Our results have shown that mean frequency of MN in irradiated lymphocytes is higher than non_irradiated lymphocytes in both right handed and left handed group. These findings are similar to former studies performed by Silva et al.
, Koksal G et al.
 and Gantonberg HW et al.
. Our results have released that radiosensitivity index is elevated in left handed women compared to right handed women and also it's evident that difference of the mean MN frequency in left-handers compared to right-handers is higher. These findings are in agreement with another study reported by khosravifarsani et al.
. Geschwind et al. have observed higher frequencies of immune disorders especially bowel, gut, learning disability, migraine and myasthenia gravis in left-handers and their relatives compared to right-handers
The study of Made K Ramadhani et al. have shown that the distribution of breast cancer in postmenopausal women is more frequent in left handed compared to right handed women
. Also Fritsch et al. showed that the risk of developing post-menopausal breast cancer in women is significantly higher in left-handers compared to right-handers
. Stellman et al. showed a high association of left handedness with disease and disease risk factors
. The study of Ashton
 Coren and Halpern
, Fleminger et al.
, Lalumiere et al.
; Porac et al.
 and Tan, have revealed shortened life span in left handed individuals compared to right handed individuals
. Investigations of Binali et al displayed that caries experience in left handed individuals have lower incidence than right handed individuals
. S Geschwind and Galaburda have declared high proportion of mental retardation and developmental problems in left handed individuals
. Former study demonstrated that the ABO blood groups are in relation with the radiation response in carcinoma of the cervix. On the basis of this study, O blood group has poorer response to radiotherapy than A and B merged and B blood group has lower response to ionizing radiation than A blood group
Molecular and genome wide association studies are consistent with a polygenic model of handedness. Few genes have been suggested as candidates for the establishment of hand preference such as the imprinted gene LRRTM1 on 2p12-q11
, PCSK6 gene on 15q26.3
 and the X-linked androgen receptor located on Xq11-12
Although among few SNPs detected in left handed subjects none was studied as a risk factor for radiosensitivity, but in light of our findings one may hypothesis that those SNPs may either directly modify radiosensitivity by influencing DNA repair pathways or indirectly as part of a haplotype harboring a polymorphism involved in cell cycle control or DNA repair. In fact a recent molecular study indicates that carriers of MSH2 gIVS12-6nt-C allele show an increased radiosensitivity
. MSH2 is one of the genes involved in DNA mismatch repair and located on chromosome 2 at 2p21. It has also been shown that polymorphism in Rad51 a gene located on chromosome 15 at 15q15.1 and involved in double strand break repair, can enhance cancer risk and in vitro chromosomal radiosensitivity
[4, 5]. It has also been postulated that genetic polymorphism of androgen receptor may act as a risk-modifier for BRCA2-associated breast cancers
Although our results have shown the association of left handedness and radiosensitivity, but to our knowledge no SNPs linked to DNA repair mechanisms or cell cycle check points have been studied in this regard. Further molecular investigations are needed to understand the possible genetic basis of this association.