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Biomedical subjects

A van der Merwe

Publications and source records attributed to A van der Merwe.

At least 19 recordsLinked to original sources
PubMed1999

Folate status, homocysteine metabolism, and methylene tetrahydrofolate reductase genotype in rural South African blacks with a history of pregnancy complicated by neural tube defects.

The birth incidence of neural tube defects (NTDs) in South Africa is threefold to sixfold higher in rural compared with urban blacks. We investigated whether folate deficiency and aberrant homocysteine metabolism could explain the high NTD incidence in rural black populations. Plasma folate and total homocyst(e)ine (tHcy) concentrations were determined in apparently healthy rural black women (n = 107), rural black women with a history of pregnancy complicated by NTDs (n = 54), and urban blacks (n = 101). Methionine load tests were performed on the 54 women with a history of NTD-affected pregnancy and 54 controls matched for age and body mass. The presence of the 677C --> T mutation in the methylene tetrahydrofolate reductase (MTHFR) gene was investigated in both groups by a polymerase chain reaction (PCR) of genomic DNA and HinfI digestion of the PCR product. Apparently healthy urban black women (n = 101) had a lower (P < .001) plasma folate concentration compared with rural black women (n = 107). Women with a history of NTD-affected pregnancy did not differ significantly from controls with respect to plasma folate, fasting homocyst(e)ine, methionine, and the post-methionine load increase in plasma homocyst(e)ine. More than 50% of both of the latter groups had a post-methionine load increase in plasma tHcy less than the fifth percentile as observed in a healthy white control group. No homozygotes for the 677C --> T mutation in the MTHFR gene were found in black mothers with NTD-affected offspring or controls. It is concluded that black urbanization is characterized by a diminished folate status that is paradoxically associated with a lower NTD birth incidence. Homozygosity for the 677C --> T mutation in the gene coding for MTHFR does not constitute a genetic risk factor for NTDs in blacks. No aberrant homocysteine metabolism could be demonstrated in black women with NTD-affected pregnancies.

Adult↗
PubMed1999

[Speech understandability test in Sepedi].

The aim of this study was to develop the "Sepedi-toets vir Spraakverstaanbaarheid" to objectively evaluate the speech intelligibility of the client and to give appropriate phonetic information. This study evolved from the present need for evaluation mechanisms and therapeutic services in the indigenous African languages. The words used in the test had to conform to the requirements of certain phonetic criteria. Words and sentences of differing lengths were included. The procedures followed by the test administrator were different for mother tongue speakers than those for non-mother tongue speakers. After the compilation of the test it was applied to four dysarthria speakers. Upon execution of the test it was evident that differences in judgment of speech intelligibility exist between mother tongue and non-mother tongue speakers. Useful phonetic information was obtained through the qualitative analysis of the speech productions. It appears that the "Sepedi-toets vir Spraakverstaanbaarheid" can be used in the clinical environment to obtain a more objective evaluation of the client.

Adolescent↗
PubMed1997

Survival of FimH-expressing enterobacteria in macrophages relies on glycolipid traffic.

Strains of Escherichia coli persist within the human gut as normal commensals, but are frequent pathogens and can cause recurrent infection. Here we show that, in contrast to E. coli subjected to opsonic interactions stimulated by the host's immune response, E. coli that bind to the macrophage surface exclusively through the bacterial lectin FimH can survive inside the cell following phagocytosis. This viability is largely due to the attenuation of intracellular free-radical release and of phagosome acidification during FimH-mediated internalization, both of which are triggered by antibody-mediated internalization. This different processing of non-opsonized bacteria is supported by morphological evidence of tight-fitting phagosomes compared with looser, antibody-mediated phagosomes. We propose that non-opsonized FimH-expressing E. coli co-opt internalization of lipid-rich microdomains following binding to the FimH receptor, the glycosylphosphatidylinositol-linked protein CD48, because (1) the sterol-binding agents filipin, nystatin and methyl beta-cyclodextrin specifically block FimH-mediated internalization; (2) CD48 and the protein caveolin both accumulate on macrophage membranes surrounding bacteria; and (3) antibodies against CD48 inhibit FimH-mediated internalization. Our findings bring the traditionally extracellular E. coli into the realm of opportunistic intracellular parasitism and suggest how opportunistic infections with FimH-expressing enterobacteria could occur in a setting deprived of opsonizing antibodies.

Adhesins, Bacterial↗
PubMed1997

An exploratory study of an undefined acquired neuromotor speech disorder within the context of the four level framework for speech sensorimotor control.

In this study, the speech of a 28-year-old male with acquired brain injury and who presents with an undefined neuromotor speech disorder which cannot be categorised as either apraxia of speech or dysarthria, is described. Voice onset time, vowel duration, utterance duration and vowel formant analyses were done acoustically. A perceptual analysis and intelligibility rating were also executed. The subject was found to present with unique perceptual symptoms, intelligible speech, prolonged sound duration and distorted vowel quality. The results are interpreted within the context of the Four Level Framework of Speech Sensorimotor Control (Van der Merwe, 1997).

Adult↗
PubMed1996

The effect of a subnormal vitamin B-6 status on homocysteine metabolism.

Homocysteine, an atherogenic amino acid, is either remethylated to methionine or metabolized to cysteine by the transsulfuration pathway. The biochemical conversion of homocysteine to cysteine is dependent upon two consecutive, vitamin B-6-dependent reactions. To study the effect of a selective vitamin B-6 deficiency on transsulfuration, we performed oral methionine load tests on 22 vitamin B-6-deficient asthma patients treated with theophylline (a vitamin B-6 antagonist) and 24 age- and sex-matched controls with a normal vitamin B-6 status. Both groups had normal circulating vitamin B-12 and folate concentrations. Methionine loading resulted in significantly higher increases in circulating total homocyst(e)ine (P < 0.01) and cystathionine (P < 0.05) concentrations in vitamin B-6-deficient patients compared with controls. 6 wk of vitamin B-6 supplementation (20 mg/d) significantly (P < 0.05) reduced post-methionine load increases in circulating total homocyst(e)ine concentrations in deficient subjects, but had no significant effect on the increase in total homocyst(e)ine concentrations in controls. The increases in post-methionine load circulating cystathionine concentrations were significantly (P < 0.01) reduced in both groups after vitamin supplementation. It is concluded that a vitamin B-6 deficiency may contribute to impaired transsulfuration and an abnormal methionine load test, which is associated with premature vascular disease.

Administration, Oral↗
PubMed1996

[Voice problems in some groups of professional users of voice: implications for prevention].

The primary prevention of communication problems is a growing part of the professional responsibility of the speech-language therapist. Functional voice hyperfunction, which often occurs in professional users of voice, can be prevented. In this article three separate studies on voice problems of people in three different professions are reported. The subjects included 183 educators, 50 ministers and 20 singers. The data were obtained using questionnaires. The results indicate that voice problems and symptoms of voice problems occur in all three groups, that these speakers have little knowledge of the subject, that they expose themselves to high risk factors, and that they do not conserve their voices. Guidelines for instruction in prevention are provided.

Adult↗
PubMed1995

Effective homocysteine metabolism may protect South African blacks against coronary heart disease.

L-Methionine (0.1 g/kg body wt) was administered to young white [n = 18; mean (+/- SD) age 20.0 +/- 1.0 y] and black [n = 12; mean (+/- SD) age 22.0 +/- 1.3 y] volunteers who had a similar lifestyle and who did not differ significantly from each other with respect to plasma folate or vitamin B-12 concentrations. Blacks, however, had significantly lower plasma pyridoxal-5'-phosphate concentrations compared with whites (P < 0.001). Fasting plasma homocysteine concentrations in blacks and whites were not significantly different. The mean (+/- SD) maximum increase in plasma homocysteine concentration measured after methionine loading was significantly lower (P < 0.01) in blacks (11.0 +/- 3.6 mumol/L) than in whites (18.0 +/- 6.2 mumol/L). Six weeks of vitamin supplementation (1.0 mg folic acid, 400 micrograms vitamin B-12, and 10 mg pyridoxine/d) reduced the mean (+/- SD) fasting plasma homocysteine concentration from 9.6 +/- 3.5 to 7.2 +/- 1.6 mumol/L in whites (P < 0.05) and from 8.4 +/- 2.4 to 5.6 +/- 1.4 mumol/L in blacks (P < 0.01). The mean (+/- SD) maximum increase in plasma homocysteine concentration after methionine loading declined from 18.0 +/- 6.2 to 11.1 +/- 2.3 mumol/L (P < 0.01) in whites, but vitamin supplementation did not have a significant effect on the methionine-load test in black volunteers. A significant race-by-time interaction shows that blacks metabolized homocysteine more effectively than did whites, which may partly explain their relative resistance against coronary heart disease despite a high prevalence of obesity, hypertension, and smoking.

Adult↗
PubMed1995

[Anticipatory labial coarticulation: an electromyographic study in Afrikaans speaking people].

Anticipatory coarticulation sheds light on the planning of speech by the brain. The aim of this study is to gain information on the temporal extent of anticipatory labial coarticulation, the course of coarticulation for utterances consisting of two rounded vowels separated by an intervening consonant without rounding specification and lastly the effect of word boundaries on the onset of coarticulation in normal Afrikaans speaking adults. The method consisted of the recording of electromiographic (EMG) activity from Musculus Orbicularis Oris using a bipolar concentric needle electrode. The results suggested that anticipatory coarticulation is demonstrated by Afrikaans speaking individuals and that the onset of liprounding for a rounded vowel commenced earlier when the duration of the nonlabial consonantal string preceding the rounded vowel increased. During the investigation of anticipatory labial coarticulation in utterances consisting of two rounded vowels separated by a nonlabial consonant, it was found that two peaks in EMG activity with a pronounced decrease in activity between the peaks occurred. Lastly it was found that anticipatory coarticulation can occur across word boundaries. The results are discussed in relation to different theoretical models of speech production which have been proposed to account for the phenomenon of anticipatory labial coarticulation.

Adult↗
PubMed1994

Vitamin requirements for the treatment of hyperhomocysteinemia in humans.

We have previously shown that a modest vitamin supplement containing folic acid, vitamin B-12 and vitamin B-6 is effective in reducing elevated plasma homocysteine concentrations. The effect of supplementation of the individual vitamins on moderate hyperhomocysteinemia has now been investigated in a placebo-controlled study. One hundred men with hyperhomocysteinemia were randomly assigned to five groups and treated with a daily dose of placebo, folic acid (0.65 mg), vitamin B-12 (0.4 mg), vitamin B-6 (10 mg) or a combination of the three vitamins for 6 wk. Folic acid supplementation reduced plasma homocysteine concentrations by 41.7% (P < 0.001), whereas the daily vitamin B-12 supplement lowered homocysteine concentrations by 14.8% (P < 0.01). The daily pyridoxine dose did not reduce significantly plasma homocysteine concentrations. The combination of the three vitamins reduced circulating homocysteine concentrations by 49.8%, which was not significantly different (P = 0.48) from the reduction achieved by folate supplementation alone. Our results indicate that folate deficiency may be an important cause of hyperhomocysteinemia in the general population.

Adult↗
PubMed1993

Hyperhomocysteinemia and the response to vitamin supplementation.

The long-term vitamin requirements of men (n = 22) with moderate hyperhomocysteinemia (plasma total homocysteine concentration > 16.3 mumol/l) were investigated over a period of 48 weeks. An initial 6-week period of vitamin supplementation (1.0 mg folic acid, 10 mg pyridoxine, 0.05 mg cyanocobalamin) reduced plasma homocysteine levels 54.7% (P < 0.001). However, 18 weeks after vitamin therapy was discontinued, only seven participants (subgroup A) still had plasma homocysteine levels of 16.3 mumol/l or lower. The remainder of the participants (subgroup B) required a second 6-week period of vitamin therapy to normalize the elevated plasma homocysteine levels. Substitution of vitamin supplementation by dietary guidelines to increase folate intake from food products failed to maintain normal plasma homocysteine levels in participants from subgroup B. Long-term vitamin supplementation may be required in some individuals to prevent hyperhomocysteinemia.

Adolescent↗
PubMed1993

Vitamin B-12, vitamin B-6, and folate nutritional status in men with hyperhomocysteinemia.

We measured the vitamin B-6, vitamin B-12, and folic acid nutritional status in a group of apparently healthy men (n = 44) with moderate hyperhomocysteinemia (plasma homocysteine concentration > 16.3 mumol/L). Compared with control subjects (n = 274) with normal plasma homocysteine (< or = 16.3 mumol/L) concentrations, significantly lower plasma concentrations of pyridoxal-5'-phosphate (P < 0.001), cobalamin (P < 0.001), and folic acid (P = 0.004) were demonstrated in hyperhomocysteinemic men. The prevalence of suboptimal vitamin B-6, B-12, and folate status in men with hyperhomocysteinemia was 25.0%, 56.8%, and 59.1%, respectively. In a placebo-controlled follow-up study, a daily vitamin supplement (10 mg pyridoxal, 1.0 mg folic acid, 0.4 mg cyanocobalamin) normalized elevated plasma homocysteine concentrations within 6 wk. Because hyperhomocysteinemia is implicated as a risk factor for premature occlusive vascular disease, appropriate vitamin therapy may be both efficient and cost-effective to control elevated plasma homocysteine concentrations.

Adult↗
PubMed1993

[Speech sound distortion of neuromotor speech disorders: a comparison between cerebral dysarthria and verbal apraxia].

Speech sound distortion is considered to be a salient feature of neuromotor speech disorders such as cerebellar dysarthria and apraxia of speech. The aim of this study was to compare the temporal and spatial aspects of speech of two persons with acquired cerebellar dysarthria and of one person with acquired apraxia of speech. Voice onset time of [d], duration of articulatory closure of [d], duration of [s] and [l], formants of [l] and the range of acoustic energy of [s] were analysed spectrographically in a number of utterances with various sound structures. The results indicated that spatial and temporal distortion of articulatory movements occurred in all three subjects. However, differences in the nature and degree of speech sound distortion in the two different disorders were observed. The theoretical implications of these differences are discussed with reference to a model of normal speech production.

Apraxias↗
PubMed1993

[An electroglottographical analysis of certain voice parameters: normative indications].

A comprehensive voice evaluation comprises more than just the evaluation of perceptual and organic aspects. Objective voice analysis should supplement the diagnostic battery. In order to obtain normative indications for the Speech Research Laboratory at the University of Pretoria, 25 men and 25 women ranging in age from 8 to 80 years and with perceptually normal voices were tested with regard to fundamental frequency, cycle to cycle frequency fluctuation (jitter), cycle to cycle amplitude fluctuation (shimmer) and harmonic/noise ratio. Results indicate that these parameters are sensitive to changes in voice production caused by ageing, changes in loudness and the production of different vowels. The implications of these results for research and clinical practice are discussed.

Adolescent↗
PubMed1992

The effect of blood sample aging and food consumption on plasma total homocysteine levels.

The stability of homocysteine in whole blood and plasma was investigated. Total homocysteine concentrations in whole blood increased rapidly to values in excess of 180% of the basal concentration if whole blood was left at ambient temperature. Sodium fluoride partially inhibited homocysteine accumulation, while refrigeration inhibited homocysteine accumulation for at least 4 h. Since intracellular concentrations of homocysteine were low, the results indicate continued metabolism of L-methionine to homocysteine after the blood sample had been obtained. In contrast to whole blood, homocysteine was stable in plasma, even at room temperature. Food consumption (normal breakfast) resulted in significantly lower plasma homocysteine concentrations, which returned to pre-prandial concentrations 8 h later. The results indicate that both blood sampling and food intake should be rigorously standardized in epidemiological studies to elucidate the possible role of elevated circulating homocysteine concentrations in premature vascular disease.

Adult↗
PubMed1990

[A comparison of the influence of certain contextual factors on the symptoms of persons with acquired verbal apraxia and verbal developmental apraxia].

Data on the individual symptoms of patients with acquired apraxia of speech and developmental apraxia of speech is of theoretical significance in the study of this disorder. A comparison of individual symptoms may shed light on error patterns in apraxia of speech, the possibility of types of apraxia of speech and on the nature of the disorder. In this study which was part of the wider investigation into the effect of variation in contextual factors on apraxia of speech (Van der Merwe, Uys, Loots and Grimbeek, 1987; 1988; Van der Merwe, Uys, Loots, Grimbeek and Jansen, 1989) the symptoms of four patients with acquired apraxia of speech and one subject with developmental apraxia of speech were compared. The auditorily perceived symptoms and the deviations in voice onset time, vowel duration and utterance duration of all the subjects were compared. The results indicated that the frequency of occurrence of certain symptoms created individual error patterns but also that all subjects had the high occurrence of symptoms which reflect the nature of the disorder in common. The subject with developmental apraxia of speech had all symptoms in common with the other subjects but exhibited less deviancy in the temporal flow of speech and in the duration of the utterance. He presented with more sound substitutions than did the acquired group. The theoretical implications of the results are discussed.

Apraxias↗
PubMed1989

[Videofluoroscopic studies of the swallowing process in children with cerebral palsy].

The swallowing problems of cerebral palsied children are clinically evaluated by means of subjective criteria. Little research has been done to analyse these problems objectively and scientifically. The aim of this study was to analyse the swallowing patterns of cerebral palsied children in two age groups by means of videofluorography. Ten cerebral palsied children between the ages of four and thirteen years were selected as subjects. During the investigation they were asked to swallow a liquid and certain aspects of the oral preparatory, oral and pharyngeal phases of swallowing were analysed. The results of the study indicated that swallowing problems do occur in cerebral palsied children, mainly during the oral phase, and in some cases take on the form of inadequate contact between the tongue and palate and poor control of the bolus. The group of younger children had more swallowing problems than the older group. In the former group the type of cerebral palsy did not seem to play any role in the swallowing problems which occurred while in the older group there were indications that the type of cerebral palsy could possibly play a role. The results of the study indicate that videofluorography can be implemented effectively to scientifically evaluate the swallowing problems of cerebral palsied children.

Adolescent↗