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Biomedical subjects

Michael Burke

Publications and source records attributed to Michael Burke.

At least 19 recordsLinked to original sources
PubMed2007

Reversible and irreversible knockout of the ventroposterolateral thalamic nucleus measured by intracerebral SEP recordings in the rat brain--an aid to neuronavigation in small nuclei.

Centrally active drugs are often hard to administer because of the blood brain barrier, and frequently high systemic doses are required to reach sufficient brain parenchyma concentrations, since these drugs are, additionally, diluted in the total blood volume. Moreover, topical administration via the systemic route is not possible. We here propose a technique for the local, quantitative deposition of active substances at defined intracerebral targets, e.g. the thalamic nuclei. We used a long micropipette and stereotactically advanced it to the desired coordinates under electrophysiological control. The pipette acted as both an electrode for intracerebral recordings and as a transportation means for the drug. The amplitude of intracerebral evoked potentials relayed by the thalamic nucleus to the sensorimotor cortex indicated the distance between the pipette tip and the neurons of the targeted nucleus. Data were obtained from anesthetized rats, where the micropipette was advanced towards the nucleus ventralis posterolateralis (VPL) during contralateral electrical forepaw stimulation and intracerebral recording of somatosensory evoked potentials. Within the VPL we either injected lidocaine or kainic acid, both resulting in an attenuation of the intracerebral as well as the cortical evoked potentials. This proposed tool may be useful for functional investigations of deep brain structures.

Animals↗
PubMed2006

Differential effects of NMDA and AMPA glutamate receptors on functional magnetic resonance imaging signals and evoked neuronal activity during forepaw stimulation of the rat.

Most of the currently used methods for functional brain imaging do not visualize neuronal activity directly but rather rely on the elicited hemodynamic and/or metabolic responses. Glutamate, the major excitatory neurotransmitter, plays an important role in the neurovascular/neurometabolic coupling, but the specific mechanisms are still poorly understood. To investigate the role of the two major ionotropic glutamate receptors [NMDA receptors (NMDA-Rs) and AMPA receptors (AMPA-Rs)] for the generation of functional magnetic resonance imaging (fMRI) signals, we used fMRI [measurements of blood oxygenation level-dependent (BOLD), perfusion-weighted imaging (PWI), and cerebral blood volume (CBV)] together with recordings of somatosensory evoked potentials (SEPs) during electrical forepaw stimulation in the alpha-chloralose anesthetized rat. Intravenous injection of the NMDA-R antagonist MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine maleate] (0.06 mg/kg plus 3.6 microg x kg(-1) x h(-1)) significantly decreased BOLD (-51 +/- 19%; n = 5) and PWI (-57 +/- 26%; n = 5) responses but reduced the SEPs only mildly (approximately -10%). Systemic application of the AMPA-R antagonist GYKI-53655 [1-(4-aminophenyl)-3-methylcarbamyl-4-methyl-7,8-methylenedioxy-3,4-dihydro-5H-2,3-benzodiazepine] significantly decreased both the hemodynamic response (BOLD, -49 +/- 13 and -65 +/- 15%; PWI, -22 +/- 48 and -68 +/- 4% for 5 and 7 mg/kg, i.v., respectively; CBV, -80 +/- 7% for 7 mg/kg; n = 4) and the SEPs (up to -60%). These data indicate that the interaction of glutamate with its postsynaptic and/or glial receptors is necessary for the generation of blood flow and BOLD responses and illustrate the differential role of NMDA-Rs and AMPA-Rs in the signaling chain leading from increased neuronal activity to the hemodynamic response in the somatosensory cortex.

Animals↗
PubMed2006

Redox-mediated bypass of restriction point via skipping of G1pm.

BACKGROUND: It is well known that cancer cells bypass the restriction point, R, and undergo uncontrolled cell proliferation. HYPOTHESIS AND EVIDENCE: We suggest here that fibrosarcoma cells enter G1ps directly from M, skipping G1pm, hence bypassing R, in response to redox modulation. Evidence is presented from the published literature that demonstrate a shortening of the cycle period of transformed fibroblasts (SV-3T3) compared to the nontransformed 3T3 fibroblasts, corresponding to the duration of G1pm in the 3T3 fibroblasts. Evidence is also presented that demonstrate that redox modulation can induce the CUA-4 fibroblasts to bypass R, resulting in a cycle period closely corresponding to the cycle period of fibrosarcoma cells (HT1080). CONCLUSION: The evidence supports our hypothesis that a low internal redox potential can cause fibrosarcoma cells to skip the G1pm phase of the cell cycle.

Bone Neoplasms↗
PubMed2006

Number of risk genotypes is a risk factor for major depressive disorder: a case control study.

BACKGROUND: The objective of the study was to determine the genetic basis of Major Depressive Disorder, and the capacity to respond to antidepressant treatment. An association study of 21 candidate polymorphisms relevant to monoamine function and the mechanism of antidepressant response was conducted in 3 phenotypically distinct samples: a group with chronic or recurrent depression unable to respond to antidepressants (non-responders) (n = 58), a group capable of symptomatic improvement with or without treatment (responders) (n = 39), and volunteer controls (n = 85). The responders and non-responders constituted a larger group of depressed subjects. METHODS: A candidate gene approach was employed to asses the genetics basis of Major Depressive Disorder. The genotypic frequencies of selected polymorphisms were compared between the controls and depressed subjects. To asses the genetics basis of the capacity to respond to antidepressant treatment, the responders were compared to the non-responders. Candidate genes were chosen based on functional studies and proximity to whole genome linkage findings in the literature. Risk genotypes were identified by previous functional studies and association studies. RESULTS: A statistically significant difference in genotype frequency for the SLC6A4 intron 2 VNTR was detected between the subjects with a history of depression and controls (p = 0.004). Surprisingly, a statistically significant difference was detected between responders and non-responders for the DRD4 exon III VNTR genotype frequencies (p = 0.009). Furthermore, a difference between the controls and depressed subjects as well as between the controls and non-responders was detected for the number and distribution of risk genotypes in each group. CONCLUSION: An association between several monoamine-related genes and Major Depressive Disorder is supported. The data suggest that the two depressive phenotypes are genetically different, inferring that the genetic basis for the capacity to respond to standard antidepressant treatment, and the genetic susceptibility to Major Depressive Disorder may be independent. In addition, a proof of concept is provided demonstrating that the number of risk genotypes may be an indication of susceptibility of major depressive disorder and the severity of the disorder.

Journal Article↗
PubMed2006

BRICK1/HSPC300 functions with SCAR and the ARP2/3 complex to regulate epidermal cell shape in Arabidopsis.

The Arp2/3 complex, a highly conserved nucleator of F-actin polymerization, is essential for a variety of eukaryotic cellular processes, including epidermal cell morphogenesis in Arabidopsis thaliana. Efficient nucleation of actin filaments by the Arp2/3 complex requires the presence of an activator such as a member of the Scar/WAVE family. In mammalian cells, a multiprotein complex consisting of WAVE, PIR121/Sra-1, Nap1, Abi-2 and HSPC300 mediates responsiveness of WAVE to upstream regulators such as Rac. Essential roles in WAVE complex assembly or function have been demonstrated for PIR121/Sra-1, Nap1 and Abi-2, but the significance of HSPC300 in this complex is unclear. Plant homologs of all mammalian WAVE complex components have been identified, including HSPC300, the mammalian homolog of maize BRICK1 (BRK1). We show that, like mutations disrupting the Arabidopsis homologs of PIR121/Sra-1, Nap1 and Scar/WAVE, mutations in the Arabidopsis BRK1 gene result in trichome and pavement cell morphology defects (and associated alterations in the F-actin cytoskeleton of expanding cells) similar to those caused by mutations disrupting the ARP2/3 complex itself. Analysis of double mutants provides genetic evidence that BRK1 functions in a pathway with the ARP2/3 complex. BRK1 is required for accumulation of SCAR1 protein in vivo, potentially explaining the apparently essential role of BRK1 in ARP2/3 complex function.

Actin-Related Protein 2-3 Complex↗
PubMed2006

Prospective, long-term, multicenter study of the naturalistic outcomes of patients with treatment-resistant depression.

BACKGROUND: Treatment-resistant depression (TRD) is a long-term, disabling illness. We report on the characteristics and outcomes of a large cohort of patients with a level of treatment resistance that is very substantial and who were treated for 2 years with standard care. METHOD: This 2-year prospective, multicenter, observational study (patients enrolled from January 2001 through July 2004) tracked the outcomes of 124 patients with treatment-resistant, nonpsychotic major depressive disorder (N = 109) or bipolar depressed phase disorder (N = 15) who received treatment as usual (TAU) (i.e., any therapeutic regimen agreed to by patients and psychiatrists, including medications, electroconvulsive therapy [ECT], and psychotherapy). Treatments could be adjusted, started, and stopped as necessary. The primary outcome, treatment response, was defined a priori as > or = 50% improvement from baseline as measured by the 30-item Inventory of Depressive Symptomatology-Self-Report (IDS-SR-30). Remission was defined as an IDS-SR-30 score of < or = 14. The Medical Outcomes Study (MOS) 36-item Short Form Health Survey (SF-36) was used to monitor quality-of-life changes. RESULTS: The 12- and 24-month IDS-SR-30 response rates were 11.6% (13/112) and 18.4% (19/103), respectively. Of the 13 responders at 12 months, only 5 were responders at 24 months. The 12- and 24-month IDS-SR-30 remission rates were 3.6% (4/112) and 7.8% (8/103), respectively. Only 1 of the 4 12-month remitters was also a remitter at 24 months. The SF-36 indicated globally poor quality of life in this sample. CONCLUSIONS: Despite the wide range of treatment options available for depression, the response rates, remission rates, and quality-of-life results in this study show that most patients with a substantial degree of treatment resistance continue to have significant symptomatology and functional disability when receiving TAU.

Adolescent↗
PubMed2005

Content-specific activation during associative long-term memory retrieval.

We tested whether visual stimulus material that is assumed to be processed in different cortical networks during perception (i.e., faces and spatial positions) is also topographically dissociable during long-term memory recall. With an extensive overlearning procedure, 12 participants learned paired associates of words and faces and words and spatial positions. Each word was combined with either one or two positions or one or two faces. fMRI was recorded several days later during a cued recall test, in which two words were presented and the participants had to decide whether these were linked to each other via a common mediator, i.e., a face or a position. This paradigm enforces retrieval from long-term memory without confounding recall with perceptual processes. A network of cortical areas was found to be differently activated during recall of positions and faces, including regions along the dorsal and ventral visual pathways, such as the parietal and precentral cortex for positions and the left prefrontal, temporal (including fusiform gyrus) and posterior cingulate cortex for faces. In a subset of these areas, the BOLD response was found to increase monotonically with the number of the to-be-re-activated associations. These results show that material-specific cortical networks are systematically activated during long-term memory retrieval that overlap with areas also activated by positions and faces during perceptual and working memory tasks.

Adult↗
PubMed2005

Effects of 12 months of vagus nerve stimulation in treatment-resistant depression: a naturalistic study.

BACKGROUND: The need for effective, long-term treatment for recurrent or chronic, treatment-resistant depression is well established. METHODS: This naturalistic follow-up describes outpatients with nonpsychotic major depressive (n = 185) or bipolar (I or II) disorder, depressed phase (n = 20) who initially received 10 weeks of active (n = 110) or sham vagus nerve stimulation (VNS) (n = 95). The initial active group received another 9 months, while the initial sham group received 12 months of VNS. Participants received antidepressant treatments and VNS, both of which could be adjusted. RESULTS: The primary analysis (repeated measures linear regression) revealed a significant reduction in 24-item Hamilton Rating Scale for Depression (HRSD(24)) scores (average improvement, .45 points [SE = .05] per month (p < .001). At exit, HRSD(24) response rate was 27.2% (55/202); remission rate (HRSD(24) < or = 9) was 15.8% (32/202). Montgomery Asberg Depression Rating Scale (28.2% [57/202]) and Clinical Global Impression-Improvement (34.0% [68/200]) showed similar response rates. Voice alteration, dyspnea, and neck pain were the most frequently reported adverse events. CONCLUSIONS: These 1-year open trial data found VNS to be well tolerated, suggesting a potential long-term, growing benefit in treatment-resistant depression, albeit in the context of changes in depression treatments. Comparative long-term data are needed to determine whether these benefits can be attributed to VNS.

Adult↗
PubMed2005

A one-year comparison of vagus nerve stimulation with treatment as usual for treatment-resistant depression.

BACKGROUND: Previous reports have described the effects of vagus nerve stimulation plus treatment as usual (VNS+TAU) during open trials of patients with treatment-resistant depression (TRD). To better understand these effects on long-term outcome, we compared 12-month VNS+TAU outcomes with those of a comparable TRD group. METHODS: Admission criteria were similar for those receiving VNS+TAU (n = 205) or only TAU (n = 124). In the primary analysis, repeated-measures linear regression was used to compare the VNS+TAU group (monthly data) with the TAU group (quarterly data) according to scores of the 30-item Inventory of Depressive Symptomatology-Self-Report (IDS-SR(30)). RESULTS: The two groups had similar baseline demographic data, psychiatric and treatment histories, and degrees of treatment resistance, except that more TAU participants had at least 10 prior major depressive episodes, and the VNS+TAU group had more electroconvulsive therapy before study entry. Vagus nerve stimulation plus treatment as usual was associated with greater improvement per month in IDS-SR(30) than TAU across 12 months (p < .001). Response rates according to the 24-item Hamilton Rating Scale for Depression (last observation carried forward) at 12 months were 27% for VNS+TAU and 13% for TAU (p < .011). Both groups received similar TAU (drugs and electroconvulsive therapy) during follow-up. CONCLUSIONS: This comparison of two similar but nonrandomized TRD groups showed that VNS+TAU was associated with a greater antidepressant benefit over 12 months.

Adolescent↗
PubMed2005

Inflammation-sensitive proteins and erythrocyte aggregation in atherothrombosis.

OBJECTIVE: To find the relative contribution of various inflammation-sensitive proteins including fibrinogen, immunoglobulins (IgG, IgM and IgA), ceruloplasmin and high sensitivity C-reactive protein (hs-CRP) to the induction and/or maintenance of enhanced erythrocyte adhesiveness/aggregation in the peripheral blood of individuals with atherothrombotic risk factors. METHODS: The degree of erythrocyte adhesiveness/aggregation was determined by a simple slide test and image analysis. In addition, we measured various inflammation-sensitive protein levels including fibrinogen, ceruloplasmin, immunoglobulins and hs-CRP in a group of 234 individuals with atherothrombotic risk factors and healthy ones. Pearson partial correlations and multiple linear regression analysis were performed. RESULTS: Fibrinogen was found to be the major protein contributing to the enhanced erythrocyte adhesiveness/aggregation, explaining 30% of the model. Fibrinogen and IgG together explained 32.4% of the model. Other inflammation-sensitive proteins did not reach statistical significance and were excluded from the model. CONCLUSIONS: Among inflammation-sensitive proteins measured in our cohort, fibrinogen is the dominant contributor to erythrocyte adhesiveness/aggregation in the peripheral blood of individuals with atherothrombotic risk factors and healthy ones. These findings may pave the way for the development of therapeutic strategies directed at the attenuation of erythrocyte aggregability in individuals with atherothrombosis.

Aged↗
PubMed2005

Viral load of the human immunodeficiency virus could be an independent risk factor for endothelial dysfunction.

BACKGROUND: Recent reports of myocardial infarction in young persons infected with human immunodeficiency virus (HIV) who are receiving protease inhibitor therapy have raised concerns about premature coronary artery disease in this population. However, endothelial dysfunction, hypercoagulability, hypertriglyceridemia, and abnormal coronary artery pathology have been observed in association with HIV infection prior to the availability of protease inhibitor therapy. HYPOTHESIS: The study was undertaken to determine the association between endothelial function, viral load, CD4+ count, and other well-established risk factors for atherosclerosis. METHODS: This prospective, case-controlled study compared viral (HIV) load and the CD4+ T-lymphocyte count and endothelial function in 24 HIV-positive carriers. Brachial artery diameter, HIV viral load, and CD4 count were measured. RESULTS: We found that viral load correlated inversely with endothelial function; the higher the viral load, the worse the endothelial dysfunction (p < 0.005). CONCLUSION: High viral load appears to be associated with endothelial dysfunction in patients with HIV. This preliminary observation supports the infectious theory that viruses may play an important role in the pathogenesis of atherosclerosis.

Adult↗
PubMed2005

Autoantibodies profile of rheumatoid arthritis patients during treatment with infliximab.

PURPOSE: Therapy with TNFa blocking agents has been associated with increased rate of anti-nuclear antibodies (ANA) and rare cases of lupus like syndromes. Our aim was to prospectively analyze a wide array of autoantibodies in rheumatoid arthritis (RA) patients before and 14 weeks after starting infliximab. MATERIAL AND METHODS: In this study, 26 consecutive active RA patients participated. All treated with infliximab at a dosage of 3 mg/kg on week 0, 2, 6 and every 8 weeks, along with weekly low dose methotrexate. Patients were evaluated at week 0 and 14. Clinical assessment included the number of tender and swollen joints, duration of morning stiffness, adverse events (AE) (including SLE-like) and ESR. Sera were collected before the 1st infusion of infliximab at week 0 and 14. The autoantibodies studied were: fluorescent ANA, anti-double-stranded-DNA (anti-ds-DNA), IgG and IgM anti-cardiolipin (ACA), anti-histone- H1 and C (H1, H2A, H2B, H3, H4), anti-SSA, -SSB, -ENA, -scleroderma 70, -thyroid peroxidase (TPO) and -neutrophilic cytoplasmatic (ANCA) antibodies. RESULTS: Of 26 patients, 17 were women. A significant decrease in duration of morning stiffness, number of tender and swollen joints and ESR were observed between week 0 and 14. During follow up (mean of 20.5+/-7.3 months), 9 patients stopped infliximab due to inefficacy or AE (most of them after the 4th infusion). Two patients developed lupus-like phenomena. ANA was found positive at baseline in 7 out of 26 patients. In 5 of them, an increase in the titer of ANA was observed at week 14. ANA negative turned positive for 8 patients. A significant increase of anti-cardiolipin (ACA)-IgM levels was observed in 8 patients and of ACA-IgG in 6, in parallel with ANA seroconversion. The mean level of anti-double-stranded-DNA (anti-ds-DNA) -IgG significantly increased from 66+/-33 to 93+/-68 IU/ml, in 4 patients to pathological levels. Four patients demonstrated an increase in anti-histone H1. Levels of ANCA, anti-ENA, -SSA, -SSB, -RNP, -scleroderma70 and -thyroid peroxidase (TPO) were negative in all patients and remained unchanged during the study. Cessation of treatment with infliximab was found to be associated with the appearance of ANA. CONCLUSION: An increased titer or a new appearance of ANA was observed in 12 out of 26 patients. The main autoantibodies found were anti-ds-DNA, ACA-IgM and -IgG and anti-histone. In our cohort, the appearance of some autoantibodies seemed to predict late cessation of treatment.

Adult↗
PubMed2005

Pneumococcal vaccination of patients with systemic lupus erythematosus: effects on generation of autoantibodies.

OBJECTIVES: To assess the effect of vaccination against streptococcus pneumoniae on the generation of autoantibodies in patients with SLE. MATERIALS AND METHODS: Twenty-four consecutive patients with SLE were vaccinated against streptococcus pneumoniae. Assessment was performed the day of vaccination and 2 months later and included evaluation of disease activity using the SLEDAI, serum levels of ESR, CRP, C3 and C4. The sera of the patients were tested by ELISA for anti-dsDNA, anticardiolipin (IgG and IgM), anti-Sm, anti-nRNP, anti-Ro/SSA, and anti-La/SSB. RESULTS: The mean age at enrollment into the study was 39, mean disease duration 6.9 years. The SLEDAI score (mean +/- SD) was 4.41 +/- 2.92 at the time of vaccination and 4.47 +/- 3.11, 2 months apart. At the time of vaccination, 10 patients had anti-dsDNA, 2 patients had anti-Sm, 5 had anti-nRNP, and 9 had anti-Ro/SSA, 4 had anti-La/SSB, 4 had anticardiolipin IgG and IgM. Two months after vaccination, no change was observed in the proportion of patients with anti-Sm, anti-dsDNA, anti-RNP, anti-Ro/SSA and anticardiolipin IgM. A single patient developed anticardiolipin IgG and another one turned anti-RNP negative. CONCLUSIONS: Vaccination against streptococcus pneumoniae did not trigger the generation of autoantibodies and confirms the clinical safety of this vaccine in SLE patients.

Adult↗
PubMed2005

Prostate cancer: a significant risk factor for late-life suicide.

OBJECTIVE: The authors sought to determine the incidence of suicide and its relevant correlates among men with prostate cancer. METHODS: This was a population-based, retrospective cohort review of men age 65 and older, residing in South Florida between 1983 and 1993. Average annual suicide rate was calculated for prostate cancer-related suicides and contrasted with age and gender-specific rates in the same geographic area. RESULTS: Of 667 completed suicides, 20 were prostate cancer-related (3% of the total male suicide sample). The average annual incidence of suicide for men was 55.32 per 100,000 persons, but for men with prostate cancer, the rate was 274.7 per 100,000. The risk of suicide in men with prostate cancer was 4.24 times that of an age- and gender-specific cohort. The clinical correlates included depression (70%), cancer diagnosis within 6 months of suicide (80%), physician visit within 1 month of suicide (60%), and being foreign-born (70%). CONCLUSION: The incidence of suicide among older men with prostate cancer is higher than previously recognized. Depression, recent diagnosis, pain, and being foreign-born are important clinical correlates. Screens for depression and suicide in older men with prostate cancer should be done after diagnosis and redone during the first 6 months regularly, particularly in the primary-care setting. Public education is needed to decrease the stigma associated with having a cancer diagnosis.

Aged↗
PubMed2005

Plasmacytoid dendritic cells (PDC) are the major DC subset innately producing cytokines in human lymph nodes.

Plasmacytoid dendritic cells (PDC) constitute a distinct subset of DC found in human peripheral lymph nodes (LN), but little is known about their function. Cell suspensions were prepared from tumor draining LN (n=20) and control LN (n=11) of women undergoing surgical resection for primary breast cancer and elective surgery for benign conditions, respectively. Using four-color flow cytometry, human leukocyte antigen-DR+ DC subsets were identified phenotypically. The proportions and numbers of cells innately producing interleukin (IL)-4, IL-10, IL-12, and interferon-gamma (IFN-gamma) were also measured from intracellular accumulation of cytokine after blocking with monensin. All flow cytometry data were collected without compensation and were compensated off-line using the Winlist algorithm (Verity software). This package also provided the subtraction program to calculate percentage positive cells and intensity of staining. PDC (CD11c-, CD123+) expressed more cytokines than did myeloid DC (CD11c+) or CD1a+ putative "migratory" DC (P<0.001). LN PDC from patients with a good prognosis (px; n=11) demonstrated a relative increase in IL-12 and IFN-gamma expression (median IL-10:IL-12 ratio=0.78 and median IL-4:IFN-gamma ratio=0.7), and PDC from LN draining poor px cancer (n=9) showed a relative increase in IL-10 and IL-4 expression (median IL-10:IL-12 ratio=1.31 and median IL-4:IFN-gamma ratio=2.6). The difference in IL-4:IFN-gamma expression between good and poor px cancer groups was significant (P<0.05). Thus, PDC innately producing cytokines were identified in cell suspensions from human LN, and the character of PDC cytokine secretion may differ between two breast cancer prognostic groups. We speculate that a shift towards PDC IL-10 and IL-4 expression could promote tumor tolerance in LN draining poor px breast cancer.

Adult↗
PubMed2004

Genetic variation at NNRTI resistance-associated positions in patients infected with HIV-1 subtype C.

OBJECTIVE: Genetic differences between subtypes of HIV-1, even when not associated with key resistance mutations, are known to affect baseline susceptibility to specific antiretroviral drugs and resistance-development pathways. We studied the prevalence and patterns of non-nucleoside reverse transcriptase inhibitor (NNRTI)-associated mutations in HIV-1 subtype C-infected patients. METHOD: We analysed the genetic variation at sites associated with NNRTI and nucleoside reverse transcriptase inhibitor resistance in subtype C- versus B-infected patients, both drug-naive and -experienced. We extended the comparison to subtype B records from the Stanford database. RESULTS: A total of 150 subtype B and 341 subtype C-infected patients were studied. No significant differences were found in treatment and clinical parameters between the groups. In NNRTI-naive patients, changes in NNRTI positions were present in 9.3% of subtype B- versus 33.1% of subtype C-infected patients (P < 0.001). Differences were seen in both drug-naive (subtype B, 10.0% versus subtype C, 50.1%; P < 0.021) and drug-experienced NNRTI-naive patients (subtype B, 9.0% versus subtype C, 23.8%; P < 0.001). In NNRTI experienced patients, the number of A98G/S changes was significantly higher in subtype C patients treated with either efavirenz or nevirapine (P < 0.0001), and V106M was higher in efavirenz-treated subtype C-infected patients (P < 0.0001). The average mutation rates were 1.26 and 1.67 per patient for subtypes B and C, respectively (P = 0.036). The frequency of nucleoside associated mutations, but not M184V, in treated patients was significantly higher in subgroup B-infected patients (P = 0.028). CONCLUSION: Collectively, these data indicate that genetic variation at NNRTI resistance-associated positions such as V106M and A98S is substantially greater in subtype C-infected patients than in subtype B-infected patients. The natural structure of each subtype probably affects the frequency and pattern of drug resistance mutations selected under treatment.

Adult↗