Molecular aspects of Down syndrome.

Molecular aspects of Down syndrome (DS), a major genetic cause for mental retardation, commonly associated with trisomy 21 are discussed. Two different hypotheses have been speculated to better understand the disease. One believes that increased gene dosage contributes to the phenotypic abnormalities; the other correlates genetic imbalance with DS pathogenesis. To sustain these hypotheses, different murine models have been developed. Experimental models as well as sequencing of human chromosome 21 helped in speculating a few possible candidate genes for DS. However, the phenotypic changes involved with this neurological disorder vis-a-vis the enhanced number of genes, still remain unexplained. Improvement in screening pattern, model system, as well as better understanding of the disease etiology may help in developing efficacious therapeutic regimes for DS.

Analysis of polymorphisms in the dopamine beta hydroxylase gene: association with attention deficit hyperactivity disorder in Indian children.

OBJECTIVE: To study the association of Attention Deficit Hyperactivity Disorder (ADHD) and polymorphism in the dopamine beta hydroxylase (DBH) gene in Indian ADHD cases. SUBJECTS: Forty one ADHD cases were diagnosed as per the DSM-IV-TR criteria and evaluated by Conners Parents and Teachers Rating Scale and Wechslers Intelligence Scale for Children. METHODS: Genomic DNA was amplified for exon 2 *444g/a and intron 5 (Taq I) polymorphism in the DBH gene followed by restriction fragment length polymorphism (RFLP) analysis. Haplotype-based haplotype relative risk (HHRR) was analyzed to ascertain the transmission pattern of these two polymorphisms in ADHD cases. Linkage disequilibrium (LD) between the two polymorphisms was calculated using EH+ and 2LD programs. RESULTS: In the limited number of samples analyzed, a slight increase in transmission of the 444a allele in ADHD subjects was observed for DBH 444g/a. The intron 5 (Taq I) polymorphism showed no significant association with ADHD in these cases. Strong disequilibrium was observed between DBH444g/a and intron 5 (Taq I) polymorphism. CONCLUSION: This is the first molecular genetic study on ADHD in Indian subjects exploring transmission of polymorphisms in the DBH gene. Preliminary investigation shows a trend towards association between the transmission of DBH444a allele and ADHD. No association was noticed between transmission of intron 5 (Taq I) polymorphism and ADHD in the Indian subjects. Presence of strong LD may point towards co-segregation of these two polymorphisms more often than expected.