Cystathionine β-synthase (CBS) mediates conversion of homocysteine to cystathionine and deficiency in enzyme activity may be lead to hyperhomocysteinemia/homocystinuria, which are often associated with Down Syndrome (DS). A large number of polymorphisms have been reported in the CBS gene, some of which impair its activity and among these, a T833C polymorphism in cis with a 68 bp insertion at 844 in the exon 8 is found to be associated with mild hyperhomocysteinemia in different ethnic groups. Our aim in the present study is to investigate the association between T833C/844ins68 polymorphism and DS. Methods: Fifty-seven DS cases parents (mothers) were recruited after psychometric evaluation. Peripheral blood was collected after obtaining informed written consent. The T833C/844ins68 polymorphism was investigated by PCR amplification of genomic DNA Results: After PCR Analysis 15 samples were found to have +/- genotype while 42 samples were found to have -/- genotype for CBS 844ins68 polymorphisms. Conclusion: This is the first molecular genetic study of CBS gene dealing with T833C/844ins68 double mutation in DS subjects in our region. The next step is to extended number of cases and to use more controls for T833C/844INS68 polymorphism.