Detection of early infarction signs with machine learning-based diagnosis by means of the Alberta Stroke Program Early CT score (ASPECTS) in the clinical routine.

PURPOSE: New software solutions emerged to support radiologists in image interpretation in acute ischemic stroke. This study aimed to validate the performance of computer-aided assessment of the Alberta Stroke Program Early CT score (ASPECTS) for detecting signs of early infarction. METHODS: ASPECT scores were assessed in 119 CT scans of patients with acute middle cerebral artery ischemia. Patient collective was differentiated according to (I) normal brain, (II) leukoencephalopathic changes, (III) infarcts, and (IV) atypical parenchymal defects (multiple sclerosis, etc.). ASPECTS assessments were automatically provided by the software package e-ASPECTS (Brainomix®, UK) (A). Subsequently, three neuroradiologists (B), (C), and (D) examined independently 2380 brain regions. Interrater comparison was performed with the definite infarct core as reference standard after best medical care (thrombolysis and/or thrombectomy). RESULTS: Interrater comparison revealed higher correlation coefficient of (B) 0.71, (C) 0.76, and of (D) 0.80 with definite infarct core compared to (A) 0.59 for ASPECTS assessment in the acute ischemic stroke setting. While (B), (C), and (D) showed a significant correlation for individual patient groups (I), (II), (III), and (IV), except for (D) (II), (A) was not significant in patient groups with pre-existing changes (II), (III), and (IV). The following sensitivities, specificities, PPV, NPV, and accuracies given in percent were achieved: (A) 83, 57, 55, 82, and 67; (B) 74, 76, 69, 83, and 77; (C) 80.8, 85.2, 76, 84, and 80; (D) 63, 90.7, 82, 79, and 80, respectively. CONCLUSION: For ASPECTS assessment, the examined software may provide valid data in case of normal brain. It may enhance the work of neuroradiologists in clinical decision making. A final human check for plausibility is needed, particularly in patient groups with pre-existing cerebral changes.

Comparison of radiation doses imparted during 128-, 256-, 384-multislice CT-scanners and cone beam computed tomography for intra- and perioperative cochlear implant assessment.

PURPOSE: To examine radiation-doses imparted during multislice (MSCT) and cone-beam computed-tomography (CBCT) for perioperative examination of cochlear-implant insertion. METHODS: Radiation-doses were assessed during standardized petrous-bone CT-protocols at different MSCT ((I) single-source CT-scanner Somatom-Definition-AS+, (II) 2nd generation of dual-source CT-scanner Somatom-Definition-Flash, (III) 3rd generation of dual-source CT-scanner Somatom-Force and at the CBCT Ziehm-Vision-RFD3D ((IV) (a) RFD-3D (Standard-modifier), (b) RFD-3D (Low-dose-modifier)). Image quality was examined by two radiologists appraising electrode-array placement, quality-control of cochlear-implant surgery and complications based on real patients' examinations (n=78). RESULTS: In MSCT-setting following radiation-doses were assessed (CTDIw; DLP): (I) 21.5mGy; 216mGycm; (II) 19.7mGy; 195mGycm; (III) 12.7mGy; 127mGycm; in the CBCT setting radiation doses were distributed as follows: (IV) (a) 1.9mGy; 19.4mGycm; (b) 1.2mGy; 12.9mGycm. Overall, image quality was evaluated as good for both, MSCT- and CBCT-examinations, with a good interrater reliability (r=0.81). CONCLUSION: CBCT bears considerable dose-saving potential for the perioperative examination of cochlear-implant insertion while maintaining adequate image quality.

Dose comparison of classical 2-plane DSA and 3D rotational angiography for the assessment of intracranial aneurysms.

INTRODUCTION: The purpose of this experimental phantom study was to compare radiation doses imparted to patients undergoing classical two-plane digital subtraction angiography (2-plane DSA) and 3D rotational angiography in interventional neuroradiology. METHODS: Thermoluminescence dosimeter (TLD) measurements were performed at an anthropomorphic phantom using a digital interventional angiography system. Two-plane DSA included posterior/anterior (PA) and lateral (LAT) projections (frame-rate, 7.6 frames (PA) and 9.8 frames (LAT) for a scan time of approximately 8 s; image intensifier 27 cm (PA) and 25 cm (LAT)). For 3D rotational angiography, 122 images were acquired from one single image run with the imaging system rotating 240° around the phantom's head (image intensifier 37 cm). RESULTS: Effective dose was 0.4 mSv for 2-plane DSA compared to 0.1 mSv for 3D rotational angiography. Organ doses were approximately two to five times higher for classical 2-plane technique compared to the 3D rotational angiography, respectively: brain (11.4 vs. 2.4 mSv), eye lens (4.5 vs.1 mSv), salivary glands (7 vs. 1,7 mSv), oral mucosa (2.7 vs.0.9 mSv), thyroid (0.5 vs. 0.2 mSv), thymus (0.2 vs. 0.05 mSv), bone marrow within imaged region (1 vs. 0.2 mSv), oesophagus (0.07 vs. 0.03 mSv), endotracheal system (2.6 vs. 0.7 mSv) and skeletal components in the imaged region (0.7 vs. 0.2 mSv). CONCLUSION: Three-dimensional rotational angiography clearly reduces radiation doses compared to the classical 2-plane technique. Replacement of additional 2-plane DSA projections with 3D rotational angiography will lead to a remarkable decrease in patient radiation dose, without loss of image quality. Thus, we recommend routine application of 3D rotational angiography, in particular for diagnostic assessment of aneurysm morphology.

Dynamic membrane structure induces temporal pattern formation.

The understanding of temporal pattern formation in biological systems is essential for insights into regulatory processes of cells. Concerning this problem, the present work introduces a model to explain the attachment/detachment cycle of MARCKS and PKC at the cell membrane, which is crucial for signal transduction processes. Our model is novel with regard to its driving mechanism: Structural changes within the membrane fuel an activator-inhibitor based global density oscillation of membrane related proteins. Based on simulated results of our model, phase diagrams were generated to illustrate the interplay of MARCKS and PKC. They predict the oscillatory behavior in the form of the number of peaks, the periodic time, and the damping constant depending on the amounts of MARCKS and PKC, respectively. The investigation of the phase space also revealed an unexpected intermediate state prior to the oscillations for high amounts of MARCKS in the system. The validation of the obtained results was carried out by stability analysis, which also accounts for further enhanced understanding of the studied system. It was shown, that the occurrence of the oscillating behavior is independent of the diffusion and the consumption of the reactants. The diffusion terms in the used reaction-diffusion equations only act as modulating terms and are not required for the oscillation. The hypothesis of our work suggests a new mechanism of temporal pattern formation in biological systems. This mechanism includes a classical activator-inhibitor system, but is based on the modifications of the membrane structure, rather than a reaction-diffusion system.

[Traumatic dissection of the carotid artery: challenges for diagnostics and therapy illustrated by a case example]. / Traumatische Karotisdissektion : Herausforderungen der Diagnostik und Therapie anhand eines Fallbeispiels.

Traumatic dissection of the carotid artery is an easily overlooked consequence of trauma with notable morbidity and mortality which can be observed in up to 4% of cases involving multiple trauma. Certain mechanisms and patterns of injury as well as specific symptoms should serve as indicators of a dissection and should therefore result in further diagnostic measures. An early diagnosis is of major relevance. This report describes the case of a 45-year-old victim of a traffic accident who showed symptoms of a dissection which had initially not been diagnosed.

HIV-1 drug resistant mutations in chronically infected treatment naive individuals in the pre-ARV era in Nigeria.

In Nigeria the Federal Government rolled out antiretroviral drugs for the management of HIV infection in year 2002. This study was carried out to determine the circulating antiviral drug mutations among ARV naïve patients with chronic HIV infection during the pre-ARV roll out era in the country. DNA was extracted from stored whole blood samples collected from 75 HIV positive patients attending the Medical outpatient clinic between December 1996 and November 2001. The Reverse transcriptase (RT) and the protease (PR) regions of the viral genome were amplified by nested PCR and then sequenced by cycle sequencing and analyzed using the ABI 3100 DNA sequencer to determine the mutations associated with protease inhibitors (PI), nucleoside reverse transcriptase inhibitors (NRTI) and non-nucleoside reverse transcriptase inhibitor (NNRTI). Ten of the 64 (15.6%) samples with positive PCR had mutations for PR inhibitors (PI) including R8D, I 15V, G16E, M36I, M46L, L63P and H69K, while 5 of 63 harbored RT inhibitor (NRTI/NNRTI); V179I, A98T, V179E and A98S. Detection ofARV drug resistant mutations when ARV was not known to be in use in Nigeria calls for caution in the interpretation of drug resistance profile of HIV-1 from infected persons on treatment ARVs in the country.

[Intratumoral Onyx embolisation in the management of juvenile nasopharyngeal angiofibroma]. / Intratumorale Onyx-Embolisation in der Therapie von juvenilen Nasenrachenangiofibromen.

Preoperative embolization for the treatment of juvenile nasopharyngeal angiofibroma was successfully accomplished with Onyx by intratumoral puncture for the first time. Extratumoral migration of Onyx particles was not observed, precluding the necessity to inflate the shield balloon. Postinterventional angiography showed complete occlusion of all supporting blood vessels. Transnasal surgery on the following day achieved complete resection of the angiofibroma without complications. Direct intratumoral embolization of juvenile nasopharyngeal angiofibromas appears to be a safe and effective preoperative method without complications. It could represent a new strategy for the treatment of JNA, as is already the case with other highly vascularized head and neck tumors. Moreover, it increases the likelihood of achieving complete resection.

[Direct percutaneous embolization of a carotid body tumor with Onyx]. / Perkutane Onyx(R)-Embolisation zur Therapie von Glomus-caroticum-Tumoren.

Carotid body tumors are highly vascularized lesions that require successful preoperative embolization to achieve favorable clinical results in terms of morbidity and complete tumor resection. The procedure of percutaneous embolization was performed using ethylene-vinyl alcohol copolymer (Onyx) in addition to balloon-catheter protection to prevent particle displacement into the internal carotid artery. The procedure resulted in nearly complete tumor embolization and facilitated the uneventful complete surgical resection. Percutaneous angiographic embolization of carotid body tumors in the head and neck was found to be safe and effective. This technique is likely to result in improved surgical outcomes and tumor resectability.

Comparison of eye-lens doses imparted during interventional and non-interventional neuroimaging techniques for assessment of intracranial aneurysms.

BACKGROUND: A neurointerventional examination of intracranial aneurysms often involves the eye lens in the primary beam of radiation. OBJECTIVE: To assess and compare eye-lens doses imparted during interventional and non-interventional imaging techniques for the examination of intracranial aneurysms. METHODS: We performed a phantom study on an anthropomorphic phantom (ATOM dosimetry phantom 702-D; CIRS, Norfolk, Virginia, USA) and assessed eye-lens doses with thermoluminescent dosimeters (TLDs) type 100 (LiF:Mg, Ti) during (1) interventional (depiction of all cerebral arteries with triple 3D-rotational angiography and twice 2-plane DSA anteroposterior and lateral projections) and (2) non-interventional (CT angiography (CTA)) diagnosis of intracranial aneurysms. Eye-lens doses were calculated following recommendations of the ICRP 103. Image quality was analysed in retrospective by two experienced radiologists on the basis of non-interventional and interventional pan-angiography examinations of patients with incidental aneurysms (n=50) on a five-point Likert scale. RESULTS: The following eye-lens doses were assessed: (1) interventional setting (triple 3D-rotational angiography and twice 2-plane DSA anteroposterior and lateral projections) 12 mGy; (2) non-interventional setting (CTA) 4.1 mGy. Image quality for depiction of intracranial aneurysms (>3 mm) was evaluated as good by both readers for both imaging techniques. CONCLUSIONS: Eye-lens doses are markedly higher during the interventional than during the non-interventional diagnosis of intracranial aneurysms. For the eye-lens dose, CTA offers considerable radiation dose savings in the diagnosis of intracranial aneurysms.

Application of the EIIP/ISM bioinformatics concept in development of new drugs.

The development of a new therapeutic drug is a complex, lengthy and expensive process. On average, only one out of 10,000 - 30,000 originally synthesized compounds will clear all the hurdles on the way to becoming a commercially available drug. The process of early and full preclinical discovery and clinical development for a new drug can take twelve to fifteen years to complete, and cost approximately 800 million dollars. The field of bioinformatics has become a major part of the drug discovery pipeline playing a key role in improvement and acceleration of this time and money consuming process. Here we reviewed the application of the EIIP/ISM bioinformatics concept for the development of new drugs. This approach, connecting the electron-ion interaction potential of organic molecules and their biological properties, can significantly reduce development time through (i) identification of promising lead compounds that have some activity against a disease by fast virtual screening of the large molecular libraries, (ii) refinement of selected lead compounds in order to increase their biological activity, and (iii) identification of domains of proteins and nucleotide sequences representing potential targets for therapy. Special attention is paid in this review to the application of the EIIP/ISM bioinformatics platform along with other experimental techniques (screening of a phage displayed peptide libraries, testing selected peptides and small molecules for antiviral activity in vitro) in development of HIV entry inhibitors, representing a new generation of the AIDS drugs.

[Limb salvage for the diabetic foot - disease management program]. / Extremitätenerhalt für den diabetischen Fuss - Disease-Management-Programm.

OBJECTIVE: Lower-extremity amputation (LEA) is a common complication among patients with diabetes. This study tests the effects of a structured disease management program for the diabetic foot (DF) aiming to reduce the number of LEA. DESIGN, METHODS: In a prospective study design we investigate patients with DF in a system of outpatient treatment, acute in-patient care and rehabilitative treatment. Subjects were recruited since January 1(st), 2000, with the latest admission being December 31, 2004. All study participants undergo a five-year follow-up observation period. The University of Texas Wound Classification System (UT) of foot ulcers serves as basis of the documentation and analysis. We evaluated numbers of LEA, rates of ulcer healing and underlying forms of peripheral vascular disease. RESULTS: We report the results of the first patient group completing the two-year follow-up examination. In 2000, 102 subjects with new foot ulcers were consecutively included into the study. 68.6% were men, the mean age of the study population was 68.1 +/- 11.4 years and the mean diabetes duration was 19.4 +/- 10.3 years. After two years, 68 patients can still be examined. Altogether, 22 patients (21.6%) died, and 12 (11.8%) dropped out for various reasons. At the point of discharge from the clinics 35.3% of the ulcers had healed and another 44.1% were in UT grade 1. After two years, a complete healing could still be determined with 51 patients (50.0% of the cohort of the original 102 patients, or 75.0% of the subjects reaching the two-year follow-up). 10 subjects (9.8% or 14.5%) were in the UT grade 1. Eight diabetics underwent major amputation (MA) during the two-year examination period (amputation rate 7.8%). CONCLUSIONS: The primary objective of the study, a significant reduction of MA with DF patients, has been achieved. The ulcer healing rates are comparable to the reports of leading centers.

The epidemiology of HIV in India.

India is the first country outside Africa where an HIV-2 epidemic is running in parallel to an HIV-1 epidemic, resulting in a significant proportion of double infections. HIV is spreading rapidly, mainly by heterosexual contact, but also among intravenous drug users. Genetic analyses of the HIV variants circulating in India point towards HIV-1 and HIV-2 having been introduced into the country recently.

PIP: The genetic strains of HIV which have been uncovered in India have a different origin from those present in Thailand. Also, both HIV-1 and HIV-2 have been detected in India. In a 1991-93 study of clients of a sexually transmitted disease clinic in Bombay, it was found that seroprevalence of HIV in 241 clients was 39%, the 78.5% positive for HIV-1, 6.5% for HIV-2, and 15% for both. Distribution was even for males and females, reflecting heterosexual transmission. HIV-2 has also been detected in other parts of India, and HIV-1 is spreading throughout the country. HIV in children is a sequelae to blood transfusion. The prevalence of HIV in areas where IV drug use is rampant is increasing rapidly and is spreading to the general population. Genetic analysis revealed that the most closely related genetic sequence to the Indian HIV-1 from Bombay occurs in a strain of the virus from South Africa. One subtype of HIV-2 and several subtypes of HIV-1 have been found, with HIV-1 subtype C and HIV-2 subtype A the most frequently encountered. An examination of phylogenetic trees shows the relationships among these different strains. The close genetic relationship between isolates of HIV-1 and HIV-2 from patients in different parts of the country reflects the recent introduction of these strains. Thus, India is an ideal site for studying the efficacy of a vaccine designed specifically for a population of highly similar strains (the high similarity among HIV-2 isolates is unique in India). Since HIV-2 strains are diverging at a rate of 1% per year, any such research would have to occur soon.

Cardiolipin, alpha-D-glucopyranosyl, and L-lysylcardiolipin from gram-positive bacteria: FAB MS, monofilm and X-ray powder diffraction studies.

Cardiolipin preparations from Streptococcus B, Listeria welshimeri, Staphylococcus aureus, and a glucosyl and lysyl derivative of cardiolipin were analysed for fatty acid composition and fatty acid combinations. Three different fatty acid patterns are described and up to 17 molecular species were identified in Streptococcus B lipids by high resolution FAB MS. The physicochemical properties of these lipids were characterised in the sodium salt form by monofilm experiments and X-ray powder diffraction. All lipids formed stable monofilms. The minimal space requirement of unsubstituted cardiolipin was dictated by the fatty acid pattern. Substitution with L-lysine led to a decrease of the molecular area, substitution with D-glucopyranosyl to an increase. On self assembly at 100% relative humidity, all preparations adopted lamellar structures. They showed a high degree of order, in spite of the heterogeneous fatty acid compositions and numerous fatty acid combinations. The repeat distances in lamellar fluid phase varied between 4.99 and 5. 52 nm, the bilayer thickness between 3.70 and 4.46 nm. Surprising were the low values of sorbed water per molecule of the glucosyl and lysyl derivatives which were 58 and 60%, compared with those of the respective cardiolipin. When Na(+) was replaced as counterion by Ba(2+), the bilayer structure was retained, but the lipids were in the lamellar gel phase and the fatty acids were tilted between 32 and 53 degrees away from the bilayer normal. Wide angle X-ray diffraction studies and electron density profiles are also reported. Particular properties of glucosyl cardiolipin are discussed.

Functional interactions of neurogenic genes of Drosophila melanogaster.

The neurogenic genes of Drosophila melanogaster are involved in the decision of ectodermal cells to take on a neural or an epidermal fate. We present evidence in support of the notion that six of the neurogenic genes are functionally related. We studied the phenotype of embryos lacking one of the neurogenic genes in the presence of an increased dosage of the wild-type allele of another neurogenic gene. Our analysis also included the Hairless locus, whose function is related to that of the neurogenic genes, as well as to many other genes. The effects observed were asymmetric in that triploidy for a given gene modified the phenotype of loss of the function of another gene, but triploidy of the latter gene did not modify the phenotype of loss of the function of the former gene. These asymmetries allowed us to establish a polarity of gene interactions, as well as to order the genes according to the assumed ability of some of them to modify the activity of others. In this sequence, almondex is the first link and Enhancer of split the last one. Our evidence suggests that the function of big brain is independent of the function of the other six. The consequences of this arrangement for the commitment of ectodermal cells are discussed.

HIV-1 strains from India are highly divergent from prototypic African and US/European strains, but are linked to a South African isolate.

OBJECTIVE: To gain molecular insights into different HIV-1 strains present in two different states of India, nucleotide sequences derived from the env region of four HIV-1 strains were analysed. DESIGN: HIV-1 was isolated from high-risk patients from the states of Maharashtra (city of Bombay) and Goa. The molecular analysis of the env region encompassed all variable domains of the external glycoprotein, gp120. METHODS: Genomic DNA from cultured cells infected with each of the four Indian HIV-1 strains independently was amplified by polymerase chain reaction (PCR). PCR fragments were cloned and sequenced and a phylogenetic tree constructed. RESULTS: All four Indian HIV-1 sequences were closely related to each other. The closest related sequence to them was from a South African isolate, HIV-1NOF, with a homology of 85-87%. In the phylogenetic tree, the Indian and the South African HIV-1 sequences cluster together and constitute a subtype different from the North American/European, Central African, Uganda/Rwanda and Northern Thailand subtypes. Interestingly, the viruses of this subtype are characterized by an additional potential N-glycosylation site C-terminal to the CD4-binding domain. CONCLUSION: The low variation between the HIV-1 sequences from randomly chosen individuals from high-risk cohorts in two Indian states suggests a rapid and recent spread of HIV and, possibly, introduction of the virus by the same route, most probably heterosexual transmission. The rapid spread of HIV-1 variants in India, which form a subgroup of their own together with a South African strain, necessitate consideration of these strains in vaccine development.

Selection of HIV-1 genotypes by cultivation in different primary cells.

OBJECTIVES: To determine the representation of particular HIV-1 genotypes during cultivation in different primary cell-culture systems compared with the spectrum of the quasispecies in vivo. METHODS: Primary isolates of HIV-1 were recovered by isolation in cultures of lymphocytes, mixed mononuclear cells (MNC), and monocytes/macrophages. Nucleotide sequence determination of the C2-V3 region of gp120 of HIV was performed on 10-20 independently isolated clones derived by polymerase chain reaction from the culture systems, the uncultured peripheral blood MNC (PBMC) as well as plasma. RESULTS: Several predominant HIV genotypes were found in the uncultured PBMC from each of the patients. The most frequent genotypes in PBMC were also the most frequent types in plasma. In addition, lymphocytes, macrophages or mixed MNC cultures allowed the outgrowth of variants that were underrepresented in uncultured PBMC. We showed that the virus cultivation systems used in this study selected differently for the genetic variants. Whereas some genotypes were present in all three culture systems, although at different frequencies, others were exclusively found in a specific culture system. CONCLUSIONS: These results demonstrate that monocyte/macrophage and mixed MNC culture systems complement the standard lymphocyte culture in terms of the spectrum of genotypically different virus variants obtained in vitro.

HIV-1 and HIV-2 infections in a high-risk population in Bombay, India: evidence for the spread of HIV-2 and presence of a divergent HIV-1 subtype.

A high-risk population (patients of a sexually transmitted disease clinic and the GT hospital in Bombay) was tested for antibodies against HIV-1 and HIV-2. Among 405 serum samples, 226 had previously been classified HIV-positive in India using different locally available enzyme-linked immunosorbent assay (ELISA) tests. The serology of 179 samples was unknown. All 405 samples were tested at the Georg-Speyer-Haus (GSH) with the Pasteur HIV-1/2-Combi-ELISA. Positive samples were further analyzed with HIV-1 and HIV-2 Western blot kits from Dupont and Pasteur, respectively. A very high seroprevalence of HIV was found in this population. Among the 179 unscreened samples, 69 (38.5%) were positive in the ELISAs as well as the Western blots for HIV-1 or HIV-2. Among the prescreened samples, only 174 (77%) were confirmed HIV-positive. Altogether, 243 of 405 sera were HIV-positive. Of these, 184 (76%) were reactive with HIV-1, 10 (4%) were reactive with HIV-2, and 49 (20%) had dual reactivity to HIV-1 and HIV-2. Previous data from the Indian Council of Medical Research had already suggested a possible high prevalence of HIV-1 in India. Our results confirm this view. The finding of a substantial spread of HIV-2 infection was, however, totally unexpected in India, but confirms our previous study which had already demonstrated the existence of HIV-2 in this country. Asia can thus no longer be considered free of HIV-2, and testing for HIV-2 appears mandatory, at least in India.(ABSTRACT TRUNCATED AT 250 WORDS)

Genotypic and phenotypic resistance to stavudine after long-term monotherapy. BMS-020 Spanish Study Group.

Protocol BMS 020 was a double-blind, prospective clinical trial in which two different doses of stavudine (20 and 40 mg twice daily) were compared in human immunodeficiency virus (HIV)-infected patients with previous exposure to zidovudine for longer than 16 weeks. Genotypic and phenotypic resistance to both zidovudine and stavudine were examined after at least 2 years of stavudine monotherapy. None of 35 tested individuals harboured the codon 50 and/or 75 mutations previously described to be associated with stavudine resistance. However, more than 80% of the individuals carried mutations associated with zidovudine resistance, despite all these patients having stopped zidovudine at least 2 years earlier. Significant phenotypic resistance to stavudine was observed only in 2 of 5 tested individuals, although IC50 values were increased only 6.6- and 9.2-fold, respectively. These two patients had suffered a decline in their CD4 count, and one of them had high levels of plasma viraemia. The sequence analysis of the reverse transcriptase (RT) gene (aa 30 to 240) in these five patients revealed no changes that could be involved in stavudine resistance. In contrast, and despite having stopped treatment with zidovudine more than 2 years before, phenotypic resistance to zidovudine was observed in all five subjects, with IC50 values raised by more than 75-fold in all of them. Moreover, all harboured codon substitutions within the RT gene associated with zidovudine resistance, and these mutations remained in viral genomes examined after virus co-culture, suggesting that they provided some biological advantage to mutants, even in the absence of drug pressure. In conclusion, both genotypic and phenotypic resistance to stavudine seem to be a rare event in patients exposed to the drug, even after long periods of exposure.

Analysis of the envelope region of the highly divergent HIV-2ALT isolate extends the known range of variability within the primate immunodeficiency viruses.

HIV-2ALT is a highly divergent HIV-2-related isolate that is genetically equidistant to the prototypic HIV-2 strains, defined by HIV-2ROD, and to the simian immunodeficiency viruses SIVmac and SIVsm. We have now cloned and sequenced the envelope region of HIV-2ALT, thus completing the analysis of the whole viral genome. The sequences of env and nef and of the second exons of tat and rev were compared with those of the other viruses of the HIV-2/SIVsm/SIVmac group. Despite of the high degree of variation of HIV-2ALT, functional domains of the genes are conserved. Although in env, the overall pattern of constant and variable domains is maintained, many single amino acid exchanges exist at positions previously thought to be constant in HIV-2 strains. In addition, when compared with a broader spectrum of immunodeficiency viruses, which includes SIVMND from mandrill and SIVAGM from African green monkey, HIV-2ALT Env has a high percentage of amino acid exchanges, which are unique to this strain. This underlines the separate branch of HIV-2ALT within the phylogenetic tree and makes obvious the inclusion of such divergent strains in preventive and therapeutic programs.