon growth and by enzymes capable of degrading molecules that inhibit axon growth. In the current study, two types of NGCs loaded with factors (both neurotrophin-3 and chondroitinase ABC) are constructed and their abilities to repair an 8 mm gap in the rat sciatic nerve are examined. The factors are encapsulated in microparticles made of a phase-change material (PCM) or collagen and then sandwiched between two layers of electrospun fibers. The use of PCM allows to achieve pulsed release of the factors upon irradiation with a near-infrared laser. The use of collagen enables slow, continuous release via diffusion. The efficacy is evaluated by measuring compound muscle action potentials (CMAP) in the gastrocnemius muscle and analyzing the nerve histology. Continuous release of the factors from collagen results in enhanced CMAP amplitude and increased axon counts in the distal nerve relative to the plain conduit. In contrast, pulsed release of the same factors from PCM shows a markedly adverse impact on the efficacy, possibly by inhibiting axon growth.

Lot-to-Lot Variation in Adeno-Associated Virus Serotype 9 (AAV9) Preparations

Viral vectors are complex drugs that pose a particular challenge for manufacturing. Previous studies have shown that, unlike small-molecule drugs, vector preparations do not yield a collection of identical particles. Instead, a mixture of particles that vary in capsid stoichiometry and impurities is created, which may differ from lot to lot. The consequences of this are unclear, but conflicting reports regarding the biological properties of vectors, including transduction patterns, suggest that this variability may have an effect. However, other variables, including differences in animal strains and techniques, make it difficult to identify a cause. Here, we report lot-to-lot variation in spinal cord gray matter transduction following intrathecal delivery of self-complementary adeno-associated virus serotype 9 vectors. Eleven lots of vector were evaluated from six vector cores, including one preclinical/Good Laboratory Practice lot. Eight of the lots, including the preclinical lot, failed to transduce the gray matter, whereas the other three provided robust transduction. The cause for this variation is unknown, but it did not correlate with vector titer, buffer, or purification method. These results highlight the need to identify the cause of this variation and to develop improved production and quality control methods to ensure lot-to-lot consistency of vector potency.

Progress in gene and cell therapies for the neuronal ceroid lipofuscinoses

INTRODUCTION

The neuronal ceroid lipofuscinoses (NCLs) are a subset of lysosomal storage diseases (LSDs) that cause myoclonic epilepsy, loss of cognitive and motor function, degeneration of the retina leading to blindness, and early death. Most are caused by loss-of-function mutations in either lysosomal proteins or transmembrane proteins. Current therapies are supportive in nature. NCLs involving lysosomal enzymes are amenable to therapies that provide an exogenous source of protein, as has been used for other LSDs. Those that involve transmembrane proteins, however, require new approaches.

AREAS COVERED

This review will discuss potential gene and cell therapy approaches that have been, are, or may be in development for these disorders and those that have entered clinical trials.

EXPERT OPINION

In animal models, gene therapy approaches have produced remarkable improvements in neurological function and lifespan. However, a complete cure has not been reached for any NCL, and a better understanding of the limits of the current crop of vectors is needed to more fully address these diseases. The prospects for gene therapy, particularly those that can be delivered systemically and treat both the brain and peripheral tissue, are high. The future is beginning to look bright for NCL patients and their families.

Gene, Stem Cell, and Alternative Therapies for SCA 1

Spinocerebellar ataxia 1 is an autosomal dominant disease characterized by neurodegeneration and motor dysfunction. In disease pathogenesis, polyglutamine expansion within Ataxin-1, a gene involved in transcriptional repression, causes protein nuclear inclusions to form. Most notably, neuronal dysfunction presents in Purkinje cells. However, the effect of mutant Ataxin-1 is not entirely understood. Two mouse models are employed to represent spinocerebellar ataxia 1, a B05 transgenic model that specifically expresses mutant Ataxin-1 in Purkinje cells, and a Sca1 154Q/2Q model that inserts the polyglutamine expansion into the mouse Ataxin-1 locus so that the mutant Ataxin-1 is expressed in all cells that express Ataxin-1. This review aims to summarize and evaluate the wide variety of therapies proposed for spinocerebellar ataxia 1, specifically gene and stem cell therapies.

Gene Therapy for the Treatment of Neurological Disorders: Amyotrophic Lateral Sclerosis

Gene therapy is a powerful tool for treating diseases, including neurological disorder such at amyotrophic lateral sclerosis. When delivered to the CNS, gene therapy vectors can provide prosurvival signals to neurons, knock down the expression of toxic proteins, or restore lost function. How to best deliver this type of therapeutic depends on the nature of the disease and the expected function of the transgene. Here we describe a method for parenchymal injection into rodent models, allowing for localized delivery of gene therapy vectors and other therapeutic molecules. This technique has been a robust mechanism for proof-of-principle experiments.

Fetal Brain-directed AAV Gene Therapy Results in Rapid, Robust, and Persistent Transduction of Mouse Choroid Plexus Epithelia

Fetal brain-directed gene addition represents an under-appreciated tool for investigating novel therapeutic approaches in animal models of central nervous system diseases with early prenatal onset. Choroid plexuses (CPs) are specialized neuroectoderm-derived structures that project into the brain's ventricles, produce cerebrospinal fluid (CSF), and regulate CSF biochemical composition. Targeting the CP may be advantageous for adeno-associated viral (AAV) gene therapy for central nervous system disorders due to its immunoprivileged location and slow rate of epithelial turnover. Yet the capacity of AAV vectors to transduce CP has not been delineated precisely. We performed intracerebroventricular injections of recombinant AAV serotype 5-green fluorescent protein (rAAV5-GFP) or rAAV9-GFP in embryonic day 15 (E15) embryos of CD-1 and C57BL/6 pregnant mice and quantified the percentages of GFP expression in CP epithelia (CPE) from lateral and fourth ventricles on E17, postnatal day 2 (P2), and P22. AAV5 was selective for CPE and showed significantly higher transduction efficiency in C57BL/6 mice (P = 0.0128). AAV9 transduced neurons and glial cells in both the mouse strains, in addition to CPE. We documented GFP expression in CPE on E17, within just 48 hours of rAAV administration to the fetal lateral ventricle, and expression by both the serotypes persisted at P130. Our results indicate that prenatal administration of rAAV5 and rAAV9 enables rapid, robust, and sustained transduction of mouse CPE and buttress the rationale for experimental therapeutics targeting the CP.Molecular Therapy-Nucleic Acids (2013) 2, e101; doi:10.1038/mtna.2013.27; published online 25 June 2013.

L-threo-dihydroxyphenylserine corrects neurochemical abnormalities in a Menkes disease mouse model

OBJECTIVE

Menkes disease is a lethal neurodegenerative disorder of infancy caused by mutations in a copper-transporting adenosine triphosphatase gene, ATP7A. Among its multiple cellular tasks, ATP7A transfers copper to dopamine beta hydroxylase (DBH) within the lumen of the Golgi network or secretory granules, catalyzing the conversion of dopamine to norepinephrine. In a well-established mouse model of Menkes disease, mottled-brindled (mo-br), we tested whether systemic administration of L-threo-dihydroxyphenylserine (L-DOPS), a drug used successfully to treat autosomal recessive norepinephrine deficiency, would improve brain neurochemical abnormalities and neuropathology.

METHODS

At 8, 10, and 12 days of age, wild-type and mo-br mice received intraperitoneal injections of 200μg/g body weight of L-DOPS, or mock solution. Five hours after the final injection, the mice were euthanized, and brains were removed. We measured catecholamine metabolites affected by DBH via high-performance liquid chromatography with electrochemical detection, and assessed brain histopathology.

RESULTS

Compared to mock-treated controls, mo-br mice that received intraperitoneal L-DOPS showed significant increases in brain norepinephrine (p < 0.001) and its deaminated metabolite, dihydroxyphenylglycol (p < 0.05). The ratio of a non-beta-hydroxylated metabolite in the catecholamine biosynthetic pathway, dihydroxyphenylacetic acid, to the beta-hydroxylated metabolite, dihydroxyphenylglycol, improved equivalently to results obtained previously with brain-directed ATP7A gene therapy (p < 0.01). However, L-DOPS treatment did not arrest global brain pathology or improve somatic growth, as gene therapy had.

INTERPRETATION

We conclude that (1) L-DOPS crosses the blood-brain barrier in mo-br mice and corrects brain neurochemical abnormalities, (2) norepinephrine deficiency is not the cause of neurodegeneration in mo-br mice, and (3) L-DOPS treatment may ameliorate noradrenergic hypofunction in Menkes disease.

Molecular and biochemical characterization of a unique mutation in CCS, the human copper chaperone to superoxide dismutase

Copper (Cu) is a trace metal that readily gains and donates electrons, a property that renders it desirable as an enzyme cofactor but dangerous as a source of free radicals. To regulate cellular Cu metabolism, an elaborate system of chaperones and transporters has evolved, although no human Cu chaperone mutations have been described to date. We describe a child from a consanguineous family who inherited homozygous mutations in the SLC33A1, encoding an acetyl CoA transporter, and in CCS, encoding the Cu chaperone for superoxide dismutase. The CCS mutation, p.Arg163Trp, predicts substitution of a highly conserved arginine residue at position 163, with tryptophan in domain II of CCS, which interacts directly with superoxide dismutase 1 (SOD1). Biochemical analyses of the patient's fibroblasts, mammalian cell transfections, immunoprecipitation assays, and Lys7Δ (CCS homolog) yeast complementation support the pathogenicity of the mutation. Expression of CCS was reduced and binding of CCS to SOD1 impaired. As a result, this mutation causes reduced SOD1 activity and may impair other mechanisms important for normal Cu homeostasis. CCS-Arg163Trp represents the primary example of a human mutation in a gene coding for a Cu chaperone.

Increased frequency of congenital heart defects in Menkes disease

ATP7A is a copper-transporting ATPase critical for central and peripheral nervous system function. Mutations in ATP7A cause Menkes disease and occipital horn syndrome (OHS), allelic X-linked recessive conditions that feature vascular abnormalities ascribed to low activity of lysyl oxidase, a copper-dependent enzyme. From a recently created Menkes disease/OHS patient registry, we identified four of 95 patients with major congenital heart defects (4.2%), a proportion exceeding the general population prevalence (≈1%). In conjunction with mouse models of Menkes disease, OHS, and lysyl oxidase deficiency (which feature aortic aneurysms, irregular attachment between vascular endothelium and mesoderm, and other defects of embryological development) our observation suggests an important role of copper metabolism in cardiac development. Congenital heart disease may be an under-appreciated abnormality in Menkes disease, and should be considered in a broad differential diagnosis of cardiac defects found prenatally in male fetuses. Conversely, newborn infants with suspected or confirmed Menkes disease should be evaluated for heart disease by careful clinical examination and echocardiography, if indicated.

Altered intracellular localization and valosin-containing protein (p97 VCP) interaction underlie ATP7A-related distal motor neuropathy

ATP7A is a P-type ATPase that regulates cellular copper homeostasis by activity at the trans-Golgi network (TGN) and plasma membrane (PM), with the location normally governed by intracellular copper concentration. Defects in ATP7A lead to Menkes disease or its milder variant, occipital horn syndrome or to a newly discovered condition, ATP7A-related distal motor neuropathy (DMN), for which the precise pathophysiology has been obscure. We investigated two ATP7A motor neuropathy mutations (T994I, P1386S) previously associated with abnormal intracellular trafficking. In the patients' fibroblasts, total internal reflection fluorescence microscopy indicated a shift in steady-state equilibrium of ATP7A(T994I) and ATP7A(P1386S), with exaggerated PM localization. Transfection of Hek293T cells and NSC-34 motor neurons with the mutant alleles tagged with the Venus fluorescent protein also revealed excess PM localization. Endocytic retrieval of the mutant alleles from the PM to the TGN was impaired. Immunoprecipitation assays revealed an abnormal interaction between ATP7A(T994I) and p97/VCP, an ubiquitin-selective chaperone which is mutated in two autosomal dominant forms of motor neuron disease: amyotrophic lateral sclerosis and inclusion body myopathy with early-onset Paget disease and fronto-temporal dementia. Small-interfering RNA (SiRNA) knockdown of p97/VCP corrected ATP7A(T994I) mislocalization. Flow cytometry documented that non-permeabilized ATP7A(P1386S) fibroblasts bound a carboxyl-terminal ATP7A antibody, consistent with relocation of the ATP7A di-leucine endocytic retrieval signal to the extracellular surface and partially destabilized insertion of the eighth transmembrane helix. Our findings illuminate the mechanisms underlying ATP7A-related DMN and establish a link between p97/VCP and genetically distinct forms of motor neuron degeneration.

Favorably skewed X-inactivation accounts for neurological sparing in female carriers of Menkes disease

Classical Menkes disease is an X-linked recessive neurodegenerative disorder caused by mutations in ATP7A, which is located at Xq13.1-q21. ATP7A encodes a copper-transporting P-type ATPase and plays a critical role in development of the central nervous system. With rare exceptions involving sex chromosome aneuploidy or X-autosome translocations, female carriers of ATP7A mutations are asymptomatic except for subtle hair and skin abnormalities, although the mechanism for this neurological sparing has not been reported. We studied a three-generation family in which a severe ATP7A mutation, a 5.5-kb genomic deletion spanning exons 13 and 14, segregated. The deletion junction fragment was amplified from the proband by long-range polymerase chain reaction and sequenced to characterize the breakpoints. We screened at-risk females in the family for this junction fragment and analyzed their X-inactivation patterns using the human androgen-receptor (HUMARA) gene methylation assay. We detected the junction fragment in the proband, two obligate heterozygotes, and four of six at-risk females. Skewed inactivation of the X chromosome harboring the deletion was noted in all female carriers of the deletion (n = 6), whereas random X-inactivation was observed in all non-carriers (n = 2). Our results formally document one mechanism for neurological sparing in female carriers of ATP7A mutations. Based on review of X-inactivation patterns in female carriers of other X-linked recessive diseases, our findings imply that substantial expression of a mutant ATP7A at the expense of the normal allele could be associated with neurologic symptoms in female carriers of Menkes disease and its allelic variants, occipital horn syndrome, and ATP7A-related distal motor neuropathy.

Somatic mosaicism in Menkes disease suggests choroid plexus-mediated copper transport to the developing brain

The primary mechanism of copper transport to the brain is unknown, although this process is drastically impaired in Menkes disease, an X-linked neurodevelopmental disorder caused by mutations in an evolutionarily conserved copper transporter, ATP7A. Potential central nervous system entry routes for copper include brain capillary endothelial cells that originate from mesodermal angioblasts and form the blood-brain barrier, and the choroid plexuses, which derive from embryonic ectoderm, and form the blood-cerebrospinal fluid barrier. We exploited a rare (and first reported) example of somatic mosaicism for an ATP7A mutation to shed light on questions about copper transport into the developing brain. In a 20-month-old Menkes disease patient evaluated before copper treatment, blood copper, and catecholamine concentrations were normal, whereas levels in cerebrospinal fluid were abnormal and consistent with his neurologically severe phenotype. We documented disparate levels of mosaicism for an ATP7A missense mutation, P1001L, in tissues derived from different embryonic origins; allele quantitation showed P1001L in approximately 27% of DNA samples from blood cells (mesoderm-derived) and 88% from cultured fibroblasts (ectoderm-derived). These findings imply that the P1001L mutation in the patient preceded formation of the three primary embryonic lineages at gastrulation, with the ectoderm layer ultimately harboring a higher percentage of mutation-bearing cells than mesoderm or endoderm. Since choroid plexus epithelia are derived from neuroectoderm, and brain capillary endothelial cells from mesodermal angioblasts, the clinical and biochemical findings in this infant support a critical role for the blood-CSF barrier (choroid plexus epithelia) in copper entry to the developing brain.

Molecular correlates of epilepsy in early diagnosed and treated Menkes disease

Epilepsy is a major feature of Menkes disease, an X-linked recessive infantile neurodegenerative disorder caused by mutations in ATP7A, which produces a copper-transporting ATPase. Three prior surveys indicated clinical seizures and electroencephalographic (EEG) abnormalities in a combined 27 of 29 (93%) symptomatic Menkes disease patients diagnosed at 2 months of age or older. To assess the influence of earlier, presymptomatic diagnosis and treatment on seizure semiology and brain electrical activity, we evaluated 71 EEGs in 24 Menkes disease patients who were diagnosed and treated with copper injections in early infancy (≤6 weeks of age), and whose ATP7A mutations we determined. Clinical seizures were observed in only 12.5% (3/24) of these patients, although 46% (11/24) had at least one abnormal EEG tracing, including 50% of patients with large deletions in ATP7A, 50% of those with small deletions, 60% of those with nonsense mutations, and 57% of those with canonical splice junction mutations. In contrast, five patients with mutations shown to retain partial function, either via some correct RNA splicing or residual copper transport capacity, had neither clinical seizures nor EEG abnormalities. Our findings suggest that early diagnosis and treatment improve brain electrical activity and decrease seizure occurrence in classical Menkes disease irrespective of the precise molecular defect. Subjects with ATP7A mutations that retain some function seem particularly well protected by early intervention against the possibility of epilepsy.

Translational read-through of a nonsense mutation in ATP7A impacts treatment outcome in Menkes disease

Protein translation ends when a stop codon in a gene's messenger RNA transcript enters the ribosomal A site. Mutations that create premature stop codons (nonsense mutations) typically cause premature translation termination. An alternative outcome, read-through translation (or nonsense suppression), is well known in prokaryotic, viral, and yeast genes but has not been clearly documented in humans except in the context of pharmacological manipulations. Here, we identify and characterize native read-through of a nonsense mutation (R201X) in the human copper transport gene, ATP7A. Western blotting, in vitro expression analyses, immunohistochemistry, and yeast complementation assays using cultured fibroblasts from a classic Menkes disease patient all indicated small amounts of native ATP7A(R201X) read-through and were associated with a dramatic clinical response to early copper treatment.

Clinical outcomes in Menkes disease patients with a copper-responsive ATP7A mutation, G727R

Menkes disease is a fatal neurodegenerative disorder of infancy caused by defects in an X-linked copper transport gene, ATP7A. Evidence from a recent clinical trial indicates that favorable response to early treatment of this disorder with copper injections involves mutations that retain some copper transport capacity. In three unrelated infants, we identified the same mutation, G727R, in the second transmembrane segment of ATP7A that complemented a Saccharomyces cerevisiae copper transport mutant, consistent with partial copper transport activity. Quantitative reverse transcription-polymerase chain reaction studies showed approximately normal levels of ATP7A(G727R) transcript in two patients' fibroblasts compared to wild-type controls, but Western blot analyses showed markedly reduced quantities of ATP7A, suggesting post-translational degradation. We confirmed the latter by comparing degradation rates of mutant and wild-type ATP7A via cyclohexamide treatment of cultured fibroblasts; half-life of the G727R mutant was 2.9h and for the wild-type, 11.4h. We also documented a X-box binding protein 1 splice variant in G727R cells-known to be associated with the cellular misfolded protein response. Patient A, diagnosed 6 months of age, began treatment at 228days (7.6 months) of age. At his current age (2.5 years), his overall neurodevelopment remains at a 2- to 4-month level. In contrast, patient B and patient C were diagnosed in the neonatal period, began treatment within 25 days of age, and show near normal neurodevelopment at their current ages, 3years (patient B), and 7 months (patient C). The poor clinical outcome in patient A with the same missense mutation as patient A and patient B with near normal oucomes, confirms the importance of early medical intervention in Menkes disease and highlights the critical potential benefit of newborn screening for this disorder.

Neonatal diagnosis and treatment of Menkes disease

BACKGROUND

Menkes disease is a fatal neurodegenerative disorder of infancy caused by diverse mutations in a copper-transport gene, ATP7A. Early treatment with copper injections may prevent death and illness, but presymptomatic detection is hindered by the inadequate sensitivity and specificity of diagnostic tests. Exploiting the deficiency of a copper enzyme, dopamine-beta-hydroxylase, we prospectively evaluated the diagnostic usefulness of plasma neurochemical levels, assessed the clinical effect of early detection, and investigated the molecular bases for treatment outcomes.

METHODS

Between May 1997 and July 2005, we measured plasma dopamine, norepinephrine, dihydroxyphenylacetic acid, and dihydroxyphenylglycol in 81 infants at risk. In 12 newborns who met the eligibility criteria and began copper-replacement therapy within 22 days after birth, we tracked survival and neurodevelopment longitudinally for 1.5 to 8 years. We characterized ATP7A mutations using yeast complementation, reverse-transcriptase-polymerase-chain-reaction analysis, and immunohistochemical analysis.

RESULTS

Of 81 infants at risk, 46 had abnormal neurochemical findings indicating low dopamine-beta-hydroxylase activity. On the basis of longitudinal follow-up, patients were classified as affected or unaffected by Menkes disease, and the neurochemical profiles were shown to have high sensitivity and specificity for detecting disease. Among 12 newborns with positive screening tests who were treated early with copper, survival at a median follow-up of 4.6 years was 92%, as compared with 13% at a median follow-up of 1.8 years for a historical control group of 15 late-diagnosis and late-treatment patients. Two of the 12 patients had normal neurodevelopment and brain myelination; 1 of these patients had a mutation that complemented a Saccharomyces cerevisiae copper-transport mutation, indicating partial ATPase activity, and the other had a mutation that allowed some correct ATP7A splicing.

CONCLUSIONS

Neonatal diagnosis of Menkes disease by plasma neurochemical measurements and early treatment with copper may improve clinical outcomes. Affected newborns who have mutations that do not completely abrogate ATP7A function may be especially responsive to early copper treatment. (ClinicalTrials.gov number, NCT00001262.)

AAV vector integration sites in mouse hepatocellular carcinoma

Adeno-associated viruses (AAV) are promising gene therapy vectors that have little or no acute toxicity. We show that normal mice and mice with mucopolysaccharidosis VII (MPS VII) develop hepatocellular carcinoma (HCC) after neonatal injection of an AAV vector expressing b-glucuronidase. AAV proviruses were isolated from four tumors and were all located within a 6-kilobase region of chromosome 12. This locus encodes several imprinted transcripts, small nucleolar RNAs (snoRNAs), and microRNAs. Transcripts from adjacent genes encoding snoRNAs and microRNAs were overexpressed in tumors. Our findings implicate this locus in the development of HCC and raise concerns over the clinical use of AAV vectors.

Differences in ATP7A gene expression underlie intrafamilial variability in Menkes disease/occipital horn syndrome

BACKGROUND

Pronounced intrafamilial variability is unusual in Menkes disease and its variants. We report two unrelated families featuring affected members with unusually disparate clinical and biochemical phenotypes and explore the underlying molecular mechanisms.

METHODS

We measured biochemical markers of impaired copper transport in five patients from two unrelated families and used RNase protection, quantitative reverse transcription (RT)-PCR, Western blot analysis and yeast complementation studies to characterise two ATP7A missense mutations, A1362D and S637L.

RESULTS

In two brothers (family A) with A1362D, RNase protection and Western blot analyses revealed higher amounts of ATP7A transcript and protein in the older, mildly affected patient, who also had a higher plasma copper level and lower cerebrospinal fluid dihydroxyphenylalanine : dihydroxyphenylglycol ratio. These findings indicate greater gastrointestinal absorption of copper and higher activity of dopamine-beta-hydroxylase, a copper-dependent enzyme, respectively. In family B, three males with a missense mutation (S637L) in an exon 8 splicing enhancer showed equally reduced amounts of ATP7A transcript and protein by quantitative RT-PCR and western blot analysis, respectively, despite a more severe phenotype in the youngest. This patient's medical history was notable for cardiac arrest as a neonate, to which we attribute his more severe neurodevelopmental outcome.

CONCLUSIONS

These families illustrate that genetic and non-genetic mechanisms may underlie intrafamilial variability in Menkes disease and its variants.

Clinical response to persistent, low-level beta-glucuronidase expression in the murine model of mucopolysaccharidosis type VII

Mucopolysaccharidosis type VII (MPS VII) is a lysosomal storage disease caused by beta-glucuronidase (GUSB) deficiency. This disease exhibits a broad spectrum of clinical signs including skeletal dysplasia, retinal degeneration, cognitive deficits and hearing impairment. Sustained, high-level expression of GUSB significantly improves the clinical course of the disease in the murine model of MPS VII. Low levels of enzyme expression (1-5% of normal) can significantly reduce the biochemical and histopathological manifestations of MPS VII. However, it has not been clear from previous studies whether persistent, low levels of circulating GUSB lead to significant improvements in the clinical presentation of this disease. We generated a rAAV2 vector that mediates persistent, low-level GUSB expression in the liver. Liver and serum levels of GUSB were maintained at approximately 5% and approximately 2.5% of normal, respectively, while other tissue ranged from background levels to 0.9%. This level of activity significantly reduced the secondary elevations of alpha-galactosidase and the levels of glycosaminoglycans in multiple tissues. Interestingly, this level of GUSB was also sufficient to reduce lysosomal storage in neurons in the brain. Although there were small but statistically significant improvements in retinal function, auditory function, skeletal dysplasia, and reproduction in rAAV-treated MPS VII mice, the clinical deficits were still profound and there was no improvement in lifespan. These data suggest that circulating levels of GUSB greater than 2.5% will be required to achieve substantial clinical improvements in MPS VII.

Central Nervous System-directed AAV2/5-Mediated Gene Therapy Synergizes with Bone Marrow Transplantation in the Murine Model of Globoid-cell Leukodystrophy

Globoid-cell leukodystrophy (GLD) is a rapidly progressing inherited neurodegenerative disorder caused by a deficiency in galactosylceramidase activity. Previous studies in the murine model of GLD (Twitcher mouse) have shown that both bone marrow transplantation (BMT) and central nervous system (CNS)-directed gene therapy can be moderately effective at ameliorating certain aspects of GLD. As BMT and CNS-directed gene therapy target fundamentally different tissues, we tested the hypothesis that combining these disparate therapies would be more efficacious than either therapy alone. Mice receiving myeloreductive conditioning at birth followed by syngeneic BMT had approximately 25-35% donor chimerism. Untreated Twitcher mice, Twitcher mice treated with BMT alone, AAV2/5 alone, or a combination of BMT and AAV2/5 had mean lifespans of 39, 44, 49, and 104 days, respectively. Twitcher mice treated with a combination of BMT and AAV2/5 also had significantly improved performance in several behavioral tests and greater reduction in demyelination, astrocytosis, and macrophage infiltration compared to untreated Twitcher mice or mice that received either therapy alone. These data suggest that CNS-directed gene therapy synergizes with BMT. The combination of these disparate therapeutic approaches may form the basis for more effective treatment of this inherited neurodegenerative disorder.

Observed incidence of tumorigenesis in long-term rodent studies of rAAV vectors

Gene therapy using recombinant adeno-associated virus vectors (rAAV) is generally considered safe. During the course of a study designed to determine the long-term efficacy of rAAV-mediated gene therapy initiated in newborn mice with the lysosomal storage disease, mucopolysaccharidosis type VII (MPSVII), a significant incidence of hepatocellular carcinomas and angiosarcomas was discovered. A hepatocellular carcinoma was first detected in a 35-week-old mouse and by 72 weeks of age, three out of five rAAV-treated MPSVII mice had similar lesions. These types of tumors had not been seen previously in long-term studies of MPSVII mice using recombinant enzyme or bone marrow transplantation. In an attempt to ascertain whether mouse strain or GUSB expression confers susceptibility to tumor formation, we histopathologically examined untreated normal mice of the same strain, untreated MPSVII mice, and normal mice overexpressing human GUSB for the presence of tumors and increased hepatocyte replication. The results of these studies do not indicate that MPSVII mice or mice overexpressing human GUSB are susceptible to tumor formation; however, the number of animals examined is too small to draw definitive conclusions. Results from quantitative PCR performed on the tumor samples suggest that the tumors are probably not caused by an insertional mutagenesis event followed by the clonal expansion of a transformed cell. In a separate study, a relatively large group of mice injected with varying doses and types of rAAV vectors had no evidence of hepatic or vascular tumors. Although the mechanism of tumor formation is currently unknown, the tumorigenic potential of rAAV vectors must be rigorously determined in long-term in vivo studies.