A forced-choice reaction time (RT) task was used to examine the efficiency of visual filtering (the inhibition of processing of irrelevant stimuli) and the concomitant ability to narrow the focus of the attentional lens in persons with Down syndrome (n = 10) and children of average intelligence (n = 13) matched for mental age (MA) (average MA = approximately 5.7 years). Conditions varied with regard to the presence or absence of distractors and their proximity to a target stimulus, and the presence or absence of a visual window within which the target stimulus was presented. Although the study yielded no significant results due to a lack of power, the mean correct reaction times (RTs) indicate that both the adults with Down syndrome and the typically developing children were less efficient at filtering close distractors as compared to far distractors or no distractors. As well, the results suggest that the presence of the visual window failed to facilitate performance in both groups. Further investigation is warranted to determine the status of visual filtering in persons with Down syndrome relative to their level of functioning at an MA level of approximately 5 years, a period that is critical in the development of attentional processes.

Down syndrome (DS), caused by an extra chromosome 21, affects 1 in 750 live births, and is characterized by cognitive impairment as well as several congenital defects. Currently, little is known about the molecular pathogenesis of DS and no direct genotype-phenotype relationship has yet been confirmed. The current screening test for DS subjects many women to undergo invasive procedures such as amniocentesis due to suboptimal sensitivity and specificity. Therefore, this study aimed to discover novel biomarkers to improve screening tests, and to discovery dysregulated molecular pathways in DS-affected fetus to better understand pathogenesis. To achieve this objective, proteomic analyses of amniotic fluid (AF) and amniotic fluid cells (amniocytes) were performed using mass spectrometry (MS), which allows discovery of a large number of proteins in complex biological samples. Since AF contains the most information of the developing fetus, we first generated the most comprehensive list of proteins present in AF by using high resolution MS. We then performed quantitative analyses of proteins from AF as well as amniocytes to reveal novel biomarkers and clues to altered molecular mechanisms of DS. Comparison between the proteome of AF from unaffected and DS-affected pregnancies allowed selection of 60 candidate biomarkers based on spectral counting. Two candidates, APP and TNC-C, were verified by immunoassays to show two-fold increase in AF from DS-pregnancies. Additionally, CPA4, MUC13, CEL, DPP4 and MMP2 were verified to be differentially expressed in trisomy 21-AF via selected reaction monitoring assays using triple-quadruple mass spectrometer. Amniocytes from DS-affected and unaffected fetuses were also quantitatively analyzed by using Stable Isotope Labelling of Amino acids in Cell culture technique. Over 4900 proteins were identified from amniocyte lysate and supernatant by LTQ-Orbitrap mass spectrometer, and 85% of these proteins were quantified based on MS/MS spectra ratios of peptides containing isotope-labelled amino acids. Proteins that consistently showed aberrant expression from affected amniocytes have been selected for further verification and molecular network analyses since they may play a role in DS pathogenesis.

Thesis (PhDPhysiotherapy)--University of South Australia, 2001

Thesis (MAppSc in Physiotherapy)--University of South Australia, 1996

Thesis (PhDPhysiotherapy)--University of South Australia, 2001

Diss. Linköping : Linköpings universitet, 2007.

Thesis (MSc Natural and Agricultural Sciences (Biochemistry))-University of Pretoria, 2007. / Summary in English and Afrikaans. Includes bibliographical references. Available on the Internet via the World Wide Web.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2007. / Title from title screen (site viewed Apr. 29, 2008). PDF text: ix, 121 p. : ill. ; 1 Mb. UMI publication number: AAT 3278295. Includes bibliographical references. Also available in microfilm and microfiche formats.

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2005. / Härtill 4 uppsatser.

Diss. (sammanfattning) Linköping : Univ., 2001. / Härtill 4 uppsatser.