Biomedical subjects

M Levander

Publications and source records attributed to M Levander.

13 recordsLinked to original sources

PubMed2001

Dissecting a population genome for targeted screening of disease mutations.

Compared to mixed populations, population isolates such as Finland show distinct differences in the prevalence of disease mutations. However, little information exists of the differences on the prevalence of different disease alleles in regional populations with different history of multiple bottlenecks. We constructed a DNA-array and monitored the prevalence of 31 rare and common disease mutations underlying 27 clinical phenotypes in a large population-based study sample. Over 64 000 genotypes were assigned in 2151 samples from four geographical areas representing early and late settlement regions of Finland. Each sample was analyzed in duplicate and a total of 142 000 array-derived genotyping calls were made. On average one in three individuals was found to be a carrier of one of the 31 monitored mutations. This should remove fears of the stigmatizing effect of a carrier-screening program monitoring multiple diseases. Regional differences were found in the prevalence of mutations, providing molecular evidence for the deviating population histories of regional subisolates. The mutations introduced early into the population revealed relatively even distribution in different subregions. More recently introduced rare mutations showed local clustering of disease alleles, indicating the persistence of population subisolates and the effect of multiple bottlenecks in molding the population gene pool. Regional differences were observed also for common disease alleles. Such precise information of the carrier frequencies could form the basis for targeted genetic screens in this population. Our approach describes a general paradigm for large-scale carrier-screening programs also in other populations.

Alleles↗

PubMed2001

MECP2 gene analysis in classical Rett syndrome and in patients with Rett-like features.

OBJECTIVE: To discuss the diagnostic criteria for Rett syndrome based on mutational screening of the methyl-CpG-binding protein 2 gene ( MECP2 ) in patients with classic Rett syndrome and patients with Rett-like features. METHODS: Thirty-nine patients with classical Rett syndrome, one with preserved speech variant (PSV), and 12 patients with developmental delay and some features of Rett syndrome were recruited for sequence analysis of the MECP2 gene coding region. The phenotype of the patients was correlated with the presence and type of the mutation as well as the X-chromosome inactivation (XCI) pattern. RESULTS: found in 100% of the patients with classical Rett syndrome originating from Finland. One novel mutation, P127L, was detected in a patient with PSV. No mutations were found in other cases. The XCI status was found to be random in 72% of the patients with classical Rett syndrome, including the patient with PSV and all patients with developmental delay informative for the analysis. CONCLUSIONS: An MECP2 mutation can be found in almost every patient with classical Rett syndrome. More patients need to be analyzed in order to clarify the mutation prevalence in patients with atypical Rett syndrome and in patients with mental retardation.

Adolescent↗

PubMed1996

Sustained attention and awareness of disability in chronic neglect.

The possible causative role of defective sustained attention and awareness of disability on the persistence of neglect was explored. The study included stroke patients who had had moderate or severe neglect 1-5 years before the start of the present examination. Questionnaire responses showed that the patients were aware of their disability. Impaired sustained attention was associated with poor performance in two out of three tests most sensitive in detecting neglect. This, together with indications of compensation on neglect tests, is interpreted as providing support for the hypothesis that chronic neglect is related to an impaired sustained attention.

Aged↗

PubMed1993

Word length coding in neglect dyslexia.

Single word reading was examined in two patients with left visual neglect. Both patients showed preservation of word length, which is the salient feature of neglect dyslexia. By varying lexical and contextual parameters we could, however, induce responses considerably shorter or longer than the stimuli. The findings are relevant to current accounts of neglect dyslexia.

Aged↗

PubMed1993

Effects of transcallosal surgery on interhemispheric transfer of information.

The effects of transcallosal surgery on interhemispheric transfer of information were investigated in five patients who underwent partial section of the corpus callosum for evacuation of a brain tumor. In comparison with normal controls, postoperative findings indicated subtle motor and/or sensory manifestations of hemispheric disconnection which tended to resolve overtime. However, in no case were the disconnection effects disabling in the performance of daily activities.

Adult↗

PubMed1993

Tactile line-bisection in normal subjects.

The effects of spatial position, handedness, and hand of performance were assessed in 36 normal subjects using a tactile line-bisection task described in 1980 by Bowers and Heilman. An interaction between hand of performance and spatial position indicated that both hemispace and anatomical pathways determine laterality effects. Neither the left-hand superiority nor the leftward error in the midline condition by both hands found in an earlier study could be observed here. Only right-handers were influenced by starting condition, which in this setting acted as a spatial cue. Finally, some subjects used nonspatial strategies, a confounding factor that needs evaluation in further studies.

Adolescent↗

PubMed1992

A tactile maze test in unilateral spatial neglect: the influence of vision and recording technique.

Right brain-damaged patients with left spatial neglect were examined on a tactile maze task. They started to explore the right side of the maze and their search times were longer on the left side. Their performance was the same whether blindfolded or not, which contrasts with the results of other studies and probably reflects differences in task demand. The present results do not support a previous observation that visual neglect can be compensated through the tactile modality. Our patients had markedly longer search times than normal controls in the right as well as the left hemifield, and search times in both hemifields were positively correlated. The outcome of the maze test in this context may therefore depend to a large extent on impaired topographical processing.

Adult↗

PubMed1991

Through a looking glass. A new technique to demonstrate directional hypokinesia in unilateral neglect.

A line cancellation task was performed by right brain-damaged patients with neglect in two response conditions. The task was presented either in normal view or through a 90 degree angle mirror with direct view prevented. The latter decouples the direction of visual attention and of arm movement. In the mirror condition, 4 of 18 patients cancelled lines only in right hemispace which means that they directed their visual attention to the left but failed to execute movements towards contralateral hemispace--what has been termed directional hypokinesia. In contrast, 10 patients cancelled lines only in left hemispace in the mirror condition, which accords better with attention-representation deficit hypotheses. Our results support a division of the neglect syndrome according to whether perceptual or premotor deficits are predominant.

Aged↗

PubMed1991

The influence of stimulus properties on visual neglect.

Twenty five patients with right cerebral hemisphere damage and neglect participated in a series of bisection experiments. As expected, long lines were bisected to the right of true midpoint. By contrast, large circles and long white paper strips were bisected accurately, or with leftward errors. Small objects were less sensitive to stimulus properties: short lines and paper strips, and small circles, were bisected to the left of true midpoint, and these leftward errors were equally common as rightward errors with long lines. When asked to draw a perpendicular line of the same length as the presented horizontal line, patients overestimated the length of short lines but underestimated that of long lines. Presenting lines in near and far extrapersonal space selectively affected bisection of short lines. The results suggest that two opposing, independent mechanisms determine bisection performance in left neglect.

Aged↗

PubMed1990

Apparent right neglect in patients with left visual neglect.

Two patients with unilateral left visual neglect were asked to bisect lines of different lengths. They showed, as expected, a rightward bias with longer lines. In contrast, they consistently transected very short lines (25 mm) to the left of the objective midpoint. The finding confirms a previous observation of similar behaviour but differs in other aspects that are of theoretical importance.

Aged↗

PubMed1989

Birth stress, handedness and cognitive performance.

Information regarding conditions during pregnancy and delivery was obtained by extensive interviews with mothers to left-handed and right-handed students. Using the same criterion as van Strien, Bouma and Bakker (1987) for defining birth stress, the present study did not replicate their findings of higher frequency of reported birth stress in left-handers. The difference in outcome was ascribed to differences in recruitment of subjects, the present sample constituting a majority of left hand writers from a population of 921 students, while the van Strien sample was less well defined. The present study was extended by comparing left-handed and right-handed subjects (separated for sex) with and without birth stress, on verbal and nonverbal abilities, and on eye dominance, early learning difficulties and familial sinistrality. Left eye dominance was more frequent in male left-handers with birth stress. Birth stress alone had negative effects on cognitive performance, different for males and females.

Adult↗

PubMed1988

Self-assessed and examiner-assessed writing hand posture in Swedish left-handers.

Writing hand posture was studied in 48 male and 54 female left-handed Swedish college students. Inverted posture was more common with examiner-assessment than with self-assessment and was more common in males. Examiner-assessed inversion frequency was lower than that reported from American samples but higher than that from Australian samples. Writing style was related to hand posture, printing being more common in non-inverted writers. Degree of lateral preference, presence of familial sinistrality and birth complications were not associated with writing hand posture.

Achievement↗

PubMed1988

Hand preference in a population of Swedish college students.

A hand preference inventory was administered to a population of 921 Swedish college students. The questions concern writing, drawing, throwing a ball, cutting with scissors, tooth brushing, cutting with a knife, and using a hammer, each with five response alternatives: always right, mostly right, either hand, mostly left and always left. A consistent preference over all activities for the left hand was rare (4%), but common for the right hand (62%). Corresponding percentages for writing hand were 9% and 89%, thus contradicting recent reports of a dramatic increase of left-handedness. There were no sex differences. Hand preference for writing was highly correlated with that for the other activities. Self-reported parental sinistrality was more common in respondents with a consistent left hand preference. There was no association between nonright-handedness and self-reported early learning difficulties, although among females mixed handers tended to report a higher frequency of difficulties in learning to write.

Adolescent↗