Handedness or hand preference of a human being is influenced by a combination of environmental and genetic factors. The genetic difference associated with handedness is found to be linked with the connections between brain parts responsible for language processing.
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What is hand preference?
Hand preference is defined as a person’s tendency to use one hand over the other for performing hand-related motor tasks, such as writing or lifting things. In the general population, 85% to 90% of people are right-handed, whereas 15% to 20% are left-handed; mixed-handedness (preferring different hands for different tasks) and ambidextrousness is rare.
Only Handedness is mostly developed as people generally find their right hand to be more skilled and comfortable to use. However, it is well-established in the literature that the hand preference is influenced by the combined effects of multiple genes.
Hand preference starts developing during early developmental processes that determine the structural and functional differences between the right and left hemispheres of the brain (right-left asymmetry).
According to scientific studies, lateralization of language, which defines the localization of language functions in the brain, in the left hemisphere is associated with the development of right-handedness in the general population. Left-handed people show higher language activation in the right hemisphere.
The association between hand preference and neurodevelopmental disorders is also well-documented in the literature. For example, it has been found that patients with schizophrenia are more likely to be left-handed.
How do genetic factors can influence hand preference?
Regarding genetic control of hand preference, it is known that some of the genes related to handedness may be responsible for shaping the right-left asymmetry during the early stage of development.
So far, only a few genes have been identified by the researchers. For example, the preference of being right-handed is influenced by the PCSK6 gene in schizophrenic patients. Similarly, in patients with dyslexia, the LRRTM1 gene is associated with left-handedness.
In this context, a recent study including genetic analysis of 400,000 people has found that left-handed people have increased connectivity between the left and right language networks in the brain.
The genome-wide association studies in these people have identified 4 chromosomal locations; of these, three contains genes that encode proteins responsible for the development and patterning of the brain.
These proteins are particularly associated with microtubules, which are filamentous structures of the cytoskeleton responsible for the intracellular structural organization, transport, and motility. Also, these proteins are involved in the development of many neurological disorders, including Alzheimer’s disease, Parkinson’s disease, and schizophrenia.
Of 4 chromosomal locations identified, one is particularly associated with handedness, psychiatric characteristics, and the structural integrity of the white matter tracts that connect language-related brain parts.
Moreover, it has been found that the communication between the language regions in the right and left hemispheres is highly coordinated in left-handed people, indicating that they are in a preferential position concerning verbal tasks.
In addition, the study has revealed that the genetic regions responsible for left-handedness is associated with a lower chance of developing Parkinson’s disease, but a higher chance of developing schizophrenia.
Taken together, it can be said that the gene regions associated with handedness exert their effects by modulating the lateralization of the brain during the early developmental process.