Efficient prime editing in mouse brain, liver and heart with dual AAVs

Realizing the promise of prime editing for the study and treatment of genetic disorders requires efficient methods for delivering prime editors (PEs) in vivo. Here we describe the identification of bottlenecks limiting adeno-associated virus (AAV)-mediated prime editing in vivo and the development of AAV-PE vectors with increased PE expression, prime editing guide RNA stability and modulation of DNA repair. The resulting dual-AAV systems, v1em and v3em PE-AAV, enable therapeutically relevant prime editing in mouse brain (up to 42% efficiency in cortex), liver (up to 46%) and heart (up to 11%). We apply these systems to install putative protective mutations in vivo for Alzheimer's disease in astrocytes and for coronary artery disease in hepatocytes. In vivo prime editing with v3em PE-AAV caused no detectable off-target effects or significant changes in liver enzymes or histology. Optimized PE-AAV systems support the highest unenriched levels of in vivo prime editing reported to date, facilitating the study and potential treatment of diseases with a genetic component.

Rescue of hearing by adenine base editing in a humanized mouse model of Usher syndrome type 1F

Usher syndrome type 1F (USH1F), characterized by congenital lack of hearing and balance and progressive loss of vision, is caused by mutations in the PCDH15 gene. In the Ashkenazi population, a recessive truncation mutation accounts for a large proportion of USH1F cases. The truncation is caused by a single C→T mutation, which converts an arginine codon to a stop (R245X). To test the potential for base editors to revert this mutation, we developed a humanized Pcdh15R245X mouse model for USH1F. Mice homozygous for the R245X mutation were deaf and exhibited profound balance deficits, while heterozygous mice were unaffected. Here we show that an adenine base editor (ABE) is capable of reversing the R245X mutation to restore the PCDH15 sequence and function. We packaged a split-intein ABE into dual adeno-associated virus (AAV) vectors and delivered them into cochleas of neonatal USH1F mice. Hearing was not restored in a Pcdh15 constitutive null mouse despite base editing, perhaps because of early disorganization of cochlear hair cells. However, injection of vectors encoding the split ABE into a late-deletion conditional Pcdh15 knockout rescued hearing. This study demonstrates the ability of an ABE to correct the PCDH15 R245X mutation in the cochlea and restore hearing.

Base editing rescue of spinal muscular atrophy in cells and in mice

Spinal muscular atrophy (SMA), the leading genetic cause of infant mortality, arises from survival motor neuron (SMN) protein insufficiency resulting from SMN1 loss. Approved therapies circumvent endogenous SMN regulation and require repeated dosing or may wane. We describe genome editing of SMN2, an insufficient copy of SMN1 harboring a C6>T mutation, to permanently restore SMN protein levels and rescue SMA phenotypes. We used nucleases or base editors to modify five SMN2 regulatory regions. Base editing converted SMN2 T6>C, restoring SMN protein levels to wild type. Adeno-associated virus serotype 9-mediated base editor delivery in Δ7SMA mice yielded 87% average T6>C conversion, improved motor function, and extended average life span, which was enhanced by one-time base editor and nusinersen coadministration (111 versus 17 days untreated). These findings demonstrate the potential of a one-time base editing treatment for SMA.

Efficient in vivo base editing via single adeno-associated viruses with size-optimized genomes encoding compact adenine base editors

The viral delivery of base editors has been complicated by their size and by the limited packaging capacity of adeno-associated viruses (AAVs). Typically, dual-AAV approaches based on trans-splicing inteins have been used. Here we show that, compared with dual-AAV systems, AAVs with size-optimized genomes incorporating compact adenine base editors (ABEs) enable efficient editing in mice at similar or lower doses. Single-AAV-encoded ABEs retro-orbitally injected in mice led to editing efficiencies in liver (66%), heart (33%) and muscle (22%) tissues that were up to 2.5-fold those of dual-AAV ABE8e, and to a 93% knockdown (on average) of human PCSK9 and of mouse Pcsk9 and Angptl3 in circulation, concomitant with substantial reductions of plasma cholesterol and triglycerides. Moreover, three size-minimized ABE8e variants, each compatible with single-AAV delivery, collectively offer compatibility with protospacer-adjacent motifs for editing approximately 82% of the adenines in the human genome. ABEs encoded within single AAVs will facilitate research and therapeutic applications of base editing by simplifying AAV production and characterization, and by reducing the dose required for the desired level of editing.

Programmable deletion, replacement, integration and inversion of large DNA sequences with twin prime editing

The targeted deletion, replacement, integration or inversion of genomic sequences could be used to study or treat human genetic diseases, but existing methods typically require double-strand DNA breaks (DSBs) that lead to undesired consequences, including uncontrolled indel mixtures and chromosomal abnormalities. Here we describe twin prime editing (twinPE), a DSB-independent method that uses a prime editor protein and two prime editing guide RNAs (pegRNAs) for the programmable replacement or excision of DNA sequences at endogenous human genomic sites. The two pegRNAs template the synthesis of complementary DNA flaps on opposing strands of genomic DNA, which replace the endogenous DNA sequence between the prime-editor-induced nick sites. When combined with a site-specific serine recombinase, twinPE enabled targeted integration of gene-sized DNA plasmids (>5,000 bp) and targeted sequence inversions of 40 kb in human cells. TwinPE expands the capabilities of precision gene editing and might synergize with other tools for the correction or complementation of large or complex human pathogenic alleles.

In vivo base editing restores sensory transduction and transiently improves auditory function in a mouse model of recessive deafness

Most genetic diseases arise from recessive point mutations that require correction, rather than disruption, of the pathogenic allele to benefit patients. Base editing has the potential to directly repair point mutations and provide therapeutic restoration of gene function. Mutations of transmembrane channel-like 1 gene (TMC1) can cause dominant or recessive deafness. We developed a base editing strategy to treat Baringo mice, which carry a recessive, loss-of-function point mutation (c.A545G; resulting in the substitution p.Y182C) in Tmc1 that causes deafness. Tmc1 encodes a protein that forms mechanosensitive ion channels in sensory hair cells of the inner ear and is required for normal auditory function. We found that sensory hair cells of Baringo mice have a complete loss of auditory sensory transduction. To repair the mutation, we tested several optimized cytosine base editors (CBEmax variants) and guide RNAs in Baringo mouse embryonic fibroblasts. We packaged the most promising CBE, derived from an activation-induced cytidine deaminase (AID), into dual adeno-associated viruses (AAVs) using a split-intein delivery system. The dual AID-CBEmax AAVs were injected into the inner ears of Baringo mice at postnatal day 1. Injected mice showed up to 51% reversion of the Tmc1 c.A545G point mutation to wild-type sequence (c.A545A) in Tmc1 transcripts. Repair of Tmc1 in vivo restored inner hair cell sensory transduction and hair cell morphology and transiently rescued low-frequency hearing 4 weeks after injection. These findings provide a foundation for a potential one-time treatment for recessive hearing loss and support further development of base editing to correct pathogenic point mutations.

In vivo base editing rescues Hutchinson-Gilford progeria syndrome in mice

Hutchinson-Gilford progeria syndrome (HGPS or progeria) is typically caused by a dominant-negative C•G-to-T•A mutation (c.1824 C>T; p.G608G) in LMNA, the gene that encodes nuclear lamin A. This mutation causes RNA mis-splicing that produces progerin, a toxic protein that induces rapid ageing and shortens the lifespan of children with progeria to approximately 14 years1-4. Adenine base editors (ABEs) convert targeted A•T base pairs to G•C base pairs with minimal by-products and without requiring double-strand DNA breaks or donor DNA templates5,6. Here we describe the use of an ABE to directly correct the pathogenic HGPS mutation in cultured fibroblasts derived from children with progeria and in a mouse model of HGPS. Lentiviral delivery of the ABE to fibroblasts from children with HGPS resulted in 87-91% correction of the pathogenic allele, mitigation of RNA mis-splicing, reduced levels of progerin and correction of nuclear abnormalities. Unbiased off-target DNA and RNA editing analysis did not detect off-target editing in treated patient-derived fibroblasts. In transgenic mice that are homozygous for the human LMNA c.1824 C>T allele, a single retro-orbital injection of adeno-associated virus 9 (AAV9) encoding the ABE resulted in substantial, durable correction of the pathogenic mutation (around 20-60% across various organs six months after injection), restoration of normal RNA splicing and reduction of progerin protein levels. In vivo base editing rescued the vascular pathology of the mice, preserving vascular smooth muscle cell counts and preventing adventitial fibrosis. A single injection of ABE-expressing AAV9 at postnatal day 14 improved vitality and greatly extended the median lifespan of the mice from 215 to 510 days. These findings demonstrate the potential of in vivo base editing as a possible treatment for HGPS and other genetic diseases by directly correcting their root cause.

Cytosine and adenine base editing of the brain, liver, retina, heart and skeletal muscle of mice via adeno-associated viruses

The success of base editors for the study and treatment of genetic diseases depends on the ability to deliver them in vivo to the relevant cell types. Delivery via adeno-associated viruses (AAVs) is limited by AAV-packaging capacity, which precludes the use of full-length base editors. Here, we report the application of dual AAVs for the delivery of split cytosine and adenine base editors that are then reconstituted by trans-splicing inteins. Optimized dual AAVs enable in vivo base editing at therapeutically relevant efficiencies and dosages in the mouse brain (up to 59% of unsorted cortical tissue), liver (38%), retina (38%), heart (20%) and skeletal muscle (9%). We also show that base editing corrects, in mouse brain tissue, a mutation that causes Niemann-Pick disease type C (a neurodegenerative ataxia), slowing down neurodegeneration and increasing the animals’ lifespan. The optimized delivery vectors should facilitate the efficient introduction of targeted point mutations into multiple tissues of therapeutic interest.

Search-and-replace genome editing without double-strand breaks or donor DNA

Most genetic variants that contribute to disease¹ are challenging to correct efficiently and without excess byproducts^2-5. Here we describe prime editing, a versatile and precise genome editing method that directly writes new genetic information into a specified DNA site using a catalytically impaired Cas9 endonuclease fused to an engineered reverse transcriptase, programmed with a prime editing guide RNA (pegRNA) that both specifies the target site and encodes the desired edit. We performed more than 175 edits in human cells, including targeted insertions, deletions, and all 12 types of point mutation, without requiring double-strand breaks or donor DNA templates. We used prime editing in human cells to correct, efficiently and with few byproducts, the primary genetic causes of sickle cell disease (requiring a transversion in HBB) and Tay-Sachs disease (requiring a deletion in HEXA); to install a protective transversion in PRNP; and to insert various tags and epitopes precisely into target loci. Four human cell lines and primary post-mitotic mouse cortical neurons support prime editing with varying efficiencies. Prime editing shows higher or similar efficiency and fewer byproducts than homology-directed repair, has complementary strengths and weaknesses compared to base editing, and induces much lower off-target editing than Cas9 nuclease at known Cas9 off-target sites. Prime editing substantially expands the scope and capabilities of genome editing, and in principle could correct up to 89% of known genetic variants associated with human diseases.

Search-and-replace genome editing without double-strand breaks or donor DNA

Most genetic variants that contribute to disease¹ are challenging to correct efficiently and without excess byproducts^2–5. Here we describe prime editing, a versatile and precise genome editing method that directly writes new genetic information into a specified DNA site using a catalytically impaired Cas9 fused to an engineered reverse transcriptase, programmed with a prime editing guide RNA (pegRNA) that both specifies the target site and encodes the desired edit. We performed >175 edits in human cells including targeted insertions, deletions, and all 12 types of point mutations without requiring double-strand breaks or donor DNA templates. We applied prime editing in human cells to correct efficiently and with few byproducts the primary genetic causes of sickle cell disease (requiring a transversion in HBB) and Tay-Sachs disease (requiring a deletion in HEXA), to install a protective transversion in PRNP, and to precisely insert various tags and epitopes into target loci. Four human cell lines and primary post-mitotic mouse cortical neurons support prime editing with varying efficiencies. Prime editing shows higher or similar efficiency and fewer byproducts than homology-directed repair, complementary strengths and weaknesses compared to base editing, and much lower off-target editing than Cas9 nuclease at known Cas9 off-target sites. Prime editing substantially expands the scope and capabilities of genome editing, and in principle can correct up to 89% of known genetic variants associated with human diseases.

Continuous evolution of base editors with expanded target compatibility and improved activity

Base editors use DNA-modifying enzymes targeted with a catalytically impaired CRISPR protein to precisely install point mutations. Here, we develop phage-assisted continuous evolution of base editors (BE-PACE) to improve their editing efficiency and target sequence compatibility. We used BE-PACE to evolve cytosine base editors (CBEs) that overcome target sequence context constraints of canonical CBEs. One evolved CBE, evoAPOBEC1-BE4max, is up to 26-fold more efficient at editing cytosine in the GC context, a disfavored context for wild-type APOBEC1 deaminase, while maintaining efficient editing in all other sequence contexts tested. Another evolved deaminase, evoFERNY, is 29% smaller than APOBEC1 and edits efficiently in all tested sequence contexts. We also evolved a CBE based on CDA1 deaminase with much higher editing efficiency at difficult target sites. Finally, we used data from evolved CBEs to illuminate the relationship between deaminase activity, base editing efficiency, editing window width and byproduct formation. These findings establish a system for rapid evolution of base editors and inform their use and improvement.

Publisher Correction: Continuous evolution of base editors with expanded target compatibility and improved activity

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Improving cytidine and adenine base editors by expression optimization and ancestral reconstruction

Base editors enable targeted single-nucleotide conversions in genomic DNA. Here we show that expression levels are a bottleneck in base-editing efficiency. We optimize cytidine (BE4) and adenine (ABE7.10) base editors by modification of nuclear localization signals (NLS) and codon usage, and ancestral reconstruction of the deaminase component. The resulting BE4max, AncBE4max, and ABEmax editors correct pathogenic SNPs with substantially increased efficiency in a variety of mammalian cell types.

Membrane-associated guanylate kinase dynamics reveal regional and developmental specificity of synapse stability

KEY POINTS

The membrane-associated guanylate kinase (MAGUK) family of synaptic scaffolding proteins anchor glutamate receptors at CNS synapses. MAGUK removal via RNAi-mediated knockdown in the CA1 hippocampal region in immature animals causes rapid and lasting reductions in glutamatergic transmission. In mature animals, the same manipulation has little acute effect. The hippocampal dentate gyrus, a region with ongoing adult neurogenesis, is sensitive to MAGUK loss in mature animals, behaving like an immature CA1. Over long time courses, removal of MAGUKs in CA1 causes reductions in glutamatergic transmission, indicating that synapses in mature animals require MAGUKs for anchoring glutamate receptors, but are much more stable. These results demonstrate regional and developmental control of synapse stability and suggest the existence of a sensitive period of heightened hippocampal plasticity in CA1 of pre-adolescent rodents, and in dentate gyrus throughout maturity.

ABSTRACT

Fast excitatory transmission in the brain requires localization of glutamate receptors to synapses. The membrane-associated guanylate kinase (MAGUK) family of synaptic scaffolding proteins is critical for localization of glutamate receptors to synapses. Although the MAGUKs are well-studied in reduced preparations and young animals, few data exist on their role in adult animals. Here, we present a detailed developmental study of the role of the MAGUKs during rat development. We first confirmed by knockdown experiments that MAGUKs are essential for glutamatergic transmission in young animals and cultured slices, and an increase in postsynaptic density protein 95 (PSD-95) by overexpression caused correlated increases in glutamatergic transmission. We found that CA1 synapses in adults, in contrast, were largely unaffected by overexpression of MAGUKs, and although adult CA1 synapses required MAGUKs to the same degree as synapses in young animals, this was only apparent over long time scales of knockdown. We additionally showed that overexpression of MAGUKs is likely to function to accelerate the developmental strengthening of excitatory transmission. Finally, we showed that adult dentate gyrus appears similar to immature CA1, demonstrating regional and developmental control of MAGUK dynamics. Together, these results demonstrate a period of juvenile instability at CA1 synapses, followed by a period of adult stability in which synapses are acutely unaffected by changes in MAGUK abundance.

The US Experience with Local Economic Development

In this paper the increasing intensity of intermunicipal and interstate economic competition in the USA is noted. It is argued that the federal structure of the USA, the present political climate, and the mobility of capital combine to produce a situation of positive feedback leading to everincreasing subsidies. The situation constitutes a classic prisoner's dilemma. Decreased competition would be in the interests of all units of government. However, there is no way that a state or local government can opt out of the competition unilaterally and no mechanism by which collective action can be taken to reduce the intensity of competition. Also considered in this paper are the aggregate effects of local economic development programs in terms of taxes and public expenditures, efficiency, and equity, and several less commonly discussed considerations.

Synaptic Consolidation Normalizes AMPAR Quantal Size following MAGUK Loss

The mechanisms controlling synapse growth and maintenance are of critical importance for learning and memory. The MAGUK family of synaptic scaffolding proteins is abundantly expressed at glutamatergic central synapses, but their importance in controlling the synaptic content of glutamate receptors is poorly understood. Here, we use a chained RNAi-mediated knockdown approach to simultaneously remove PSD-93, PSD-95, and SAP102, the MAGUKs previously shown to be responsible for synaptic localization of glutamate receptors. We find that MAGUKs are specifically responsible for creating functional synapses after initial spine formation by filling functionally silent spines with glutamate receptors. Removal of the MAGUKs causes a transient reduction in AMPA receptor quantal size followed by synaptic consolidation resulting in a normalization of quantal size at the few remaining functional synapses. Consolidation requires signaling through L-type calcium channels, CaM kinase kinase, and the GluA2 AMPA receptor subunit, akin to a homeostatic process.

Indication of electron neutrino appearance from an accelerator-produced off-axis muon neutrino beam

The T2K experiment observes indications of ν(μ) → ν(e) appearance in data accumulated with 1.43×10(20) protons on target. Six events pass all selection criteria at the far detector. In a three-flavor neutrino oscillation scenario with |Δm(23)(2)| = 2.4×10(-3)  eV(2), sin(2)2θ(23) = 1 and sin(2)2θ(13) = 0, the expected number of such events is 1.5±0.3(syst). Under this hypothesis, the probability to observe six or more candidate events is 7×10(-3), equivalent to 2.5σ significance. At 90% C.L., the data are consistent with 0.03(0.04) < sin(2)2θ(13) < 0.28(0.34) for δ(CP) = 0 and a normal (inverted) hierarchy.

Partial anomalous pulmonary venous return: iatrogenic occlusion of the innominate vein producing right-to-left shunt

A patient experienced acute dyspnea and hypoxia upon removal of a thrombosed peripherally inserted central venous catheter. This was shown to be caused by innominate vein occlusion complicated by a right-to-left shunt, via an anomalous pulmonary vein, causing arterial desaturation. A stent was placed in the occluded innominate vein and arterial saturation returned to normal.

Reactivation of herpes zoster after liver biopsy

A patient developed reactivation of herpes zoster infection (shingles) after a routine liver biopsy. Reactivation of herpes is often related to trauma. This entity should be considered when patients report postbiopsy pain inappropriate to the procedure. If the typical rash of shingles develops, antiviral therapy should be considered.

Favorable selection in the Medicare+Choice program: new evidence

Historically, studying the Medicare managed care favorable-selection issue has been difficult because direct data on managed care enrollees have been unavailable. In this study, we analyzed the first year of Balanced Budget Act (BBA)-mandated inpatient encounter data. Based on this comparison of actual managed care and fee-for-service (FFS) beneficiaries, it appears that there are significant differences between these populations. The most striking differences are found in the comparison of average risk factors, indicating a clear bias in the managed care populations toward beneficiaries predicted to be less costly.

Risk Adjustment for the Medicare program: lessons learned from research and demonstrations

The Balanced Budget Act (BBA) of 1997 requires numerous changes in Medicare. Medicare's managed care program has been reinvented as "Medicare + Choice," offering an expanded range of delivery system options for beneficiaries and a schedule of payment changes that will dramatically affect managed care plans. Preceding some of these BBA-legislated changes to Medicare were years of research and demonstrations. Risk-adjusted payment in the Medicare + Choice program, which is mandated for implementation in 2000, is one example of a longstanding developmental initiative. This paper provides a brief overview of risk adjustment-related research and demonstration activities carried out by the Health Care Financing Administration (HCFA) since the 1980s, and describes a possible technical approach for the implementation of risk-adjusted Medicare managed care payments in 2000.

Delivering home-based case management to families with children with mental retardation and developmental disabilities

To meet the needs of individuals with mental retardation and developmental disabilities (MR/DD) and their families living in urban setting, a noncenter-based model of case management was implemented. In contrast to traditional case management in which families and consumers come to the case manager and most service coordination is done by telephone or in meetings at the case manager/social worker's worksite, the case manager in a noncenter-based model is mobile and able to meet the consumer and family in their domains. In this model, case management is provided in conjunction with in-home residential habilitation and funded by Medicaid under the Home and Community Based Services Waiver. This funding stream provides monies for nontraditional services delivered in noncertified settings. Case managers used the Family Resource Scale to get an immediate indication of the resources and needs of each family. The scale highlights the adequacy of a person's basic and caregiving resources, as well as financial needs. The findings from this study suggest that an understanding of both disability and entitlements is essential for case managers who may have to help advocate for consumers around services and benefits. Moreover, to build and maintain an egalitarian and supportive relationship with families, the importance of caregiver-specified resources and needs must be recognized by case managers. Access to resource information and the ability to engage the family in problem-solving depends on a well-trained staff with the ability to respond to individuals with different needs and from a variety of circumstances. These essential skills prepare a case manager to assist families with their immediate requirements as well as to mobilize them to plan for future needs.

Tuberculoma presenting as an en plaque meningioma. Case report

Intracranial tuberculomas generally present as either solitary or multiple lesions in the brain parenchyma. They are characterized by a ring-enhancing area on either computerized tomography scans or magnetic resonance images. A case is presented in which an intracranial tuberculoma was dural based and had an appearance similar to an en plaque meningioma.

Employers' attitudes towards persons with disabilities: a comparison of national and New York State data

This paper compares the results of two large-scale studies conducted as part of an ongoing research programme on employers' attitudes towards the employability of persons with severe disabilities--a study of Fortune 500 corporations and a study of employers doing business in New York State. The results indicated that both groups of employers were favourable towards the employability of persons with disabilities. Executives from large national corporations were more favourable than those from the predominantly small companies doing business in New York State. Prior contact with persons with disabilities that was positively evaluated appeared to differentiate those more and less favourable in both study groups, especially in the smaller companies of the New York State study group. Employers' characteristics associated with differences in attitudes in the literature (e.g. education, work experience) also appeared to be confirmed by data from New York State companies more than from the corporations of the Fortune 500.

Differences in job placements between men and women with mental retardation

Thirty-three men and women with mental retardation living in the New York metropolitan area (USA), who entered a supported employment programme were followed during their first 9 months in competitive employment. Differences in placement outcomes were consistently associated with gender differences. The implications of these findings are discussed in terms of providing employment services to men and women with mental retardation and developmental disabilities.

[Retroperitoneal teratomas in the perinatal period. Review of the literature concerning a neonatal, immature, aggressive teratoma]

A neonate with an immature, poorly demarcated retroperitoneal teratoma invading the aorta-vena cava space died immediately after surgery. Among 34 cases of retroperitoneal teratoma discovered during the first postnatal month, including one renal case and ours, eight can be considered malignant on the basis of histology in two cases and clinical course in six. Five of these tumors exhibited a significant immature component. In neonates, the proportion of malignant teratomas is greater for retroperitoneal tumors than for other sites: sacrum and coccyx, heart, neck, mediastinum, and abdomen. Evaluation of chemotherapy in teratomas with significant immature components is difficult because few of the patients of this small sample received such treatment. As in other sites, regardless of the degree of maturity, exeresis must be as complete as possible.

Understanding the Medicare Fee Schedule and its impact on physicians under the final rule

On January 1, 1992, the Medicare program unveiled a new method for paying physicians known as the Medicare Fee Schedule (MFS). The new fee schedule is a complex system of administrative pricing based on the resource inputs used in producing physician services. The MFS consists of three parts: 1) a Relative Value Scale, which assigns to each medical service a value relative to all other services; 2) a conversion factor, which converts the relative values into dollars; and 3) a geographic adjustment factor, which adjusts payments based on geographic differences in the cost of producing physician services. In this article, the following are addressed: how the relative values were determined; how the geographic adjustment factor was constructed; and how the conversion factor was calculated. In addition, balance billing limits and the Medicare Volume Performance Standards (MVPS) are described. Computer simulations of the impact of the MFS on payments to physicians are presented. The authors found that the MFS will 1) redistribute payments away from surgeons, radiologists, and other procedure-based specialties toward the primary care specialties; 2) redistribute payments away from urban areas toward rural areas; and 3) redistribute payments away from invasive procedures and diagnostic tests toward evaluation and management services. The authors conclude with a discussion of the future refinements of the MFS, its applicability to other payers, and whether it will accomplish its intended purposes.

The Medicare Fee Schedule unveiled: an account of physician payment reform

On January 1, 1992, the Medicare program unveiled a new method for paying physicians known as the Medicare Fee Schedule (MFS). The new fee schedule is a complex system of administrative pricing based on the resource inputs used in producing physician services. The MFS consists of three parts: (1) a Relative Value Scale (RVS) which assigns to each medical service a value relative to all other services; (2) a Conversion Factor (CF) which converts the relative values into dollars; and (3) a Geographic Adjustment Factor (GAF) which adjusts payments based on geographic differences in the cost of producing physician services. In the paper we explain: how the relative values were determined; how the GAF was constructed; and how the CF was calculated. In addition, we explain balancing billing limits and the Medicare Volume Performance Standards (MVPS). We then present computer simulations of the impact of the MFS on payments to physicians. We find that the MFS will: (1) redistribute payments away from surgeons, radiologists, and other procedure-based specialties toward the primary care specialties, (2) redistribute payment away from urban areas toward rural areas, (3) redistribute payments away from invasive procedures and diagnostic tests toward evaluation and management services. We conclude with a discussion of the future refinements of the MFS, its applicability to other payors, and whether it will accomplish its intended purposes.

A one year follow-up of urban young adults with mental retardation in supported employment

There is little information available about the provision of supported employment services for individuals from diverse cultural, ethnic and economic backgrounds. To fill this gap, in relation to the specific experiences of urban youth with mental retardation, we initiated an agency based longitudinal study of our employment training programmes. Data from the first year follow up of 45 young adults with mental retardation is presented. Information regarding all phases of the job training and job placement process was examined. The major findings are that 71% of the trainees were employed during the first nine months post-training, with approximately 30% of the trainees working for six months or more. Overall, 75% of the trainees' placements were in service industries and the amount of direct support the trainees required decreased over time. Additional findings and their implications for programme development are discussed in relation to the unique needs of urban young adults with developmental disabilities.

Role of "buttoned" double-disc device in the management of atrial septal defects

Sixteen patients seen over a 9-month period ending in August 1990 were offered transcatheter closure of their ASD with a custom-made "buttoned" double-disc device. The study was approved by the Institutional Review Board and informed consent was obtained in each case. The device consists of an occluder, a counteroccluder, and a loading wire and is delivered to the ASD site via an 8F sheath. Parents of two children elected surgical closure. In five children the stretched diameter of the ASD was too large (greater than 20 mm) and transcatheter closure was not attempted. These seven children underwent elective surgical closure without incident. In one child the defect measured 5 mm and the Qp:Qs was 1.4:1 and therefore ASD closure was not recommended. In the remaining eight children transcatheter closure was attempted. In two of the children the occluder pulled through the ASD and was successfully retrieved and the children later underwent uneventful elective surgical closure. The device was implanted across the ASD in six children. In one child the device dislodged from the ASD site within minutes after implantation and the child was sent to emergency surgery, where the device was removed and the ASD was closed. In the remaining five patients, aged 7 months to 45 years (weight 3.6 to 50 kg), with a Qp:Qs range of 1.3 to 2.3 and a stretched diameter of 10 to 19 mm, the ASD closure was successful with 25 to 40 mm size devices. Repeat echo-Doppler studies 2 weeks and 3 months after the procedure in all patients and 6 months later in two children did not reveal any residual shunt. It is concluded that (1) the custom-made "buttoned" double-disc device can be implanted across the ASD safely and effectively via an 8F sheath, thus making transcatheter ASD closure feasible even in very young infants; (2) measurement of stretched diameter of the ASD in the catheterization laboratory is a useful guide for selection of an appropriate-sized device; and (3) additional clinical trials are warranted to confirm the efficacy and safety of the device.

Employment of persons with severe disabilities in large businesses in the United States

A mail survey of the largest businesses in the US, the Fortune 500 industrial and service corporations, examined the attitudes of personnel and human resource executives towards the employability of persons with severe disabilities and actual corporate practices regarding the employment of persons with disabilities. The 341 executives who responded are found to be favourable to the employment of persons with disabilities, especially if the executives work in corporations that have hired persons with disabilities within the past three years, and/or have had personally good contact with persons with disabilities in the past. Almost two-thirds of the corporations have a policy regarding hiring persons with disabilities; over one-half have hired such persons within the past three years; and over one-third have supported work programmes.

Tricuspid atresia: association with persistent truncus arteriosus

Clinical, echo-Doppler, and pathologic data of a rare case of tricuspid atresia in association with truncus arteriosus are presented. There are only six patients (including the patient reported here) with this anomaly in whom detailed pathologic and/or clinical descriptions are available in the literature. An additional six cases were mentioned in the literature but without any details. A prevalence rate of 1.4% among tricuspid atresia cases is estimated. All infants presented with symptoms of cyanosis and/or congestive heart failure within a few days to 2 months after birth and died shortly thereafter. Cardiomegaly and increased pulmonary vascular markings on the chest x-ray film and left axis deviation with left ventricular hypertrophy on the ECG are usually present. Echocardiographic, catheterization, and angiocardiographic studies are helpful in documenting anatomic and physiologic features of this anomaly. Pathologically, the muscular type of tricuspid atresia, type I or II truncus arteriosus, a large subtruncal VSD, and a hypoplastic right ventricle are present. It is concluded that coexistence of tricuspid atresia and truncus arteriosus is rare; clinical, laboratory, and pathologic features are distinctive; the clinical presentation early in life with rapid demise is common; and prompt palliative surgery immediately after recognition of this anomaly should be undertaken.

A 3-year-old boy with neck pain after motor-vehicle accident. Pseudospread of the atlas

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