Left-handedness and myasthenia gravis

The association between handedness and clinicodemographic characteristics in people with multiple sclerosis: a brief report

A relationship between handedness and clinicodemographic profiles of people with multiple sclerosis was sought using data from the Multiple Sclerosis Partners Advancing Technology Health Solutions network of 10 multiple sclerosis centers in the USA and Europe. Handedness data were available for 8888 multiple sclerosis patients, of which 917 (10.3%) were left-handed. Clinicodemographic profiles of right versus left-handed multiple sclerosis patients were similar except for a slightly increased proportion of men who were left-handed, and slightly reduced performance on the manual dexterity test using the non-dominant hand in left-handed patients. We found no evidence to suggest a prognostic implication of handedness in multiple sclerosis.

The inheritance of left-handedness

Left-handedness occurs in about 8% of the human population. It runs in families and an adoption study suggests a genetic rather than an environmental origin; however, monozygotic twins show substantial discordance. The only genetic models that successfully explain the family and twin data are those of McManus and Annett, which share the feature of incorporating a random component reflecting the biological phenomenon of 'fluctuating asymmetry'. The models have each been modified to explain the greater incidence of left-handedness in males. The McManus model is more successful at explaining the maternal effect--left-handed mothers have more left-handed offspring than do left-handed fathers. Both models explain the association of handedness with cerebral language dominance. The models differ principally in their conception of the phenotypes of handedness: Annett proposes a unimodal continuum, McManus proposes two discrete categories of handedness. Finding the gene for handedness and hence for language dominance would unlock the neurobiology of language. Two ways of finding the gene for handedness are proposed: searching the pseudoautosomal region of the X chromosome or invoking a specific evolutionary model of lateralization in which the handedness gene has evolved from the situs gene then searching the human genome for homologues to the mouse situs gene.

Laterality in five-year-olds conceived by intracytoplasmic sperm injection, standardin vitrofertilisation and natural conception: a European study

OBJECTIVE

To assess laterality in a group of European children conceived with the help of assisted reproductive therapy, or naturally conceived.

DESIGN

Prospective cohort study.

SETTING

Five European countries.

POPULATION

A total of 1525 five-year-old children divided into three groups according to conception status: naturally conceived; intracytoplasmic sperm injection (ICSI); in vitro fertilisation (IVF) group.

METHODS

All children were assessed using the McCarthy Scale of Children's Abilities (Motor Scale) with additional items using a comb, a spoon and an indirect measure was made of the parental handedness scores, using a questionnaire.

MAIN OUTCOME MEASURES

Child handedness for drawing and writing.

RESULTS

Observed handedness did not differ significantly between natural conception, IVF and ICSI in girls or boys, except for ICSI-conceived girls, fewer of whom were left-handed than the naturally conceived controls, 7.0%versus 12.4% (P < 0.05), however, this was close to the population norm of 8%. The degree of parental handedness did not significantly vary in the three groups.

CONCLUSIONS

Laterality, as assessed by handedness, may be marginally less common in girls conceived with assisted reproductive therapies than with children conceived naturally.

The handedness of Leonardo da Vinci: A tale of the complexities of lateralisation

The handedness of Leonardo da Vinci is controversial. Although there is little doubt that many of his well-attributed drawings were drawn with the left hand, the hatch marks of the shading going downwards from left to right, it is not clear that he was a natural left-hander, there being some suggestion that he may have become left-handed as the result of an injury to his right hand in early adulthood. Leonardo's lateralisation may be illuminated by an obscure passage in his notebooks in which he describes crouching down to look into a dark cave, putting his left hand on his knee, and shading his eyes with his right hand. We carried out a questionnaire survey, using 33 written and photographic items, to find whether this behaviour was typical of right handers or left handers. In fact the 'Leonardo task' showed almost no direct association with handedness, meaning that it contributes little to the immediate problem of elucidating Leonardo's handedness. However, the lateralisation of the task did relate to other aspects of behavioural laterality in surprisingly complex ways. This suggests that individual differences in handedness, and behavioural laterality in general, have a structural complexity which is not fully encompassed by simple measures of direction or degree of handedness.

Personality, brain asymmetry, and neuroendocrine reactivity in two immune-mediated disorders: a preliminary report

Development of some immune-mediated disorders may depend on dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis. To explore neuropsychologic mechanisms in relation to the abnormal endocrine reactivity in patients with systemic lupus erythematosus (SLE) and chronic hepatitis C (CHC) we used the corticotropin releasing hormone (CRH) test, the Minnesota Multiphasic Personality Inventory (MMPI), and the Edinburgh Inventory of Manual Preference Inventory (EIMP). Compared to controls, the adrenocorticotrophic hormone (ACTH) response to CRH was reduced in CHC, while SLE presented reduced baseline dehydroepiandrosterone sulfate levels; higher neurotic scores were found in SLE and higher behavior deviant scores in CHC. Peak ACTH levels were a significant factor for the MMPI profile variability, while the manual preference score was a significant factor for the ACTH response. Personality and manual preference contribute to neuroendocrine abnormalities. Different behavioral and neuroimmunoendocrine models emerge for these disorders.

Sexual orientation and handedness in men and women: a meta-analysis

Recent findings suggest that sexual orientation has an early neurodevelopmental basis. Handedness, a behavioral marker of early neurodevelopment, has been associated with sexual orientation in some studies but not in others. The authors conducted a meta-analysis of 20 studies that compared the rates of non-right-handedness in 6,987 homosexual (6,182 men and 805 women) and 16,423 heterosexual (14,808 men and 1,615 women) participants. Homosexual participants had 39% greater odds of being non-right-handed. The corresponding values for homosexual men (20 contrasts) and women (9 contrasts) were 34% and 91%, respectively. The results support the notion that sexual orientation in some men and women has an early neurodevelopmental basis, but the factors responsible for the handedness-sexual orientation association require elucidation. The authors discuss 3 possibilities: cerebral laterality and prenatal exposure to sex hormones, maternal immunological reactions to the fetus, and developmental instability.

Differences in serum interleukin-6 (IL-6) between healthy dextral and non-dextral subjects

Serum interleukin-6 (IL-6) was measured in picograms/ml pg/ml using an immunoassay (ELISA) in healthy individuals (n = 148), of whom 128 were classified as dextral and 20 as non-dextral, as per a laterality questionnaire. Only 3 (15%) non-dextral individuals had serum IL-6 levels above the lower limit of the assay sensitivity as compared to 59 (46%) of dextral individuals (P < 0.013). There were no significant correlations between previously determined mitogen stimulated interleukin-2 production and autoantibodies in a subset of the same individuals. While this data does not provide casual information, it adds to the evidence of the asymmetric regulation of immune functions by the cerebral hemispheres.

Gender, laterality, learning difficulties and health problems

This paper examines the association between self-reported laterality, learning difficulties and health problems. Responses to questionnaire data were obtained from 3829 males and 3631 females. Males reported increased cardiovascular disease, ulcers, and diabetes. Learning problems were increased in males, nonright-handers and those with a left eye preference. The highest proportion of difficulty learning to read was in males who were nonright-handed and right-eyed. Mixed dominance, however, did not fully explain the results since nonright-handers with left eye preferences had the next highest rate.

Neuroendocrine brain asymmetry and physical complaints

It was examined whether there is an association between physical health and alterations of normal brain asymmetry in cerebral control of neuroendocrine activity. In particular, it was studied whether right-handed subjects showing a high amount of physical complaints and recurrent diseases differ in direction and degree of brain asymmetry in cerebral control of cortisol secretion from subjects with only few physical complaints. Lateralized brain activation was achieved by presenting an emotionally aversive film to the subjects' left or right visual hemifield, using a technique for lateralizing visual input that allows prolonged viewing while permitting free ocular scanning. Results revealed a clear association between a high degree of physical complaints and altered brain asymmetry in cerebral control of neuroendocrine activity.

Handedness is not related to self-reported disease incidence

A hand preference inventory and a disease questionnaire were administered to a sample of 743 undergraduate students. The incidence of left-handedness was not related to the report of any of the diseases surveyed. Among right-handers, preference scores were slightly lower (less right-handed) in those reporting drug allergies or migraine. These data provide no support for the argument that handedness and immune disorders are related.