A M Prentice

London School of Hygiene and Tropical Medicine, Londinium, England, United Kingdom

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Publications (480)3028.45 Total impact

  • Ka Ward, A Riddell, A Prentice
    The Journal of clinical endocrinology and metabolism. 01/2015; 100(1):L8.
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    Sharon E Cox, Julie Makani, Elizabeth A Ellins, Beatrice Kamala, Gurishaeli Walter, Selemani Mtunguja, Nassor Khalfan, Fenella J Kirkham, Charles Rjc Newton, Julian P Halcox, Andrew M Prentice
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    ABSTRACT: Ready-to-use supplementary food supplements improve endothelial function, hemoglobin and growth in Tanzanian children with sickle cell anaemia: The Vascular Function Intervention Study (V-FIT), a random order crossover trial
    American Society of Hematology; 12/2014
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    ABSTRACT: Hepcidin inhibits ferroportin-mediated iron efflux, leading to intracellular macrophage iron retention, possibly favoring Mycobacterium tuberculosis iron acquisition and tuberculosis (TB) pathogenesis. Plasma hepcidin was measured at human immunodeficiency virus (HIV) diagnosis in a retrospective HIV-prevalent, antiretroviral-naïve African cohort to investigate the association with incident pulmonary and/or extra-pulmonary TB. One hundred ninety-six participants were followed between 5 August 1992 and 1 June 2002, with 32 incident TB cases identified. Greater hepcidin was associated with significantly increased likelihood of TB after a median time to TB of 6 months. Elucidation of iron-related causal mechanisms and time-sensitive biomarkers that identify individual changes in TB risk are needed.
    The International Journal of Tuberculosis and Lung Disease 11/2014; 18(11). · 2.76 Impact Factor
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    ABSTRACT: Ethnic differences in renal calcium and phosphate excretion exist, which may depend on differences in their dietary intakes and regulatory factors. We report highly significant differences in urinary calcium and phosphate excretion between white British and Gambian adults after statistical adjustment for mineral intakes, indicating an independent effect of ethnicity.
    Osteoporosis International 10/2014; · 4.17 Impact Factor
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    ABSTRACT: Predictors of 25(OH)D3 half-life were factors associated with vitamin D metabolism, but were different between people in The Gambia and the UK. Country was the strongest predictor of plasma 25(OH)D concentration, probably as a marker of UVB exposure. 25(OH)D3 half-life may be applied as a tool to investigate vitamin D expenditure.
    Osteoporosis International 10/2014; · 4.17 Impact Factor
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    ABSTRACT: During HIV type-1 (HIV-1), hepatitis C virus (HCV), and hepatitis B virus (HBV) infections, altered iron balance correlates with morbidity. The liver-produced hormone hepcidin dictates systemic iron homeostasis. We measured hepcidin, iron parameters, cytokines, and inflammatory markers in three cohorts: plasma donors who developed acute HIV-1, HBV, or HCV viremia during the course of donations; HIV-1-positive individuals progressing from early to chronic infection; and chronically HIV-1-infected individuals (receiving antiretroviral therapy or untreated). Hepcidin increased and plasma iron decreased during acute HIV-1 infection, as viremia was initially detected. In patients transitioning from early to chronic HIV-1 infection, hepcidin in the first 60 d of infection positively correlated with the later plasma viral load set-point. Hepcidin remained elevated in individuals with untreated chronic HIV-1 infection and in subjects on ART. In contrast to HIV-1, there was no evidence of hepcidin up-regulation or hypoferremia during the primary viremic phases of HCV or HBV infection; serum iron marginally increased during acute HBV infection. In conclusion, hepcidin induction is part of the pathogenically important systemic inflammatory cascade triggered during HIV-1 infection and may contribute to the establishment and maintenance of viral set-point, which is a strong predictor of progression to AIDS and death. However, distinct patterns of hepcidin and iron regulation occur during different viral infections that have particular tissue tropisms and elicit different systemic inflammatory responses. The hypoferremia of acute infection is therefore a pathogen-specific, not universal, phenomenon.
    Proceedings of the National Academy of Sciences 08/2014; · 9.81 Impact Factor
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    ABSTRACT: Iron deficiency and malaria have similar global distributions, and frequently co-exist in pregnant women and young children. Where both conditions are prevalent, iron supplementation is complicated by observations that iron deficiency anaemia protects against falciparum malaria, and that iron supplements increase susceptibility to clinically significant malaria, but the mechanisms remain obscure. Here, using an in vitro parasite culture system with erythrocytes from iron-deficient and replete human donors, we demonstrate that Plasmodium falciparum infects iron-deficient erythrocytes less efficiently. In addition, owing to merozoite preference for young erythrocytes, iron supplementation of iron-deficient individuals reverses the protective effects of iron deficiency. Our results provide experimental validation of field observations reporting protective effects of iron deficiency and harmful effects of iron administration on human malaria susceptibility. Because recovery from anaemia requires transient reticulocytosis, our findings imply that in malarious regions iron supplementation should be accompanied by effective measures to prevent falciparum malaria.
    Nature Communications 07/2014; 5:4446. · 10.74 Impact Factor
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    ABSTRACT: Context: There is uncertainty over the equivalence of vitamins D2 and D3 to maintain plasma 25-hydroxyvitamin D (25(OH)D). Objective: To compare the plasma half-lives of 25(OH)D2 and 25(OH)D3 in two distinct populations with different dietary calcium intake and 25(OH)D status. Participants: Healthy men (aged 24 and 39 years), resident in The Gambia (n=18) or UK (n=18). Interventions: Oral tracer dose of deuterated-25(OH)D2 and deuterated-25(OH)D3 (both 40 nmol). Blood samples were collected over 33 days. Main outcome measures: 25(OH)D2 and 25(OH)D3 plasma half-lives, concentrations of 25(OH)D and DBP and DBP genotypes. Results: 25(OH)D2 half-life (mean (SD)) (13.9 (2.6) d) was shorter than 25(OH)D3 half-life (15.1 (3.1) d; P=0.001) for countries combined, and in Gambians (12.8 (2.3) d vs. 14.7 (3.5) d; P<0.001), but not in the UK (15.1 (2.4) d vs. 15.6 (2.5) d; P=0.3). 25(OH)D concentration was 69 (13) and 29 (11) nmol/L (P<0.0001) and DBP concentration was 259 (33) and 269 (23) mg/l (P=0.4) in The Gambia and UK, respectively. Half-lives were positively associated with plasma DBP concentration for countries combined: (25(OH)D2 half-life: regression coefficient (SE) 0.03 (0.01) d per 1 mg/l DBP; P=0.03; 25(OH)D3 half-life: 0.04 (0.02) d; P=0.02) and in Gambians (25(OH)D2 half-life: 0.04 (0.01) d; P=0.02; 25(OH)D3 half-life: 0.06 (0.02) d; P=0.01), but not in UK participants. DBP concentration*country interactions were not significant. DBP Gc1f/1f homozygotes had shorter 25(OH)D2 half-lives compared to other combined genotypes (P=0.007), after correction for country. Conclusions: 25(OH)D2 half-life was shorter than 25(OH)D3 half-life, and half-lives were affected by DBP concentration and genotype. Stable isotope 25(OH)D half-life measurements provide a novel tool to investigate vitamin D metabolism and vitamin D expenditure, and aid in the assessment of vitamin D requirements.
    Journal of Clinical Endocrinology &amp Metabolism 06/2014; · 6.31 Impact Factor
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    ABSTRACT: To compare mothers' perceptions of their own infants' nutritional status with anthropometric indicators of undernutrition.
    Public Health Nutrition 05/2014; · 2.48 Impact Factor
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    ABSTRACT: Childhood anemia is a major global health problem resulting from multiple causes. Iron supplementation addresses iron deficiency anemia but is undesirable for other types of anemia and may exacerbate infections. The peptide hormone hepcidin governs iron absorption; hepcidin transcription is mediated by iron, inflammation, and erythropoietic signals. However, the behavior of hepcidin in populations where anemia is prevalent is not well established. We show that hepcidin measurements in 1313 African children from The Gambia and Tanzania (samples taken in 2001 and 2008, respectively) could be used to identify iron deficiency anemia. A retrospective secondary analysis of published data from 25 Gambian children with either postmalarial or nonmalarial anemia demonstrated that hepcidin measurements identified individuals who incorporated >20% oral iron into their erythrocytes. Modeling showed that this sensitivity of hepcidin expression at the population level could potentially enable simple groupings of individuals with anemia into iron-responsive and non-iron-responsive subtypes and hence could guide iron supplementation for those who would most benefit.
    Science translational medicine 05/2014; 6(235):235re3. · 14.41 Impact Factor
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    ABSTRACT: In experimental animals, maternal diet during the periconceptional period influences the establishment of DNA methylation at metastable epialleles in the offspring, with permanent phenotypic consequences. Pronounced naturally occurring seasonal differences in the diet of rural Gambian women allowed us to test this in humans. We show that significant seasonal variations in methyl-donor nutrient intake of mothers around the time of conception influence 13 relevant plasma biomarkers. The level of several of these maternal biomarkers predicts increased/decreased methylation at metastable epialleles in DNA extracted from lymphocytes and hair follicles in infants postnatally. Our results demonstrate that maternal nutritional status during early pregnancy causes persistent and systemic epigenetic changes at human metastable epialleles.
    Nature Communications 04/2014; 5:3746. · 10.74 Impact Factor
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    ABSTRACT: Context: Calcium intake during growth is essential for future bone health but varies widely between individuals and populations. The impact on bone of increasing calcium intake is unknown in a population where low calcium intake, stunting and delayed puberty are common. Objective: To determine the effect of prepubertal calcium supplementation on mean age at peak velocity (APV) for bone growth and mineral accrual. Design: Prospective follow-up of boys who had participated in a double-blind, randomised, placebo-controlled trial of calcium supplementation (ISRCTN28836000). Setting: Rural Gambia, West Africa. Participants: 80 boys, initially aged 8.0-11.9 years, followed-up for 12 years. Interventions: One-year of calcium carbonate supplementation (1000mg/day. 5 days/week). Main outcome measures: DXA measurements of whole body (WB), lumbar spine and total hip bone mineral content (BMC), bone area (BA) and WB lean mass. Super Imposition by Translation And Rotation (SITAR) models to assess bone growth. Results: APV was consistently earlier in the calcium group compared to the placebo group, for WB BMC (-6.2 [3.1], p=0.05), WB BA (mean -7.0 [SE 3.2] months, p=0.03), lumbar spine and total hip BA. By young adulthood, supplementation did not change the amount of bone accrued (mineral or size) or the rate of bone growth. Conclusions: 12 months of prepubertal calcium carbonate supplementation in boys with a low calcium diet advanced the adolescent growth spurt but had no lasting effect on bone mineral or bone size. There is a need for caution when applying international recommendations to different populations.
    The Journal of Clinical Endocrinology and Metabolism 04/2014; · 6.31 Impact Factor
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    ABSTRACT: Cortical mapping of cognitive function during infancy is poorly understood in low-income countries due to the lack of transportable neuroimaging methods. We have successfully piloted functional near infrared spectroscopy (fNIRS) as a neuroimaging tool in rural Gambia. Four-to-eight month old infants watched videos of Gambian adults perform social movements, while haemodynamic responses were recorded using fNIRS. We found distinct regions of the posterior superior temporal and inferior frontal cortex that evidenced either visual-social activation or vocally selective activation (vocal > non-vocal). The patterns of selective cortical activation in Gambian infants replicated those observed within similar aged infants in the UK. These are the first reported data on the measurement of localized functional brain activity in young infants in Africa and demonstrate the potential that fNIRS offers for field-based neuroimaging research of cognitive function in resource-poor rural communities.
    Scientific Reports 04/2014; 4:4740. · 5.08 Impact Factor
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    ABSTRACT: Vitamin A supplementation significantly reduces all-cause mortality when given between 6-59 months of age, but has a null or detrimental effect when given between 1-5 months. Studies of neonatal vitamin A supplementation conducted across Africa and South Asia have produced conflicting findings. These age-pattern variations might result from immunological interactions between vitamin A supplementation and vaccines. Knowledge on the potential immunological sequelae of human neonatal vitamin A supplementation is so scarce that the foremost aim of this study is to seek indicative data on aspects of immunity likely to be affected by neonatal vitamin A supplementation. The objective of this trial is to test whether human neonatal vitamin A supplementation modulates immune function including improved thymic maturation in infancy and improved systemic immune responses to routine immunization.Methods/design: In an area of moderate vitamin A deficiency in a peri-urban area of The Gambia, 200 mother-infant pairs were enrolled in a double-blind randomised controlled trial. Within 48 hours of birth, neonates were randomised with stratification by birth weight and sex to receive either an oral dose of 50,000 IU vitamin A or placebo. Expanded Programme of Immunisation birth vaccinations were administered after supplementation, with subsequent vaccinations administered at 8, 12 and 16 weeks of age. A range of immunological outcomes were examined up to 17 weeks of age, with additional morbidity and anthropometry follow-up carried out throughout the first year of life. The primary endpoint of this trial is the frequency of circulating T regulatory (Treg) cells expressing gut homing receptors in infants at 17 week post-supplementation, with secondary outcomes including thymus maturation and B cell immune responses. Indicative immunological data from this trial (and its Bangladeshi counterpart), will complement the larger randomised controlled trials (conducted in India, Tanzania and Ghana), on the effectiveness and safety of neonatal vitamin A supplementation in improving infant survival. Combined these trials, in addition to the existing trials, will inform policy.Trial registration: clinicaltrials.gov NCT01476358.
    BMC Pediatrics 04/2014; 14(1):92. · 1.92 Impact Factor
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    ABSTRACT: The prevalence of osteoporosis and the incidence of age-related fragility fracture vary by ethnicity. There is greater than 10-fold variation in fracture probabilities between countries across the world. Mineral and bone metabolism are intimately interlinked, and both are known to exhibit patterns of daily variation, known as the diurnal rhythm (DR). Ethnic differences are described for Ca and P metabolism. The importance of these differences is described in detail between select ethnic groups, within the USA between African-Americans and White-Americans, between the Gambia and the UK and between China and the UK. Dietary Ca intake is higher in White-Americans compared with African-Americans, and is higher in White-British compared with Gambian and Chinese adults. Differences are observed also for plasma 25-hydroxy vitamin D, related to lifestyle differences, skin pigmentation and skin exposure to UVB-containing sunshine. Higher plasma 1,25-dihydroxy vitamin D and parathyroid hormone are observed in African-American compared with White-American adults. Plasma parathyroid hormone is also higher in Gambian adults and, in winter, in Chinese compared with White-British adults. There may be ethnic differences in the bone resorptive effects of parathyroid hormone, with a relative skeletal resistance to parathyroid hormone observed in some, but not all ethnic groups. Renal mineral excretion is also influenced by ethnicity; urinary Ca (uCa) and urinary P (uP) excretions are lower in African-Americans compared with White-Americans, and in Gambians compared with their White-British counterparts. Little is known about ethnic differences in the DR of Ca and P metabolism, but differences may be expected due to known differences in lifestyle factors, such as dietary intake and sleep/wake pattern. The ethnic-specific DR of Ca and P metabolism may influence the net balance of Ca and P conservation and bone remodelling. These ethnic differences in Ca, P and the bone metabolism may be important factors in the variation in skeletal health.
    Proceedings of The Nutrition Society 03/2014; · 3.67 Impact Factor
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    ABSTRACT: Hepcidin is the master regulatory hormone that governs iron homeostasis and has a role in innate immunity. Although hepcidin has been studied extensively in model systems there is less information on hepcidin regulation in global health contexts where iron deficiency, anemia and high infectious burdens (including malaria) all co-exist but fluctuate over time. We evaluated iron status, hepcidin levels and determinants of hepcidin in two populations of rural children aged ≤8 years, in The Gambia and Kenya (total n=848), at the start and end of a malaria season. Regression analyses and structural-equation-modeling demonstrated, for both populations, similar combinatorial effects of up-regulating stimuli (iron stores and to a lesser extent inflammation) and down-regulating stimuli (erythropoietic drive) on hepcidin levels. However malaria season was also a significant factor and was associated with an altered balance of these opposing factors. Consistent with these changes, hepcidin levels were reduced while prevalence of iron deficiency was increased at the end of the malaria season. More prevalent iron deficiency and lower hepcidin likely reflect an enhanced requirement for iron, and an ability to efficiently absorb it at the end of the malaria season. These results therefore have implications for iron deficiency and malaria control programs.
    Blood 03/2014; · 9.78 Impact Factor
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    ABSTRACT: Ramadan fasting imposes a diurnal rather than a chronic energetic challenge. When Ramadan occurs during the agricultural season in subsistence populations, diurnal and chronic effects combine. The impact of layered energetic challenges on adolescent activity, metabolism, and body composition have not been quantified. This study compares the effects of a Ramadan (30 July-3 October 2009) and subsequent non-Ramadan (14 July-12 August 2010) agricultural season in 67 Gambian subsistence agriculturalist women between 14 and 20 years old. Researchers collected body composition, anthropometric, metabolic, and activity data. Metabolic hormones were measured in weekly urine (C-peptide of insulin) and serum (leptin). Energy expenditure was estimated from heart rate calibrated for oxygen consumption. Participants lost more weight (Wald Chi-square 8.7, P < 0.01) and lean mass (Wald Chi-square 4.7, P < 0.05) in Ramadan than in the non-Ramadan agricultural season. Energy expenditure was lower (Wald Chi-square 11.2, P = 0.001) and there was a negative correlation between resting metabolic rate and energy expenditure in activity (R(2) = 0.097, F = 5.366, P = 0.025) during Ramadan. Leptin and C-peptide were higher during Ramadan (Wald Chi-square 53.7, P < 0.001 and Wald Chi-square 15.0, P < 0.001). Even using energy sparing behaviors, adolescent women enter negative energy balance when Ramadan and the agricultural season co-occur. Metabolic physiology shows a transient response to high glycemic index foods consumed at night. Older and larger individuals sustain greater losses during Ramadan. Am. J. Hum. Biol., 2014. © 2014 Wiley Periodicals, Inc.
    American Journal of Human Biology 03/2014; · 1.93 Impact Factor
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    ABSTRACT: Transcranial Doppler ultrasonography measures cerebral blood flow velocity (CBFv) of basal intracranial vessels and is used clinically to detect stroke risk in children with sickle cell anaemia (SCA). Co-inheritance in SCA of alpha-thalassaemia and glucose-6-phosphate dehydrogenase (G6PD) polymorphisms is reported to associate with high CBFv and/or risk of stroke. The effect of a common functional polymorphism of haptoglobin (HP) is unknown. We investigated the effect of co-inheritance of these polymorphisms on CBFv in 601 stroke-free Tanzanian SCA patients aged <24 years. Homozygosity for alpha-thalassaemia 3·7 deletion was significantly associated with reduced mean CBFv compared to wild-type (β-coefficient -16·1 cm/s, P = 0·002) adjusted for age and survey year. Inheritance of 1 or 2 alpha-thalassaemia deletions was associated with decreased risk of abnormally high CBFv, compared to published data from Kenyan healthy control children (Relative risk ratio [RRR] = 0·53 [95% confidence interval (CI):0·35-0·8] & RRR = 0·43 [95% CI:0·23-0·78]), and reduced risk of abnormally low CBFv for 1 deletion only (RRR = 0·38 [95% CI:0·17-0·83]). No effects were observed for G6PD or HP polymorphisms. This is the first report of the effects of co-inheritance of common polymorphisms, including the HP polymorphism, on CBFv in SCA patients resident in Africa and confirms the importance of alpha-thalassaemia in reducing risk of abnormal CBFv.
    British Journal of Haematology 02/2014; · 4.94 Impact Factor
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    Haematologica 01/2014; 99(1):e1-4. · 5.94 Impact Factor
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    ABSTRACT: We used optical topography (OT) to investigate cognitive function in infants in rural Gambia. Images of changes in oxyhaemoglobin and deoxyhaemoglobin concentrations were reconstructed using a multispectral algorithm which uses the finite element method (FEM) to model the propagation of light through scattering tissue using the diffusion equation. High quality OT data enabled us to reconstruct images with robust representation of haemodynamic changes. OT is a feasible neuroimage technology for this resource-poor setting.
    Advances in Experimental Medicine and Biology 01/2014; 812:263-9. · 2.01 Impact Factor

Publication Stats

17k Citations
3,028.45 Total Impact Points

Institutions

  • 1996–2014
    • London School of Hygiene and Tropical Medicine
      • Department of Nutrition and Public Health Interventions Research
      Londinium, England, United Kingdom
    • University of Aberdeen
      Aberdeen, Scotland, United Kingdom
    • Sheba Medical Center
      Gan, Tel Aviv, Israel
    • University of the Witwatersrand
      • School of Physiology
      Johannesburg, Gauteng, South Africa
  • 2011–2013
    • Muhimbili University of Health and Allied Sciences
      • Department of Haematology and Blood Transfusion
      Dar es Salaam, Dar es Salaam Region, Tanzania
    • Cranfield University
      Cranfield, England, United Kingdom
  • 2006–2013
    • London Metropolitan University
      • • School of Human Sciences
      • • Institute for Health Research and Policy
      London, ENG, United Kingdom
  • 1995–2013
    • University of Cambridge
      • Department of Medicine
      Cambridge, England, United Kingdom
  • 2012
    • University of London
      Londinium, England, United Kingdom
  • 2011–2012
    • KEMRI-Wellcome Trust Research Programme
      Kilifi, Kilifi, Kenya
  • 2008–2012
    • University of Oxford
      • Department of Paediatrics
      Oxford, England, United Kingdom
    • King Edward Medical University
      Lāhaur, Punjab, Pakistan
    • Institute of Genetics and Molecular Medicine
      Edinburgh, Scotland, United Kingdom
    • Royal Devon and Exeter NHS Foundation Trust
      Exeter, England, United Kingdom
  • 1980–2012
    • Medical Research Council Unit, The Gambia Unit
      Bakau, Banjul, Gambia
  • 2010
    • Baylor College of Medicine
      • Department of Pediatrics
      Houston, TX, United States
  • 2009
    • Cornell University
      • Department of Nutritional Sciences
      Ithaca, NY, United States
    • Western Sydney Area Health Service
      Blacktown, New South Wales, Australia
  • 2003–2008
    • The Bracton Centre, Oxleas NHS Trust
      Дартфорде, England, United Kingdom
    • St. George's School
      • Division of Infectious Diseases
      Middletown, Rhode Island, United States
  • 2000–2008
    • WWF United Kingdom
      Londinium, England, United Kingdom
    • MRC International Nutrition Group
      Londinium, England, United Kingdom
  • 2007
    • Wageningen University
      Wageningen, Gelderland, Netherlands
  • 2004
    • University of North Carolina at Chapel Hill
      • Department of Nutrition
      Chapel Hill, NC, United States
  • 2002
    • University of Glasgow
      • Child Health Section
      Glasgow, SCT, United Kingdom
  • 2000–2002
    • Scotland's Rural College
      Edinburgh, Scotland, United Kingdom
  • 1990–2002
    • University of Ulster
      • Biomedical Sciences Research Institute
      Aontroim, N Ireland, United Kingdom
  • 2001
    • University of Colorado
      • Department of Pediatrics
      Denver, CO, United States
  • 1989–1999
    • Medical Research Council (UK)
      Londinium, England, United Kingdom
  • 1998
    • University of Auckland
      Окленд, Auckland, New Zealand
  • 1997
    • Hôtel-Dieu de Paris – Hôpitaux universitaires Paris Centre
      Lutetia Parisorum, Île-de-France, France
  • 1987–1996
    • MRC Clinical Sciences Centre
      London Borough of Harrow, England, United Kingdom