Genetics of left handedness

Although there are many causes of left handedness, the genetic cause has also been identified. It has been suggested that the gene identified as "Leucine-rich repeat transmembrane neuronal 1" (LRRTM1) causes a person to be left handed. However this gene also causes a slight enhanced possibility of developing certain mental illnesses such as schizophrenia. Schizophrenics have the usual patterns of brain asymmetry as handed people.

Very little is known about this gene. However it is known that "leucine-rich repeat" containing membrane proteins like the LRRTM1 regulate neuronal growth and synapse formation. Scientists are of the view that the LRRTM1 gene on chromosome 2p12 affects the symmetry of the brain. Abnormal cerebral asymmetries are known to be associated with schizophrenia and other neuropsychiatric disorders such as Schizophrenia, autism and dyslexia. The gene is down regulated maternally in humans while linked paternally with handedness and schizophrenia. In simple words it is transmitted by the father. This gene also controls regions of the brain accounting for certain tasks such as speech and emotion. It is believed that in right handed individuals the left side of the brain controls functions such as speech and language and the right side directs emotions. While in left handlers the opposite happens where the LRRTM1 gene is responsible for take over and control. Moreover, in comparison to normal cells LRRTM1 is over expressed on the surface of cancer cells.

The LRRTM1 gene expresses its mRNA and protein in the endoplasmic reticulum (ER) of mammalian cells normally expressed during the growth of certain regions of the fetal forebrain structures. However it has also been known to express in neural tube, otic vesicle, apical ectodermal ridge, forebrain and midbrain in experimental mouse models. Although other studies have shown that the LRRTM mRNA is also expressed in the nervous system. RT-PCR and in situ hybridization studies of human tissues have also shown LRRTM1 expression in salivary gland and in the brain. Interestingly, human LRRTM1 shares 96% homology with mouse LRRTM1.

It is possible that together with the complexities of environmental effects and other genes LRRTM1 gene could be a major contributing factor for schizophrenia and left handedness but needs further investigation into the genetics of brain development.

References

Francks C, Maegawa S, Laurén J. et al. 2007. Mol Psychiatry. 12(12)

Haines BP, Rigby PW. 2007. Gene Expr Patterns. 7(1-2)3.

Laurén J, Airaksinen MS, Saarma M, Timmusk T. 2003. Genomics. 81(4) 4.

Francks C, DeLisi LE, Shaw SH, et al. 2003. Human Mol Genetics 12

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