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Stijn Vansteelandt

Publications and source records attributed to Stijn Vansteelandt.

7 recordsLinked to original sources
PubMed2006

An improved statistical method for detecting heterotachy in nucleotide sequences.

The principle of heterotachy states that the substitution rate of sites in a gene can change through time. In this article, we propose a powerful statistical test to detect sites that evolve according to the process of heterotachy. We apply this test to an alignment of 1289 eukaryotic rRNA molecules to 1) determine how widespread the phenomenon of heterotachy is in ribosomal RNA, 2) to test whether these heterotachous sites are nonrandomly distributed, that is, linked to secondary structure features of ribosomal RNA, and 3) to determine the impact of heterotachous sites on the bootstrap support of monophyletic groupings. Our study revealed that with 21 monophyletic taxa, approximately two-thirds of the sites in the considered set of sequences is heterotachous. Although the detected heterotachous sites do not appear bound to specific structural features of the small subunit rRNA, their presence is shown to have a large beneficial influence on the bootstrap support of monophyletic groups. Using extensive testing, we show that this may not be due to heterotachy itself but merely due to the increased substitution rate at the detected heterotachous sites.

Chi-Square Distribution↗
PubMed2005

Preterm birth in twins after subfertility treatment: population based cohort study.

OBJECTIVES: To assess gestational length and prevalence of preterm birth among medically and naturally conceived twins; to establish the role of zygosity and chorionicity in assessing gestational length in twins born after subfertility treatment. DESIGN: Population based cohort study. SETTING: Collaborative network of 19 maternity facilities in East Flanders, Belgium (East Flanders prospective twin survey). PARTICIPANTS: 4368 twin pairs born between 1976 and 2002, including 2915 spontaneous twin pairs, 710 twin pairs born after ovarian stimulation, and 743 twin pairs born after in vitro fertilisation or intracytoplasmic sperm injection. MAIN OUTCOME MEASURES: Gestational length and prevalence of preterm birth. RESULTS: Compared with naturally conceived twins, twins resulting from subfertility treatment had on average a slightly decreased gestational age at birth (mean difference 4.0 days, 95% confidence interval 2.7 to 5.2), corresponding to an odds ratio of 1.6 (1.4 to 1.8) for preterm birth, albeit confined to mild preterm birth (34-36 weeks). The adjusted odds ratios of preterm birth after subfertility treatment were 1.3 (1.1 to 1.5) when controlled for birth year, maternal age, and parity and 1.6 (1.3 to 1.8) with additional control for fetal sex, caesarean section, zygosity, and chorionicity. Although an increased risk of preterm birth was therefore seen among twins resulting from subfertility treatment, the risk was largely caused by a first birth effect among subfertile couples; conversely, the risk of prematurity was substantially levelled off by the protective effect of dizygotic twinning. CONCLUSIONS: Twins resulting from subfertility treatment have an increased risk of preterm birth, but the risk is limited to mild preterm birth, primarily by virtue of dizygotic twinning.

Birth Weight↗
PubMed2004

Both low and high activities of platelet monoamine oxidase increase the probability of becoming a smoker.

Platelet monoamine oxidase (MAO) activity is a marker of personality and psychiatric vulnerability, but the direct inhibitory action of tobacco constituents on the enzyme distorts the association. In the present investigation, data from a prospective longitudinal study of smoking behaviour and platelet MAO activity in adolescents at ages 15 and 18 years were sequentially analysed using a second-order multiple logistic regression analysis. The odds of regular smoking at 18 years increased significantly with increasing absolute deviation of platelet MAO activity at 15 years from the mean. That is, both low and high platelet MAO activity at 15 years predicted a higher probability of becoming a smoker. These data suggest that smoking is associated with low platelet MAO activity not only because of the direct inhibitory effect of tobacco constituents on the enzyme, but also because subjects with low platelet MAO activity are more likely to become smokers. Furthermore, the possible association between above-average platelet MAO activity and behavioural phenotypes should be reexamined.

Adolescent↗
PubMed2003

Distribution of human papillomavirus in a family planning population in nairobi, kenya.

BACKGROUND: In sub-Saharan Africa, cervical cancer is the leading cancer among women. The causative role of different human papillomavirus (HPV) types in cervical cancer is established, but the distribution of HPV types within this region is largely unknown. GOAL: The goal was to study the distribution of HPV among family planning clinic attendees in Nairobi, Kenya. STUDY DESIGN: This was a cross-sectional study of persons attending a family planning center in Nairobi, Kenya. RESULTS: HPV data of 429 women were analyzed; 7.0% had low-grade intraepithelial lesions, 6.8% had high-grade intraepithelial lesions, and 0.23% had invasive cancer. One hundred ninety samples (44.3%) were HPV-positive (28.4% were positive for multiple types). The most common HPV types were HPV 52 (17.9% of positive samples), HPV 16 (14.7%), HPV 35 (11.6%), and HPV 66 (9.0%). The risk of high-grade squamous intraepithelial lesions (HSIL) was 88.5 times higher (95% CI, 8.5-1.4 x 10 ) in HPV 16-positive women than in HPV-negative women. Relative risks were 54.3 (95% CI, 4.0-1.4 x 10 ) for HPV 35, 49.2 (95% CI, 3.6-9.5 x 10 ) for HPV 52, and 21.7 (95% CI, 0.0-1.9 x 10 ) for HPV 18. The prevalence of HSIL was not increased in association with HIV-positivity, yet HIV-1 was significantly associated with high-risk HPV types ( P< 0.00001). CONCLUSION: The pattern of HPV distribution in this population was different from that in other regions in the world, which has important consequences for HPV vaccine development.

Adult↗
PubMed2002

Placental inflammation and perinatal transmission of HIV-1.

The effect of placental membrane inflammation on mother-to-child transmission (MTCT) of HIV-1 is reported. Placentas from HIV-1-infected women were examined as part of a perinatal HIV-1 project in Mombasa, Kenya. Polymerase chain reaction analysis was used to test for HIV-1 in the infants at birth and at 6 weeks. The maternal HIV-1 seroprevalence was 13.3% (298 of 2,235). The overall rate of MTCT of HIV-1 was 25.4%; polymerase chain reaction analysis revealed that of the 201 infants 6.0% (12) were already HIV-1-positive at birth (intrauterine transmission) and 19.4% (39) were infected during the peripartum period or in early neonatal life (perinatal transmission). The prevalence of acute chorioamnionitis was 8.8%, that of deciduitis was 10.8%, and that of villitis was 1.6%. Acute chorioamnionitis was independently associated with peripartum HIV-1 transmission but not with in utero MTCT (17.9% vs. 6.7%, respectively; adjusted odds ratio, 3.9; 95% confidence interval, 1.2-12.5; p =.025). Other correlates of perinatal MTCT were presence of HIV in the genital tract and in the baby's oral cavity and a high maternal viral load in peripheral blood. The adjusted population attributable fraction of 12.8% (95% confidence interval, 1.5%-22.8%) indicated that approximately 3% of MTCT could be prevented if acute chorioamnionitis was eliminated. We suggest that further research on the role of antimicrobial treatment in the prevention of chorioamnionitis and the reduction of peripartum MTCT needs to be performed.

Chorioamnionitis↗